fix(ai): honor chunkTimeout on HTTP SSE streams

[holny]

Issue for this PR

Fixes #46692

Type of change

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

What does this PR do?

chunkTimeout was accepted in provider settings but never read on the native path — HttpOptions had no field, the HTTP transport applied no stall guard, and the setting was silently dropped. A stalled provider stream was bounded only by the OS socket.

• Add chunkTimeout (ms) to HttpOptions and thread it through mergeHttpOptions
• Apply it as a per-chunk timeout on the response stream in the HTTP transport (transport/http.ts), failing with a typed TransportError (chunk-timeout) when no chunk arrives within the window
• Add chunkTimeout to ProviderPackage.Settings and wire it through the azure provider first; remaining providers share the same config() pattern and can adopt the same field
• Preserve chunkTimeout when model.request hooks rebuild HttpOptions

How did you verify your code works?

• New test/chunk-timeout.test.ts: a stalled SSE stream (one frame then silence) aborts with code: chunk-timeout under a real clock; mergeHttpOptions keeps the rightmost configured value
• bun typecheck + bun test in packages/ai (954 passing) and packages/core (only pre-existing environment-dependent failures in git-worktree/pty tests, confirmed on a clean baseline)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

---

Supersedes #46802 — the PR head fork was accidentally deleted on 2026-09-09 (not intentional, see the notification comment there); re-filing so the review can continue. Original conversation: #46802

[github-actions]

Thanks for your contribution!

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2. Add Fixes #<number> or Closes #<number> to this PR description

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found related PRs that may be duplicates or closely related to PR #48158:

Potentially Related PRs:

1. fix(provider): enforce chunk timeout regardless of content type #47621 - fix(provider): enforce chunk timeout regardless of content type

   • fix(provider): enforce chunk timeout regardless of content type #47621
   • Related to chunk timeout enforcement on provider streams

2. fix(core): default provider header and chunk timeouts to five minutes #46917 - fix(core): default provider header and chunk timeouts to five minutes

   • fix(core): default provider header and chunk timeouts to five minutes #46917
   • Related to chunk timeout defaults for providers

3. fix(provider): ignore SSE comment heartbeats for chunk timeout #43607 - fix(provider): ignore SSE comment heartbeats for chunk timeout

   • fix(provider): ignore SSE comment heartbeats for chunk timeout #43607
   • Related to chunk timeout handling on SSE streams

These PRs may have overlapping concerns with honoring chunkTimeout on HTTP SSE streams. Note that the current PR (#48158) explicitly supersedes #46802 (as mentioned in the description).