[AW Top 10] 01 Fix Codex engine unsupported exec tool failures #65771

Priority 1/10 | 11 source issues | Impact 5/5 | Confidence 4/5 | Effort 2/5

One assignment, one coherent fix

Codex-engine workflows fail within seconds because the Copilot compatibility adapter rejects the Responses custom tool call named exec and accepts only apply_patch. The driver treats the HTTP 400 as non-retryable, so each run ends with no safe output.

Implementation scope

Make the Codex harness and its configuration avoid emitting custom exec tool calls through the Copilot adapter, for example by selecting a compatible tool profile or model, and route this specific error to a clear preflight diagnostic instead of a silent incomplete result.

Done when

• A regression test covers the unsupported_custom_tool error and the harness chooses a compatible configuration or fails with an explicit preflight diagnostic.
• A Codex-engine workflow such as Daily Go Test Parallelizer completes a run with a terminal safe output.

Why now

Eleven open incidents across many scheduled Codex workflows share the same adapter error within three seconds of start. The error text is identical in each run, so confidence is high and the fix is local to the Codex harness.

Unchanged AW sources close only after this summary is completed. Newer source activity and not-planned retirement do not trigger source closure. Assigned summaries are frozen; unassign to allow reclustering.

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