feat(dispatch): port retro to harness CEL trigger

[ifireball]

What is missing

retro routing logic lives in bash in reusable-dispatch.yml. It is not expressed as a CEL trigger: on the harness file, so routing cannot be customized without editing shared dispatch bash.

What should happen

One vertical PR ports retro only:

Harness

• Add trigger: CEL expressing today's bash routing for: PR closed
• CEL lint/type-check in the same PR

Gating

• Decide retro-specific gates (may differ from GCD): what moves into fullsend dispatch, what stays in workflow, whether new ADR or harness format extension is needed
• Decide whether roles: config check still applies for retro in a custom-agents world

Workflow

• harness-dispatch handles retro when CEL matches
• Bash route still runs in parallel for shadow/diff until cutover epic child
• Do not remove bash routing for retro in this PR

Tests (same PR)

• Extend behaviour scenarios from test(behaviour): add retro dispatch trigger scenarios (bash routing) #2894 to cover harness-dispatch path
• Unit parity golden: normative fixtures for retro events match bash routing

Prerequisites

• feat(dispatch): add harness-dispatch job with ADR 54 auth, kill switch, and custom-agent behaviour test #2889 (harness-dispatch + custom agent)
• test(behaviour): add retro dispatch trigger scenarios (bash routing) #2894 (retro bash trigger behaviour baseline)

Merge criterion

retro behaviour scenarios green on harness-dispatch; shadow diff shows parity with bash for its trigger set.

Related

Part of epic #2888

[fullsend-ai-triage]

🤖 Finished Triage · ✅ Success · Started 8:34 AM UTC · Completed 8:37 AM UTC
Commit: 9f4f2b6 · View workflow run →

[fullsend-ai-triage]

Triage Summary

This issue requests porting retro agent routing from bash in reusable-dispatch.yml to a CEL trigger: expression in the harness file, as part of the broader harness CEL dispatch epic (#2888).

Assessment

The issue is well-structured with clear scope — harness CEL trigger, gating decisions, workflow integration, and test requirements are all specified. However, two prerequisites are still open and must land first:

Prerequisite	Status	Why it blocks
#2889 — harness-dispatch job + custom-agent behaviour test	Open	Provides the harness-dispatch infrastructure that retro CEL routing will plug into
#2894 — retro bash trigger behaviour baseline	Open	Establishes the normative test fixtures that this PR must achieve parity against

No open PRs currently address this issue or its prerequisites.

Next steps

Work on this issue can begin once both prerequisites are merged. Until then, this issue is blocked.

Blocked by:

• feat(dispatch): add harness-dispatch job with ADR 54 auth, kill switch, and custom-agent behaviour test #2889
• test(behaviour): add retro dispatch trigger scenarios (bash routing) #2894