fix(mcp): retain transport owner outside agent context

[whoiskatrin]

Fixes #1490.

Problem

McpAgent server-to-client requests could fail when invoked from a host callback reached through Worker Loader RPC, a service binding, or another entrypoint that does not inherit the original agent AsyncLocalStorage context.

The Streamable HTTP transport looked up its owning agent from ALS at send time and threw:

Error: Agent was not found in send

This affected requests such as elicitation, sampling, and roots initiated from sandbox-backed tool execution.

Fix

StreamableHTTPServerTransport now retains its owning McpAgent when the transport is created. The transport and agent share the same Durable Object lifetime, and this matches the existing McpSSETransport, which already captures its owner.

The transport still reads the request-scoped connection from ALS when available, but only to disambiguate a protocol-invalid case where multiple live streams claim the same active request ID. Normal explicit relatedRequestId routing uses the sole matching stream and does not depend on ALS. If context is absent and routing is ambiguous, the existing code fails closed rather than guessing.

No public API is added.

Why not re-enter ALS?

Re-entering agent context at a cross-isolate callback would synthesize an agent store without restoring the original connection or request. The transport already owns the agent reference it needs, so retaining that owner fixes the correct boundary without asking applications to wrap callbacks or import internal context state.

Tests

Added regressions that clear the agent ALS store before issuing an SDK elicitation and verify:

• an elicitation with relatedRequestId completes on the originating POST stream;
• an elicitation without relatedRequestId completes on the standalone GET stream.

Validation after rebasing onto current main:

• focused outside-context regressions: 2/2
• full MCP Workers suite: 492/492
• packages/agents build
• changed-file formatting and lint

Related Codemode work

#1793 preserves the outer MCP tool-call context through openApiMcpServer, allowing a host callback to supply the exact relatedRequestId. Together, the two changes cover the McpAgent.serve() + Dynamic Worker RPC setup reported in #1510:

• fix(codemode): preserve MCP request context #1793 preserves the semantic parent request;
• this PR lets the transport send after RPC loses agent ALS ancestry.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6e58373

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

This PR includes changesets to release 1 package

Name	Type
agents	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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commit: 6e58373