fix(provider): ignore SSE comment heartbeats for chunk timeout

[1052326311]

Issue for this PR

Closes#43519

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

chunkTimeout currently restarts for every response body read. SSE comment frames such as : keepalive therefore prevent an otherwise stalled model stream from timing out. This keeps one deadline across reads and resets it only after a complete SSE event containing data:. It leaves header timeouts and non-SSE responses unchanged.

The regression starts the existing loopback OpenAI-compatible test server with one data event followed by comment heartbeats every 20 ms. With a 50 ms chunkTimeout, the stream must produce the existing typed response-stream error.

How did you verify your code works?

• Compared exact base b155b15694dbcc6768f11d2f25cc2bdd1f738ab4 to head b9234e31edc25d9f1334b27aaf9b4dd9c918484f: one commit and only the provider wrapper plus its existing test file changed.
• Reviewed exact generated source and test blobs against dev.
• Executed the exact candidate wrapSSE function extracted from its Git blob against a loopback SSE server: after one data event and ongoing 20 ms comment heartbeats, its 50 ms deadline raised SSE read timed out.
• The normal local checkout cannot execute the repository test because ordinary source reads and Git fetches hang in this environment. The added repository regression covers the same flow through Provider.getLanguage() and streamText() in CI.

Screenshots / recordings

Not a UI change.

Checklist

• I have tested the exact candidate timeout logic locally with a loopback SSE server
• I have not included unrelated changes in this PR

[github-actions]

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[1052326311]

Current head b9234e31edc25d9f1334b27aaf9b4dd9c918484f is mergeable and the repository duplicate, standards, and compliance checks are green. The loopback SSE regression exercises the provider boundary without external credentials. Please review this exact head.

[1052326311]

Follow-up head 8de252f7aed6b8fc4d93a650be397fd385c7c433 closes two exact-head validation gaps: the regression now handles the existing stream error part/throw behavior, and the deadline is narrowed safely for TypeScript. On the repository-pinned Bun 1.3.14, the provider timeout file passes 7/7; package typecheck and the pre-push repository typecheck (30/30 tasks) pass. Upstream test, typecheck, and nix-eval remain action_required pending maintainer approval.