fix(codemode): preserve MCP request context

[mattzcarey]

Summary

openApiMcpServer now passes the outer MCP execute tool-call context to its host-side request callback:

request: async (options, context) => {
  // context.requestId, context.signal, context.sendRequest(), ...
}

This lets host callbacks associate elicitation, sampling, roots, and notifications with the originating tool call instead of sending them as standalone messages. The context stays in trusted host code and is not exposed to generated sandbox code. Existing callbacks that only accept options remain compatible.

Why

In #1510 tool registration is delegated to @cloudflare/codemode's openApiMcpServer. The MCP SDK supplies RequestHandlerExtra to every tool handler, but Codemode previously discarded that second argument before invoking the application's request callback. The callback therefore had no request id to pass as relatedRequestId, so server-to-client requests could not use the originating POST response stream. This PR preserves that SDK context in the per-execution host closure and exports it as OpenApiMcpRequestContext.

Relationship to #1734 (now merged)

The McpAgent.serve() + Dynamic Worker RPC path reported in #1510 needs both halves:

• fix(mcp): retain transport owner outside agent context #1734 (merged) lets StreamableHTTPServerTransport send after the child-to-host RPC boundary drops agent ALS.
• this PR preserves the semantic parent request id so the transport can route the elicitation onto the originating POST.

createMcpHandler / WorkerTransport only needs this PR.

Hibernation note

For the McpAgent deployment, prefer McpAgent.elicitInput(params, { relatedRequestId: context.requestId }). It wraps the wait in keepAliveWhile, which holds an alarm-backed keepAlive lease so the Durable Object is not evicted mid-elicitation. The pending elicitation resolver is in-memory by design: an elicitation cannot be resumed across a hard eviction, so the contract is to prevent hibernation during the bounded wait, not to persist the pending request. The new integration test asserts that lease is held during the wait and released after.

Tests

Codemode unit/contract (packages/codemode/src/tests/mcp.test.ts, in-memory transport + real DynamicWorkerExecutor):

• the callback receives the exact outer JSON-RPC request id and cancellation signal;
• overlapping Dynamic Worker executions retain separate request contexts;
• a callback elicits input associated with the outer tool call and receives the client's answer.

Real McpAgent integration (packages/agents/src/tests/mcp/codemode-context.test.ts), no mocks of the transport, executor, or RPC boundary:

• a TestCodemodeMcpAgent registers openApiMcpServer and elicits via McpAgent.elicitInput;
• a real Streamable HTTP POST with no standalone GET stream goes through the Worker Loader executor;
• the elicitation/create request arrives on the originating POST stream;
• the client's response POST is accepted and the final tool result follows on the same stream;
• the keepAlive lease is 1 while waiting and returns to 0 after completion.

Validation on the rebased branch:

• agents MCP suite: 493 passed (includes the new integration test)
• codemode: 299 unit/Workers + 38 runtime + 33 browser
• pnpm run build (24 projects)
• pnpm run check (exports, format, lint, 113 TypeScript projects)

Related: #1510, #1490, #1734

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🦋 Changeset detected

Latest commit: d167fe4

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

This PR includes changesets to release 1 package

Name	Type
@cloudflare/codemode	Patch

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