Fix background task liveness probe after session resume

[SwordFaith]

Problem

When a Claude Code session is resumed or continued, the current transcript may have a different session id from the session that originally launched a
background task. The task's .output file physically lives under the old session directory, but the stop hook's liveness probe derived the output path
from the current transcript's session id. As a result, dead/orphaned tasks were never pruned and the loop was blocked from reaching Codex review.

Fix

Teach is_bg_task_alive to look up the real output file path recorded in the transcript's launch message:

• Add extract_bg_task_output_path_from_transcript() to parse the "Output is being written to: " line.
• Prefer the real path when available; fall back to the derived tasks_dir path when the transcript is unreadable or the message is missing.
• Pipe the new optional transcript_path argument through prune_dead_bg_task_ids and list_pending_background_task_ids.

Test

Add regression test AC-25: simulate a session resume with a new-session transcript that records an old-session output path, then assert the dead task is
pruned using the real path rather than the derived new-session path.

42/42 tests pass.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle whitespace in recorded output paths

If the recorded Claude output path contains whitespace, this pattern fails to match anything because it requires the path to be a single non-whitespace token up to .output. In that case is_bg_task_alive falls back to the derived path for the resumed session; when that file is absent it fail-opens as alive, so a dead/orphaned background task remains parked forever for projects whose generated task-output path includes a space.

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