[JacobStephens2]

Summary

Malformed Harness diagnostics now preserve a child Run's actual ending. Child Run execution owns its process and readers through completion; Spec runs poll owned handles, and Base fixes keep their synchronous wait and Running mark.

 child Run
- start → wait → relay stderr → read stdout after exit
+ spawn → own process → start stdout capture and byte-tolerant stderr relay
+ try_wait / wait / drop → graceful stop when needed → reap and join → ending

 Spec run
- waiter threads → completion channel
+ owned child handles → poll every active Ticket

Closes #463

Evidence

• Before: malformed_stderr_preserves_a_successful_ending_and_base_fix_account failed with could not read the Run for #248: stream did not contain valid UTF-8.
  After: It passes and relays the replacement character while retaining the PR URL and Base fix account.
• Before: The finite stdout-pressure fixture blocked until its eight-second deadline killed it.
  After: It drains over 1 MiB before the caller waits and returns the last stdout line as the PR URL.
• The new concurrent parent-only interruption integration test makes each Ticket's failure push wait for its sibling's push. Both children save unfinished work before the Spec run finishes; no dependent Ticket starts.
• Review against main: Standards found one minor duplicated fixture setup, addressed with Fixture::start_with_fault; Spec found no issues.
• Validation: cargo fmt --check, cargo clippy --all-targets -- -D warnings, and cargo test passed (1,252 tests; zero failures). The full suite includes all 58 Spec run and 13 Base fix integration tests.

Seams under test: child Run execution through start/try_wait/wait/drop with finite local executable fixtures and private fault injection; Spec run and Base fix command interfaces through their integration fixtures. Existing hidden-argument and Run ending tests remain separate.

Merge Danger

Door: two-way

Reversible execution refactor; no persistent-format changes. Child Runs retain their existing unbounded graceful shutdown and shared process groups.

Blast Radius: execution

Child Ticket Runs and Base fixes, including output relay and interruption cleanup.

Unaddressed findings

Standards

None. The single finding was addressed.

Spec

None. No findings were reported.

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