Route review/start through a bundled review skill

[jif-oai]

Why

review/start currently invokes a bespoke core review task with its own prompt, model switching,
output parsing, and review-mode events. That duplicates orchestration the regular agent already
knows how to do.

This keeps the app-server API while moving its implementation to a normal delegated turn backed by
an explicit bundled skill.

What changed

• add an explicit-only bundled $review-agent skill with the defect-first rubric and merge-base
  guidance for base-branch reviews
• translate each review target into a synthetic user prompt that tells the parent to spawn one
  reviewer, wait for it, close it after collecting the response when supported, and return that
  response
• submit ordinary user input for both inline and detached delivery instead of Op::Review
• keep the app-server invariants that still matter: bundled skills must be enabled, inline delivery
  requires an idle thread, and detached delivery remains available from multi-agent v2 child
  threads
• document the normal turn and collaboration event flow while retaining legacy review-mode item
  types for rollout replay

Behavior changes

• new reviews emit normal turn, collaboration, and agentMessage events instead of
  enteredReviewMode and exitedReviewMode
• inline review requests now fail clearly when the thread already has an active turn
• if collaboration tools are unavailable, the parent returns an explanation instead of reviewing
  the change itself
• reviewer workers use ordinary collaboration lineage and lifecycle semantics; this path no longer
  applies review_model, review-specific metadata, or bespoke review-task restrictions

Follow-up

#31923 removes the now-unused core review session, task, prompt resolver, protocol operation, and
one-shot delegate path while retaining serialized legacy review events for rollout replay.

[chatgpt-codex-connector]

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