[kitlangton]

What

Make runtime MCP lifecycle mutations read-your-writes consistent with the ToolRegistry and Code Mode catalog. After an MCP add, remove, connect, or disconnect request returns, the next session tool snapshot now reflects that mutation.

Before / After

Before: MCP.add connected the server, discovered its tools, published mcp.tools.changed, and returned. McpTool consumed that event on an asynchronously forked stream, so an immediate session request could snapshot the previous direct-tool or Code Mode catalog while reconciliation was still in flight.

After: runtime MCP handlers await an explicit McpTool.reconcile fence after mutating MCP state. The fence serializes behind any event-driven reconciliation and returns only after the complete current MCP tool set has replaced the prior registry scope.

How

• packages/core/src/tool/mcp.ts exposes the existing serialized reconciliation effect as a Location-scoped service while retaining asynchronous reconciliation for server-originated tool-list updates.
• packages/server/src/handlers/mcp.ts awaits that service after runtime add, remove, connect, and disconnect operations.
• packages/core/test/mcp-tool-reconciliation.test.ts blocks event-driven reconciliation to prove publication can complete while a snapshot is stale, then verifies the explicit fence waits and makes the Code Mode path immediately visible.

Scope

This does not make all event-bus subscribers synchronous and does not change server-originated MCP list-change behavior. The stronger guarantee applies at the runtime MCP HTTP lifecycle boundary.

Testing

• bun typecheck in packages/core
• bun run test test/mcp.test.ts test/mcp-tool-reconciliation.test.ts in packages/core: 23 tests, 67 expectations
• bun typecheck in packages/server
• bun run test in packages/server: 16 tests, 39 expectations
• Repository pre-push typecheck: 33 package tasks passed

Flow

sequenceDiagram
  participant Client
  participant MCP
  participant McpTool
  participant Registry as ToolRegistry / Code Mode

  Client->>MCP: add / remove / connect / disconnect
  MCP-->>McpTool: mcp.tools.changed (async)
  Client->>McpTool: reconcile fence
  McpTool->>MCP: read complete current tool set
  McpTool->>Registry: register replacement scope
  McpTool->>Registry: close previous scope
  McpTool-->>Client: mutation is observable

Loading

[kitlangton]

Closing this implementation for now. The consistency gap and deterministic reproduction are tracked in #39902 so we can revisit the general runtime MCP contract separately. This was not the cause of the original voice tool failure.