agents@0.21.0

Minor Changes

• #2052 f9d71d6 Thanks @cjol! - Expose WebSocketChatTransport and its connection types from the framework-neutral agents/chat/transport entry point. React peers are now optional for framework-neutral clients and servers.

  Existing users of agents/chat/react or @cloudflare/ai-chat/react must continue to declare compatible react and @ai-sdk/react dependencies explicitly.

• #2091 4d2084c Thanks @cjol! - Accept AI SDK flexible schemas in agentTool, including Valibot adapters, while preserving schema-driven input inference and structured output validation. Zod is no longer a peer requirement of @cloudflare/ai-chat.

  Existing custom schemas that no longer type-check as AI SDK FlexibleSchema must use the schema library's AI SDK adapter or wrap raw JSON Schema with jsonSchema(). Validation-only Standard Schema implementations are insufficient because tool inputs must expose JSON Schema to the model.

• #2098 fe82e05 Thanks @cjol! - Add connection-scoped Kitesurf support to Browser Tools through the browser: "kitesurf" session option. Unsupported durable session, Live View, recording, pause/resume, and Kitesurf-backed Quick Action surfaces remain unavailable.

  Existing Browser Tools users should note:

  • Large base64 values returned outside the canonical { type: "browser_screenshot", mediaType, data } shape are now redacted. Return screenshots in that shape or store binary output elsewhere.
  • TanStack browser tools have one output channel, so screenshot output is reduced to the compact model-facing summary rather than returning raw base64 data.

• #1948 aed6d8f Thanks @ericclemmons! - Pass Workflow retention through Agent.runWorkflow().

Patch Changes

• #2037 1bca2a6 Thanks @cjol! - Add buildAgentPath() and buildAgentUrl() for constructing canonical root-first Agent and sub-agent addresses for external HTTP requests, WebSocket connections, callbacks, and webhooks. React sub-agent connections now share the same descendant path encoder.

• #2051 b9343a0 Thanks @AntoniTok! - Stream forwarded request bodies into sub-agents instead of buffering them in the parent Durable Object.

  Agent._cf_forwardToFacet and routeSubAgentRequest both did forwardInit.body = await req.arrayBuffer() before dispatching to a child facet, materialising the entire request body in the parent's isolate. Two consequences:

  • The read sat in front of application-level validation. Agent.fetch returns before onRequest whenever the path matches /sub/{class}/{name}, so an app that carefully bounded request bodies in onRequest still had an unbounded read ahead of it — and no way to bound it itself.
  • The cost was per hop. A nested /sub/.../sub/... address re-materialised the same bytes at every level.

  Both call sites now pass req.body through as a stream. Measured on wrangler dev --local with a handler that never reads the body, peak RSS across the workerd processes for a single POST:

  Request body	facet route, before	facet route, after	canonical route (control)
  16 MB	+75 MB	+4 MB	+2 MB
  64 MB	+268 MB	+4 MB	+2 MB
  128 MB	+546 MB	+4 MB	+2 MB

  This restores the behaviour from before #1443, which switched to an explicit RequestInit in order to set a header on WebSocket upgrades and re-attached the body with arrayBuffer() as a side effect. The Upgrade header handling from that fix is unchanged.

  One behavioural note: backpressure now reaches the client. A child that returns without reading the body will cause the remainder of the upload to be cancelled, where previously the parent drained it in full. Existing handlers that require the complete upload must consume or stream request.body before returning.

• #2034 efcb316 Thanks @cjol! - Send Browser Run extraction schemas under response_format.json_schema, matching the Quick Actions /json contract.

  Direct browserExtract() and runQuickAction() callers must rename response_format.schema to response_format.json_schema. The model-facing browser_extract tool still accepts its schema in the top-level schema field.

• #2023 2b2b598 Thanks @threepointone! - Treat useAgentChat observer error frames as terminal responses.

  Plain-text error bodies are no longer parsed as stream chunks or merged into an empty assistant message. Error frames now clear observer streaming, replay, recovery, and tool-continuation state even when they omit done, matching the transport-owned stream behavior.

  Existing observer UIs that displayed error bodies as assistant messages must move those diagnostics to a dedicated error surface.

• #1996 753a674 Thanks @mattzcarey! - Update PartyServer and the Cloudflare Workers development toolchain for @cloudflare/workers-types v5 compatibility. New Think projects now use Workers Types v5 with matching Wrangler and Vite plugin versions.

• #1994 6e77f62 Thanks @mattzcarey! - Use wrapAISDK() as the single AI SDK v6 and v7 tracing integration, removing the separate createAISDKTelemetry() callback adapter that could not preserve the invoke_agent parent hierarchy. Mark asynchronously decided AI SDK v7 top-level approval spans when they outlive their invocation.

  Existing createAISDKTelemetry() users must:

  • Remove it from registerTelemetry() and per-call telemetry integrations.

  • Wrap the AI SDK namespace and call the wrapped functions instead:

    import * as ai from "ai";
    import { wrapAISDK } from "agents/observability/ai";
    
    const tracedAI = wrapAISDK(ai, {
      storeMessages: true,
      storeTools: true,
    });
    
    await tracedAI.generateText(/* ... */);

  • Update telemetry queries that use the removed callback-only cloudflare.agents.call.id or cloudflare.agents.tool_context.* attributes.

• #2035 5d66723 Thanks @cjol! - Validate BrowserConnector tool arguments before execution and reject JSON-stringified Browser Run extraction schemas with an actionable error.

  Existing callers that pass values outside the documented schemas must correct them before execution:

  • Pass extraction schemas as JSON objects, not JSON strings.
  • Pass the string returned in attachToTarget().sessionId to cdp.send, not the complete attachment result.

• #2049 ce0e608 Thanks @cjol! - Preserve spacing between streamed text segments separated by tool calls. Think messenger delivery and Voice now share the same boundary-aware text joining logic from agents/chat.

  Existing users must:

  • Replace imports of textDeltaFromStreamChunk() from @cloudflare/think/messengers with TextStreamCallback, passing it the complete structured stream events.
  • Upgrade to agents@0.21.0 when installing @cloudflare/think@0.16.0 or @cloudflare/voice@0.3.6; both now require agents >=0.20.2.
  • Update exact-text expectations if they relied on segments around tool calls being concatenated without a space.