diff --git a/src/config/index.mjs b/src/config/index.mjs
index 48c2d98b..22b64df3 100644
--- a/src/config/index.mjs
+++ b/src/config/index.mjs
@@ -10,6 +10,7 @@ import {
 } from '../utils/model-name-convert.mjs'
 import { t } from 'i18next'
 import {
+  LEGACY_API_KEY_FIELD_BY_PROVIDER_ID,
   LEGACY_SECRET_KEY_TO_PROVIDER_ID,
   OPENAI_COMPATIBLE_GROUP_TO_PROVIDER_ID as API_MODE_GROUP_TO_PROVIDER_ID,
 } from './openai-provider-mappings.mjs'
@@ -38,6 +39,9 @@ export const ModelMode = {
   fast: 'Fast',
 }
 
+// Provider IDs added after custom providers became configurable need one-time secret migration.
+const NEWLY_RESERVED_BUILTIN_PROVIDER_IDS = new Set(['xai', 'nvidia-nim', 'mistral'])
+
 export const chatgptWebModelKeys = [
   'chatgptFree35',
   'chatgptFree4oMini',
@@ -853,6 +857,7 @@ export const defaultConfig = {
   knownApiModeDefaultIds: [],
   customOpenAIProviders: [],
   providerSecrets: {},
+  completedBuiltinProviderIdMigrations: [],
   configSchemaVersion: 2,
   activeSelectionTools: ['translate', 'translateToEn', 'summary', 'polish', 'code', 'ask'],
   customSelectionTools: [
@@ -1059,6 +1064,28 @@ function normalizeEndpointUrlForCompare(value) {
   return normalizeText(value).replace(/\/+$/, '')
 }
 
+function ensureLeadingSlash(value, fallback = '') {
+  const normalized = normalizeText(value)
+  if (!normalized) return fallback
+  return normalized.startsWith('/') ? normalized : `/${normalized}`
+}
+
+function getProviderChatCompletionsUrlForCompare(provider) {
+  const directUrl = normalizeEndpointUrlForCompare(provider?.chatCompletionsUrl)
+  if (directUrl) return directUrl
+
+  let baseUrl = normalizeEndpointUrlForCompare(provider?.baseUrl)
+  const path = ensureLeadingSlash(provider?.chatCompletionsPath)
+  if (!baseUrl || !path) return ''
+  const usesDefaultV1Paths =
+    path === '/v1/chat/completions' &&
+    ensureLeadingSlash(provider?.completionsPath) === '/v1/completions'
+  if (!normalizeText(provider?.completionsUrl) && usesDefaultV1Paths) {
+    baseUrl = baseUrl.replace(/\/v1$/i, '')
+  }
+  return normalizeEndpointUrlForCompare(`${baseUrl}/${path.replace(/^\/+/, '')}`)
+}
+
 function isPlainObject(value) {
   return Boolean(value) && typeof value === 'object' && !Array.isArray(value)
 }
@@ -1091,6 +1118,31 @@ function ensureUniqueProviderId(providerIdSet, preferredId) {
   return id
 }
 
+function getLegacyProviderIds(value, currentProviderId = '') {
+  const normalizedCurrentProviderId = normalizeProviderId(currentProviderId)
+  return Array.from(
+    new Set(
+      (Array.isArray(value) ? value : [])
+        .map(normalizeProviderId)
+        .filter((providerId) => providerId && providerId !== normalizedCurrentProviderId),
+    ),
+  )
+}
+
+function addLegacyProviderId(target, providerId) {
+  const normalizedProviderId = normalizeProviderId(providerId)
+  if (!target || !normalizedProviderId) return false
+  const legacyProviderIds = getLegacyProviderIds(target.legacyProviderIds, target.providerId)
+  if (
+    normalizedProviderId === normalizeProviderId(target.providerId) ||
+    legacyProviderIds.includes(normalizedProviderId)
+  ) {
+    return false
+  }
+  target.legacyProviderIds = [...legacyProviderIds, normalizedProviderId]
+  return true
+}
+
 function normalizeCustomProviderForStorage(provider, index, providerIdSet) {
   if (!provider || typeof provider !== 'object') return null
   const originalRawId = normalizeText(provider.id)
@@ -1100,22 +1152,39 @@ function normalizeCustomProviderForStorage(provider, index, providerIdSet) {
   const preferredId = originalId || `custom-provider-${index + 1}`
   const id = ensureUniqueProviderId(providerIdSet, preferredId)
   providerIdSet.add(id)
+  const legacyProviderIds = getLegacyProviderIds(
+    [...(Array.isArray(provider.legacyProviderIds) ? provider.legacyProviderIds : []), originalId],
+    id,
+  )
+  const chatCompletionsPath = ensureLeadingSlash(
+    provider.chatCompletionsPath,
+    '/v1/chat/completions',
+  )
+  const completionsPath = ensureLeadingSlash(provider.completionsPath, '/v1/completions')
+  const normalizedLegacyProviderIds = legacyProviderIds.length > 0 ? legacyProviderIds : undefined
+  const storageShapeChanged =
+    (normalizeText(provider.chatCompletionsPath) || '/v1/chat/completions') !==
+      chatCompletionsPath ||
+    (normalizeText(provider.completionsPath) || '/v1/completions') !== completionsPath ||
+    JSON.stringify(provider.legacyProviderIds) !== JSON.stringify(normalizedLegacyProviderIds)
   return {
     originalId,
     originalRawId,
     sourceProviderOriginalId: sourceProviderId,
     sourceProviderOriginalRawId,
+    storageShapeChanged,
     provider: {
       id,
       name: normalizeText(provider.name) || `Custom Provider ${index + 1}`,
       baseUrl: normalizeText(provider.baseUrl),
-      chatCompletionsPath: normalizeText(provider.chatCompletionsPath) || '/v1/chat/completions',
-      completionsPath: normalizeText(provider.completionsPath) || '/v1/completions',
+      chatCompletionsPath,
+      completionsPath,
       chatCompletionsUrl: normalizeText(provider.chatCompletionsUrl),
       completionsUrl: normalizeText(provider.completionsUrl),
       enabled: provider.enabled !== false,
       allowLegacyResponseField: provider.allowLegacyResponseField !== false,
       ...(sourceProviderId ? { sourceProviderId } : {}),
+      ...(normalizedLegacyProviderIds ? { legacyProviderIds: normalizedLegacyProviderIds } : {}),
     },
   }
 }
@@ -1158,6 +1227,7 @@ function migrateUserConfig(options) {
   if (!hasProviderSecretsRecord) {
     dirty = true
   }
+  const providerSecretSnapshot = { ...providerSecrets }
   for (const [legacyKey, providerId] of Object.entries(LEGACY_SECRET_KEY_TO_PROVIDER_ID)) {
     const legacyKeyValue = normalizeText(migrated[legacyKey])
     const hasProviderSecret = Object.hasOwn(providerSecrets, providerId)
@@ -1166,6 +1236,23 @@ function migrateUserConfig(options) {
       dirty = true
     }
   }
+  const completedBuiltinProviderIdMigrations = new Set(
+    Array.isArray(migrated.completedBuiltinProviderIdMigrations)
+      ? migrated.completedBuiltinProviderIdMigrations.map(normalizeProviderId).filter(Boolean)
+      : [],
+  )
+  const currentBuiltinProviderIdCollisions = new Set(
+    (Array.isArray(migrated.customOpenAIProviders) ? migrated.customOpenAIProviders : [])
+      .map((provider) => normalizeProviderId(provider?.id))
+      .filter((providerId) => NEWLY_RESERVED_BUILTIN_PROVIDER_IDS.has(providerId)),
+  )
+  const pendingBuiltinProviderIdMigrations = new Set(
+    [...NEWLY_RESERVED_BUILTIN_PROVIDER_IDS].filter(
+      (providerId) =>
+        !completedBuiltinProviderIdMigrations.has(providerId) ||
+        currentBuiltinProviderIdCollisions.has(providerId),
+    ),
+  )
 
   const builtinProviderIds = new Set(
     Object.values(API_MODE_GROUP_TO_PROVIDER_ID)
@@ -1195,7 +1282,10 @@ function migrateUserConfig(options) {
       .filter((id) => id),
   )
   const customOpenAIProviders = normalizedProviderResults.map(
-    ({ originalId, originalRawId, sourceProviderOriginalRawId, provider }) => {
+    ({ originalId, originalRawId, sourceProviderOriginalRawId, storageShapeChanged, provider }) => {
+      if (storageShapeChanged) {
+        dirty = true
+      }
       if (normalizeText(originalRawId) !== normalizeText(provider.id)) {
         dirty = true
       }
@@ -1215,7 +1305,52 @@ function migrateUserConfig(options) {
       return provider
     },
   )
+  for (const provider of customOpenAIProviders) {
+    for (const legacyProviderId of getLegacyProviderIds(provider.legacyProviderIds)) {
+      providerIdSet.add(legacyProviderId)
+    }
+  }
   if (!Array.isArray(migrated.customOpenAIProviders)) dirty = true
+  const hasCanonicalProviderIdCollision = (providerId) =>
+    normalizedProviderResults.filter(({ originalId }) => originalId === providerId).length > 1
+  const resolveRenamedProviderId = (providerId, providerIdRaw, customUrl) => {
+    const providerIdCandidates = normalizedProviderResults.filter(
+      ({ originalId }) => originalId === providerId,
+    )
+    if (providerIdCandidates.length > 1) {
+      const normalizedProviderIdRaw = normalizeText(providerIdRaw)
+      const rawIdMatches = providerIdCandidates.filter(
+        ({ originalRawId }) => normalizeText(originalRawId) === normalizedProviderIdRaw,
+      )
+      if (rawIdMatches.length === 1) {
+        return rawIdMatches[0].provider.id
+      }
+      const normalizedCustomUrl = normalizeEndpointUrlForCompare(customUrl)
+      if (normalizedCustomUrl) {
+        const matchingProviderIds = providerIdCandidates
+          .filter(
+            ({ provider }) =>
+              getProviderChatCompletionsUrlForCompare(provider) === normalizedCustomUrl,
+          )
+          .map(({ provider }) => provider.id)
+        if (matchingProviderIds.length === 1) {
+          return matchingProviderIds[0]
+        }
+      }
+      return undefined
+    }
+    const renamedProviderId = providerIdRenameLookup.get(providerId)
+    if (renamedProviderId) return renamedProviderId
+    if (!NEWLY_RESERVED_BUILTIN_PROVIDER_IDS.has(providerId)) return undefined
+
+    const legacyProviderIdMatches = customOpenAIProviders.filter((provider) =>
+      getLegacyProviderIds(provider.legacyProviderIds).includes(providerId),
+    )
+    if (legacyProviderIdMatches.length !== 1 || legacyProviderIdMatches[0].enabled === false) {
+      return undefined
+    }
+    return legacyProviderIdMatches[0].id
+  }
 
   for (const {
     sourceProviderOriginalId,
@@ -1244,40 +1379,147 @@ function migrateUserConfig(options) {
     }
   }
 
-  for (let index = providerIdRenames.length - 1; index >= 0; index -= 1) {
-    const {
-      oldId: oldProviderId,
-      oldRawId: oldRawProviderId,
-      newId: newProviderId,
-    } = providerIdRenames[index]
+  const rawProviderSecretIdsToDelete = new Set()
+  const builtinProviderSecretIdsToDelete = new Map()
+  for (const {
+    oldId: oldProviderId,
+    oldRawId: oldRawProviderId,
+    newId: newProviderId,
+  } of providerIdRenames) {
     if (oldProviderId === newProviderId) continue
     if (!legacyCustomProviderIds.has(oldProviderId)) continue
-    const hasRawIdSecret = Object.hasOwn(providerSecrets, oldRawProviderId)
-    const hasNormalizedIdSecret = Object.hasOwn(providerSecrets, oldProviderId)
+    const hasRawIdSecret = Object.hasOwn(providerSecretSnapshot, oldRawProviderId)
+    const hasNormalizedIdSecret = Object.hasOwn(providerSecretSnapshot, oldProviderId)
+    const hasDistinctRawId = oldRawProviderId !== oldProviderId
     const usesBuiltinSecretSlot = builtinProviderIds.has(oldProviderId)
-    if (usesBuiltinSecretSlot && !hasRawIdSecret) continue
-    if (!usesBuiltinSecretSlot && !hasRawIdSecret && !hasNormalizedIdSecret) continue
-    const rawIdSecret = hasRawIdSecret ? providerSecrets[oldRawProviderId] : undefined
-    const normalizedIdSecret = hasNormalizedIdSecret ? providerSecrets[oldProviderId] : undefined
-    const oldSecret = usesBuiltinSecretSlot
-      ? rawIdSecret
-      : hasRawIdSecret && rawIdSecret !== ''
-      ? rawIdSecret
-      : hasNormalizedIdSecret
-      ? normalizedIdSecret
-      : rawIdSecret
+    const isPendingBuiltinProviderIdMigration =
+      usesBuiltinSecretSlot && pendingBuiltinProviderIdMigrations.has(oldProviderId)
+    const hasMultipleProviderIdRenames =
+      normalizedProviderResults.filter(({ originalId }) => originalId === oldProviderId).length > 1
+    const hasUniqueCanonicalRawIdOwner =
+      normalizedProviderResults.filter(
+        ({ originalId, originalRawId }) =>
+          originalId === oldProviderId && originalRawId === oldProviderId,
+      ).length === 1
+    const rawIdSecret = hasRawIdSecret ? providerSecretSnapshot[oldRawProviderId] : undefined
+    const normalizedIdSecret = hasNormalizedIdSecret
+      ? providerSecretSnapshot[oldProviderId]
+      : undefined
+    const rawSecretValue = normalizeText(rawIdSecret)
+    const normalizedSecretValue = normalizeText(normalizedIdSecret)
+    const builtinLegacyKey = LEGACY_API_KEY_FIELD_BY_PROVIDER_ID[oldProviderId]
+    const builtinLegacySecret = builtinLegacyKey ? normalizeText(migrated[builtinLegacyKey]) : ''
+    const normalizedSecretBelongsToBuiltin =
+      isPendingBuiltinProviderIdMigration &&
+      builtinLegacySecret &&
+      builtinLegacySecret === normalizeText(normalizedIdSecret)
+    if (hasDistinctRawId && hasRawIdSecret && !unchangedProviderIds.has(oldProviderId)) {
+      rawProviderSecretIdsToDelete.add(oldRawProviderId)
+    }
+    if (
+      !usesBuiltinSecretSlot &&
+      hasMultipleProviderIdRenames &&
+      hasUniqueCanonicalRawIdOwner &&
+      !hasDistinctRawId &&
+      hasRawIdSecret
+    ) {
+      rawProviderSecretIdsToDelete.add(oldProviderId)
+    }
+    let hasOldSecret = false
+    let oldSecret
+    let usesNormalizedBuiltinSecretSlot = false
     if (
-      !Object.hasOwn(providerSecrets, newProviderId) ||
-      providerSecrets[newProviderId] !== oldSecret
+      hasDistinctRawId &&
+      hasRawIdSecret &&
+      (hasMultipleProviderIdRenames ||
+        !isPendingBuiltinProviderIdMigration ||
+        !hasNormalizedIdSecret ||
+        normalizedSecretBelongsToBuiltin ||
+        rawSecretValue)
+    ) {
+      hasOldSecret = true
+      oldSecret =
+        !usesBuiltinSecretSlot && rawIdSecret === '' && hasNormalizedIdSecret
+          ? normalizedIdSecret
+          : rawIdSecret
+    } else if (
+      isPendingBuiltinProviderIdMigration &&
+      hasNormalizedIdSecret &&
+      !normalizedSecretBelongsToBuiltin &&
+      (!hasMultipleProviderIdRenames || !hasUniqueCanonicalRawIdOwner || !hasDistinctRawId) &&
+      (normalizedSecretValue || !rawSecretValue)
+    ) {
+      hasOldSecret = true
+      oldSecret = normalizedIdSecret
+      usesNormalizedBuiltinSecretSlot = true
+    } else if (
+      !usesBuiltinSecretSlot &&
+      (!hasMultipleProviderIdRenames || !hasDistinctRawId) &&
+      (hasRawIdSecret || hasNormalizedIdSecret)
+    ) {
+      hasOldSecret = true
+      oldSecret =
+        hasRawIdSecret && rawIdSecret !== ''
+          ? rawIdSecret
+          : hasNormalizedIdSecret
+          ? normalizedIdSecret
+          : rawIdSecret
+    }
+    if (
+      hasOldSecret &&
+      (!Object.hasOwn(providerSecrets, newProviderId) ||
+        providerSecrets[newProviderId] !== oldSecret)
     ) {
       providerSecrets[newProviderId] = oldSecret
       dirty = true
     }
-    if (hasRawIdSecret && oldRawProviderId !== oldProviderId) {
-      delete providerSecrets[oldRawProviderId]
+    if (
+      usesNormalizedBuiltinSecretSlot ||
+      (isPendingBuiltinProviderIdMigration &&
+        hasNormalizedIdSecret &&
+        !normalizedSecretBelongsToBuiltin &&
+        !normalizedSecretValue &&
+        rawSecretValue)
+    ) {
+      builtinProviderSecretIdsToDelete.set(oldProviderId, normalizedIdSecret)
+    }
+  }
+  for (const providerId of rawProviderSecretIdsToDelete) {
+    if (Object.hasOwn(providerSecrets, providerId)) {
+      delete providerSecrets[providerId]
       dirty = true
     }
   }
+  for (const [providerId, migratedCustomSecret] of builtinProviderSecretIdsToDelete) {
+    const legacyKey = LEGACY_API_KEY_FIELD_BY_PROVIDER_ID[providerId]
+    const builtinLegacySecret = legacyKey ? normalizeText(migrated[legacyKey]) : ''
+    if (builtinLegacySecret && builtinLegacySecret !== normalizeText(migratedCustomSecret)) {
+      if (providerSecrets[providerId] !== builtinLegacySecret) {
+        providerSecrets[providerId] = builtinLegacySecret
+        dirty = true
+      }
+      continue
+    }
+    if (Object.hasOwn(providerSecrets, providerId)) {
+      delete providerSecrets[providerId]
+      dirty = true
+    }
+    if (legacyKey && normalizeText(migrated[legacyKey])) {
+      migrated[legacyKey] = ''
+      dirty = true
+    }
+  }
+  for (const providerId of NEWLY_RESERVED_BUILTIN_PROVIDER_IDS) {
+    completedBuiltinProviderIdMigrations.add(providerId)
+  }
+  const completedBuiltinProviderIdMigrationList = [...completedBuiltinProviderIdMigrations]
+  if (
+    JSON.stringify(migrated.completedBuiltinProviderIdMigrations) !==
+    JSON.stringify(completedBuiltinProviderIdMigrationList)
+  ) {
+    migrated.completedBuiltinProviderIdMigrations = completedBuiltinProviderIdMigrationList
+    dirty = true
+  }
 
