fix(error-status): parse "Error: <status>" with no colon after the status - #64

Summary

• GitHub Copilot reports quota exhaustion as Error: 429 quota exceeded, and parseStatusFromErrorMessage returns undefined for it. turn_end then returns early, no rule can match, and the fallback never fires.
• The message falls between two existing patterns. The leading-bare-status pattern accepts an Error: prefix but requires a colon after the status (Error: 401: {...}, added in fix: parse leading bare status codes in error messages #55). The error <status> pattern requires whitespace directly after error, so the colon in Error: defeats it.
• Adds an anchored pattern that requires the literal word error, and adds quota to the trailing-noun list so a bare 429 quota exceeded parses too.

Observed in a real session (Pi 0.85.1, github-copilot provider):

 hi

 Error: 429 quota exceeded

/model-fallback:status showed Rules: 3, Config warnings: none, and state.json was never created — persistFailure() was never reached.

Before / after:

"error 429"                  -> 429        (both)
"Error: 429 quota exceeded"  -> undefined  ->  429
"429 quota exceeded"         -> undefined  ->  429

Not broadening the match

The prefix requirement is deliberate. Dropping it would also match prose the existing tests require to stay unmatched:

parseStatusFromErrorMessage("429 tokens remaining in context window") // undefined
parseStatusFromErrorMessage("processed 404 items before retry")       // undefined

The quota noun relies on adjacency for the same reason, so 429 tokens left before the quota resets still does not match. Both cases are added as regression assertions.

Note on #58

#58 also touches lib/error-status.ts (adding reasons). The two changes are independent — this one only widens status extraction — but whichever lands second will need a trivial rebase.

Testing

• npm run ci — 39 tests pass, up from 37 on main
• pi -e .

On pi -e .: the fix was validated by applying it to an installed 0.4.0 and re-running parseStatusFromErrorMessage against the verbatim error string from the session above, which now yields 429. A full interactive confirmation needs another Copilot quota exhaustion to reproduce, so I have not checked that box. Happy to follow up with it once the allowance next runs out.

Checklist

• README updated if user-facing behavior changed — no user-facing surface changed, so no README change
• CHANGELOG updated if needed — added under Unreleased
• Package contents checked with npm pack --dry-run — unchanged, no docs/ files added or renamed

Summary by CodeRabbit

• New Features

  • Added optional failure-reason matching for fallback rules.
  • Fallbacks can now cascade across multiple models without revisiting models used in the current run.
  • Rules no longer fall back to the model that produced the failure.

• Bug Fixes

  • Improved detection of provider errors such as Error: 429 quota exceeded.
  • Added recognition of context-length failure reasons for more precise fallback behavior.

• Documentation

  • Updated configuration and usage guidance for reason-based rules and cascading fallbacks.