fix[notask]: dispatch runs now cancel previous same-branch run

[tobi-legan]

Summary

• The concurrency group fallback used github.run_id for non-PR triggers (workflow_dispatch), making every dispatch a unique group. Multiple dispatches on the same branch ran in parallel, all competing for the same DF device slots.
• Switch to github.ref so same-branch dispatches cancel the previous run. The cancel handler already calls stop-run which frees Device Farm devices immediately.
• Affects all 16 on-pr-*.yml workflows.

Context

Part of QIP: Reduce LLM Mobile CI Run Time. DF device concurrency is the main bottleneck — shards wait up to 78m for a device during working hours. Duplicate dispatch runs waste device slots and make the queue worse for everyone.

Test plan

• Trigger two workflow_dispatch runs on the same branch — second should cancel the first
• Verify stop-run fires on the cancelled run (check cancel-device-farm-runs step)
• Verify PR-based concurrency still works (new push to same PR cancels old run)
• Verify dispatches on different branches do NOT cancel each other

Related

• Asana: https://app.asana.com/1/45238840754660/project/1214153063536860/task/1215953274910531

Made with Cursor

[github-actions]

Review Status

Current Status: ❌ PENDING
Approvals so far: none

Pending reviews: Needs 1 Management or Team Lead, and 1 more from Management, Team Lead, or Member.

[tobi-legan]

Test Results

Tested by triggering two workflow_dispatch runs on the same branch (fix/dispatch-concurrency) back to back:

• Run 1 (28040731678): dispatched first → cancelled by Run 2 ✅
• Run 2 (28040769089): dispatched second → ran (then manually cancelled to free DF devices) ✅

The concurrency group with github.ref correctly identifies same-branch dispatches and cancels the previous run. Before this fix, both would have run in parallel competing for DF device slots.

[github-actions]

Tier-based Approval Status

**PR Tier:** TIER1

**Current Status:** ❌ PENDING

**Requirements:**
- 1 Team Member approval ❌ (0/1)
- 1 Team Lead OR Management approval ❌ (0/1)



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*This comment is automatically updated when reviews change.*