   const activeCustomProviderIds = new Set(
     customOpenAIProviders.map((provider) => normalizeText(provider?.id)).filter(Boolean),
@@ -1287,11 +1529,25 @@ function migrateUserConfig(options) {
     const rawProviderId = normalizeText(originalRawId)
     const normalizedProviderId = normalizeText(provider?.id)
     if (!rawProviderId || !normalizedProviderId || rawProviderId === normalizedProviderId) continue
+    if (builtinProviderIds.has(normalizeProviderId(rawProviderId))) continue
     if (!Object.hasOwn(providerSecrets, rawProviderId)) continue
-    const rawSecret = providerSecrets[rawProviderId]
+    const snapshotHasRawSecret = Object.hasOwn(providerSecretSnapshot, rawProviderId)
+    const snapshotRawSecret = snapshotHasRawSecret
+      ? providerSecretSnapshot[rawProviderId]
+      : undefined
+    const hasCanonicalProviderIdCollision =
+      normalizedProviderResults.filter(
+        ({ originalId }) => originalId === normalizeProviderId(rawProviderId),
+      ).length > 1
+    if (hasCanonicalProviderIdCollision && !snapshotHasRawSecret) continue
+    const shouldPreferDistinctRawSecret =
+      snapshotHasRawSecret && snapshotRawSecret !== '' && hasCanonicalProviderIdCollision
+    const rawSecret = shouldPreferDistinctRawSecret
+      ? snapshotRawSecret
+      : providerSecrets[rawProviderId]
     const shouldPreserveRawSecretSlot =
       builtinProviderIds.has(rawProviderId) || activeCustomProviderIds.has(rawProviderId)
-    if (!Object.hasOwn(providerSecrets, normalizedProviderId)) {
+    if (shouldPreferDistinctRawSecret || !Object.hasOwn(providerSecrets, normalizedProviderId)) {
       providerSecrets[normalizedProviderId] = rawSecret
       dirty = true
     }
@@ -1312,6 +1568,7 @@ function migrateUserConfig(options) {
     JSON.stringify(customApiModes) !== JSON.stringify(migrated.customApiModes)
   let customProvidersDirty = false
   const migratedCustomModeProviderIds = new Map()
+  const migratedCustomModeProviderIdsByCanonicalSignature = new Map()
   const pendingLegacyCustomUrlProviderSecretBackfillIds = new Set()
   const getLegacyCustomProviderSecret = () =>
     normalizeText(providerSecrets['legacy-custom-default'])
@@ -1345,13 +1602,20 @@ function migrateUserConfig(options) {
       }
     }
   }
-  const getCustomModeMigrationSignature = (apiMode) =>
+  const getCustomModeMigrationSignature = (apiMode, includeRawProviderId = true) =>
     JSON.stringify({
       groupName: normalizeText(apiMode?.groupName),
       itemName: normalizeText(apiMode?.itemName),
       isCustom: Boolean(apiMode?.isCustom),
       customName: normalizeText(apiMode?.customName),
       customUrl: normalizeEndpointUrlForCompare(normalizeText(apiMode?.customUrl)),
+      ...(includeRawProviderId
+        ? {
+            providerIdRaw: normalizeText(
+              typeof apiMode?.providerId === 'string' ? apiMode.providerId : '',
+            ),
+          }
+        : {}),
       providerId: normalizeProviderId(
         typeof apiMode?.providerId === 'string' ? apiMode.providerId : '',
       ),
@@ -1377,11 +1641,21 @@ function migrateUserConfig(options) {
       `custom-provider-${customProviderCounter}`
     const providerId = ensureUniqueProviderId(providerIdSet, preferredId)
     providerIdSet.add(providerId)
+    const legacyProviderIds = getLegacyProviderIds(
+      [
+        ...(Array.isArray(sourceProvider?.legacyProviderIds)
+          ? sourceProvider.legacyProviderIds
+          : []),
+        ...(targetProviderId === 'legacy-custom-default' ? [] : [targetProviderId]),
+      ],
+      providerId,
+    )
     const provider = sourceProvider
       ? {
           ...sourceProvider,
           id: providerId,
           name: providerName,
+          ...(legacyProviderIds.length > 0 ? { legacyProviderIds } : {}),
         }
       : {
           id: providerId,
@@ -1394,6 +1668,7 @@ function migrateUserConfig(options) {
           completionsUrl: '',
           enabled: true,
           allowLegacyResponseField: true,
+          ...(legacyProviderIds.length > 0 ? { legacyProviderIds } : {}),
         }
     customOpenAIProviders.push(provider)
     customProvidersDirty = true
@@ -1401,7 +1676,12 @@ function migrateUserConfig(options) {
     return providerId
   }
   const promoteCustomModeApiKeyToProvider = (apiMode, apiModeKey) => {
-    const targetProviderId = normalizeText(apiMode.providerId) || 'legacy-custom-default'
+    const targetProviderId = normalizeProviderId(apiMode.providerId) || 'legacy-custom-default'
+    const targetsUnresolvedReservedBuiltin =
+      NEWLY_RESERVED_BUILTIN_PROVIDER_IDS.has(targetProviderId) &&
+      !customOpenAIProviders.some((provider) => provider.id === targetProviderId)
+    if (targetsUnresolvedReservedBuiltin) return ''
+
     const existingProviderSecret = normalizeText(providerSecrets[targetProviderId])
     if (!hasOwnProviderSecret(targetProviderId)) {
       providerSecrets[targetProviderId] = apiModeKey
@@ -1444,6 +1724,7 @@ function migrateUserConfig(options) {
     }
 
     const originalCustomModeSignature = getCustomModeMigrationSignature(apiMode)
+    const originalCanonicalCustomModeSignature = getCustomModeMigrationSignature(apiMode, false)
     const existingProviderIdRaw = typeof apiMode.providerId === 'string' ? apiMode.providerId : ''
     const existingProviderId = normalizeProviderId(existingProviderIdRaw)
     if (existingProviderId && existingProviderIdRaw !== existingProviderId) {
@@ -1451,9 +1732,14 @@ function migrateUserConfig(options) {
       customApiModesDirty = true
     }
     let providerIdAssignedFromLegacyCustomUrl = false
-    const renamedProviderId = providerIdRenameLookup.get(existingProviderId)
+    const renamedProviderId = resolveRenamedProviderId(
+      existingProviderId,
+      existingProviderIdRaw,
+      apiMode.customUrl,
+    )
     if (renamedProviderId && normalizeText(apiMode.providerId) !== renamedProviderId) {
       apiMode.providerId = renamedProviderId
+      addLegacyProviderId(apiMode, existingProviderId)
       customApiModesDirty = true
     }
 
@@ -1502,15 +1788,19 @@ function migrateUserConfig(options) {
     const apiModeKey = normalizeText(apiMode.apiKey)
     if (apiModeKey) {
       const promotedProviderId = promoteCustomModeApiKeyToProvider(apiMode, apiModeKey)
-      if (normalizeText(apiMode.providerId) !== promotedProviderId) {
-        apiMode.providerId = promotedProviderId
-        customApiModesDirty = true
-      }
-      if (normalizeText(apiMode.apiKey)) {
-        // Mode-level custom keys are treated as legacy data; after migration,
-        // providerSecrets is the single source of truth.
-        apiMode.apiKey = ''
-        customApiModesDirty = true
+      if (promotedProviderId) {
+        if (normalizeText(apiMode.providerId) !== promotedProviderId) {
+          const previousProviderId = apiMode.providerId
+          apiMode.providerId = promotedProviderId
+          addLegacyProviderId(apiMode, previousProviderId)
+          customApiModesDirty = true
+        }
+        if (normalizeText(apiMode.apiKey)) {
+          // Mode-level custom keys are treated as legacy data; after migration,
+          // providerSecrets is the single source of truth.
+          apiMode.apiKey = ''
+          customApiModesDirty = true
+        }
       }
     } else if (providerIdAssignedFromLegacyCustomUrl) {
       queueLegacyCustomUrlProviderSecretBackfill(apiMode.providerId)
@@ -1520,6 +1810,24 @@ function migrateUserConfig(options) {
       originalCustomModeSignature,
       normalizeText(apiMode.providerId),
     )
+    const migratedProviderId = normalizeText(apiMode.providerId)
+    if (
+      !migratedCustomModeProviderIdsByCanonicalSignature.has(originalCanonicalCustomModeSignature)
+    ) {
+      migratedCustomModeProviderIdsByCanonicalSignature.set(
+        originalCanonicalCustomModeSignature,
+        migratedProviderId,
+      )
+    } else if (
+      migratedCustomModeProviderIdsByCanonicalSignature.get(
+        originalCanonicalCustomModeSignature,
+      ) !== migratedProviderId
+    ) {
+      migratedCustomModeProviderIdsByCanonicalSignature.set(
+        originalCanonicalCustomModeSignature,
+        '',
+      )
+    }
   }
   backfillPendingLegacyCustomUrlProviderSecrets()
 
@@ -1531,6 +1839,14 @@ function migrateUserConfig(options) {
     const originalSelectedCustomModeSignature = selectedIsCustom
       ? getCustomModeMigrationSignature(selectedApiMode)
       : ''
+    const originalSelectedCanonicalCustomModeSignature = selectedIsCustom
+      ? getCustomModeMigrationSignature(selectedApiMode, false)
+      : ''
+    const originalSelectedCanonicalProviderId = selectedIsCustom
+      ? normalizeProviderId(selectedApiMode.providerId)
+      : ''
+    const selectedCanonicalProviderIdHasCollision =
+      selectedIsCustom && hasCanonicalProviderIdCollision(originalSelectedCanonicalProviderId)
 
     if (selectedIsCustom) {
       const existingSelectedProviderIdRaw =
@@ -1543,22 +1859,37 @@ function migrateUserConfig(options) {
         selectedApiMode.providerId = existingSelectedProviderId
         selectedApiModeDirty = true
       }
-      const renamedSelectedProviderId = providerIdRenameLookup.get(existingSelectedProviderId)
+      const renamedSelectedProviderId = resolveRenamedProviderId(
+        existingSelectedProviderId,
+        existingSelectedProviderIdRaw,
+        selectedApiMode.customUrl,
+      )
       if (
         renamedSelectedProviderId &&
         normalizeText(selectedApiMode.providerId) !== renamedSelectedProviderId
       ) {
         selectedApiMode.providerId = renamedSelectedProviderId
+        addLegacyProviderId(selectedApiMode, existingSelectedProviderId)
         selectedApiModeDirty = true
       }
     }
 
