flake: TestSubscribeAfterMessageID

[flake-investigator]

CI Run

• https://github.com/coder/coder/actions/runs/24796386538
• Failed job: test-go-pg (ubuntu-latest) (https://github.com/coder/coder/actions/runs/24796386538/job/72567255793)

Commit

• SHA: 514b4994c696ffd86b03878dee014c0964e191e5
• Author: Jeremy Ruppel
• coder/coder@514b499

Failure

=== FAIL: coderd/x/chatd TestSubscribeAfterMessageID (0.39s)
    chatd_test.go:3847:
        Error:       "[{message d28d5bcb-96af-410c-9955-278ca826287b 0xc0006fd730 <nil> <nil> <nil> <nil> [] <nil>} {message d28d5bcb-96af-410c-9955-278ca826287b 0xc0006fd7a0 <nil> <nil> <nil> <nil> [] <nil>}]" should have 1 item(s), but has 2
        Messages:    afterMessageID=msg2.ID should return only messages after msg2

Error Analysis

• Test inserts three messages (initial user message + two manual inserts), then subscribes with afterMessageID=msg2.ID.
• Snapshot filtering returned two message events instead of one, indicating an extra message (likely msg2 or duplicate) was included in the snapshot.
• No panic/OOM indicators or data race warnings observed in the job logs.

Root Cause Assessment

• Flaky test / snapshot filtering inconsistency in Subscribe when afterMessageID is used (duplicate or off-by-one message inclusion).

Assignment Analysis

• Failing test function: coderd/x/chatd/chatd_test.go lines ~3757-3847 (TestSubscribeAfterMessageID).
• Unable to run git blame via API tooling; used recent file history instead:
  • git log --oneline -10 --follow coderd/x/chatd/chatd_test.go → most recent subscribe-related stabilization commit: b3d5b8d ("fix: stabilize flaky chatd subscribe/promote queued tests") by Kyle Carberry.
• Assigning to the most recent substantive modifier of chatd subscribe tests: @kylecarbs.

Related Issues

Searched coder/internal for:

• "TestSubscribeAfterMessageID"
• "afterMessageID"
• "chatd_test.go"
• "chatd subscribe message"

Related but not duplicates:

• CODAGT-81 (closed) flake: chatd subscribe/promote queued (different tests, prior fix)
• ENG-2524 (open) chatd tests failed without specific output (different failure mode)

Reproduction

go test ./coderd/x/chatd -run TestSubscribeAfterMessageID -count=1