Introduce a typed DocumentUri identifier

[Firehed]

Document URIs are currently passed as bare string throughout the codebase — e.g. DocumentManager::get(string $uri), the uri field on the new TextDocumentPositionParams value object (#352), and every handler that extracts textDocument.uri. This is stringly-typed: a document URI, a class name, and an arbitrary string are indistinguishable to the type system, and nothing prevents an unrelated string from being passed where a URI is expected.

Proposal

Introduce a DocumentUri value object (likely in src/Protocol/ or src/Document/) and thread it through the URI-handling surface:

• DocumentManager::get() / storage keys
• TextDocumentPositionParams::$uri
• Handler param extraction and any TextDocumentSyncHandler open/change/close paths
• Location/definition results that carry a URI back to the client

Notes

• This is a broader refactor than the Extract TextDocumentPositionParams value object #352 extraction, which deliberately preserved the existing string type to stay in scope.
• Worth deciding up front whether DocumentUri should validate/normalize (file:// scheme, percent-encoding) or remain a thin wrapper, and whether it should be introduced incrementally (one boundary at a time) to keep diffs reviewable.

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This issue body was written by AI (Claude Code) at the request of the maintainer.