#15815: Fallback LLM doesn't trigger if primary model is local

## Summary - classify plain local/network connection failures as failover-eligible timeout errors - include common local transport phrases (for example, `Connection error.` and `Failed to connect`) in timeout failover patterns - extend failover tests to cover these connection-failure cases ## Problem When a primary local model endpoint is down, the embedded runner can emit `Connection error.`. That message was not treated as a failover reason, so model fallback was not triggered. ## Fix - `src/agents/pi-embedded-helpers/errors.ts` - expanded timeout failover patterns to include common connection-failure text and transport error codes - `src/agents/failover-error.ts` - expanded timeout code mapping to include common network/host resolution failures - updated tests: - `src/agents/pi-embedded-helpers.classifyfailoverreason.e2e.test.ts` - `src/agents/failover-error.e2e.test.ts` ## Validation - `pnpm vitest run --config vitest.e2e.config.ts src/agents/pi-embedded-helpers.classifyfailoverreason.e2e.test.ts src/agents/failover-error.e2e.test.ts` <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR broadens failover eligibility for local transport failures by: - Mapping additional common network error codes (e.g., `ECONNREFUSED`, `ENOTFOUND`) to the `timeout` failover reason in `resolveFailoverReasonFromError`. - Expanding embedded helper timeout text patterns to include connection/transport phrasing and common errno-like tokens. - Extending the e2e test suites to cover these newly recognized failure shapes. These changes integrate into the existing model fallback flow via `coerceToFailoverError` → `resolveFailoverReasonFromError` → `classifyFailoverReason`, allowing the fallback runner to treat local endpoint outages as retry/fallback-eligible errors. <h3>Confidence Score: 5/5</h3> - This PR looks safe to merge with low risk of regressions. - Changes are narrowly scoped to failover classification heuristics and are covered by updated e2e tests asserting the new error shapes. I traced the fallback path to confirm these signals are used for model fallback, and the mappings/patterns align with the stated goal (trigger fallback when local endpoints are unreachable). - src/agents/pi-embedded-helpers/errors.ts (classification patterns), src/agents/failover-error.ts (error-code mapping) _{Last reviewed commit: 2c15d25} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->