[rafaeldrincon]

Restores two local safeguards lost while updating from release/v3.8.49:

• Mark Cerebras models as rejecting Claude-style thinking.
• Return a clear conflict response when test-all targets a provider with no active connections.

The stale Qwen SPA version change was discarded because open-sse/executors/qwen-web.ts no longer exists in current upstream.

[diegosouzapw]

Verified this branch actually contains #13486's commit as a direct ancestor, so this PR is a
strict superset (Cerebras thinking safeguard + the mistral GLM 5-2 fix from #13486 + the
test-all 409 response). Ran the shared test file: 25/25 pass. Since #13486 is fully included
here, we'll treat it as subsumed by this PR (same author, no credit concern) rather than
merging both. Two asks before merge: a changelog fragment, and a small test for the test-all
409 response (currently untested).

[rafaeldrincon]

Follow-up on CI run 34972791255:

• Added test tests/unit/models-test-all-route.test.ts passes: test-all returns 409 when provider has no active connections.
• PR-specific checks pass: API route typecheck, changelog/merge integrity, docs, ESLint, Semgrep, Vitest.
• Remaining unit/quality failures are outside this PR diff: missing serve.ready_timeout translation key, persistAttemptLogs, hidePaidModels, Jina catalog naming, and hard-lease inventory tests.
• Worktree is clean at commit 381aa614c.

No further PR-scoped changes appear necessary; these failures need baseline maintenance or separate fixes.