     if (selectedIsCustom) {
-      const migratedProviderId = migratedCustomModeProviderIds.get(
+      const exactMigratedProviderId = migratedCustomModeProviderIds.get(
         originalSelectedCustomModeSignature,
       )
+      const migratedProviderId =
+        exactMigratedProviderId ||
+        (!selectedCanonicalProviderIdHasCollision &&
+        normalizeText(selectedApiMode.providerId) === originalSelectedCanonicalProviderId
+          ? migratedCustomModeProviderIdsByCanonicalSignature.get(
+              originalSelectedCanonicalCustomModeSignature,
+            )
+          : '')
       if (migratedProviderId && normalizeText(selectedApiMode.providerId) !== migratedProviderId) {
+        const previousSelectedProviderId = selectedApiMode.providerId
         selectedApiMode.providerId = migratedProviderId
+        addLegacyProviderId(selectedApiMode, previousSelectedProviderId)
         selectedApiModeDirty = true
       }
     }
@@ -1626,30 +1957,31 @@ function migrateUserConfig(options) {
       const migratedProviderId = selectedIsCustom
         ? migratedCustomModeProviderIds.get(originalSelectedCustomModeSignature)
         : ''
-      if (migratedProviderId) {
-        if (normalizeText(selectedApiMode.providerId) !== migratedProviderId) {
-          selectedApiMode.providerId = migratedProviderId
-          selectedApiModeDirty = true
+      if (migratedProviderId && normalizeText(selectedApiMode.providerId) !== migratedProviderId) {
+        const previousSelectedProviderId = selectedApiMode.providerId
+        selectedApiMode.providerId = migratedProviderId
+        addLegacyProviderId(selectedApiMode, previousSelectedProviderId)
+        selectedApiModeDirty = true
+      }
+      const targetProviderId = selectedIsCustom
+        ? promoteCustomModeApiKeyToProvider(selectedApiMode, selectedApiModeKey)
+        : API_MODE_GROUP_TO_PROVIDER_ID[normalizeText(selectedApiMode.groupName)] ||
+          normalizeText(selectedApiMode.providerId)
+      if (targetProviderId && normalizeText(selectedApiMode.providerId) !== targetProviderId) {
+        const previousSelectedProviderId = selectedApiMode.providerId
+        selectedApiMode.providerId = targetProviderId
+        if (selectedIsCustom) {
+          addLegacyProviderId(selectedApiMode, previousSelectedProviderId)
         }
+        selectedApiModeDirty = true
+      }
+      if (targetProviderId && !selectedIsCustom && !hasOwnProviderSecret(targetProviderId)) {
+        providerSecrets[targetProviderId] = selectedApiModeKey
+        dirty = true
+      }
+      if (targetProviderId) {
         selectedApiMode.apiKey = ''
         selectedApiModeDirty = true
-      } else {
-        const targetProviderId = selectedIsCustom
-          ? promoteCustomModeApiKeyToProvider(selectedApiMode, selectedApiModeKey)
-          : API_MODE_GROUP_TO_PROVIDER_ID[normalizeText(selectedApiMode.groupName)] ||
-            normalizeText(selectedApiMode.providerId)
-        if (targetProviderId && normalizeText(selectedApiMode.providerId) !== targetProviderId) {
-          selectedApiMode.providerId = targetProviderId
-          selectedApiModeDirty = true
-        }
-        if (targetProviderId && !selectedIsCustom && !hasOwnProviderSecret(targetProviderId)) {
-          providerSecrets[targetProviderId] = selectedApiModeKey
-          dirty = true
-        }
-        if (targetProviderId) {
-          selectedApiMode.apiKey = ''
-          selectedApiModeDirty = true
-        }
       }
     }
     backfillPendingLegacyCustomUrlProviderSecrets()
@@ -1865,6 +2197,12 @@ export async function getUserConfig() {
     if (options.configSchemaVersion !== migrated.configSchemaVersion) {
       payload.configSchemaVersion = migrated.configSchemaVersion
     }
+    if (
+      JSON.stringify(options.completedBuiltinProviderIdMigrations) !==
+      JSON.stringify(migrated.completedBuiltinProviderIdMigrations)
+    ) {
+      payload.completedBuiltinProviderIdMigrations = migrated.completedBuiltinProviderIdMigrations
+    }
     if (migrated.customChatGptWebApiUrl !== undefined) {
       if (options.customChatGptWebApiUrl !== migrated.customChatGptWebApiUrl) {
         payload.customChatGptWebApiUrl = migrated.customChatGptWebApiUrl
diff --git a/src/popup/sections/ApiModes.jsx b/src/popup/sections/ApiModes.jsx
index 56ef7cd0..5f39e0fa 100644
--- a/src/popup/sections/ApiModes.jsx
+++ b/src/popup/sections/ApiModes.jsx
@@ -17,6 +17,7 @@ import {
   applySelectedProviderToApiMode,
   applyDeletedProviderSecrets,
   applyPendingProviderChanges,
+  areProviderIdsEquivalent,
   buildEditedProvider,
   createProviderId,
   getApiModeDisplayLabel,
@@ -400,7 +401,7 @@ export function ApiModes({ config, updateConfig }) {
         return
       }
       const shouldClearProviderDerivedFields =
-        editingIndex !== -1 && selectedProviderId !== previousProviderId
+        editingIndex !== -1 && !areProviderIdsEquivalent(selectedProviderId, previousProviderId)
       const isEndpointProviderManaged = editingIndex === -1
       nextApiMode = applySelectedProviderToApiMode(
         nextApiMode,
diff --git a/src/popup/sections/api-modes-provider-utils.mjs b/src/popup/sections/api-modes-provider-utils.mjs
index 90d41780..a4eaf32c 100644
--- a/src/popup/sections/api-modes-provider-utils.mjs
+++ b/src/popup/sections/api-modes-provider-utils.mjs
@@ -25,6 +25,15 @@ function normalizeProviderId(value) {
     .replace(/^-+|-+$/g, '')
 }
 
+export function areProviderIdsEquivalent(firstProviderId, secondProviderId) {
+  const normalizedFirstProviderId = normalizeProviderId(firstProviderId)
+  const normalizedSecondProviderId = normalizeProviderId(secondProviderId)
+  if (!normalizedFirstProviderId || !normalizedSecondProviderId) {
+    return normalizeText(firstProviderId) === normalizeText(secondProviderId)
+  }
+  return normalizedFirstProviderId === normalizedSecondProviderId
+}
+
 function normalizeProviderEndpointUrl(value) {
   return normalizeText(value).replace(/\/+$/, '')
 }
@@ -95,6 +104,11 @@ export function createProviderId(providerName, existingProviders, reservedProvid
   const usedIds = new Set([
     ...reservedProviderIds.map((providerId) => normalizeProviderId(providerId)),
     ...providers.map((provider) => normalizeProviderId(provider.id)),
+    ...providers.flatMap((provider) =>
+      (Array.isArray(provider?.legacyProviderIds) ? provider.legacyProviderIds : []).map(
+        normalizeProviderId,
+      ),
+    ),
   ])
 
   const baseId = normalizeProviderId(providerName) || `custom-provider-${providers.length + 1}`
@@ -310,6 +324,9 @@ export function applySelectedProviderToApiMode(
   const currentProviderId = normalizeText(nextApiMode.providerId)
   const nextProviderId = normalizeText(selectedProviderId)
   nextApiMode.providerId = nextProviderId
+  if (!areProviderIdsEquivalent(currentProviderId, nextProviderId)) {
+    delete nextApiMode.legacyProviderIds
+  }
   const shouldPreserveLegacyCustomUrl =
     !isEndpointProviderManaged &&
     !shouldClearProviderDerivedFields &&
@@ -332,6 +349,7 @@ export function sanitizeApiModeForSave(apiMode) {
     nextApiMode.apiKey = ''
     nextApiMode.customUrl = ''
     delete nextApiMode.sourceProviderId
+    delete nextApiMode.legacyProviderIds
   }
   return nextApiMode
 }
@@ -425,7 +443,7 @@ export function isProviderReferencedByApiModes(providerId, apiModes = []) {
   return (Array.isArray(apiModes) ? apiModes : []).some(
     (apiMode) =>
       normalizeText(apiMode?.groupName) === 'customApiModelKeys' &&
-      normalizeText(apiMode?.providerId) === normalizedProviderId,
+      areProviderIdsEquivalent(apiMode?.providerId, normalizedProviderId),
   )
 }
 
@@ -444,12 +462,16 @@ export function getProviderDeleteDisabledReasonKey(
   return ''
 }
 
-function getProvidersMatchingLegacySessionUrl(providers = [], session = null) {
+function getProvidersMatchingLegacySessionUrl(
+  providers = [],
+  session = null,
+  { includeDisabled = false } = {},
+) {
   const customUrl = normalizeProviderEndpointUrl(session?.apiMode?.customUrl)
   if (!customUrl) return []
 
   return (Array.isArray(providers) ? providers : []).filter((provider) => {
-    if (provider?.enabled === false) return false
+    if (!includeDisabled && provider?.enabled === false) return false
 
     const directChatCompletionsUrl = normalizeProviderEndpointUrl(provider?.chatCompletionsUrl)
     if (directChatCompletionsUrl && directChatCompletionsUrl === customUrl) return true
@@ -460,21 +482,25 @@ function getProvidersMatchingLegacySessionUrl(providers = [], session = null) {
   })
 }
 
-function getProvidersMatchingSessionProviderId(providers = [], providerId = '') {
+function getProvidersMatchingSessionProviderId(
+  providers = [],
+  providerId = '',
+  { includeDisabled = false } = {},
+) {
   const normalizedProviderId = normalizeText(providerId)
   if (!normalizedProviderId) return []
 
-  const exactMatches = (Array.isArray(providers) ? providers : []).filter(
-    (provider) =>
-      provider?.enabled !== false && normalizeText(provider?.id) === normalizedProviderId,
-  )
-  if (exactMatches.length > 0) return exactMatches
-
   const migratedProviderId = normalizeProviderId(normalizedProviderId)
-  if (!migratedProviderId || migratedProviderId === normalizedProviderId) return []
-
-  return (Array.isArray(providers) ? providers : []).filter(
-    (provider) => provider?.enabled !== false && normalizeText(provider?.id) === migratedProviderId,
+  if (!migratedProviderId) return []
+  const availableProviders = (Array.isArray(providers) ? providers : []).filter(
+    (provider) => includeDisabled || provider?.enabled !== false,
+  )
+  return availableProviders.filter(
+    (provider) =>
+      normalizeText(provider?.id) === normalizedProviderId ||
+      (Array.isArray(provider?.legacyProviderIds) &&
+        provider.legacyProviderIds.map(normalizeProviderId).includes(migratedProviderId)) ||
+      normalizeProviderId(provider?.id) === migratedProviderId,
   )
 }
 
@@ -527,17 +553,20 @@ export function getReferencedCustomProviderIdsFromSessions(
   const referencedProviderIds = new Set()
   for (const session of Array.isArray(sessions) ? sessions : []) {
     if (normalizeText(session?.apiMode?.groupName) !== 'customApiModelKeys') continue
+    let ambiguousProviderIdMatches = []
     const providerId = normalizeText(session?.apiMode?.providerId)
     if (providerId && providerId !== 'legacy-custom-default') {
-      const matchedProviders = getProvidersMatchingSessionProviderId(providers, providerId)
-      if (matchedProviders.length > 0) {
-        for (const provider of matchedProviders) {
-          const matchedProviderId = normalizeText(provider?.id)
-          if (matchedProviderId && matchedProviderId !== 'legacy-custom-default') {
-            referencedProviderIds.add(matchedProviderId)
-          }
+      const matchedProviders = getProvidersMatchingSessionProviderId(providers, providerId, {
+        includeDisabled: true,
+      })
+      if (matchedProviders.length === 1) {
+        const matchedProviderId = normalizeText(matchedProviders[0]?.id)
+        if (matchedProviderId && matchedProviderId !== 'legacy-custom-default') {
+          referencedProviderIds.add(matchedProviderId)
+          continue
         }
-        continue
+      } else if (matchedProviders.length > 1) {
+        ambiguousProviderIdMatches = matchedProviders
       }
       if (!(Array.isArray(providers) ? providers : []).length) {
         referencedProviderIds.add(providerId)
@@ -545,7 +574,11 @@ export function getReferencedCustomProviderIdsFromSessions(
       }
     }
 
-    const matchedByCustomUrl = getProvidersMatchingLegacySessionUrl(providers, session)
+    const recoveryProviders =
+      ambiguousProviderIdMatches.length > 0 ? ambiguousProviderIdMatches : providers
+    const matchedByCustomUrl = getProvidersMatchingLegacySessionUrl(recoveryProviders, session, {
+      includeDisabled: ambiguousProviderIdMatches.length > 0,
+    })
     if (matchedByCustomUrl.length > 0) {
       for (const provider of matchedByCustomUrl) {
         const matchedProviderId = normalizeText(provider?.id)
@@ -556,15 +589,34 @@ export function getReferencedCustomProviderIdsFromSessions(
       continue
     }
 
-    for (const matchedProviderId of getProviderIdsMatchingSessionLabel(
-      session,
-      providers,
-      apiModes,
-    )) {
+    for (const provider of ambiguousProviderIdMatches) {
+      const matchedProviderId = normalizeText(provider?.id)
+      if (
+        provider?.enabled === false &&
+        areProviderIdsEquivalent(matchedProviderId, providerId) &&
+        matchedProviderId !== 'legacy-custom-default'
+      ) {
+        referencedProviderIds.add(matchedProviderId)
+      }
+    }
+
+    const matchedProviderIdsByLabel =
+      ambiguousProviderIdMatches.length === 0
+        ? getProviderIdsMatchingSessionLabel(session, providers, apiModes)
+        : []
+    for (const matchedProviderId of matchedProviderIdsByLabel) {
       if (matchedProviderId && matchedProviderId !== 'legacy-custom-default') {
         referencedProviderIds.add(matchedProviderId)
       }
     }
+    if (matchedProviderIdsByLabel.length === 0) {
+      for (const provider of ambiguousProviderIdMatches) {
+        const matchedProviderId = normalizeText(provider?.id)
+        if (matchedProviderId && matchedProviderId !== 'legacy-custom-default') {
+          referencedProviderIds.add(matchedProviderId)
+        }
+      }
+    }
   }
   return Array.from(referencedProviderIds)
 }
@@ -577,15 +629,30 @@ export function getApiModeDisplayLabel(apiMode, t, providers = []) {
     return fallbackLabel
   }
 
-  const providerId = normalizeProviderId(apiMode?.providerId)
+  const rawProviderId = apiMode?.providerId
+  const providerId = normalizeProviderId(rawProviderId)
   const customModelName = normalizeText(apiMode?.customName)
   if (!providerId || providerId === 'legacy-custom-default') {
     return fallbackLabel
   }
 
-  const provider = (Array.isArray(providers) ? providers : []).find(
-    (item) => normalizeProviderId(item?.id) === providerId,
-  )
+  const matchedProviders = getProvidersMatchingSessionProviderId(providers, rawProviderId, {
+    includeDisabled: true,
+  })
+  const matchedProvidersByUrl =
+    matchedProviders.length > 1
+      ? getProvidersMatchingLegacySessionUrl(
+          matchedProviders,
+          { apiMode },
+          { includeDisabled: true },
+        )
+      : []
+  const provider =
+    matchedProviders.length === 1
+      ? matchedProviders[0]
+      : matchedProvidersByUrl.length === 1
+      ? matchedProvidersByUrl[0]
+      : null
   const providerName = normalizeText(provider?.name)
   if (!providerName) return fallbackLabel
   if (!customModelName) return providerName
@@ -599,9 +666,9 @@ export function getConversationAiName(session, t, providers = []) {
     normalizeText(apiMode?.groupName) === 'customApiModelKeys' &&
     normalizeProviderId(apiMode?.providerId) &&
     normalizeProviderId(apiMode?.providerId) !== 'legacy-custom-default' &&
-    !(Array.isArray(providers) ? providers : []).some(
-      (provider) => normalizeProviderId(provider?.id) === normalizeProviderId(apiMode?.providerId),
-    )
+    getProvidersMatchingSessionProviderId(providers, apiMode?.providerId, {
+      includeDisabled: true,
+    }).length === 0
 
   if (hasMissingCustomProvider) {
     providerAwareName = ''
diff --git a/src/popup/sections/import-data-cleanup.mjs b/src/popup/sections/import-data-cleanup.mjs
index 125a0ebc..83e307b7 100644
--- a/src/popup/sections/import-data-cleanup.mjs
+++ b/src/popup/sections/import-data-cleanup.mjs
@@ -4,6 +4,7 @@ import {
   canonicalizeModelKeyArray,
   canonicalizeSessionModelFields,
 } from '../../config/model-key-migrations.mjs'
+import { LEGACY_API_KEY_FIELD_BY_PROVIDER_ID } from '../../config/openai-provider-mappings.mjs'
 
 const conflictingKeyPairs = [
   ['claudeApiKey', 'anthropicApiKey'],
@@ -13,9 +14,82 @@ const conflictingKeyPairs = [
 const apiModeListKeys = ['activeApiModes', 'customApiModes', 'knownApiModeDefaultIds']
 const apiModeSelectionKeys = ['modelName', 'apiMode']
 
