Chameleon

Reviewer model ladder (roadmap #6). The main loop may run a stronger model than
the flat-sonnet correctness reviewer, so the reviewer is structurally weaker than
the author it checks. This escalates the reviewer on exactly the turns that
matter most. All advisory — no deny path, no hook hot-path cost.

Added

• Route-keyed correctness-judge model (default on; kill with
  CHAMELEON_JUDGE_TIERING=0). A high-risk route (risk_high / intent-forced /
  security-surface — security and blast-unknown both fold into risk_high)
  escalates the turn-end judge to CHAMELEON_JUDGE_MODEL_HIGH (default opus);
  low-risk routes (risk_elevated / first_low_risk) keep
  CHAMELEON_JUDGE_MODEL (sonnet). The escalation runs ONLY on the detached
  async path (CHAMELEON_JUDGE_ASYNC=1 or the auto-detach on a known bare-auth
  failure), whose generous fallback budget the slower model needs; the sync Stop
  path (capped by the 55s hook wrapper) keeps the base model, because a slower
  model there would time out and fail-open to zero findings on exactly the
  high-risk turns — a coverage regression, not a win. So a default sync turn is
  unchanged. Raise-only and never garbage: an unrecognized model (not an exact
  tier token or a claude-… id) falls back to the valid base rather than being
  spawned, because a bad --model would fail-open the judge to zero findings —
  the ladder can only strengthen the reviewer or leave it unchanged, never
  silently disable it.
• Severity-keyed refuter model: a BLOCK / high / critical finding is refuted
  with CHAMELEON_REFUTER_MODEL_HIGH (default opus), nits keep
  CHAMELEON_REFUTER_MODEL. Same raise-only guard and CHAMELEON_JUDGE_TIERING=0
  kill switch.
• CHAMELEON_DUP_MODEL knob for the duplication confirm spawn (default
  sonnet, unchanged from riding the judge default), now independently tunable.

Notes

• Escalation lift (opus-beats-sonnet as a reviewer) is unmeasured; A/B it via the
  effectiveness harness's model-tier arms (shipped in 2.42.0) before locking the
  default. Because the escalation is gated to the detached path, a default (sync)
  session is behaviorally unchanged — enable CHAMELEON_JUDGE_ASYNC=1 to activate
  it under the generous budget. Deferred to a follow-up: per-repo committable
  model fields and statusline session-model capture (the hot-path piece).