[renkun-ken]

Accepting a function completion such as fun1 inserts fun1() but previously left parameter hints closed because snippet insertion does not fire signature-help trigger characters. Add completion middleware that runs VS Code's parameter-hints command after accepting function, method, or constructor snippets that place the cursor inside the call.

The middleware respects the document's editor.parameterHints.enabled setting and preserves existing completion commands. The behavior is implemented entirely in vscode-R and works with the existing languageserver snippets.

Automatically opening signature help after completion is an established editor integration pattern. The implementation location varies:

Implementation	Practice
VS Code TypeScript support	Adds editor.action.triggerParameterHints on the client for function-call snippets with parameters, respecting the parameter-hints setting.
Go / gopls VS Code extension	Adds the same command in completion middleware for function and method items, respecting the document's parameter-hints setting.
clangd VS Code extension	Adds the command in client middleware when a snippet enters an argument placeholder, preserving existing commands.
rust-analyzer	Supplies a server-side command when the client advertises support, and can defer it until completion-item resolution.

LSP allows a command to run after completion insertion, but the parameter-hints command is editor-specific. This PR follows Go and clangd by keeping that behavior in VS Code's completion middleware. This avoids adding a command to every eligible item in the server's initial completion response and keeps editor settings in the client; the selected item's command can still round-trip during completion resolution.

Validation:

• pnpm run pretest
• pnpm run typecheck
• pnpm run lint
• Seven focused tests passed in VS Code 1.141.1, including actual completion acceptance through an in-memory LSP server with parameter hints enabled and disabled. Coverage also includes completion-list metadata, cancellation, text-edit conversion, and command preservation through completion resolution.
• git diff --check origin/main...HEAD

[renkun-ken]

@eitsupi Would you like to review this PR?

[eitsupi]

I'm sorry, I didn't notice. I'll take a look.