+function normalizeProviderId(value) {
+  return typeof value === 'string'
+    ? value
+        .trim()
+        .toLowerCase()
+        .replace(/[^a-z0-9]+/g, '-')
+        .replace(/^-+|-+$/g, '')
+    : ''
+}
+
+async function preserveExistingBuiltinSecrets(storageArea, data, normalizedData) {
+  if (
+    !Object.hasOwn(data, 'customOpenAIProviders') ||
+    Object.hasOwn(data, 'providerSecrets') ||
+    !Array.isArray(data.customOpenAIProviders) ||
+    typeof storageArea.get !== 'function'
+  ) {
+    return
+  }
+
+  const importedProviderIds = new Set(
+    data.customOpenAIProviders.map((provider) => normalizeProviderId(provider?.id)).filter(Boolean),
+  )
+  const relevantProviderIds = [...importedProviderIds].filter((providerId) =>
+    Object.hasOwn(LEGACY_API_KEY_FIELD_BY_PROVIDER_ID, providerId),
+  )
+  if (relevantProviderIds.length === 0) return
+
+  const legacyKeys = relevantProviderIds.map(
+    (providerId) => LEGACY_API_KEY_FIELD_BY_PROVIDER_ID[providerId],
+  )
+  const stored = await storageArea.get([
+    'completedBuiltinProviderIdMigrations',
+    'customOpenAIProviders',
+    'providerSecrets',
+    ...legacyKeys,
+  ])
+  const completedMigrations = new Set(
+    Array.isArray(stored.completedBuiltinProviderIdMigrations)
+      ? stored.completedBuiltinProviderIdMigrations.map(normalizeProviderId).filter(Boolean)
+      : [],
+  )
+  const existingProviderIds = new Set(
+    (Array.isArray(stored.customOpenAIProviders) ? stored.customOpenAIProviders : [])
+      .map((provider) => normalizeProviderId(provider?.id))
+      .filter(Boolean),
+  )
+  const existingProviderSecrets =
+    stored.providerSecrets && typeof stored.providerSecrets === 'object'
+      ? stored.providerSecrets
+      : {}
+
+  for (const providerId of relevantProviderIds) {
+    const legacyKey = LEGACY_API_KEY_FIELD_BY_PROVIDER_ID[providerId]
+    if (
+      completedMigrations.has(providerId) &&
+      !existingProviderIds.has(providerId) &&
+      Object.hasOwn(existingProviderSecrets, providerId)
+    ) {
+      normalizedData[legacyKey] = existingProviderSecrets[providerId]
+    }
+  }
+}
+
 export function prepareImportData(data) {
   const normalizedData = { ...data }
   const keysToRemove = []
+  const importsCompleteProviderState =
+    Object.hasOwn(data, 'customOpenAIProviders') && Object.hasOwn(data, 'providerSecrets')
+
+  if (
+    importsCompleteProviderState &&
+    !Object.hasOwn(data, 'completedBuiltinProviderIdMigrations')
+  ) {
+    normalizedData.completedBuiltinProviderIdMigrations = []
+  }
 
   if (apiModeListKeys.some((key) => Object.hasOwn(data, key))) {
     for (const key of apiModeListKeys) {
@@ -69,6 +143,8 @@ export function prepareImportData(data) {
 export async function importDataIntoStorage(storageArea, data) {
   const { normalizedData, keysToRemove } = prepareImportData(data)
 
+  await preserveExistingBuiltinSecrets(storageArea, data, normalizedData)
+
   await storageArea.set(normalizedData)
 
   if (keysToRemove.length > 0) {
diff --git a/src/services/apis/provider-registry.mjs b/src/services/apis/provider-registry.mjs
index 0f072467..206cc448 100644
--- a/src/services/apis/provider-registry.mjs
+++ b/src/services/apis/provider-registry.mjs
@@ -198,7 +198,7 @@ function getConfiguredCustomApiModes(config) {
         itemName: toStringOrEmpty(apiMode.itemName).trim(),
         isCustom: Boolean(apiMode.isCustom),
         customName: toStringOrEmpty(apiMode.customName).trim(),
-        providerId: normalizeProviderId(apiMode.providerId),
+        providerId: toStringOrEmpty(apiMode.providerId).trim(),
       })
       if (seen.has(signature)) return false
       seen.add(signature)
@@ -207,21 +207,27 @@ function getConfiguredCustomApiModes(config) {
 }
 
 function getConfiguredCustomApiModesForProvider(config, providerId) {
+  const exactProviderId = toStringOrEmpty(providerId).trim()
   const normalizedProviderId = normalizeProviderId(providerId)
   if (!normalizedProviderId) return []
-  return getConfiguredCustomApiModes(config).filter(
-    (apiMode) => normalizeProviderId(apiMode?.providerId) === normalizedProviderId,
+  const hasCanonicalProviderIdCollision =
+    getAllOpenAIProviders(config).filter(
+      (provider) => normalizeProviderId(provider.id) === normalizedProviderId,
+    ).length > 1
+  return getConfiguredCustomApiModes(config).filter((apiMode) =>
+    hasCanonicalProviderIdCollision
+      ? toStringOrEmpty(apiMode?.providerId).trim() === exactProviderId
+      : normalizeProviderId(apiMode?.providerId) === normalizedProviderId,
   )
 }
 
 function findConfiguredCustomApiMode(config, sessionApiMode, providerId) {
-  const normalizedProviderId = normalizeProviderId(providerId)
   const normalizedSessionApiMode = normalizeStableCustomApiModeIdentity(sessionApiMode, providerId)
   if (!normalizedSessionApiMode || normalizedSessionApiMode.groupName !== 'customApiModelKeys') {
     return null
   }
 
-  const providerCandidates = getConfiguredCustomApiModesForProvider(config, normalizedProviderId)
+  const providerCandidates = getConfiguredCustomApiModesForProvider(config, providerId)
   const exactCandidates = providerCandidates.filter((apiMode) => {
     const normalizedCandidate = normalizeStableCustomApiModeIdentity(apiMode)
     return (
@@ -234,7 +240,11 @@ function findConfiguredCustomApiMode(config, sessionApiMode, providerId) {
   return null
 }
 
-function findConfiguredCustomApiModeBySessionLabel(config, sessionApiMode) {
+function findConfiguredCustomApiModeBySessionLabel(
+  config,
+  sessionApiMode,
+  allowedProviderIds = [],
+) {
   if (!sessionApiMode || typeof sessionApiMode !== 'object') return null
   if (toStringOrEmpty(sessionApiMode.groupName).trim() !== 'customApiModelKeys') return null
 
@@ -244,8 +254,15 @@ function findConfiguredCustomApiModeBySessionLabel(config, sessionApiMode) {
     isCustom: Boolean(sessionApiMode.isCustom),
     customName: toStringOrEmpty(sessionApiMode.customName).trim(),
   }
+  const normalizedAllowedProviderIds = new Set(allowedProviderIds.map(normalizeProviderId))
   const allCandidates = getConfiguredCustomApiModes(config).filter((apiMode) => {
     if (!apiMode || typeof apiMode !== 'object') return false
+    if (
+      normalizedAllowedProviderIds.size > 0 &&
+      !normalizedAllowedProviderIds.has(normalizeProviderId(apiMode.providerId))
+    ) {
+      return false
+    }
     return (
       toStringOrEmpty(apiMode.groupName).trim() === normalizedSessionLabel.groupName &&
       toStringOrEmpty(apiMode.customName).trim() === normalizedSessionLabel.customName
@@ -324,6 +341,13 @@ function normalizeCustomProvider(provider, index) {
   if (!provider || typeof provider !== 'object') return null
   const id = toStringOrEmpty(provider.id).trim() || `custom-provider-${index + 1}`
   const sourceProviderId = normalizeProviderId(provider.sourceProviderId)
+  const legacyProviderIds = Array.from(
+    new Set(
+      (Array.isArray(provider.legacyProviderIds) ? provider.legacyProviderIds : [])
+        .map(normalizeProviderId)
+        .filter((providerId) => providerId && providerId !== normalizeProviderId(id)),
+    ),
+  )
   const chatCompletionsPath = ensureLeadingSlash(provider.chatCompletionsPath, DEFAULT_CHAT_PATH)
   const completionsPath = ensureLeadingSlash(provider.completionsPath, DEFAULT_COMPLETION_PATH)
   const chatCompletionsUrl = toStringOrEmpty(provider.chatCompletionsUrl).trim()
@@ -349,6 +373,7 @@ function normalizeCustomProvider(provider, index) {
     enabled: provider.enabled !== false,
     allowLegacyResponseField: provider.allowLegacyResponseField !== false,
     ...(sourceProviderId ? { sourceProviderId } : {}),
+    ...(legacyProviderIds.length > 0 ? { legacyProviderIds } : {}),
   }
 }
 
@@ -364,6 +389,16 @@ export function getAllOpenAIProviders(config) {
   return [...buildBuiltinProviders(config), ...customProviders]
 }
 
+function resolveSecretProviderId(config, providerId) {
+  const exactProviderId = toStringOrEmpty(providerId).trim()
+  const normalizedProviderId = normalizeProviderId(providerId)
+  const hasCanonicalProviderIdCollision =
+    getAllOpenAIProviders(config).filter(
+      (provider) => normalizeProviderId(provider.id) === normalizedProviderId,
+    ).length > 1
+  return hasCanonicalProviderIdCollision ? exactProviderId : normalizedProviderId
+}
+
 export function resolveProviderIdForSession(session) {
   const apiMode = session?.apiMode
   if (apiMode && typeof apiMode === 'object') {
@@ -422,18 +457,31 @@ function hasConfiguredProviderSecretEntry(config, providerId) {
 
 export function getProviderSecret(config, providerId, session) {
   if (!providerId) return ''
+  const exactProviderId = toStringOrEmpty(providerId).trim()
   const normalizedProviderId = normalizeProviderId(providerId)
+  const hasCanonicalProviderIdCollision =
+    getAllOpenAIProviders(config).filter(
+      (provider) => normalizeProviderId(provider.id) === normalizedProviderId,
+    ).length > 1
+  const configuredProviderId = hasConfiguredProviderSecretEntry(config, exactProviderId)
+    ? exactProviderId
+    : hasCanonicalProviderIdCollision
+    ? exactProviderId
+    : normalizedProviderId
+  const sessionProviderId = toStringOrEmpty(session?.apiMode?.providerId).trim()
+  const canUseApiModeApiKey =
+    !hasCanonicalProviderIdCollision || !sessionProviderId || sessionProviderId === exactProviderId
   const apiModeApiKey =
-    session?.apiMode && typeof session.apiMode === 'object'
+    canUseApiModeApiKey && session?.apiMode && typeof session.apiMode === 'object'
       ? toStringOrEmpty(session.apiMode.apiKey).trim()
       : ''
-  const hasConfiguredSecretEntry = hasConfiguredProviderSecretEntry(config, normalizedProviderId)
-  const configuredSecret = getConfiguredProviderSecret(config, normalizedProviderId)
+  const hasConfiguredSecretEntry = hasConfiguredProviderSecretEntry(config, configuredProviderId)
+  const configuredSecret = getConfiguredProviderSecret(config, configuredProviderId)
   if (session?.apiMode?.groupName === 'customApiModelKeys') {
     const configuredCustomApiMode = findConfiguredCustomApiMode(
       config,
       session.apiMode,
-      normalizedProviderId,
+      exactProviderId,
     )
     if (configuredCustomApiMode) {
       const configuredModeApiKey = toStringOrEmpty(configuredCustomApiMode.apiKey).trim()
@@ -441,7 +489,7 @@ export function getProviderSecret(config, providerId, session) {
       if (configuredSecret || hasConfiguredSecretEntry) return configuredSecret
       return apiModeApiKey
     }
-    const providerCandidates = getConfiguredCustomApiModesForProvider(config, normalizedProviderId)
+    const providerCandidates = getConfiguredCustomApiModesForProvider(config, exactProviderId)
     if (providerCandidates.length > 0) {
       const hasAnyModeSpecificKey = providerCandidates.some((apiMode) =>
         toStringOrEmpty(apiMode.apiKey).trim(),
@@ -589,6 +637,17 @@ function hasEnabledCustomProviderMatchByLegacySessionUrl(customProviders, sessio
   })
 }
 
