fix: re-trace system prompt on agent switch

[VJ-yadav]

Summary

• The step === 1 guard in prompt.ts only traced the first agent's system prompt because step increments continuously and is never reset on agent switches
• Added a tracedAgent variable to track the last-traced agent name, so each agent's system prompt is logged when it first becomes active
• Fixed the inaccurate comment that claimed agent switches reset step to 0

Fixes #291

Test Plan

• Verify typecheck passes on prompt.ts (pre-existing test file failures are unrelated)
• Start a session, switch agents mid-conversation, confirm both agents' system prompts appear in trace output
• Confirm single-agent sessions still trace the system prompt exactly once

Checklist

• Change is minimal and focused on the reported issue
• No functional behavior change — tracing/observability only
• Comment updated to accurately describe the logic

Summary by CodeRabbit

• Refactor
  • Improved session tracing so traces are emitted on the initial step and whenever a new agent begins execution. This reduces redundant trace noise and provides clearer visibility of agent transitions in session logs, ensuring each agent’s system prompt appears once per switch for more accurate and readable session traces.

[claude]

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 593d94ab-c29d-4f1c-8578-cc35020e96c8

📥 Commits

Reviewing files that changed from the base of the PR and between 89b8cbc and 3b691b5.

📒 Files selected for processing (1)

• packages/opencode/src/session/prompt.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• packages/opencode/src/session/prompt.ts

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📝 Walkthrough

Walkthrough

Session prompt tracing now tracks the most-recently traced agent and re-traces the system prompt whenever the active agent changes, instead of only tracing on the loop's first step. This ensures each agent's system prompt is logged once when it becomes active.

Changes

Cohort / File(s)	Summary
Agent Tracing Logic packages/opencode/src/session/prompt.ts	Added a tracedAgent variable and changed the tracing guard from step === 1 to `step === 1

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Suggested labels

contributor

Poem

🐰 I hopped through prompts both near and far,

Traced each agent like a twinkling star.
No prompt left out, no trace misplaced,
Each furry name now gently traced.
Hop, log, repeat — a tidy little race.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'fix: re-trace system prompt on agent switch' directly and precisely describes the main change—re-tracing system prompts when agents switch mid-session.
Description check	✅ Passed	The PR description includes all required sections: Summary (root cause, implementation, comment fix), Test Plan (with specific verification steps), and Checklist (with all items addressed).
Linked Issues check	✅ Passed	The implementation fully addresses issue #291: it tracks the last-traced agent via tracedAgent variable and re-traces when agent.name changes, ensuring each agent's system prompt is logged once when becoming active.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the linked issue #291: adding tracedAgent tracking and updating the tracing condition and comment—no unrelated modifications introduced.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[dev-punia-altimate]

❌ Tests — Failures Detected

TypeScript — 15 failure(s)

• connection_refused [2.73ms]
• timeout [2.41ms]
• permission_denied [2.67ms]
• parse_error [2.35ms]
• oom [2.49ms]
• network_error [2.33ms]
• auth_failure [2.50ms]
• rate_limit [2.59ms]
• internal_error [2.63ms]
• empty_error [0.25ms]
• connection_refused [0.16ms]
• timeout [0.10ms]
• permission_denied [0.07ms]
• parse_error [0.07ms]
• oom [0.07ms]

cc @VJ-yadav
_{Tested at 3b691b5a | Run log | Powered by QA Autopilot}