[askalf]

What

A review's fallback model is used only when it is of the same family as the model that stopped.

Why

Which family reads a repository is a choice. Where one vendor's coding agent writes the pull requests, another vendor's model reads them, so the reviewer does not share the author's blind spots.

The fallback could undo that choice without anyone making it. A review whose model the endpoint parked or could not route continued on REDLINE_FALLBACK_MODEL whatever that model was, and the default is claude-opus-5-5. On a host that reads on GPT models, a parked seat would have handed the review to Claude, with one log line to show for it.

How

• modelFamily(id) in scripts/redline/review.mjs: claude for claude-*, gpt for gpt-*, chatgpt-*, codex-* and the o3 / o4-mini style ids, else the id's leading run of letters and digits (gemini-3-pro is gemini). A provider path before the id is not part of it. sameModelFamily(a, b) is false when either id has no family.
• The fallback branch of reviewChange checks the family at the point of use, so it covers the routine, deep and pin models alike. A fallback of another family is not used: the run logs <reason>; the fallback <model> is of another model family, so it is not used and the review stops and fails with the same error as a run with no fallback.
• A fallback of the same family behaves as before, with the same log lines.

What changes for a host

• A host that reads on Claude: nothing.
• A host that reads on another family and leaves REDLINE_FALLBACK_MODEL unset: a parked or unroutable model now fails the review. It gets a fallback back by naming a model of its own family.
• Hosted mode: nothing. It already sets no fallback.

Docs

• README: the paragraph on the pin and fallback settings.
• docs/hosted-quickstart.md: how to choose the reviewer's family.
• CHANGELOG.md: November entry.

Tests

node scripts/redline/review.test.mjs: ten new checks.

• A parked GPT model with a Claude fallback fails on the one call, posts nothing and logs the refusal.
• The same the other way round (a Claude model, a GPT fallback).
• An unroutable GPT model with a Claude fallback fails with ModelUnroutable.
• A GPT model falls back to another GPT model, parked or unroutable.
• modelFamily and sameModelFamily over listed ids, unlisted ids, provider paths and empty values.

The existing Claude to Claude fallback checks pass unchanged. node test-all.mjs passes but for two path checks in review.test.mjs that fail the same way on main on a Windows checkout; CI runs them on Linux.

[sprayberry-redline]

Verdict: approve. The family check runs before switching models, preserving the original error when a fallback is refused and retaining conversation history when it is allowed. The tests cover cross-family refusals for parked and unroutable models, same-family continuation, and model ID normalization; the documentation explains the configuration change.