+function hasNormalizedProviderIdMatch(provider, normalizedProviderId) {
+  if (!normalizedProviderId) return false
+  return (
+    normalizeProviderId(provider?.id) === normalizedProviderId ||
+    (Array.isArray(provider?.legacyProviderIds) &&
+      provider.legacyProviderIds.some(
+        (legacyProviderId) => normalizeProviderId(legacyProviderId) === normalizedProviderId,
+      ))
+  )
+}
+
 export function getOpenAICompatibleRequestDiagnostic(config, session) {
   const apiMode = session?.apiMode && typeof session.apiMode === 'object' ? session.apiMode : null
   const rawProviderId = apiMode ? toStringOrEmpty(apiMode.providerId) : ''
@@ -603,14 +662,15 @@ export function getOpenAICompatibleRequestDiagnostic(config, session) {
     hasCustomUrl: Boolean(normalizeEndpointUrlForCompare(apiMode?.customUrl)),
     hasMatchingCustomProvider: normalizedProviderId
       ? customProviders.some(
-          (item) => item.enabled !== false && normalizeProviderId(item.id) === normalizedProviderId,
+          (item) =>
+            item.enabled !== false && hasNormalizedProviderIdMatch(item, normalizedProviderId),
         )
       : false,
     hasDisabledMatchingCustomProvider: normalizedProviderId
       ? Array.isArray(config?.customOpenAIProviders) &&
         config.customOpenAIProviders.some(
           (item) =>
-            item?.enabled === false && normalizeProviderId(item?.id) === normalizedProviderId,
+            item?.enabled === false && hasNormalizedProviderIdMatch(item, normalizedProviderId),
         )
       : false,
     hasMatchingCustomProviderByLegacyUrl: hasEnabledCustomProviderMatchByLegacySessionUrl(
@@ -681,31 +741,49 @@ export function resolveOpenAICompatibleRequest(config, session) {
   let recoveredProviderId = ''
   if (session?.apiMode?.groupName === 'customApiModelKeys') {
     const customProviders = getCustomOpenAIProviders(config)
-    const hasAmbiguousLegacyCustomUrlMatch = hasAmbiguousCustomProviderMatchByLegacySessionUrl(
-      customProviders,
-      config,
-      session,
-    )
-    const matchedByProviderId = customProviders.find(
-      (item) => item.enabled !== false && item.id === providerId,
-    )
-    if (matchedByProviderId) {
-      provider = matchedByProviderId
-      resolvedProviderId = matchedByProviderId.id
-    }
     const normalizedProviderId = normalizeProviderId(providerId)
-    if (!provider && normalizedProviderId) {
-      const matchedByNormalizedProviderId = customProviders.find(
-        (item) => item.enabled !== false && item.id === normalizedProviderId,
+    let matchedByProviderId = []
+    let matchedByLegacyProviderId = []
+    let matchedByNormalizedProviderId = []
+    let providerIdCandidates = []
+    if (normalizedProviderId) {
+      matchedByProviderId = customProviders.filter((item) => item.id === providerId)
+      matchedByLegacyProviderId = customProviders.filter(
+        (item) =>
+          Array.isArray(item.legacyProviderIds) &&
+          item.legacyProviderIds.includes(normalizedProviderId),
+      )
+      matchedByNormalizedProviderId = customProviders.filter(
+        (item) => normalizeProviderId(item.id) === normalizedProviderId,
       )
-      if (matchedByNormalizedProviderId) {
-        provider = matchedByNormalizedProviderId
-        resolvedProviderId = matchedByNormalizedProviderId.id
+      providerIdCandidates = Array.from(
+        new Map(
+          [
+            ...matchedByProviderId,
+            ...matchedByLegacyProviderId,
+            ...matchedByNormalizedProviderId,
+          ].map((item) => [item.id, item]),
+        ).values(),
+      )
+      if (providerIdCandidates.length === 1 && providerIdCandidates[0].enabled !== false) {
+        provider = providerIdCandidates[0]
+        resolvedProviderId = provider.id
       }
     }
-    if (!provider && !hasAmbiguousLegacyCustomUrlMatch) {
+    const recoveryProviders =
+      providerIdCandidates.length > 0 ? providerIdCandidates : customProviders
+    const hasDisabledRecoveryProviderMatchByUrl = hasDisabledCustomProviderMatchByLegacySessionUrl(
+      recoveryProviders,
+      session,
+    )
+    const hasAmbiguousLegacyCustomUrlMatch = hasAmbiguousCustomProviderMatchByLegacySessionUrl(
+      recoveryProviders,
+      config,
+      session,
+    )
+    if (!provider && !hasDisabledRecoveryProviderMatchByUrl && !hasAmbiguousLegacyCustomUrlMatch) {
       const matchedByCustomUrl = resolveCustomProviderByLegacySessionUrl(
-        customProviders,
+        recoveryProviders,
         config,
         session,
       )
@@ -714,30 +792,61 @@ export function resolveOpenAICompatibleRequest(config, session) {
         resolvedProviderId = matchedByCustomUrl.id
       }
     }
-    if (!provider) {
+    const hasStableSessionModeLabel = Boolean(
+      toStringOrEmpty(session?.apiMode?.itemName).trim() &&
+        typeof session?.apiMode?.isCustom === 'boolean',
+    )
+    const canUseStableLabelToDisambiguateCandidates =
+      hasStableSessionModeLabel && providerIdCandidates.length > 1
+    if (
+      !provider &&
+      ((providerIdCandidates.length <= 1 && !hasDisabledRecoveryProviderMatchByUrl) ||
+        canUseStableLabelToDisambiguateCandidates)
+    ) {
       const matchedConfiguredApiMode = findConfiguredCustomApiModeBySessionLabel(
         config,
         session?.apiMode,
+        providerIdCandidates.map((item) => item.id),
       )
-      const matchedConfiguredProviderId = normalizeProviderId(matchedConfiguredApiMode?.providerId)
-      if (matchedConfiguredProviderId) {
-        const matchedConfiguredProvider = customProviders.find(
-          (item) => item.enabled !== false && item.id === matchedConfiguredProviderId,
+      const matchedConfiguredProviderId = toStringOrEmpty(
+        matchedConfiguredApiMode?.providerId,
+      ).trim()
+      const normalizedMatchedConfiguredProviderId = normalizeProviderId(matchedConfiguredProviderId)
+      if (normalizedMatchedConfiguredProviderId) {
+        const configuredProviderCandidates =
+          providerIdCandidates.length > 0 ? providerIdCandidates : customProviders
+        const exactConfiguredProviderCandidates = configuredProviderCandidates.filter(
+          (item) => item.id === matchedConfiguredProviderId,
         )
+        const exactConfiguredProviderMatches = exactConfiguredProviderCandidates.filter(
+          (item) => item.enabled !== false,
+        )
+        const canonicalConfiguredProviderMatches = configuredProviderCandidates.filter(
+          (item) =>
+            item.enabled !== false &&
+            normalizeProviderId(item.id) === normalizedMatchedConfiguredProviderId,
+        )
+        const matchedConfiguredProvider =
+          exactConfiguredProviderMatches.length === 1
+            ? exactConfiguredProviderMatches[0]
+            : exactConfiguredProviderCandidates.length === 0 &&
+              canonicalConfiguredProviderMatches.length === 1
+            ? canonicalConfiguredProviderMatches[0]
+            : null
         if (matchedConfiguredProvider) {
           provider = matchedConfiguredProvider
           resolvedProviderId = matchedConfiguredProvider.id
-        } else if (matchedConfiguredProviderId === 'legacy-custom-default') {
-          provider = getProviderById(config, matchedConfiguredProviderId)
+        } else if (normalizedMatchedConfiguredProviderId === 'legacy-custom-default') {
+          provider = getProviderById(config, normalizedMatchedConfiguredProviderId)
           if (provider) {
-            resolvedProviderId = matchedConfiguredProviderId
+            resolvedProviderId = normalizedMatchedConfiguredProviderId
           }
         }
       }
     }
-    if (!provider && hasAmbiguousLegacyCustomUrlMatch) {
+    if (!provider && !hasDisabledRecoveryProviderMatchByUrl && hasAmbiguousLegacyCustomUrlMatch) {
       const matchedByCustomUrl = resolveCustomProviderByLegacySessionUrl(
-        customProviders,
+        recoveryProviders,
         config,
         session,
       )
@@ -747,11 +856,13 @@ export function resolveOpenAICompatibleRequest(config, session) {
       }
     }
     if (!provider) {
-      const normalizedProviderId = normalizeProviderId(providerId)
       const hasDisabledCustomProviderMatch = Array.isArray(config?.customOpenAIProviders)
         ? config.customOpenAIProviders.some(
             (item) =>
-              normalizeProviderId(item?.id) === normalizedProviderId && item?.enabled === false,
+              item?.enabled === false &&
+              (normalizeProviderId(item?.id) === normalizedProviderId ||
+                (Array.isArray(item?.legacyProviderIds) &&
+                  item.legacyProviderIds.map(normalizeProviderId).includes(normalizedProviderId))),
           )
         : false
       const hasDisabledCustomProviderMatchByUrl = hasDisabledCustomProviderMatchByLegacySessionUrl(
@@ -812,7 +923,7 @@ export function resolveOpenAICompatibleRequest(config, session) {
   if (!requestUrl) return null
   return {
     providerId: resolvedProviderId,
-    secretProviderId: normalizeProviderId(recoveredProviderId || resolvedProviderId),
+    secretProviderId: resolveSecretProviderId(config, recoveredProviderId || resolvedProviderId),
     provider,
     endpointType,
     requestUrl,
diff --git a/src/utils/model-name-convert.mjs b/src/utils/model-name-convert.mjs
index 838456c2..fdda5457 100644
--- a/src/utils/model-name-convert.mjs
+++ b/src/utils/model-name-convert.mjs
@@ -1,5 +1,28 @@
 import { AlwaysCustomGroups, ModelGroups, ModelMode, Models } from '../config/index.mjs'
 
+function normalizeProviderId(value) {
+  return String(value || '')
+    .trim()
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, '-')
+    .replace(/^-+|-+$/g, '')
+}
+
+function areProviderIdsEquivalent(firstProviderId, secondProviderId) {
+  const normalizedFirstProviderId = normalizeProviderId(firstProviderId)
+  const normalizedSecondProviderId = normalizeProviderId(secondProviderId)
+  if (!normalizedFirstProviderId || !normalizedSecondProviderId) {
+    return String(firstProviderId || '').trim() === String(secondProviderId || '').trim()
+  }
+  return normalizedFirstProviderId === normalizedSecondProviderId
+}
+
+function normalizeProviderEndpointUrl(value) {
+  return String(value || '')
+    .trim()
+    .replace(/\/+$/, '')
+}
+
 export function modelNameToDesc(modelName, t, extraCustomModelName = '') {
   if (!t) t = (x) => x
   if (modelName in Models) {
@@ -348,6 +371,17 @@ export function isApiModeSelected(apiMode, configOrSession, { sessionCompat = fa
 
     if (!selectedApiMode.providerId) return true
     if (selectedApiMode.providerId === targetApiMode.providerId) return true
+    if (areProviderIdsEquivalent(selectedApiMode.providerId, targetApiMode.providerId)) {
+      return true
+    }
+    if (
+      Array.isArray(targetApiMode.legacyProviderIds) &&
+      targetApiMode.legacyProviderIds.some((providerId) =>
+        areProviderIdsEquivalent(providerId, selectedApiMode.providerId),
+      )
+    ) {
+      return true
+    }
     if (!targetApiMode.providerId) return isLegacyCustomSession
     return isLegacyCustomSession
   }
@@ -390,14 +424,21 @@ export function getUniquelySelectedApiModeIndex(
 ) {
   if (!Array.isArray(apiModes) || apiModes.length === 0) return -1
 
-  let selectedIndex = -1
+  const selectedIndexes = []
   for (const [index, apiMode] of apiModes.entries()) {
     if (!isApiModeSelected(apiMode, configOrSession, { sessionCompat })) continue
-    if (selectedIndex !== -1) return -1
-    selectedIndex = index
+    selectedIndexes.push(index)
   }
 
-  return selectedIndex
+  if (selectedIndexes.length === 1) return selectedIndexes[0]
+  if (!sessionCompat || selectedIndexes.length === 0) return -1
+
+  const selectedCustomUrl = normalizeProviderEndpointUrl(configOrSession?.apiMode?.customUrl)
+  if (!selectedCustomUrl) return -1
+  const urlMatchedIndexes = selectedIndexes.filter(
+    (index) => normalizeProviderEndpointUrl(apiModes[index]?.customUrl) === selectedCustomUrl,
+  )
+  return urlMatchedIndexes.length === 1 ? urlMatchedIndexes[0] : -1
 }
 
 // also match custom modelName, e.g. when modelName is bingFree4, configOrSession model is bingFree4-fast, it returns true
diff --git a/tests/unit/config/migrate-user-config.test.mjs b/tests/unit/config/migrate-user-config.test.mjs
index 992e1afe..e4104b02 100644
--- a/tests/unit/config/migrate-user-config.test.mjs
+++ b/tests/unit/config/migrate-user-config.test.mjs
@@ -6,6 +6,13 @@ import {
   getApiModesFromConfig,
   modelNameToApiMode,
 } from '../../../src/utils/model-name-convert.mjs'
+import { resolveOpenAICompatibleRequest } from '../../../src/services/apis/provider-registry.mjs'
+
+const newlyReservedBuiltinProviders = [
+  { id: 'xai', legacyKey: 'xaiApiKey' },
+  { id: 'nvidia-nim', legacyKey: 'nvidiaNimApiKey' },
+  { id: 'mistral', legacyKey: 'mistralApiKey' },
+]
 
 function createCustomApiMode(overrides = {}) {
   return {
@@ -279,6 +286,38 @@ test('getUserConfig persists normalization-only sourceProviderId migrations', as
   assert.equal(storedProvider.sourceProviderId, 'openai')
 })
 
+test('getUserConfig persists provider lineage and path normalization by itself', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 2,
+    completedBuiltinProviderIdMigrations: ['xai', 'nvidia-nim', 'mistral'],
+    providerSecrets: {},
+    customApiModes: [],
+    activeApiModes: [],
+    knownApiModeDefaultIds: defaultApiModeIds,
+    customOpenAIProviders: [
+      {
+        id: 'foo',
+        name: 'Foo Proxy',
+        baseUrl: '',
+        chatCompletionsPath: 'v1/chat/completions',
+        completionsPath: 'v1/completions',
+        chatCompletionsUrl: 'https://foo.example.com/v1/chat/completions',
+        completionsUrl: '',
+        enabled: true,
+        allowLegacyResponseField: true,
+        legacyProviderIds: ['FOO', 'Old_Id', 'old-id'],
+      },
+    ],
+  })
+
+  await getUserConfig()
+  const storedProvider = globalThis.__TEST_BROWSER_SHIM__.getStorage().customOpenAIProviders[0]
+
+  assert.equal(storedProvider.chatCompletionsPath, '/v1/chat/completions')
+  assert.equal(storedProvider.completionsPath, '/v1/completions')
+  assert.deepEqual(storedProvider.legacyProviderIds, ['old-id'])
+})
+
 test('getUserConfig remaps preserved custom sourceProviderId when provider ids are renamed', async () => {
   globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
     configSchemaVersion: 0,
@@ -446,20 +485,20 @@ test('getUserConfig does not reuse builtin provider secret for renamed colliding
   assert.equal(config.providerSecrets['openai-2'], undefined)
 })
 
