[WIP] Enhance get cwd function to resolve additional file-related variables

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Context

PR #260 added a configurable cwd setting with variable substitution. The TypeScript client (src/common/settings.ts resolveVariables()) pre-resolves ${workspaceFolder}, ${userHome}, ${cwd}, and ${workspaceFolder:name} before sending settings to the Python server. The Python server's get_cwd() in bundled/tool/lsp_server.py then handles document-dependent variables that can't be resolved at settings-load time.

However, as @rchiodo pointed out in #260 (comment), the current get_cwd() only resolves ${fileDirname}. There are more file-related variables from VS Code's variables reference (https://code.visualstudio.com/docs/reference/variables-reference) that should also be resolved server-side since they depend on the current document.

Required Change

Only modify bundled/tool/lsp_server.py — expand the get_cwd() function (currently at line 292) to resolve additional file-related VS Code variables using a substitution-map approach. The current implementation is:

def get_cwd(settings: dict, document: Optional[workspace.Document]) -> str:
    """Returns the working directory for running the tool.

    Resolves ``${fileDirname}`` to the directory of the current document.
    If no document is available, falls back to the workspace root.

    Examples of supported patterns: ``${fileDirname}``, ``${fileDirname}/subdir``.
    """
    cwd = settings.get("cwd", settings["workspaceFS"])
    if "${fileDirname}" in cwd:
        if document and document.path:
            cwd = cwd.replace("${fileDirname}", os.path.dirname(document.path))
        else:
            cwd = settings["workspaceFS"]
    return cwd

Replace it with a version that builds a substitution map of all document-dependent variables and applies them. When a document is available and has a path, resolve:

• ${file} → absolute path of the document (document.path)
• ${fileBasename} → file name with extension (os.path.basename(document.path))
• ${fileBasenameNoExtension} → file name without extension (use os.path.splitext on the basename)
• ${fileExtname} → file extension including the dot (use os.path.splitext)
• ${fileDirname} → directory of the document (os.path.dirname(document.path)) — already supported
• ${fileDirnameBasename} → just the name of the containing directory (os.path.basename(os.path.dirname(document.path)))
• ${relativeFile} → document path relative to settings["workspaceFS"] (use os.path.relpath)
• ${relativeFileDirname} → directory of the document relative to settings["workspaceFS"]
• ${fileWorkspaceFolder} → settings["workspaceFS"]

If no document is available (or document.path is falsy), and the cwd string contains any ${file...} or ${relativeFile...} pattern, fall back to settings["workspaceFS"].

Update the docstring to list all supported variables.

Do NOT modify settings.ts, package.json, or any other file — only bundled/tool/lsp_server.py.

This pull request was created from Copilot chat.

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