chore: add Hex package build CI

[marandaneto]

💡 Motivation and Context

Add CI coverage to ensure the Hex package can be built successfully. This helps catch packaging issues before release.

Changes:

• Added a dedicated package workflow job.
• Checks out the repository, sets up Elixir/OTP, and runs mix hex.build.

💚 How did you test it?

• Ran mix hex.build locally.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
.github/workflows/ci.yml:178-192
`mix hex.build` only packages source files listed in `mix.exs` — it does not compile the project or require fetched dependencies. The cache-restore and `mix deps.get` steps add CI time without contributing anything to the build check.

```suggestion
      - name: Build Hex package
        run: mix hex.build
```

_{Reviews (1): Last reviewed commit: "chore: add Hex package build CI" | Re-trigger Greptile}

[github-actions]

posthog-elixir Compliance Report

Date: 2026-06-12 07:54:30 UTC
Duration: 107430ms

⚠️ Some Tests Failed

42/45 tests passed, 3 failed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	610ms
Format Validation.Event Has Uuid	✅	610ms
Format Validation.Event Has Lib Properties	✅	610ms
Format Validation.Distinct Id Is String	✅	610ms
Format Validation.Token Is Present	✅	610ms
Format Validation.Custom Properties Preserved	✅	609ms
Format Validation.Event Has Timestamp	✅	610ms
Retry Behavior.Retries On 503	✅	5615ms
Retry Behavior.Does Not Retry On 400	✅	2612ms
Retry Behavior.Does Not Retry On 401	✅	2612ms
Retry Behavior.Respects Retry After Header	✅	5615ms
Retry Behavior.Implements Backoff	✅	15626ms
Retry Behavior.Retries On 500	✅	5616ms
Retry Behavior.Retries On 502	✅	5616ms
Retry Behavior.Retries On 504	✅	5616ms
Retry Behavior.Max Retries Respected	✅	15626ms
Deduplication.Generates Unique Uuids	✅	621ms
Deduplication.Preserves Uuid On Retry	✅	5615ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10621ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5615ms
Deduplication.No Duplicate Events In Batch	✅	616ms
Deduplication.Different Events Have Different Uuids	✅	613ms
Compression.Sends Gzip When Enabled	✅	610ms
Batch Format.Uses Proper Batch Structure	✅	609ms
Batch Format.Flush With No Events Sends Nothing	✅	607ms
Batch Format.Multiple Events Batched Together	✅	615ms
Error Handling.Does Not Retry On 403	✅	2612ms
Error Handling.Does Not Retry On 413	✅	2613ms
Error Handling.Retries On 408	✅	5616ms

Feature_Flags Tests

⚠️ 13/16 tests passed, 3 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	8ms
Request Payload.Flags Request Uses V2 Query Param	✅	8ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	7ms
Request Payload.Flags Request Omits Authorization Header	✅	8ms
Request Payload.Token In Flags Body Matches Init	✅	7ms
Request Payload.Groups Round Trip	✅	7ms
Request Payload.Groups Default To Empty Object	✅	7ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	9ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	8ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	8ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	8ms
Request Lifecycle.No Flags Request On Init Alone	✅	4ms
Request Lifecycle.No Flags Request On Normal Capture	✅	609ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	11ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	7ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	610ms

Failures

request_payload.disable_geoip_omitted_defaults_to_false

Field 'geoip_disable' not found in /flags request body at path 'geoip_disable'. Available keys: ['groups', 'api_key', 'distinct_id', 'flag_keys_to_evaluate', 'group_properties', 'person_properties']

request_lifecycle.mock_response_value_is_returned_to_caller

Last action result missing field 'value'. Keys: ['error', 'success']

side_effect_events.get_feature_flag_captures_feature_flag_called_event

Expected 1 events with name '$feature_flag_called', got 0

[greptile-apps]

_{Reviews (2): Last reviewed commit: "chore: tidy package build workflow" | Re-trigger Greptile}

[ioannisj]

Did we have issues with this package or just a precaution?