-test('getUserConfig keeps original secret when colliding custom provider raw id is already normalized', async () => {
+test('getUserConfig keeps a raw-id secret on unchanged and renamed duplicate providers', async () => {
   globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
     configSchemaVersion: 0,
     providerSecrets: {
-      myproxy: 'shared-provider-secret',
+      MyProxy: 'shared-provider-secret',
     },
     customOpenAIProviders: [
       {
-        id: 'myproxy',
+        id: 'MyProxy',
         name: 'Primary Proxy',
         chatCompletionsUrl: 'https://primary.example.com/v1/chat/completions',
       },
       {
-        id: 'myproxy',
+        id: 'MyProxy',
         name: 'Duplicate Proxy',
         chatCompletionsUrl: 'https://duplicate.example.com/v1/chat/completions',
       },
@@ -478,6 +517,340 @@ test('getUserConfig keeps original secret when colliding custom provider raw id
   assert.equal(duplicateProvider.id, 'myproxy-2')
   assert.equal(config.providerSecrets.myproxy, 'shared-provider-secret')
   assert.equal(config.providerSecrets['myproxy-2'], 'shared-provider-secret')
+  assert.equal(Object.hasOwn(config.providerSecrets, 'MyProxy'), false)
+})
+
+test('getUserConfig keeps a shared secret on already-normalized duplicate providers', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 0,
+    providerSecrets: {
+      myproxy: 'shared-provider-secret',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'myproxy',
+        name: 'Primary Proxy',
+        chatCompletionsUrl: 'https://primary.example.com/v1/chat/completions',
+      },
+      {
+        id: 'myproxy',
+        name: 'Duplicate Proxy',
+        chatCompletionsUrl: 'https://duplicate.example.com/v1/chat/completions',
+      },
+    ],
+  })
+
+  const config = await getUserConfig()
+
+  assert.equal(config.providerSecrets.myproxy, 'shared-provider-secret')
+  assert.equal(config.providerSecrets['myproxy-2'], 'shared-provider-secret')
+})
+
+test('getUserConfig keeps distinct secrets for canonically duplicate provider IDs', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 0,
+    providerSecrets: {
+      Foo: 'primary-provider-secret',
+      foo: 'duplicate-provider-secret',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'Foo',
+        name: 'Primary Proxy',
+        chatCompletionsUrl: 'https://primary.example.com/v1/chat/completions',
+      },
+      {
+        id: 'foo',
+        name: 'Duplicate Proxy',
+        chatCompletionsUrl: 'https://duplicate.example.com/v1/chat/completions',
+      },
+    ],
+  })
+
+  const config = await getUserConfig()
+
+  assert.equal(config.providerSecrets.foo, 'primary-provider-secret')
+  assert.equal(config.providerSecrets['foo-2'], 'duplicate-provider-secret')
+  assert.equal(Object.hasOwn(config.providerSecrets, 'Foo'), false)
+})
+
+test('getUserConfig keeps asymmetric secrets on their raw canonical provider', async () => {
+  const providers = [
+    {
+      id: 'Foo',
+      name: 'Uppercase Proxy',
+      chatCompletionsUrl: 'https://uppercase.example.com/v1/chat/completions',
+    },
+    {
+      id: 'foo',
+      name: 'Lowercase Proxy',
+      chatCompletionsUrl: 'https://lowercase.example.com/v1/chat/completions',
+    },
+  ]
+
+  for (const orderedProviders of [providers, [...providers].reverse()]) {
+    for (const [secretId, secret, expectedUpperSecret, expectedLowerSecret] of [
+      ['Foo', 'uppercase-secret', 'uppercase-secret', undefined],
+      ['foo', 'lowercase-secret', undefined, 'lowercase-secret'],
+    ]) {
+      globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+        configSchemaVersion: 0,
+        providerSecrets: { [secretId]: secret },
+        customOpenAIProviders: orderedProviders,
+      })
+
+      const config = await getUserConfig()
+      const uppercaseProvider = config.customOpenAIProviders.find(
+        (provider) => provider.name === 'Uppercase Proxy',
+      )
+      const lowercaseProvider = config.customOpenAIProviders.find(
+        (provider) => provider.name === 'Lowercase Proxy',
+      )
+
+      assert.equal(config.providerSecrets[uppercaseProvider.id], expectedUpperSecret)
+      assert.equal(config.providerSecrets[lowercaseProvider.id], expectedLowerSecret)
+
+      const remigratedConfig = await getUserConfig()
+      assert.deepEqual(remigratedConfig.customOpenAIProviders, config.customOpenAIProviders)
+      assert.deepEqual(remigratedConfig.providerSecrets, config.providerSecrets)
+    }
+  }
+})
+
+test('getUserConfig uses raw IDs to remap modes for canonically duplicate providers', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 0,
+    providerSecrets: {
+      Foo: 'primary-provider-secret',
+      foo: 'duplicate-provider-secret',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'Foo',
+        name: 'Primary Proxy',
+        chatCompletionsUrl: 'https://primary.example.com/v1/chat/completions',
+      },
+      {
+        id: 'foo',
+        name: 'Duplicate Proxy',
+        chatCompletionsUrl: 'https://duplicate.example.com/v1/chat/completions',
+      },
+    ],
+    customApiModes: [
+      createCustomApiMode({ customName: 'Primary mode', providerId: 'Foo' }),
+      createCustomApiMode({ customName: 'Duplicate mode', providerId: 'foo' }),
+    ],
+    apiMode: createCustomApiMode({ customName: 'Duplicate mode', providerId: 'foo' }),
+  })
+
+  const config = await getUserConfig()
+  const primaryMode = config.customApiModes.find((mode) => mode.customName === 'Primary mode')
+  const duplicateMode = config.customApiModes.find((mode) => mode.customName === 'Duplicate mode')
+
+  assert.equal(primaryMode.providerId, 'foo')
+  assert.equal(duplicateMode.providerId, 'foo-2')
+  assert.equal(config.apiMode.providerId, 'foo-2')
+  assert.equal(
+    resolveOpenAICompatibleRequest(config, { apiMode: primaryMode })?.apiKey,
+    'primary-provider-secret',
+  )
+  assert.equal(
+    resolveOpenAICompatibleRequest(config, { apiMode: duplicateMode })?.apiKey,
+    'duplicate-provider-secret',
+  )
+})
+
+test('getUserConfig keeps selected raw provider ID distinct in matching mode signatures', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 0,
+    providerSecrets: {
+      Foo: 'primary-provider-secret',
+      foo: 'duplicate-provider-secret',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'Foo',
+        name: 'Primary Proxy',
+        chatCompletionsUrl: 'https://primary.example.com/v1/chat/completions',
+      },
+      {
+        id: 'foo',
+        name: 'Duplicate Proxy',
+        chatCompletionsUrl: 'https://duplicate.example.com/v1/chat/completions',
+      },
+    ],
+    customApiModes: [
+      createCustomApiMode({ customName: 'Shared mode', providerId: 'Foo' }),
+      createCustomApiMode({ customName: 'Shared mode', providerId: 'foo' }),
+    ],
+    apiMode: createCustomApiMode({ customName: 'Shared mode', providerId: 'Foo' }),
+  })
+
+  const config = await getUserConfig()
+
+  assert.deepEqual(
+    config.customApiModes
+      .filter((mode) => mode.customName === 'Shared mode')
+      .map((mode) => mode.providerId),
+    ['foo', 'foo-2'],
+  )
+  assert.equal(config.apiMode.providerId, 'foo')
+  assert.equal(config.providerSecrets[config.apiMode.providerId], 'primary-provider-secret')
+})
+
+test('getUserConfig preserves selected raw provider disambiguation without a listed match', async () => {
+  for (const [listedProviderId, selectedProviderId, migratedListedId, migratedSelectedId] of [
+    ['Foo', 'foo', 'foo', 'foo-2'],
+    ['foo', 'Foo', 'foo-2', 'foo'],
+  ]) {
+    globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+      configSchemaVersion: 0,
+      providerSecrets: {
+        Foo: 'primary-provider-secret',
+        foo: 'duplicate-provider-secret',
+      },
+      customOpenAIProviders: [
+        {
+          id: 'Foo',
+          name: 'Primary Proxy',
+          chatCompletionsUrl: 'https://primary.example.com/v1/chat/completions',
+        },
+        {
+          id: 'foo',
+          name: 'Duplicate Proxy',
+          chatCompletionsUrl: 'https://duplicate.example.com/v1/chat/completions',
+        },
+      ],
+      customApiModes: [
+        createCustomApiMode({ customName: 'Shared mode', providerId: listedProviderId }),
+      ],
+      apiMode: createCustomApiMode({
+        customName: 'Shared mode',
+        providerId: selectedProviderId,
+      }),
+    })
+
+    const config = await getUserConfig()
+    const migratedMode = config.customApiModes.find((mode) => mode.customName === 'Shared mode')
+
+    assert.equal(migratedMode.providerId, migratedListedId)
+    assert.equal(config.apiMode.providerId, migratedSelectedId)
+  }
+})
+
+test('getUserConfig reuses key promotion for canonically equivalent selected provider ID', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 0,
+    providerSecrets: { MyProxy: 'provider-key' },
+    customOpenAIProviders: [
+      {
+        id: 'MyProxy',
+        name: 'My Proxy',
+        chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
+      },
+    ],
+    customApiModes: [
+      createCustomApiMode({
+        customName: 'Shared mode',
+        providerId: 'MyProxy',
+        apiKey: 'mode-key',
+      }),
+    ],
+    apiMode: createCustomApiMode({
+      customName: 'Shared mode',
+      providerId: 'myproxy',
+      apiKey: 'mode-key',
+    }),
+  })
+
+  const config = await getUserConfig()
+  const migratedMode = config.customApiModes.find((mode) => mode.customName === 'Shared mode')
+
+  assert.equal(migratedMode.providerId, 'shared-mode')
+  assert.equal(config.apiMode.providerId, migratedMode.providerId)
+  assert.equal(config.providerSecrets[migratedMode.providerId], 'mode-key')
+  assert.equal(
+    config.customOpenAIProviders.some((provider) => provider.id === 'shared-mode-2'),
+    false,
+  )
+})
+
+test('getUserConfig remaps modes for duplicate newly reserved provider IDs', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 1,
+    providerSecrets: {
+      XAI: 'uppercase-provider-secret',
+      xai: 'lowercase-provider-secret',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'XAI',
+        name: 'Uppercase xAI Proxy',
+        chatCompletionsUrl: 'https://uppercase.example.com/v1/chat/completions',
+      },
+      {
+        id: 'xai',
+        name: 'Lowercase xAI Proxy',
+        chatCompletionsUrl: 'https://lowercase.example.com/v1/chat/completions',
+      },
+    ],
+    customApiModes: [
+      createCustomApiMode({ customName: 'Uppercase mode', providerId: 'XAI' }),
+      createCustomApiMode({ customName: 'Lowercase mode', providerId: 'xai' }),
+    ],
+  })
+
+  const config = await getUserConfig()
+  const uppercaseMode = config.customApiModes.find((mode) => mode.customName === 'Uppercase mode')
+  const lowercaseMode = config.customApiModes.find((mode) => mode.customName === 'Lowercase mode')
+
+  assert.equal(uppercaseMode.providerId, 'xai-2')
+  assert.equal(lowercaseMode.providerId, 'xai-3')
+  assert.equal(
+    resolveOpenAICompatibleRequest(config, { apiMode: uppercaseMode })?.apiKey,
+    'uppercase-provider-secret',
+  )
+  assert.equal(
+    resolveOpenAICompatibleRequest(config, { apiMode: lowercaseMode })?.apiKey,
+    'lowercase-provider-secret',
+  )
+})
+
+test('getUserConfig keeps a reserved canonical secret on its exact raw provider', async () => {
+  for (const { id } of newlyReservedBuiltinProviders) {
+    const canonicalAliasProvider = {
+      id: id.toUpperCase(),
+      name: 'Canonical alias provider',
+      chatCompletionsUrl: 'https://alias.example.com/v1/chat/completions',
+    }
+    const exactProvider = {
+      id,
+      name: 'Exact provider',
+      chatCompletionsUrl: 'https://exact.example.com/v1/chat/completions',
+    }
+
+    for (const customOpenAIProviders of [
+      [canonicalAliasProvider, exactProvider],
+      [exactProvider, canonicalAliasProvider],
+    ]) {
+      globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+        configSchemaVersion: 1,
+        providerSecrets: { [id]: 'exact-provider-secret' },
+        customOpenAIProviders,
+      })
+
+      const config = await getUserConfig()
+      const canonicalAlias = config.customOpenAIProviders.find(
+        (provider) => provider.name === canonicalAliasProvider.name,
+      )
+      const exact = config.customOpenAIProviders.find(
+        (provider) => provider.name === exactProvider.name,
+      )
+
+      assert.equal(config.providerSecrets[canonicalAlias.id], undefined)
+      assert.equal(config.providerSecrets[exact.id], 'exact-provider-secret')
+    }
+  }
 })
 
 test('getUserConfig prefers normalized provider secret when raw alias is explicitly empty', async () => {
@@ -810,10 +1183,27 @@ test('getUserConfig materializes distinct providers for legacy custom default ke
   assert.equal(config.apiMode.providerId, modeB.providerId)
   assert.equal(config.providerSecrets['legacy-custom-default'], 'key-a')
   assert.equal(config.providerSecrets[modeB.providerId], 'key-b')
+  assert.equal(materializedProvider.legacyProviderIds, undefined)
   assert.equal(
     materializedProvider.chatCompletionsUrl,
     'https://legacy.example.com/v1/chat/completions',
   )
+  const resolvedModeA = resolveOpenAICompatibleRequest(config, {
+    apiMode: createCustomApiMode({
+      customName: 'legacy-a',
+      providerId: 'legacy-custom-default',
+    }),
+  })
+  const resolvedModeB = resolveOpenAICompatibleRequest(config, {
+    apiMode: createCustomApiMode({
+      customName: 'legacy-b',
+      providerId: 'legacy-custom-default',
+    }),
+  })
+  assert.equal(resolvedModeA?.providerId, 'legacy-custom-default')
+  assert.equal(resolvedModeA?.apiKey, 'key-a')
+  assert.equal(resolvedModeB?.providerId, modeB.providerId)
+  assert.equal(resolvedModeB?.apiKey, 'key-b')
   assert.equal(modeA.apiKey, '')
   assert.equal(modeB.apiKey, '')
   assert.equal(config.apiMode.apiKey, '')
@@ -1401,6 +1791,264 @@ test('getUserConfig persists generated custom provider ids when schema version i
   assert.equal(storage.customOpenAIProviders[0].id, 'custom-provider-1')
 })
 
+test('getUserConfig migrates custom providers that collide with newly reserved IDs', async () => {
+  for (const { id } of newlyReservedBuiltinProviders) {
+    globalThis.__TEST_BROWSER_SHIM__.clearStorage()
+    const customUrl = `https://${id}.example.com/v1/chat/completions`
+    globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+      configSchemaVersion: 1,
+      providerSecrets: { [id]: `${id}-custom-secret` },
+      customOpenAIProviders: [
+        {
+          id,
+          name: `${id} proxy`,
+          chatCompletionsUrl: customUrl,
+        },
+      ],
+      customApiModes: [
+        createCustomApiMode({
+          customName: `${id} proxy`,
+          providerId: id,
+        }),
+      ],
+    })
+
+    const config = await getUserConfig()
+    const migratedProvider = config.customOpenAIProviders[0]
+    const migratedMode = config.customApiModes.find(
+      (apiMode) => apiMode.customName === `${id} proxy`,
+    )
+
+    assert.equal(migratedProvider.id, `${id}-2`)
+    assert.deepEqual(migratedProvider.legacyProviderIds, [id])
+    assert.equal(migratedMode.providerId, `${id}-2`)
+    assert.deepEqual(migratedMode.legacyProviderIds, [id])
+    assert.equal(config.providerSecrets[`${id}-2`], `${id}-custom-secret`)
+    assert.equal(Object.hasOwn(config.providerSecrets, id), false)
+    assert.ok(config.completedBuiltinProviderIdMigrations.includes(id))
+
+    const resolved = resolveOpenAICompatibleRequest(config, {
+      apiMode: createCustomApiMode({
+        customName: `${id} proxy`,
+        customUrl,
+        providerId: id,
+      }),
+    })
+    assert.equal(resolved?.providerId, `${id}-2`)
+    assert.equal(resolved?.apiKey, `${id}-custom-secret`)
+
+    const snapshot = JSON.stringify(globalThis.__TEST_BROWSER_SHIM__.getStorage())
+    await getUserConfig()
+    assert.equal(JSON.stringify(globalThis.__TEST_BROWSER_SHIM__.getStorage()), snapshot)
+
+    globalThis.__TEST_BROWSER_SHIM__.clearStorage()
+    const rawId = id.toUpperCase()
+    globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+      configSchemaVersion: 1,
+      providerSecrets: {
+        [rawId]: `${id}-raw-secret`,
+        [id]: `${id}-normalized-secret`,
+      },
+      customOpenAIProviders: [
+        {
+          id: rawId,
+          name: `${id} raw proxy`,
+          chatCompletionsUrl: customUrl,
+        },
+      ],
+    })
+
+    const rawIdConfig = await getUserConfig()
+
+    assert.equal(rawIdConfig.providerSecrets[`${id}-2`], `${id}-raw-secret`)
+    assert.equal(rawIdConfig.providerSecrets[id], `${id}-normalized-secret`)
+    assert.equal(Object.hasOwn(rawIdConfig.providerSecrets, rawId), false)
+  }
+})
+
+test('getUserConfig keeps builtin secrets out of colliding custom providers', async () => {
+  for (const { id, legacyKey } of newlyReservedBuiltinProviders) {
+    globalThis.__TEST_BROWSER_SHIM__.clearStorage()
+    globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+      configSchemaVersion: 1,
+      [legacyKey]: `${id}-builtin-secret`,
+      providerSecrets: { [id]: `${id}-builtin-secret` },
+      customOpenAIProviders: [
+        {
+          id,
+          name: `${id} proxy`,
+          chatCompletionsUrl: `https://${id}.example.com/v1/chat/completions`,
+        },
+      ],
+    })
+
+    const config = await getUserConfig()
+
+    assert.equal(config.customOpenAIProviders[0].id, `${id}-2`)
+    assert.equal(config.providerSecrets[id], `${id}-builtin-secret`)
+    assert.equal(Object.hasOwn(config.providerSecrets, `${id}-2`), false)
+    assert.equal(config[legacyKey], `${id}-builtin-secret`)
+  }
+})
+
+test('getUserConfig reruns a completed builtin ID migration for a new collision', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 2,
+    completedBuiltinProviderIdMigrations: ['xai', 'nvidia-nim', 'mistral'],
+    providerSecrets: {
+      xai: 'custom-xai-secret',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'xai',
+        name: 'Synced xAI Proxy',
+        chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
+      },
+    ],
+  })
+
+  const config = await getUserConfig()
+
+  assert.equal(config.customOpenAIProviders[0].id, 'xai-2')
+  assert.equal(config.providerSecrets['xai-2'], 'custom-xai-secret')
+  assert.equal(Object.hasOwn(config.providerSecrets, 'xai'), false)
+})
+
+test('getUserConfig does not move a known builtin secret for a later custom collision', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 2,
+    completedBuiltinProviderIdMigrations: ['xai', 'nvidia-nim', 'mistral'],
+    xaiApiKey: 'builtin-xai-secret',
+    providerSecrets: {
+      xai: 'builtin-xai-secret',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'xai',
+        name: 'Synced xAI Proxy',
+        chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
+      },
+    ],
+  })
+
+  const config = await getUserConfig()
+
+  assert.equal(config.customOpenAIProviders[0].id, 'xai-2')
+  assert.equal(config.providerSecrets.xai, 'builtin-xai-secret')
+  assert.equal(Object.hasOwn(config.providerSecrets, 'xai-2'), false)
+})
+
+test('getUserConfig reconnects modes only for a unique enabled legacy provider match', async () => {
+  const cases = [
+    {
+      providers: [{ id: 'xai-2', legacyProviderIds: ['xai'] }],
+      expectedProviderId: 'xai-2',
+      expectedModeKey: '',
+      expectedProviderKey: 'custom-xai-secret',
+    },
+    {
+      providers: [
+        { id: 'xai-2', legacyProviderIds: ['xai'] },
+        { id: 'xai-3', legacyProviderIds: ['xai'] },
+      ],
+      expectedProviderId: 'xai',
+      expectedModeKey: 'custom-xai-secret',
+      expectedProviderKey: undefined,
+    },
+    {
+      providers: [{ id: 'xai-2', legacyProviderIds: ['xai'], enabled: false }],
+      expectedProviderId: 'xai',
+      expectedModeKey: 'custom-xai-secret',
+      expectedProviderKey: undefined,
+    },
+  ]
+
+  for (const testCase of cases) {
+    globalThis.__TEST_BROWSER_SHIM__.clearStorage()
+    globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+      configSchemaVersion: 2,
+      completedBuiltinProviderIdMigrations: ['xai', 'nvidia-nim', 'mistral'],
+      xaiApiKey: 'builtin-xai-secret',
+      providerSecrets: {
+        xai: 'builtin-xai-secret',
+      },
+      customOpenAIProviders: testCase.providers.map((provider) => ({
+        ...provider,
+        name: provider.id,
+        chatCompletionsUrl: `https://${provider.id}.example.com/v1/chat/completions`,
+      })),
+      customApiModes: [
+        createCustomApiMode({
+          customName: 'Existing xAI Proxy mode',
+          providerId: 'xai',
+          apiKey: 'custom-xai-secret',
+        }),
+      ],
+    })
+
+    const config = await getUserConfig()
+    const migratedMode = config.customApiModes.find(
+      (apiMode) => apiMode.customName === 'Existing xAI Proxy mode',
+    )
+
+    assert.equal(migratedMode.providerId, testCase.expectedProviderId)
+    assert.equal(migratedMode.apiKey, testCase.expectedModeKey)
+    assert.equal(config.providerSecrets.xai, 'builtin-xai-secret')
+    assert.equal(config.providerSecrets['xai-2'], testCase.expectedProviderKey)
+    assert.equal(Object.hasOwn(config.providerSecrets, 'xai-3'), false)
+  }
+})
+
+test('getUserConfig uses URLs to disambiguate unchanged and renamed provider IDs', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 1,
+    providerSecrets: {
+      proxy: 'first-key',
+    },
+    customOpenAIProviders: [
+      {
+        id: 'proxy',
+        name: 'First proxy',
+        baseUrl: 'https://first.example.com/v1',
+        chatCompletionsPath: 'v1/chat/completions',
+        completionsPath: 'v1/completions',
+      },
+      {
+        id: 'proxy',
+        name: 'Second proxy',
+        baseUrl: 'https://second.example.com/v1',
+        chatCompletionsPath: 'v1/chat/completions',
+        completionsPath: 'v1/completions',
+      },
+    ],
+    customApiModes: [
+      createCustomApiMode({
+        customName: 'Second proxy mode',
+        customUrl: 'https://second.example.com/v1/chat/completions',
+        apiKey: 'second-key',
+        providerId: 'proxy',
+      }),
+    ],
+  })
+
+  const config = await getUserConfig()
+
+  assert.deepEqual(
+    config.customOpenAIProviders.map((provider) => provider.id),
+    ['proxy', 'proxy-2', 'second-proxy-mode'],
+  )
+  const secondProxyMode = config.customApiModes.find(
+    (apiMode) => apiMode.customName === 'Second proxy mode',
+  )
+  assert.equal(secondProxyMode.providerId, 'second-proxy-mode')
+  assert.deepEqual(secondProxyMode.legacyProviderIds, ['proxy', 'proxy-2'])
+  assert.equal(config.customOpenAIProviders[2].baseUrl, 'https://second.example.com/v1')
+  assert.deepEqual(config.customOpenAIProviders[2].legacyProviderIds, ['proxy', 'proxy-2'])
+  assert.equal(config.providerSecrets['second-proxy-mode'], 'second-key')
+  assert.equal(config.customOpenAIProviders[0].chatCompletionsPath, '/v1/chat/completions')
+  assert.equal(config.customOpenAIProviders[1].completionsPath, '/v1/completions')
+})
+
 test('getUserConfig normalizes providerSecrets when legacy data is not a plain object', async () => {
   globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
     configSchemaVersion: 1,
diff --git a/tests/unit/popup/api-modes-provider-utils.test.mjs b/tests/unit/popup/api-modes-provider-utils.test.mjs
index 520e57d7..64dc14da 100644
--- a/tests/unit/popup/api-modes-provider-utils.test.mjs
+++ b/tests/unit/popup/api-modes-provider-utils.test.mjs
@@ -131,6 +131,12 @@ test('createProviderId does not reuse ids reserved by staged provider deletions'
   assert.equal(createProviderId('My Proxy', existingProviders, reservedProviderIds), 'my-proxy-3')
 })
 
