fix: allow dynamic handler registration after connect with pre-supplied capabilities#1602
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giulio-leone wants to merge 2 commits intomodelcontextprotocol:v1.xfrom
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February 28, 2026 15:50
…ed capabilities When capabilities were provided at McpServer construction, registering tools/resources/prompts after connect() threw 'Cannot register capabilities after connecting to transport'. This occurred because setToolRequestHandlers, setResourceRequestHandlers, and setPromptRequestHandlers unconditionally call registerCapabilities, which rejected all post-connect calls. Now registerCapabilities is idempotent for already-present capability keys: if the transport is connected and all requested capability keys already exist in the server's capabilities, the call is a silent no-op. Genuinely new capabilities still throw the error, maintaining the safety invariant. Fixes modelcontextprotocol#893
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Summary
When
McpServeris created withcapabilitiesinServerOptions, registering tools/resources/prompts afterconnect()throws:This occurs because
setToolRequestHandlers,setResourceRequestHandlers, andsetPromptRequestHandlersunconditionally callregisterCapabilities(), which rejects all post-connect calls.Fix
registerCapabilitiesis now idempotent for already-present capability keys: if the transport is connected and all requested capability keys already exist in the server's capabilities, the call is a silent no-op. Genuinely new capabilities still throw the error, maintaining the safety invariant.Test
Added 2 tests:
toolscapabilityresourcescapabilityVerification
2 consecutive clean test runs: 1551/1551 tests passed, 0 failures.
Fixes #893