completions capability is advertised but completion/complete is not implemented #269

handleInitialize passes the configured capabilities through, so capabilities: { completions: {} } is advertised, but handleRequest has no completion/complete case: the call returns -32601. Spec: "Both parties SHOULD respect capability negotiation".

Repro

Register with capabilities: { prompts: {}, completions: {} } → initialize returns {"prompts":{},"completions":{}}; completion/complete → -32601.

Suggested fix

Strip completions from the advertised capabilities until the method is implemented (or implement it with a handler decorator).

Found during the round-7 review of #170; also on main.

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