feat(router): log affected route hints when provider warmup fails

[Copilot]

The docs promised "runtime warning names the failed provider and the affected route hints" but RouterProvider::warmup() only logged the provider name — leaving operators unable to correlate a warmup failure to which hint:* selectors would stop working.

Changes

clients/agent-runtime/src/providers/router.rs

• Added provider_hints: HashMap<usize, Vec<String>> field built once at construction — a reverse map of provider index → sorted hint names. Avoids per-failure allocation and makes the index↔hints relationship explicit.
• warmup() now emits affected_hints in the warning event:

tracing::warn!(
    provider = name,
    affected_hints = affected_hints,  // e.g. "code, reasoning"
    "Warmup failed; routes using this provider may not be available: {e}"
);

• Two new regression tests:
  • warmup_logs_affected_route_hints_on_failure — asserts provider name + all wired hint names appear in the warning.
  • warmup_reports_no_affected_hints_when_provider_has_no_routes — asserts "none" is reported when no routes reference the failing provider.

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Related Issues

Closes the operator-facing diagnostics gap described in the model routing UX issue.

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Summary

RouterProvider::warmup now logs which route hints (hint:code, hint:reasoning, …) are impacted when a non-primary provider fails to initialise, matching the behaviour documented in the operator guide and troubleshooting table.

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Tested Information

All 19 router unit tests pass, including the 2 new regression tests. 26 doctor tests and 7 classifier tests unchanged and passing. Clippy -D warnings clean.

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Documentation Impact

• No docs update required because: the operator guide (guides/model-routing.md) already described this warning behaviour — this change makes the runtime match the documented contract.
• I verified the documentation matches the current behavior.

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Breaking Changes

None. Additive field on an internal struct; no public API changed.

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Checklist

• I have checked that there isn't already a PR solving the same problem.
• I have read the Contributing Guidelines.
• I ensured my code follows the project's style guidelines.
• I have added or updated tests that prove my fix is effective or that my feature works.
• I have updated the documentation, or I explained above why no documentation update is needed.
• I verified the documentation matches the current behavior.
• I have documented any breaking changes in the Breaking Changes section.
• I have linked the related issue (if any).

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
97.9% Coverage on New Code
0.0% Duplication on New Code

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