## [mirendev/mflags#18](https://github.com/mirendev/mflags/pull/18)

I think this is ready. `handleInitialize` now follows MCP's version negotiation: if a client asks for a revision the server doesn't support, the server answers with one it does support (`2025-06-18`) and lets the client decide whether to go on. Before, it sent back `-32602`, and that's what was breaking clients that requested `2025-11-25`. Since only one revision is supported, "echo it back if it matches, otherwise offer ours" comes down to always returning `MCPProtocolVersion`. That's correct, and the comment where the result is built says so.

I walked each row of `TestMCPServerInitializeInvalidParams` through the handler to make sure every rejection comes from the check it's meant to test:
- **Missing params, `null` params, `{}`, an empty version and a `null` version** all decode to an empty `ProtocolVersion`. They hit the new nonempty check and get `"Invalid params"`.
- **Array or string params, a numeric version, array `capabilities`, and string `clientInfo`** all cause a `json.Unmarshal` type error. That goes down the existing `-32602 "Invalid params"` path.

So the suite covers both the type-checking rejections and the new empty-string check. The negotiation test sends real wire input. It checks the returned revision and the `initialized` flag across matching, newer, older and arbitrary version strings, which is the behaviour that matters here.

Changing the old `"wrong protocol version"` case to `"missing protocol version"` is the right call. A test asserting the old rejection would now be asserting behaviour that breaks the spec. The new case still covers the remaining `-32602` path in `handleInitialize`. No other test or doc in the repo depended on the old rejection.

Why I'm recommending approval: the change is one small, focused handler edit. It matches the protocol's documented negotiation rules. It only touches `initialize`, and both the success and rejection paths have wire-level tests that I traced by hand. I don't see anything a human reviewer would need to weigh in on beyond that. As the description says, Portal will still need its pinned dependency bumped after this merges.

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**Verdict:** ready