diff --git a/design-system/packages/design-tokens/README.md b/design-system/packages/design-tokens/README.md
index 12b61448fb..6ca987c9cc 100644
--- a/design-system/packages/design-tokens/README.md
+++ b/design-system/packages/design-tokens/README.md
@@ -23,6 +23,15 @@ line travel and intrinsic-width changes. It has its own token so tuning content
 replacement does not change the existing hover-feedback and larger-view
 transition durations. It is zeroed in the reduced-motion projection.
 
+## Overlay layers
+
+Portaled tooltips must paint above the popovers containing their triggers.
+Use `layer.popover` for menus and panels, with adjacent offsets for their
+backdrops (-1) and nested menus (+1); keep those offsets below `layer.tooltip`.
+Toast, notification, and context-menu layers remain above ordinary hover hints.
+These values order siblings within a stacking context; a portal host still
+needs its own layer above the app content it serves.
+
 ## Semantic typography roles
 
 Text-bearing components consume a complete semantic role rather than assembling
diff --git a/design-system/packages/design-tokens/src/system.tokens.json b/design-system/packages/design-tokens/src/system.tokens.json
index c02306ed89..65f311664d 100644
--- a/design-system/packages/design-tokens/src/system.tokens.json
+++ b/design-system/packages/design-tokens/src/system.tokens.json
@@ -989,7 +989,7 @@
     "modalActive": { "$value": 250 },
     "fullscreen": { "$value": 280 },
     "overlayHost": { "$value": 300 },
-    "tooltip": { "$value": 350 },
+    "tooltip": { "$value": 370 },
     "popover": { "$value": 360 },
     "toast": { "$value": 400 },
     "notification": { "$value": 400 },
diff --git a/design-system/packages/design-tokens/tests/contract.test.mjs b/design-system/packages/design-tokens/tests/contract.test.mjs
index 314210cd73..1160895fb3 100644
--- a/design-system/packages/design-tokens/tests/contract.test.mjs
+++ b/design-system/packages/design-tokens/tests/contract.test.mjs
@@ -436,6 +436,20 @@ test("shared system scales preserve the migrated Web UI foundation contract", ()
   assert.equal(tokens["layer.contextMenu"], 500);
 });
 
+test("tooltips outrank popovers and nested menus without covering priority chrome", () => {
+  for (const mode of tokenModes) {
+    const modeTokens = Object.fromEntries(
+      tokenCatalog.filter(token => token.category === "layer")
+        .map(token => [token.name, Number(token.values[mode])]),
+    );
+    assert.ok(modeTokens["layer.modal"] < modeTokens["layer.popover"]);
+    assert.ok(modeTokens["layer.popover"] + 1 < modeTokens["layer.tooltip"]);
+    for (const layer of ["toast", "notification", "contextMenu"]) {
+      assert.ok(modeTokens["layer.tooltip"] < modeTokens[`layer.${layer}`]);
+    }
+  }
+});
+
 test("semantic typography roles resolve to the canonical foundation", async () => {
   const systemDocument = await readSource("system.tokens.json");
 
diff --git a/src/apps/data-migrator/ui/generated/design-system.css b/src/apps/data-migrator/ui/generated/design-system.css
index b40a352906..43d4457d80 100644
--- a/src/apps/data-migrator/ui/generated/design-system.css
+++ b/src/apps/data-migrator/ui/generated/design-system.css
@@ -200,7 +200,7 @@
     --openbitfun-layer-popover: 360;
     --openbitfun-layer-sticky: 15;
     --openbitfun-layer-toast: 400;
-    --openbitfun-layer-tooltip: 350;
+    --openbitfun-layer-tooltip: 370;
     --openbitfun-layout-card-footer-gap: var(--openbitfun-space-2);
     --openbitfun-layout-card-gap-lg: 30px;
     --openbitfun-layout-card-gap-md: var(--openbitfun-space-3);
diff --git a/src/web-ui/src/app/components/NavPanel/NavPanel.scss b/src/web-ui/src/app/components/NavPanel/NavPanel.scss
index 8141a2216e..ca23b08b01 100644
--- a/src/web-ui/src/app/components/NavPanel/NavPanel.scss
+++ b/src/web-ui/src/app/components/NavPanel/NavPanel.scss
@@ -981,7 +981,7 @@ $_section-header-height: 22px;
     width: fit-content;
     max-width: min(440px, calc(100vw - 32px));
     max-height: min(560px, calc(100vh - 16px));
-    z-index: 9999;
+    z-index: var(--openbitfun-layer-popover);
     transform-origin: top left;
     animation: openbitfun-footer-menu-in var(--openbitfun-motion-duration-fast) var(--openbitfun-motion-easing-decelerate) forwards;
 
