[deep-report] Instrument copilot CLI exec step to emit stderr + exit code into run artifacts

[github-actions]

Description

The Agentic Workflow Audit (#42575) found that 25/32 fleet failures (78%) share one signature: the copilot Execute GitHub Copilot CLI step fails 0-turn / 0-token, and the failing step emits no stderr into artifacts, so these failures are opaque and cannot be root-caused. This blocks diagnosis of the current Smoke CI + PR Sous Chef + long-run copilot clusters.

Fix

Instrument the generated Execute GitHub Copilot CLI step (in the copilot engine step generation) to capture stderr and the exit code into the run artifact bundle on failure, so the instant-vs-longrun causes (startup abort vs session-idle/network) can be separated.

Expected Impact

Turns the single largest opaque failure class into a diagnosable one; unblocks root-cause of ~78% of current fleet failures.

Suggested Agent

Copilot SWE Agent (workflow/engine step generation).

Estimated Effort

Medium (1-4 hours)

Data Source

Agentic Workflow Audit #42575 (rec-copilot-cli-0turn-rootcause). DeepReport run https://github.com/github/gh-aw/actions/runs/28528843163

Generated by 🔬 Deep Report · 214.1 AIC · ⌖ 17.7 AIC · ⊞ 10.2K · ◷

• expires on Jul 3, 2026, 7:43 AM UTC-08:00

[github-actions]

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If assignment succeeds, the Copilot coding agent will analyze the issue and create a pull request with the fix.

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