#432 Stranded test fixes: timeout stack capture, task-file lookup retry, backup opt-in

Accepted agent delivery; branch-keyed search descriptor included.

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Summary by cubic

Fixes flaky integration tests stranded on response timeouts, transient task-layout resolution errors, and missing backup coverage.

• Captures bounded child stacks, the last sent request, and stderr tail on response timeouts so failures carry diagnostic evidence.
• Retries task-file layout resolution in the test helper, avoiding a transient resolver error being mistaken for a legacy flat layout.
• Opts internal docs and scripts into the .engram backup.

Confidence Score: 5/5

The PR appears safe to merge, with a non-blocking gap in timeout evidence.

Findings

1.  Collected stacks disappear ▶

Summary

This PR adds timeout evidence, retries task-file lookups, and opts internal documents and scripts into backup.

• Response-timeout panics include the request and child-process details.
• Background-task tests retry task-file lookup before choosing a legacy path.
• Repository records mark internal folders for backup and describe the landing slice.

_{Reviews (2) · Last reviewed commit: "mason: capture userspace timeout stacks ..." · Reviewed by Greptile}