@@ -1028,6 +1028,8 @@ $_section-header-height: 22px;
   }
 
   &__workspace-menu-workspaces {
+    display: flex;
+    flex-direction: column;
     max-height: 240px;
     overscroll-behavior: contain;
   }
@@ -1604,7 +1606,7 @@ $_section-header-height: 22px;
 .openbitfun-nav-panel__footer-backdrop {
   position: fixed;
   inset: 0;
-  z-index: 9998;
+  z-index: calc(var(--openbitfun-layer-popover) - 1);
 }
 
 /* Positioning-only overrides; the design-system Menu owns the surface look. */
@@ -1613,7 +1615,7 @@ $_section-header-height: 22px;
   min-width: 148px;
   max-width: calc(100vw - 16px);
   max-height: calc(100vh - 16px);
-  z-index: 9999;
+  z-index: var(--openbitfun-layer-popover);
   transform-origin: bottom right;
   animation: openbitfun-footer-menu-in var(--openbitfun-motion-duration-fast) var(--openbitfun-motion-easing-decelerate) forwards;
 
@@ -1640,7 +1642,7 @@ $_section-header-height: 22px;
   position: fixed;
   max-width: calc(100vw - 16px);
   max-height: calc(100vh - 16px);
-  z-index: 10000;
+  z-index: calc(var(--openbitfun-layer-popover) + 1);
   animation: openbitfun-nav-popover-in 150ms cubic-bezier(0.23, 1, 0.32, 1) both;
 
   &[data-placement='right'] {
@@ -1658,7 +1660,7 @@ $_section-header-height: 22px;
 
 .openbitfun-device-overview {
   position: fixed;
-  z-index: 9999;
+  z-index: var(--openbitfun-layer-popover);
   width: min(280px, calc(100vw - 16px));
   max-height: calc(100vh - 16px);
   display: flex;
diff --git a/src/web-ui/src/app/components/NavPanel/sections/sessions/SessionsSection.scss b/src/web-ui/src/app/components/NavPanel/sections/sessions/SessionsSection.scss
index 609218e64b..68c3515185 100644
--- a/src/web-ui/src/app/components/NavPanel/sections/sessions/SessionsSection.scss
+++ b/src/web-ui/src/app/components/NavPanel/sections/sessions/SessionsSection.scss
@@ -460,7 +460,7 @@
 
   &__inline-item-menu-popover {
     position: fixed;
-    z-index: 10000;
+    z-index: var(--openbitfun-layer-popover);
   }
 
   &__inline-item-edit {
diff --git a/src/web-ui/src/app/components/NavPanel/sections/workspaces/WorkspaceListSection.scss b/src/web-ui/src/app/components/NavPanel/sections/workspaces/WorkspaceListSection.scss
index e808331bfb..d9fde898c5 100644
--- a/src/web-ui/src/app/components/NavPanel/sections/workspaces/WorkspaceListSection.scss
+++ b/src/web-ui/src/app/components/NavPanel/sections/workspaces/WorkspaceListSection.scss
@@ -910,7 +910,7 @@
     min-inline-size: 180px;
     max-inline-size: min(320px, calc(100vw - 24px));
     max-block-size: min(560px, calc(100vh - 16px));
-    z-index: 10000;
+    z-index: var(--openbitfun-layer-popover);
     transform-origin: top left;
     animation: openbitfun-footer-menu-in var(--openbitfun-motion-duration-fast) var(--openbitfun-motion-easing-decelerate) forwards;
   }
diff --git a/src/web-ui/src/app/components/panels/content-canvas/tab-bar/TabOverflowMenu.scss b/src/web-ui/src/app/components/panels/content-canvas/tab-bar/TabOverflowMenu.scss
index b98d662a06..ef4bc22744 100644
--- a/src/web-ui/src/app/components/panels/content-canvas/tab-bar/TabOverflowMenu.scss
+++ b/src/web-ui/src/app/components/panels/content-canvas/tab-bar/TabOverflowMenu.scss
@@ -83,7 +83,7 @@
   --openbitfun-overlay-menu-inline-size: min(280px, calc(100vw - 16px));
   --openbitfun-overlay-menu-max-block-size: min(360px, calc(100vh - 16px));
   min-width: 200px;
-  z-index: 99999;
+  z-index: var(--openbitfun-layer-popover);
   animation: menuSlideIn 0.12s ease-out;
 