+test('createProviderId does not reuse legacy provider IDs', () => {
+  const existingProviders = [{ id: 'renamed-provider', legacyProviderIds: ['my-proxy'] }]
+
+  assert.equal(createProviderId('My Proxy', existingProviders), 'my-proxy-2')
+})
+
 test('parseChatCompletionsEndpointUrl accepts full chat endpoint url', () => {
   const parsed = parseChatCompletionsEndpointUrl('https://api.example.com/v1/chat/completions/')
 
@@ -607,6 +613,7 @@ test('sanitizeApiModeForSave clears custom-provider metadata for non-custom mode
     apiKey: 'sk-test',
     customUrl: 'https://proxy.example.com/v1/chat/completions',
     sourceProviderId: 'openai',
+    legacyProviderIds: ['legacy-provider'],
   })
 
   assert.deepEqual(sanitizedApiMode, {
@@ -635,6 +642,7 @@ test('applySelectedProviderToApiMode clears provider-derived fields when provide
       providerId: 'selected-mode-2',
       apiKey: 'override-key',
       sourceProviderId: 'openai',
+      legacyProviderIds: ['selected-mode'],
       customUrl: 'https://example.com',
     },
     'myproxy',
@@ -756,6 +764,7 @@ test('isProviderReferencedByApiModes only matches custom modes with the same pro
   ]
 
   assert.equal(isProviderReferencedByApiModes('provider-a', apiModes), true)
+  assert.equal(isProviderReferencedByApiModes('Provider_A', apiModes), true)
   assert.equal(isProviderReferencedByApiModes('provider-b', apiModes), false)
 })
 
@@ -1497,3 +1506,84 @@ test('getConversationAiName does not treat canonical provider id matches as miss
 
   assert.equal(getConversationAiName(session, t, providers), 'My Proxy (deepseek-v3.2)')
 })
+
+test('legacy provider IDs keep saved conversations linked to renamed providers', () => {
+  const providers = [
+    {
+      id: 'renamed-provider',
+      name: 'Renamed Provider',
+      legacyProviderIds: ['legacy-provider'],
+      enabled: false,
+    },
+  ]
+  const session = {
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      providerId: 'legacy-provider',
+      customName: 'proxy-model',
+    },
+  }
+  const t = (value) => value
+
+  assert.deepEqual(getReferencedCustomProviderIdsFromSessions([session], providers), [
+    'renamed-provider',
+  ])
+  assert.equal(getConversationAiName(session, t, providers), 'Renamed Provider (proxy-model)')
+})
+
+test('canonical and legacy provider ID collisions use the session URL for display and references', () => {
+  const providers = [
+    {
+      id: 'proxy-v1',
+      name: 'Current ID Match',
+      chatCompletionsUrl: 'https://current.example.com/v1/chat/completions',
+    },
+    {
+      id: 'renamed-provider',
+      name: 'Legacy ID Match',
+      chatCompletionsUrl: 'https://legacy.example.com/v1/chat/completions',
+      legacyProviderIds: ['proxy-v1'],
+      enabled: false,
+    },
+    {
+      id: 'unrelated-provider',
+      name: 'Unrelated',
+      chatCompletionsUrl: 'https://unrelated.example.com/v1/chat/completions',
+    },
+  ]
+  const createSession = (customUrl = '') => ({
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      providerId: 'proxy_v1',
+      customName: 'custom-model',
+      customUrl,
+    },
+  })
+  const apiModes = [
+    {
+      groupName: 'customApiModelKeys',
+      itemName: 'customModel',
+      isCustom: true,
+      customName: 'custom-model',
+      providerId: 'proxy-v1',
+    },
+  ]
+  const t = (value) => value
+  const legacySession = createSession('https://legacy.example.com/v1/chat/completions')
+
+  assert.deepEqual(
+    getReferencedCustomProviderIdsFromSessions([legacySession], providers, apiModes),
+    ['renamed-provider'],
+  )
+  assert.equal(getConversationAiName(legacySession, t, providers), 'Legacy ID Match (custom-model)')
+  assert.deepEqual(
+    getReferencedCustomProviderIdsFromSessions([createSession()], providers, apiModes),
+    ['proxy-v1', 'renamed-provider'],
+  )
+  const unrelatedSession = createSession('https://unrelated.example.com/v1/chat/completions')
+  assert.deepEqual(
+    getReferencedCustomProviderIdsFromSessions([unrelatedSession], providers, apiModes),
+    ['proxy-v1', 'renamed-provider'],
+  )
+  assert.equal(getConversationAiName(unrelatedSession, t, providers), 'Custom Model (custom-model)')
+})
diff --git a/tests/unit/popup/import-data-cleanup.test.mjs b/tests/unit/popup/import-data-cleanup.test.mjs
index c1571ce0..e5979aed 100644
--- a/tests/unit/popup/import-data-cleanup.test.mjs
+++ b/tests/unit/popup/import-data-cleanup.test.mjs
@@ -74,6 +74,43 @@ test('prepareImportData leaves unrelated imports untouched', () => {
   assert.deepEqual(keysToRemove, [])
 })
 
+test('prepareImportData reruns builtin provider ID migrations for legacy provider state', () => {
+  const { normalizedData, keysToRemove } = prepareImportData({
+    customOpenAIProviders: [{ id: 'legacy-provider' }],
+    providerSecrets: { 'legacy-provider': 'legacy-secret' },
+  })
+
+  assert.deepEqual(normalizedData, {
+    customOpenAIProviders: [{ id: 'legacy-provider' }],
+    providerSecrets: { 'legacy-provider': 'legacy-secret' },
+    completedBuiltinProviderIdMigrations: [],
+  })
+  assert.deepEqual(keysToRemove, [])
+})
+
+test('prepareImportData preserves migration markers for provider-only imports', () => {
+  const { normalizedData, keysToRemove } = prepareImportData({
+    customOpenAIProviders: [{ id: 'xai' }],
+  })
+
+  assert.deepEqual(normalizedData, {
+    customOpenAIProviders: [{ id: 'xai' }],
+  })
+  assert.deepEqual(keysToRemove, [])
+})
+
+test('prepareImportData preserves imported builtin provider ID migration markers', () => {
+  const input = {
+    customOpenAIProviders: [{ id: 'current-provider' }],
+    providerSecrets: { 'current-provider': 'current-secret' },
+    completedBuiltinProviderIdMigrations: ['current-provider'],
+  }
+  const { normalizedData, keysToRemove } = prepareImportData(input)
+
+  assert.deepEqual(normalizedData, input)
+  assert.deepEqual(keysToRemove, [])
+})
+
 test('prepareImportData migrates legacy model keys in imported config and sessions', () => {
   const { normalizedData, keysToRemove } = prepareImportData({
     modelName: 'chatgptFree4o',
@@ -177,6 +214,29 @@ test('importDataIntoStorage writes normalized data before removing legacy keys',
   ])
 })
 
+test('importDataIntoStorage ignores inherited provider mapping names', async () => {
+  const calls = []
+  const storageArea = {
+    async get(keys) {
+      calls.push(['get', keys])
+      return {}
+    },
+    async set(data) {
+      calls.push(['set', data])
+    },
+    async remove(keys) {
+      calls.push(['remove', keys])
+    },
+  }
+  const data = {
+    customOpenAIProviders: [{ id: 'constructor' }],
+  }
+
+  await importDataIntoStorage(storageArea, data)
+
+  assert.deepEqual(calls, [['set', data]])
+})
+
 test('importDataIntoStorage replaces stale API mode state before legacy migration', async () => {
   globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
     configSchemaVersion: 2,
@@ -207,6 +267,93 @@ test('importDataIntoStorage replaces stale API mode state before legacy migratio
   assert.equal(Object.hasOwn(migratedStorage, 'knownApiModeDefaultIds'), false)
 })
 
+test('importDataIntoStorage does not assign an existing builtin secret to an imported provider', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 2,
+    completedBuiltinProviderIdMigrations: ['xai', 'nvidia-nim', 'mistral'],
+    providerSecrets: { xai: 'builtin-xai-key' },
+    customOpenAIProviders: [],
+  })
+
+  await importDataIntoStorage(Browser.storage.local, {
+    customOpenAIProviders: [
+      {
+        id: 'xai',
+        name: 'Imported xAI proxy',
+        chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
+      },
+    ],
+  })
+  const config = await getUserConfig()
+
+  assert.equal(config.customOpenAIProviders[0].id, 'xai-2')
+  assert.equal(config.providerSecrets.xai, 'builtin-xai-key')
+  assert.equal(config.providerSecrets['xai-2'], undefined)
+})
+
+test('importDataIntoStorage preserves a builtin secret when its legacy mirror is stale', async () => {
+  for (const { storedXaiApiKey, importedXaiApiKey } of [
+    { storedXaiApiKey: '' },
+    { storedXaiApiKey: 'stale-stored-key' },
+    { storedXaiApiKey: 'builtin-xai-key', importedXaiApiKey: '' },
+    { storedXaiApiKey: 'builtin-xai-key', importedXaiApiKey: 'stale-imported-key' },
+  ]) {
+    globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+      configSchemaVersion: 2,
+      completedBuiltinProviderIdMigrations: ['xai', 'nvidia-nim', 'mistral'],
+      xaiApiKey: storedXaiApiKey,
+      providerSecrets: { xai: 'builtin-xai-key' },
+      customOpenAIProviders: [],
+    })
+
+    await importDataIntoStorage(Browser.storage.local, {
+      ...(importedXaiApiKey !== undefined ? { xaiApiKey: importedXaiApiKey } : {}),
+      customOpenAIProviders: [
+        {
+          id: 'xai',
+          name: 'Imported xAI proxy',
+          chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
+        },
+      ],
+    })
+    const config = await getUserConfig()
+
+    assert.equal(config.customOpenAIProviders[0].id, 'xai-2')
+    assert.equal(config.providerSecrets.xai, 'builtin-xai-key')
+    assert.equal(config.providerSecrets['xai-2'], undefined)
+  }
+})
+
+test('importDataIntoStorage still migrates a secret from an existing custom collision', async () => {
+  globalThis.__TEST_BROWSER_SHIM__.replaceStorage({
+    configSchemaVersion: 2,
+    completedBuiltinProviderIdMigrations: ['xai', 'nvidia-nim', 'mistral'],
+    providerSecrets: { xai: 'custom-xai-key' },
+    customOpenAIProviders: [
+      {
+        id: 'xai',
+        name: 'Existing xAI proxy',
+        chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
+      },
+    ],
+  })
+
+  await importDataIntoStorage(Browser.storage.local, {
+    customOpenAIProviders: [
+      {
+        id: 'xai',
+        name: 'Imported xAI proxy',
+        chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
+      },
+    ],
+  })
+  const config = await getUserConfig()
+
+  assert.equal(config.customOpenAIProviders[0].id, 'xai-2')
+  assert.equal(config.providerSecrets['xai-2'], 'custom-xai-key')
+  assert.equal(Object.hasOwn(config.providerSecrets, 'xai'), false)
+})
+
 test('importDataIntoStorage does not remove existing keys when set fails', async () => {
   const calls = []
   const storageArea = {
diff --git a/tests/unit/services/apis/provider-registry.test.mjs b/tests/unit/services/apis/provider-registry.test.mjs
index b23cba50..df2765fd 100644
--- a/tests/unit/services/apis/provider-registry.test.mjs
+++ b/tests/unit/services/apis/provider-registry.test.mjs
@@ -9,6 +9,40 @@ import {
   resolveProviderIdForSession,
 } from '../../../../src/services/apis/provider-registry.mjs'
 
+function createCanonicalSiblingProviders() {
+  return [
+    {
+      id: 'Foo',
+      name: 'Uppercase provider',
+      chatCompletionsUrl: 'https://uppercase.example.com/v1/chat/completions',
+    },
+    {
+      id: 'foo',
+      name: 'Lowercase provider',
+      chatCompletionsUrl: 'https://lowercase.example.com/v1/chat/completions',
+    },
+  ]
+}
+
+function createCanonicalSiblingMode(providerId, customName) {
+  return {
+    groupName: 'customApiModelKeys',
+    itemName: 'customModel',
+    isCustom: true,
+    customName,
+    providerId,
+  }
+}
+
+function createCanonicalSiblingSession(customName) {
+  return {
+    apiMode: {
+      ...createCanonicalSiblingMode('foo', customName),
+      customUrl: '',
+    },
+  }
+}
+
 test('resolveEndpointTypeForSession prefers apiMode when present', () => {
   const session = {
     apiMode: {
@@ -97,6 +131,262 @@ test('resolveOpenAICompatibleRequest resolves custom provider from normalized se
   assert.equal(resolved.apiKey, 'proxy-key')
 })
 
