test(behaviour): add retro dispatch trigger scenarios (bash routing)

[ifireball]

What is missing

Behaviour tests cover triage dispatch triggers partially, but retro has no behaviour scenarios that verify dispatch triggers fire the correct agent run on the current bash router in reusable-dispatch.yml.

We need this baseline before porting retro's trigger logic to harness CEL expressions.

What should happen

One vertical PR adds Godog scenarios for retro dispatch triggers:

• Triggers: PR closed
• Uses bash route job only (no CEL, no harness-dispatch)
• Agent runs via dummy runtime; assert outcome (e.g. behaviour-results.json or expected side effect)
• Requires behaviour framework (PR #1982)

Merge criterion

make behaviour-test green with new retro trigger scenarios.

Blocks

Port retro to harness CEL trigger (#2900).

Related

Part of epic #2888. Does not block the custom-agent harness-dispatch issue (#2889).

[fullsend-ai-triage]

🤖 Triage · ⚠️ Cancelled · Started 8:33 AM UTC · Ended 8:34 AM UTC
Commit: 9f4f2b6 · View workflow run →

[fullsend-ai-triage]

🤖 Finished Triage · ✅ Success · Started 8:35 AM UTC · Completed 8:37 AM UTC
Commit: 9f4f2b6 · View workflow run →