Fix dropped async callable replies on facets

[cjol]

This PR routes callable replies on facet WebSockets through the bridge that delivered the originating RPC frame. Fixes #1991.

Why

• Facet WebSocket frames share one durable virtual Connection, but each forwarded frame arrives with a temporary SubAgentConnectionBridge.
• Concurrent frames replace the bridge stored on the virtual connection. When an asynchronous callable resumes, its reply can therefore use a newer frame's already-disposed bridge and never reach the client.
• We could pin the entire virtual connection to the originating bridge, but general connection.send() calls and broadcasts represent durable connection operations and must not inherit a short-lived frame transport.
• We could pass the bridge through a private dispatcher, but that would bypass onMessage wrappers installed by AIChatAgent, Think, or application middleware.
• An invocation-local reply context keeps only framework RPC replies scoped to their originating frame while preserving the existing connection and wrapper semantics.

Architectural Changes

Before:

RPC frame A
  → shared virtual Connection
  → stored bridge replaced by frame B
  → async reply uses frame B's disposed bridge

After:

RPC frame A
  → invocation-local reply bridge A
  → async framework reply uses bridge A

durable connection operations
  → shared virtual Connection
  → existing connection routing

Code Changes

• Capture the originating facet reply bridge across asynchronous onMessage wrappers without changing general virtual connection behavior.
• Route callable success and error responses through that captured target and await delivery before the forwarding RPC completes.
• Preserve the synchronous StreamingResponse API while tracking pending bridge deliveries and flushing them before the callable invocation returns.
• Carry the originating reply bridge through downstream facet forwarding so intermediate virtual connections cannot replace it.
• Add an agents patch changeset.

---

[changeset-bot]

🦋 Changeset detected

Latest commit: dea62cf

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

This PR includes changesets to release 2 packages

Name	Type
agents	Patch
@cloudflare/agent-think	Patch

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[devin-ai-integration]

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commit: dea62cf