feat(server): add TCL signature help support

Adds a signature help system for TCL commands.
The LSP server now exposes signature help for custom and
built-in MOM procedures, enabling parameter hints while editing.
Tests and documentation were added to cover common usage.

- Adds signature_help module to parse and present signatures
- Integrates with LSP server to provide signature help on the client
- Adds tests for custom and built-in procedures

server/src/lsp_server.py

@@ -46,6 +46,7 @@ from tools.folding_ranges import build_folding_ranges
 from tools.semantic_tokens import _Highlighter, TOKEN_TYPES, TokenModifier
 from tools.completion_items import completion, remove_existing_items, remove_shared_keys
 from tools.inlay_hint import InlayHintGenerator
+from tools.signature_help import build_signature_help
 from tools.file_sourcing import get_all_psc_files, read_psc_file
 from lsp_tclserver import TclLanguageServer
 
@@ -182,6 +183,43 @@ def on_completion(params: lsp.CompletionParams) -> lsp.CompletionList:
     return lsp.CompletionList(is_incomplete=False, items=merged)
 
 
+@LSP_SERVER.feature(
+    lsp.TEXT_DOCUMENT_SIGNATURE_HELP,
+    lsp.SignatureHelpOptions(
+        trigger_characters=[" "],
+        retrigger_characters=[" "],
+    ),
+)
+def signature_help(params: lsp.SignatureHelpParams) -> lsp.SignatureHelp | None:
+    document = LSP_SERVER.workspace.get_text_document(params.text_document.uri)
+    tree = LSP_SERVER.get_tree(document)
+
+    filepath = str(pathlib.Path(uris.to_fs_path(document.uri)))
+    custom_signatures: dict[str, list[str]] = {}
+    custom_docs: dict[str, str] = {}
+
+    # Prefer declarations from the current document if duplicate proc names
+    # exist in the workspace.
+    for indexed_path, signatures in LSP_SERVER.proc_signatures.items():
+        if indexed_path != filepath:
+            custom_signatures.update(signatures)
+    custom_signatures.update(LSP_SERVER.proc_signatures.get(filepath, {}))
+
+    for indexed_path, docs in LSP_SERVER.proc_docs.items():
+        if indexed_path != filepath:
+            custom_docs.update(docs)
+    custom_docs.update(LSP_SERVER.proc_docs.get(filepath, {}))
+
+    return build_signature_help(
+        document.source,
+        tree,
+        params.position,
+        custom_signatures,
+        custom_docs,
+        standard_items.json_data.get("MOM_procs", []),
+    )
+
+
 # @LSP_SERVER.feature(lsp.TEXT_DOCUMENT_DOCUMENT_SYMBOL)
 # def document_symbols(params: lsp.DocumentSymbolParams):
 #     doc = LSP_SERVER.workspace.get_text_document(params.text_document.uri)