Propagate MCP tool cancellation to host executors

[Aymericr]

Description

MCP hosts that queue tool handlers need the SDK request cancellation signal before executing queued work. The server wrapper now passes each handler's AbortSignal to executeTool and applies the wrapper to both registerTool() and the deprecated tool() registration surface, so tools added after server creation cannot bypass host sequencing or cancellation policy.

Validation

• bun test packages/mcp/src — 359 tests, 1,361 assertions passed.
• bunx ultracite check packages/mcp/src/server.ts packages/mcp/src/server.test.ts
• git diff --check

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Note

Medium Risk
Extends the public executeTool contract and changes when queued hosts may run or skip tool callbacks on cancellation.

Overview
MCP hosts that wrap tool execution (e.g. to queue work) can now observe request cancellation before the underlying handler runs.

PascalMcpToolExecutor gains a required signal: AbortSignal, and installToolExecutor forwards the SDK request signal from handler arguments for both registerTool and the deprecated tool() path so late-registered tools still go through the host wrapper. Tests cover signal presence, abort-before-callback (tool body never runs), and legacy registration.

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[pascal]

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Error id: 180318f6-425c-46ee-acfc-1d58c991f3d9