   @keyframes menuSlideIn {
diff --git a/src/web-ui/src/flow_chat/components/modern/FlowChatHeader.scss b/src/web-ui/src/flow_chat/components/modern/FlowChatHeader.scss
index 777016e68c..c195b0b864 100644
--- a/src/web-ui/src/flow_chat/components/modern/FlowChatHeader.scss
+++ b/src/web-ui/src/flow_chat/components/modern/FlowChatHeader.scss
@@ -467,7 +467,7 @@
 
   &__background-command-menu {
     position: fixed;
-    z-index: 10000;
+    z-index: calc(var(--openbitfun-layer-popover) + 1);
 
     &--portal {
       top: auto;
diff --git a/src/web-ui/src/flow_chat/components/modern/SessionTreePopover.scss b/src/web-ui/src/flow_chat/components/modern/SessionTreePopover.scss
index a604bd6ec3..3c2902576e 100644
--- a/src/web-ui/src/flow_chat/components/modern/SessionTreePopover.scss
+++ b/src/web-ui/src/flow_chat/components/modern/SessionTreePopover.scss
@@ -250,7 +250,7 @@
     position: fixed;
     top: auto;
     right: auto;
-    z-index: 10000;
+    z-index: calc(var(--openbitfun-layer-popover) + 1);
   }
 
   &__node-copy {
diff --git a/src/web-ui/src/infrastructure/appearance/runtime/AppearanceOverlayHost.test.ts b/src/web-ui/src/infrastructure/appearance/runtime/AppearanceOverlayHost.test.ts
index d2e11a9d4a..07df025a7c 100644
--- a/src/web-ui/src/infrastructure/appearance/runtime/AppearanceOverlayHost.test.ts
+++ b/src/web-ui/src/infrastructure/appearance/runtime/AppearanceOverlayHost.test.ts
@@ -53,6 +53,26 @@ describe('appearance overlay host', () => {
     expect(systemTokens.layer.overlayHost.$value).toBeLessThan(systemTokens.layer.contextMenu.$value);
   });
 
+  it.each([
+    'src/app/components/NavPanel/NavPanel.scss',
+    'src/app/components/NavPanel/sections/sessions/SessionsSection.scss',
+    'src/app/components/NavPanel/sections/workspaces/WorkspaceListSection.scss',
+    'src/app/components/panels/content-canvas/tab-bar/TabOverflowMenu.scss',
+    'src/flow_chat/components/modern/FlowChatHeader.scss',
+    'src/flow_chat/components/modern/SessionTreePopover.scss',
+    'src/infrastructure/peer-device/DeviceSurfaceSwitcher.scss',
+  ])('keeps %s below portaled tooltips', (path) => {
+    const styles = readSource(path);
+    // Legacy 9999/10000 menu layers bypassed the shared scale and covered
+    // Tooltip/OverflowText siblings even after the portal escaped clipping.
+    for (const [, value] of styles.matchAll(/z-index:\s*(\d+)\s*;/g)) {
+      expect(Number(value), `${path}: z-index ${value}`).toBeLessThan(
+        systemTokens.layer.tooltip.$value,
+      );
+    }
+    expect(systemTokens.layer.popover.$value + 1).toBeLessThan(systemTokens.layer.tooltip.$value);
+  });
+
   // A containing block on the host would re-anchor every `position: fixed`
   // overlay to the host box instead of the viewport, moving all of them.
   it('never becomes a containing block for fixed-position overlays', () => {
diff --git a/src/web-ui/src/infrastructure/peer-device/DeviceSurfaceSwitcher.scss b/src/web-ui/src/infrastructure/peer-device/DeviceSurfaceSwitcher.scss
index 9196c32e74..18b4d6ffb4 100644
--- a/src/web-ui/src/infrastructure/peer-device/DeviceSurfaceSwitcher.scss
+++ b/src/web-ui/src/infrastructure/peer-device/DeviceSurfaceSwitcher.scss
@@ -82,12 +82,12 @@
   &__backdrop {
     position: fixed;
     inset: 0;
-    z-index: 9998;
+    z-index: calc(var(--openbitfun-layer-popover) - 1);
   }
 
   &__menu {
     position: fixed;
-    z-index: 9999;
+    z-index: var(--openbitfun-layer-popover);
   }
 
   &__item-metadata {