[AW Top 10] 01 Stop Codex runs failing on unsupported custom tools #65930

Priority 1/10 | 11 source issues | Impact 5/5 | Confidence 4/5 | Effort 3/5

One assignment, one coherent fix

Codex and Pi runs routed through the Copilot compatibility adapter fail with HTTP 400 because the adapter only supports the apply_patch custom tool and rejects exec and codemode tool calls. The engine driver then exits without a terminal safe output, and these source issues share that single failure.

Implementation scope

Make the Codex and Pi engine configuration avoid or translate non-apply_patch custom tools when the endpoint is the Copilot adapter, and detect this invalid_request_error to emit a clear actionable diagnostic. Verify against the harness code in actions/setup/js and the engine definitions in pkg/workflow before changing.

Done when

• A regression test shows a Codex run through the Copilot adapter does not issue unsupported custom tool calls.
• The harness reports unsupported_custom_tool as a named configuration failure with remediation guidance.

Why now

Ten or more daily failure issues across different workflows show the same rejected custom tool message on the same day, so one fix removes many recurring failures. The failure is deterministic and the harness already refuses to retry it.

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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