test: cover provider error session events

[moose-lab]

Summary

• add runProviderSessionTurn regression coverage for provider non-200 responses
• verify stream event order stays ["status", "message", "error", "status"]
• verify the failed user message remains in session_messages and the session becomes failed

Tests

• git diff --check origin/main..HEAD
• bun run test src/core/tests/api-session-runtime.test.ts (165/165 passed because the test script runs the full suite)
• bun run typecheck

[claude]

Claude finished @moose-lab's task in 2m 2s —— View job

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PR Review

• Gather context
• Read changed files
• Review for correctness, type safety, and test quality
• Post findings

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Findings

• [nit] The two "status" events are only verified by type, not value — the test doesn't assert the first is { status: "running" } and the second is { status: "failed" }. If the implementation swapped the emitted status values the event-order assertion would still pass. Low risk here but reduces diagnostic clarity (api-session-runtime.test.ts:174).

• [nit] No assertion on the error message content (the "error" event's message field or result.error). If the error text from the provider changes shape the test won't catch it (api-session-runtime.test.ts:173).

• [nit] The fetch-throws (network error) path is a distinct failure mode from non-200 and isn't covered by any test yet. Out of scope for this PR but worth a follow-up.

Verdict: APPROVE

The test is correct and fills a real gap. I traced the implementation path for a 500 response through api-session-runtime.ts:

1. validateProviderRuntimeConfig passes (key present) → user message inserted → status(running) emitted.
2. runProviderChatCompletion resolves to { ok: false } from the 500 response.
3. postRequestStatus is still "running" → no early return / no message deletion.
4. message(user) emitted, then session set to "failed", error emitted, status(failed) emitted.

That matches the asserted sequence ["status", "message", "error", "status"] and the DB state (user message retained, session failed). The test faithfully verifies all three invariants stated in the PR description.

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