fix(routing): auto-map respects explicit [[models]] entries

[Destynova2]

Summary

Router::route step 3 (auto-mapping) was rewriting request.model to router.default for any name matching auto_map_regex — even when the user had an explicit [[models]] virtual entry with that name. The virtual entry's fallback chain was therefore bypassed entirely.

The bug surfaces in production with errors like:

Provider API error: 400 - {"error":{"message":"default-model is not a valid model ID","code":400},"user_id":"user_..."}

Repro

1. Client sends claude-sonnet-4-6.
2. Auto-map regex ^claude- matches → request.model rewritten to default-model.
3. The user's explicit [[models]] name = "claude-sonnet-4-6" with fallbacks (anthropic native → OR anthropic/claude-sonnet-4.6 → deepseek-v4-flash) is never consulted.
4. default-model chain runs; on exhaustion try_direct_provider_lookup forwards model = "default-model" to a pass-through provider (OpenRouter), which 400s.

This is the failure mode I hit while debugging Anthropic 429 fallback chains: when the primary anthropic/claude-sonnet-4-6 mapping returned 429, the fallback to openrouter/anthropic/claude-sonnet-4.6 should have succeeded (and does succeed when called directly), but auto-map prevented it from ever being tried.

Fix

let has_explicit_virtual = self.config.models.iter().any(|m| m.name == request.model);
if !has_explicit_virtual {
    request.model.clone_from(&self.config.router.default);
}

The check is regex-agnostic: it covers every auto_map_regex configuration (claude, gpt, gemini, mixed, custom) — no provider-specific code path needed.

Auto-map continues to rewrite the model when no explicit virtual exists, preserving the original "catch-all rewrite for unconfigured models" intent.

Other routing steps audited

Step	Mutation pattern	Same bug?
1 WebSearch	decision.model_name = ... direct	No
2 Background	decision.model_name = ... direct	No
3 Auto-map	request.model = ... then falls through	Yes — fixed here
4 Subagent	decision.model_name = ... direct	No
5 PromptRule	decision.model_name = ... direct	No
6 Think	decision.model_name = ... direct	No

Auto-map is the only step that mutates request.model and falls through; the other steps either return early or set decision.model_name without touching request.model. No other leak path exists.

Tests

Adds two regression tests:

• test_auto_map_skips_explicit_virtual_model — confirms the new behaviour.
• test_auto_map_still_rewrites_unmapped_claude — counter-test confirming the original catch-all path is intact.

Existing tests still pass: test_auto_map_claude_models, test_auto_map_custom_regex, test_no_auto_map_non_matching, test_auto_map_routes_to_default.

Test plan

• cargo nextest run -E 'test(auto_map)' — 9/9 passing
• cargo fmt --all -- --check clean
• cargo clippy --all-features -- -D warnings clean
• CI: full suite

🤖 Generated with Claude Code