Classify Copilot SDK session.idle timeouts as agentic_engine_timeout

[Copilot]

PR Code Quality Reviewer intermittently hard-reds on long Copilot SDK runs with Timeout after <n>ms waiting for session.idle, but those failures were not mapped to the timeout class in conclusion outputs. This left a real timeout signature unclassified and skewed failure accounting/handling.

• Timeout signature coverage

  • Expanded AGENTIC_ENGINE_TIMEOUT_PATTERN in actions/setup/js/detect_agent_errors.cjs to match both existing signal-based timeouts and SDK idle-timeout messages:
    • signal=SIGTERM|SIGKILL|SIGINT
    • Timeout after <n>ms waiting for session.idle

• Classifier behavior alignment

  • Keeps timeout detection centralized in detect_agent_errors so workflows consuming steps.detect-agent-errors.outputs.agentic_engine_timeout receive the correct flag for SDK idle-timeout runs.

• Regression tests

  • Added focused tests in actions/setup/js/detect_agent_errors.test.cjs for:
    • direct regex match on session.idle timeout log lines
    • detectErrors(...) returning agenticEngineTimeout: true for that signature

const AGENTIC_ENGINE_TIMEOUT_PATTERN =
  /(?:signal=SIG(?:TERM|KILL|INT)|Timeout after \d+ms waiting for session\.idle)/;

[github-actions]

🤖 PR Triage — Run §28715668077

Field	Value
Category	bug
Risk	🟢 Low
Score	58/100
Impact	28/50 — classifies Copilot SDK session.idle timeouts as agentic_engine_timeout
Urgency	18/30 — draft, no CI
Quality	12/20 — adds 15-line test; small +9/-8 JS patch
Action	🔄 batch_review
Batch	pr-batch:go-bugfix

Small targeted JS fix with test. Batch with other similar Go/JS bugfix PRs for review.

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