+test('resolveOpenAICompatibleRequest disambiguates legacy and normalized ID matches by URL', () => {
+  const config = {
+    customOpenAIProviders: [
+      {
+        id: 'proxy-v1',
+        name: 'Normalized Match',
+        chatCompletionsUrl: 'https://normalized.example.com/v1/chat/completions',
+      },
+      {
+        id: 'renamed-provider',
+        name: 'Legacy Match',
+        chatCompletionsUrl: 'https://legacy.example.com/v1/chat/completions',
+        legacyProviderIds: ['proxy-v1'],
+      },
+    ],
+    customApiModes: [
+      {
+        groupName: 'customApiModelKeys',
+        itemName: 'customModel',
+        isCustom: true,
+        customName: 'collision-model',
+        providerId: 'proxy-v1',
+      },
+    ],
+    providerSecrets: {
+      'proxy-v1': 'normalized-key',
+      'renamed-provider': 'legacy-key',
+    },
+  }
+  const createSession = (customUrl = '') => ({
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      providerId: 'proxy_v1',
+      customName: 'collision-model',
+      customUrl,
+    },
+  })
+
+  assert.equal(
+    resolveOpenAICompatibleRequest(
+      config,
+      createSession('https://legacy.example.com/v1/chat/completions'),
+    )?.providerId,
+    'renamed-provider',
+  )
+  assert.equal(
+    resolveOpenAICompatibleRequest(
+      config,
+      createSession('https://normalized.example.com/v1/chat/completions'),
+    )?.providerId,
+    'proxy-v1',
+  )
+  assert.equal(resolveOpenAICompatibleRequest(config, createSession()), null)
+})
+
+test('resolveOpenAICompatibleRequest disambiguates exact and legacy provider ID collisions by URL', () => {
+  const config = {
+    customOpenAIProviders: [
+      {
+        id: 'proxy-v1',
+        name: 'Current ID Match',
+        chatCompletionsUrl: 'https://current.example.com/v1/chat/completions',
+      },
+      {
+        id: 'renamed-provider',
+        name: 'Legacy ID Match',
+        chatCompletionsUrl: 'https://legacy.example.com/v1/chat/completions',
+        legacyProviderIds: ['proxy-v1'],
+      },
+      {
+        id: 'unrelated-provider',
+        name: 'Unrelated',
+        chatCompletionsUrl: 'https://unrelated.example.com/v1/chat/completions',
+      },
+    ],
+    customApiModes: [
+      {
+        groupName: 'customApiModelKeys',
+        itemName: 'customModel',
+        isCustom: true,
+        customName: 'collision-model',
+        providerId: 'unrelated-provider',
+      },
+    ],
+  }
+  const createSession = (customUrl = '') => ({
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      providerId: 'proxy-v1',
+      customName: 'collision-model',
+      customUrl,
+    },
+  })
+
+  assert.equal(
+    resolveOpenAICompatibleRequest(
+      config,
+      createSession('https://legacy.example.com/v1/chat/completions'),
+    )?.providerId,
+    'renamed-provider',
+  )
+  assert.equal(
+    resolveOpenAICompatibleRequest(
+      config,
+      createSession('https://current.example.com/v1/chat/completions'),
+    )?.providerId,
+    'proxy-v1',
+  )
+  assert.equal(resolveOpenAICompatibleRequest(config, createSession()), null)
+  assert.equal(
+    resolveOpenAICompatibleRequest(
+      config,
+      createSession('https://unrelated.example.com/v1/chat/completions'),
+    ),
+    null,
+  )
+})
+
+test('resolveOpenAICompatibleRequest disambiguates exact and legacy provider ID collisions by mode label', () => {
+  const config = {
+    customOpenAIProviders: [
+      {
+        id: 'proxy-v1',
+        name: 'Current ID Match',
+        chatCompletionsUrl: 'https://current.example.com/v1/chat/completions',
+      },
+      {
+        id: 'renamed-provider',
+        name: 'Legacy ID Match',
+        chatCompletionsUrl: 'https://legacy.example.com/v1/chat/completions',
+        legacyProviderIds: ['proxy-v1'],
+      },
+    ],
+    customApiModes: [
+      {
+        groupName: 'customApiModelKeys',
+        itemName: 'customModel',
+        isCustom: true,
+        customName: 'current-model',
+        providerId: 'proxy-v1',
+      },
+      {
+        groupName: 'customApiModelKeys',
+        itemName: 'customModel',
+        isCustom: false,
+        customName: 'current-model',
+        providerId: 'renamed-provider',
+      },
+    ],
+  }
+  const session = {
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      itemName: 'customModel',
+      isCustom: true,
+      providerId: 'proxy-v1',
+      customName: 'current-model',
+      customUrl: '',
+    },
+  }
+
+  assert.equal(resolveOpenAICompatibleRequest(config, session)?.providerId, 'proxy-v1')
+  delete session.apiMode.isCustom
+  assert.equal(resolveOpenAICompatibleRequest(config, session), null)
+})
+
+test('resolveOpenAICompatibleRequest preserves raw provider ID disambiguation by mode label', () => {
+  const config = {
+    customOpenAIProviders: createCanonicalSiblingProviders(),
+    customApiModes: [createCanonicalSiblingMode('Foo', 'uppercase-model')],
+    providerSecrets: {
+      Foo: 'uppercase-key',
+      foo: 'lowercase-key',
+    },
+  }
+  const session = createCanonicalSiblingSession('uppercase-model')
+
+  const resolved = resolveOpenAICompatibleRequest(config, session)
+
+  assert.equal(resolved?.providerId, 'Foo')
+  assert.equal(resolved?.requestUrl, 'https://uppercase.example.com/v1/chat/completions')
+  assert.equal(resolved?.apiKey, 'uppercase-key')
+})
+
+test('resolveOpenAICompatibleRequest does not borrow a canonical sibling secret', () => {
+  const config = {
+    customOpenAIProviders: createCanonicalSiblingProviders(),
+    customApiModes: [createCanonicalSiblingMode('Foo', 'uppercase-model')],
+    providerSecrets: {
+      foo: 'lowercase-key',
+    },
+  }
+  const session = createCanonicalSiblingSession('uppercase-model')
+
+  const resolved = resolveOpenAICompatibleRequest(config, session)
+
+  assert.equal(resolved?.providerId, 'Foo')
+  assert.equal(resolved?.secretProviderId, 'Foo')
+  assert.equal(resolved?.apiKey, '')
+})
+
+test('resolveOpenAICompatibleRequest does not borrow canonical sibling mode or session secrets', () => {
+  const config = {
+    customOpenAIProviders: createCanonicalSiblingProviders(),
+    customApiModes: [
+      {
+        ...createCanonicalSiblingMode('foo', 'lowercase-model'),
+        apiKey: 'lowercase-mode-key',
+      },
+    ],
+    providerSecrets: {},
+  }
+  const session = createCanonicalSiblingSession('lowercase-model')
+  session.apiMode.customUrl = 'https://uppercase.example.com/v1/chat/completions'
+  session.apiMode.apiKey = 'lowercase-session-key'
+
+  const resolved = resolveOpenAICompatibleRequest(config, session)
+
+  assert.equal(resolved?.providerId, 'Foo')
+  assert.equal(resolved?.requestUrl, 'https://uppercase.example.com/v1/chat/completions')
+  assert.equal(resolved?.apiKey, '')
+})
+
+test('resolveOpenAICompatibleRequest fails closed for duplicate labels on canonical siblings', () => {
+  const config = {
+    customOpenAIProviders: createCanonicalSiblingProviders(),
+    customApiModes: [
+      createCanonicalSiblingMode('Foo', 'shared-model'),
+      createCanonicalSiblingMode('foo', 'shared-model'),
+    ],
+    providerSecrets: {
+      Foo: 'uppercase-key',
+      foo: 'lowercase-key',
+    },
+  }
+  const session = createCanonicalSiblingSession('shared-model')
+
+  assert.equal(resolveOpenAICompatibleRequest(config, session), null)
+})
+
+test('resolveOpenAICompatibleRequest does not replace a disabled exact label provider', () => {
+  const providers = createCanonicalSiblingProviders()
+  providers[0].enabled = false
+  const config = {
+    customOpenAIProviders: providers,
+    customApiModes: [createCanonicalSiblingMode('Foo', 'uppercase-model')],
+    providerSecrets: {
+      Foo: 'uppercase-key',
+      foo: 'lowercase-key',
+    },
+  }
+  const session = createCanonicalSiblingSession('uppercase-model')
+
+  assert.equal(resolveOpenAICompatibleRequest(config, session), null)
+})
+
 test('getOpenAICompatibleRequestDiagnostic reports safe context for missing custom provider', () => {
   const config = {
     customOpenAIProviders: [
@@ -864,6 +1154,7 @@ test('resolveOpenAICompatibleRequest recovers by legacy customUrl when provider
   const resolved = resolveOpenAICompatibleRequest(config, session)
 
   assert.equal(resolved.providerId, 'legacy-custom-default')
+  assert.equal(resolved.secretProviderId, 'openai')
   assert.equal(resolved.requestUrl, 'https://derived.example.com/v1/chat/completions')
   assert.equal(resolved.apiKey, '')
 })
@@ -909,8 +1200,23 @@ test('resolveOpenAICompatibleRequest does not fall back when customUrl points at
         chatCompletionsUrl: 'https://proxy.example.com/v1/chat/completions',
         enabled: false,
       },
+      {
+        id: 'label-provider',
+        name: 'Label Provider',
+        chatCompletionsUrl: 'https://other.example.com/v1/chat/completions',
+        enabled: true,
+      },
+    ],
+    customApiModes: [
+      {
+        groupName: 'customApiModelKeys',
+        itemName: 'customModel',
+        isCustom: true,
+        providerId: 'label-provider',
+        customName: 'proxy-model',
+        active: true,
+      },
     ],
-    customApiModes: [],
   }
   const session = {
     apiMode: {
@@ -2354,6 +2660,94 @@ test('resolveOpenAICompatibleRequest fails closed when shared legacy custom url
   assert.equal(resolved, null)
 })
 
+test('resolveOpenAICompatibleRequest does not bypass a disabled provider through its legacy ID', () => {
+  const config = {
+    customOpenAIProviders: [
+      {
+        id: 'stale-provider',
+        name: 'Current Provider',
+        chatCompletionsUrl: 'https://current.example.com/v1/chat/completions',
+      },
+      {
+        id: 'renamed-provider',
+        name: 'Disabled Provider',
+        chatCompletionsUrl: 'https://disabled.example.com/v1/chat/completions',
+        legacyProviderIds: ['stale-provider'],
+        enabled: false,
+      },
+    ],
+    customApiModes: [
+      {
+        groupName: 'customApiModelKeys',
+        customName: 'shared-label',
+        providerId: 'stale-provider',
+      },
+    ],
+    providerSecrets: {
+      'stale-provider': 'current-key',
+      'renamed-provider': 'disabled-key',
+    },
+  }
+  const session = {
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      providerId: 'stale-provider',
+      customName: 'shared-label',
+      customUrl: 'https://disabled.example.com/v1/chat/completions',
+    },
+  }
+
+  assert.equal(resolveOpenAICompatibleRequest(config, session), null)
+})
+
+test('resolveOpenAICompatibleRequest uses a stable mode label despite a disabled legacy URL match', () => {
+  const config = {
+    customOpenAIProviders: [
+      {
+        id: 'provider-a',
+        name: 'Current Provider',
+        chatCompletionsUrl: 'https://current.example.com/v1/chat/completions',
+      },
+      {
+        id: 'provider-b-renamed',
+        name: 'Disabled Legacy Provider',
+        chatCompletionsUrl: 'https://legacy.example.com/v1/chat/completions',
+        legacyProviderIds: ['provider-a'],
+        enabled: false,
+      },
+    ],
+    customApiModes: [
+      {
+        groupName: 'customApiModelKeys',
+        itemName: 'customModel',
+        isCustom: true,
+        customName: 'current-model',
+        providerId: 'provider-a',
+      },
+    ],
+    providerSecrets: {
+      'provider-a': 'current-key',
+      'provider-b-renamed': 'legacy-key',
+    },
+  }
+  const session = {
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      itemName: 'customModel',
+      isCustom: true,
+      customName: 'current-model',
+      providerId: 'provider-a',
+      customUrl: 'https://legacy.example.com/v1/chat/completions',
+    },
+  }
+
+  const resolved = resolveOpenAICompatibleRequest(config, session)
+
+  assert.equal(resolved?.providerId, 'provider-a')
+  assert.equal(resolved?.requestUrl, 'https://current.example.com/v1/chat/completions')
+  assert.equal(resolved?.apiKey, 'current-key')
+})
+
 test('resolveOpenAICompatibleRequest fails closed when legacy customUrl has only provider secrets and no session key signal', () => {
   const config = {
     customOpenAIProviders: [
diff --git a/tests/unit/utils/model-name-convert.test.mjs b/tests/unit/utils/model-name-convert.test.mjs
index 5222f6a5..4bc15040 100644
--- a/tests/unit/utils/model-name-convert.test.mjs
+++ b/tests/unit/utils/model-name-convert.test.mjs
@@ -1121,6 +1121,65 @@ test('isApiModeSelected keeps provider mismatch fail-closed for non-legacy sessi
   assert.equal(isApiModeSelected(apiMode, session, { sessionCompat: true }), false)
 })
 
+test('isApiModeSelected accepts a canonically equivalent session provider ID', () => {
+  const apiMode = {
+    groupName: 'customApiModelKeys',
+    itemName: 'customModel',
+    isCustom: true,
+    customName: 'proxy-model',
+    providerId: 'proxy-v1',
+    active: true,
+  }
+  const session = {
+    apiMode: {
+      ...apiMode,
+      providerId: 'Proxy_V1',
+    },
+  }
+
+  assert.equal(isApiModeSelected(apiMode, session), false)
+  assert.equal(isApiModeSelected(apiMode, session, { sessionCompat: true }), true)
+})
+
+test('getUniquelySelectedApiModeIndex disambiguates provider ID collisions by customUrl', () => {
+  const apiModes = [
+    {
+      groupName: 'customApiModelKeys',
+      itemName: 'customModel',
+      isCustom: true,
+      customName: 'proxy-model',
+      customUrl: 'https://current.example.com/v1/chat/completions',
+      providerId: 'legacy-provider',
+      active: true,
+    },
+    {
+      groupName: 'customApiModelKeys',
+      itemName: 'customModel',
+      isCustom: true,
+      customName: 'proxy-model',
+      customUrl: 'https://renamed.example.com/v1/chat/completions/',
+      providerId: 'renamed-provider',
+      legacyProviderIds: ['legacy-provider'],
+      active: true,
+    },
+  ]
+  const session = {
+    apiMode: {
+      groupName: 'customApiModelKeys',
+      itemName: 'customModel',
+      isCustom: true,
+      customName: 'proxy-model',
+      customUrl: 'https://renamed.example.com/v1/chat/completions',
+      providerId: 'legacy-provider',
+      active: true,
+    },
+  }
+
+  assert.equal(getUniquelySelectedApiModeIndex(apiModes, session, { sessionCompat: true }), 1)
+  session.apiMode.customUrl = 'https://current.example.com/v1/chat/completions/'
+  assert.equal(getUniquelySelectedApiModeIndex(apiModes, session, { sessionCompat: true }), 0)
+})
+
 test('isApiModeSelected keeps modern custom session provider mismatch fail-closed with customUrl and apiKey', () => {
   const apiMode = {
     groupName: 'customApiModelKeys',