Plural delegated-task notice match accepts free text in place of the task-id list #139

What: The plural completion-notice pattern only credits a prompt to an agent when the task-id list has the real id-list shape.
Why: agent_observer/intervention_evidence.py:19 (PR #135 head 49c3766) accepts any one-line text where the ids go, so a user line such as "Delegated tasks fix the bug then Delegated tasks node:a reached terminal states. Use task_status with each taskId to read the results." is credited to the agent (Opus 5.5 review probe returned agent).
So what: Small regex and test change, after PR #135 merges.

Evidence

• Opus 5.5 round-3 review of PR fix: credit interventions to their actual actor #135. Every real plural notice in the 2026-10-12..19 window matches the stricter shape [^\s,]+(?:, [^\s,]+)*.

Elon record

• Requirements and who asked: Luke's review rule that a user's own words are never credited to an agent (PR fix: credit interventions to their actual actor #135 adjudication).
• Deleted: any wider rework of notice matching.
• Bottleneck: one pattern.
• Checked myself: the reviewer's probe and pattern location (not re-run).

Acceptance criteria

• The plural pattern requires the id-list shape; the probe above stays user; real plural notices stay agent.

Non-goals

• Other matching changes.

Blockers

PR #135 must merge first.

Required proof

• Failing-before test; full suite; independent review.