fix(chat): reconcile errored reconnect streams

[mattzcarey]

Summary

• allow useAgentChat to reconcile a server turn after the AI SDK client has entered error, rather than limiting reconnect probes to ready
• correlate resume probes across replacement sockets and distinguish globally idle agents from active continuations owned by another connection
• retain reconnect-open edges while status or an existing resume settles, retransmit an in-flight handshake on the new socket, and serialize mount/reconnect/tool/public resume entry points
• add real-hook regression coverage for the reported client-error/server-still-running split, plus reconnect races, StrictMode, tool continuations, agent replacement, and resume: false
• ship patch changesets for agents, @cloudflare/ai-chat, and @cloudflare/think

Why

isServerStreaming tracks server broadcasts independently from the AI SDK chat status. If a client-side failure moved the chat to error and the terminal server frame was missed, every later reconnect was rejected by the status === "ready" re-probe guard. The server could finish normally while the client remained stuck in a streaming state until reload.

Removing that guard alone is not sufficient:

• STREAM_RESUME_NONE can mean either global inactivity or that another live connection owns an active continuation
• a resume request or response can be lost with the socket that carried it
• overlapping AI SDK resume operations regress the activeResponse race fixed in fix(chat): serialize reconnect-driven resumes to stop activeResponse race (#1837) #1838

Resume requests therefore carry optional probe IDs that direct server responses echo. STREAM_RESUME_NONE also carries an optional reason (idle or continuation-owned). The hook clears fallback streaming state only after a correlated idle response. These fields are additive: older clients ignore them, while uncorrelated responses still settle the transport without being treated as authoritative global-idle evidence.

Testing

• pnpm --filter agents exec vitest --run --project react src/react-tests/resume-overlap-race.test.tsx
• pnpm --filter agents run test:react
• pnpm --filter agents run test:chat
• pnpm --filter @cloudflare/ai-chat exec vitest --run src/tests/ws-transport-resume.test.ts
• pnpm --filter @cloudflare/ai-chat run test:react
• pnpm --filter @cloudflare/think run test:react
• pnpm run check

Closes #1914

---

[changeset-bot]

🦋 Changeset detected

Latest commit: eb79893

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

This PR includes changesets to release 4 packages

Name	Type
agents	Patch
@cloudflare/ai-chat	Patch
@cloudflare/think	Patch
@cloudflare/agent-think	Patch

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

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