Focus independent review on correctness, minimalism and performance - #1049

Why

Independent review should find defects, unnecessary complexity and consequential performance costs. Identity checks and review bookkeeping belong to the workflow or coordinator rather than another model investigation.

What changes

Adds a shared .agents/reviewer.md for existing Fable and Codex Astra review assignments, with three priorities:

• Correctness: trace real callers and relevant failure paths; judge whether evidence demonstrates the accepted behavior.
• Minimalism: identify code, APIs, state and tests that can be removed while preserving that behavior. Trace existing APIs and supported composition before accepting new surface; necessary extensions need a concrete gap and a real consumer.
• Performance: when UI interactions or performance-sensitive paths are affected, inspect responsiveness, repeated work, allocations, I/O, retention and scaling with content/history. Reuse measurements and run targeted comparisons where consequential costs are uncertain; avoid speculative optimization and unrelated benchmarks.

The repository rules and workflow guide direct independent reviewers to this role. Mechanical validation, provider selection, receipts and bookkeeping stay with their existing owners. The guide adds no workflow phase or review stage.

Fable reviews start when the exact feedback commit and focused evidence are ready, without waiting for CI on main or the reviewed branch. When Fable is unavailable, including exhausted Claude quota, use an independent Codex Astra (gpt-6-astra) reviewer under the same scope, effort policy and correction limits. Preserve prior findings and reconcile in-flight calls before fallback.

Main health and required CI remain merge gates; a review pass waives neither.

How to verify it

• git diff --check passes.
• Verified 16 local documentation links in the changed documents.
• Three documentation files change; Planner and Architect guides retain their existing focused-review rules.
• Documentation-only change; no runtime tests run.

Scope confirmation

• Every changed file supports the focused independent-review role and its scheduling/fallback rules.
• Unrelated cleanup and formatting changes are excluded.
• No generated artifacts or dependencies change.
• The description matches the final diff and verification.