Reconcile Think follow-ups and extend runTurn stream input

[threepointone]

Summary

• Reconcile stale design/RFC status for shipped Turns, sub-agent routing, and Channels work, and document the accepted tool-approval-dedup SIGKILL coverage gap separately from skipped test debt.
• Broaden chat:turn:* metadata coverage for wait/continuation/RPC/sequential turns, skipped empty input, and the current absence of channel on the turn observability payload.
• Extend Think.runTurn({ mode: "stream" }) to accept array and function inputs by widening chat() to resolve TurnInputMessages inside the queued turn.
• Keep submit + function input rejected because durable submission cannot serialize a function input yet.

Why

The design docs had drifted behind implementation state, and runTurn stream mode still had an artificial input-shape gap after _admitTurn shipped. This PR lines the docs up with the code, adds executable coverage for the turn metadata contract, and makes stream mode match the practical wait mode input surface for arrays/functions.

Implementation notes

• Static empty stream input ("" / []) still creates a request id, calls onStart, then calls onDone without running inference or persisting messages.
• Function input is evaluated inside _admitTurn against the in-queue transcript. A function returning [] preserves existing programmatic behavior: it runs against existing history when present rather than being pre-skipped.
• Array stream input is stamped with channel metadata consistently with other message-input paths.
• D6 client retry hardening is intentionally not included here because agents pins partysocket at 1.2.0; it should land after the upstream shouldReconnectOnClose release from Add partysocket terminal close reconnect predicate partykit#409.

Test plan

• pnpm exec vitest --run -c src/tests/vitest.config.ts src/tests/run-turn.test.ts from packages/think: passed, 26 tests.
• pnpm run check: passed, including Sherif, export checks, format check, oxlint, and typecheck across 113 projects.

Made with Cursor

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[changeset-bot]

🦋 Changeset detected

Latest commit: a3633e6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
agents	Minor
@cloudflare/ai-chat	Minor
@cloudflare/think	Minor

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commit: a3633e6

[devin-ai-integration]

Devin Review found 1 potential issue.