Emit unified exec end on startup failure

[starr-openai]

Why

Remote rust-ci-full exposed unified exec startup failures that happen before a process record exists. In that path, clients could receive the startup error without the matching exec end lifecycle event, leaving the tool call half-open from the app-server/client perspective. Approval rejections in the same startup path also need to stay declined rather than being reported as generic execution failures.

Failure evidence: remote Ubuntu test job with uploaded nextest JUnit artifact

What changed

• emit the matching unified exec end event when startup fails before the process is stored
• preserve captured sandbox-denial output in that startup-failure event path
• preserve startup approval rejections as declined exec endings
• keep the successful-startup begin event at its original point after process creation so long-running session interrupt behavior does not regress
• add focused regression coverage for failed, sandbox-denied, and rejected startup endings

Validation

• cargo test -p codex-core startup_ -- --nocapture
• cargo test -p codex-core --test all unified_exec_interrupt_preserves_long_running_session -- --nocapture

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Classify guardian denials as declined

In sessions where approval is routed through Guardian or strict auto-review, reject_if_not_approved returns ToolError::Rejected with a guardian-specific denial or timeout message rather than exactly "rejected by user", so this branch falls through to CreateProcess and the startup failure event is emitted as Failed. That means a unified exec that was declined before any process was started appears to app-server clients as a command failure instead of a declined command, unlike the shell ToolEmitter::finish path that treats ToolError::Rejected as Declined; preserve rejection semantics for these approval-denial messages instead of only the literal local-user string.

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