fix: allow registering tools/resources/prompts after connect when capabilities pre-declared (#893)#1666
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…abilities pre-declared (modelcontextprotocol#893) When McpServer is constructed with pre-declared capabilities (e.g. `{ capabilities: { tools: { listChanged: true } } }`), calling `registerTool()` / `registerResource()` / `registerPrompt()` after `connect()` used to throw "Cannot register capabilities after connecting to transport" because the first handler registration always called `server.registerCapabilities()` unconditionally. Fix: - Pass capabilities through `withDefaultListChangedCapabilities()` so `listChanged` defaults are applied before `connect()`. - Eagerly initialize the corresponding request handlers in the constructor when capabilities are pre-declared, so the lazy path in `set*RequestHandlers()` is already done before `connect()`. - Guard every `registerCapabilities()` call inside the four `set*RequestHandlers()` / `setCompletionRequestHandler()` methods with `!this.server.transport`, so post-connect invocations skip the now-redundant re-registration. Fixes modelcontextprotocol#893 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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@modelcontextprotocol/client
@modelcontextprotocol/server
@modelcontextprotocol/express
@modelcontextprotocol/hono
@modelcontextprotocol/node
commit: |
…lcontextprotocol#893) { listChanged: X ?? true, ...capabilities.tools } puts the default first so the spread overwrites it — explicit undefined defeats the default. Fix to { ...capabilities.tools, listChanged: X ?? true } so the ?? true only applies when the user did not set listChanged. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
Fixes #893.
When
McpServeris constructed with pre-declared capabilities (e.g.{ capabilities: { tools: { listChanged: true } } }), callingregisterTool()/registerResource()/registerPrompt()afterconnect()used to throw:Because the first handler registration always called
server.registerCapabilities()unconditionally, which fails post-connect.Root Cause
setToolRequestHandlers(),setResourceRequestHandlers(),setPromptRequestHandlers(), andsetCompletionRequestHandler()all unconditionally calledthis.server.registerCapabilities()on first invocation — even when those capabilities were already declared at construction time.Fix
withDefaultListChangedCapabilities()helper that applieslistChangeddefaults when capabilities are pre-declared inoptions.set*RequestHandlers()in theMcpServerconstructor (beforeconnect()is ever called), so the handlers are already registered when the user later callsregister*()after connect.registerCapabilities()call insideset*RequestHandlers()andsetCompletionRequestHandler()with!this.server.transport, so post-connect invocations skip the now-redundant re-registration.Test Plan
test/integration/test/issues/test893.post-connect-registration.test.ts— 5 tests covering:capabilities.toolspre-declaredcapabilities.resourcespre-declaredcapabilities.promptspre-declaredsetCompletionRequestHandlerguard)pnpm test:all)pnpm check:allpasses (typecheck + lint)🤖 Generated with Claude Code