feat(lsp): add context-aware completion ranking and document highlights

Adds context-aware completion ranking and document highlights for Tcl.
Adds completion_context to distinguish variables and commands.
Wires per-file completion snapshots and ranking into the flow.
Adds document_highlight provider support and tests for highlights.

- Context-aware ranking of completion items using per-file snapshots
- Document highlight provider wired into initialization and tests
- Tests for completion context, ranking, and document highlights

server/src/tools/completion_items.py

@@ -1,3 +1,10 @@
+from __future__ import annotations
+
+import copy
+import re
+from collections.abc import Iterable, Sequence
+from enum import Enum
+
 import lsprotocol.types as lsp
 from common.load_data import standard_items
 from tclint.syntax_tree import BareWord, Command, List, Visitor
@@ -6,6 +13,86 @@ BUILTIN_VAR_LABELS = {ci.label for ci in standard_items.nx_variables}
 BUILTIN_PROC_LABELS = {ci.label for ci in standard_items.nx_procs}
 
 
+class CompletionContext(Enum):
+    VARIABLE = "variable"
+    COMMAND = "command"
+    GENERAL = "general"
+
+
+VARIABLE_KINDS = {
+    lsp.CompletionItemKind.Variable,
+    lsp.CompletionItemKind.Field,
+    lsp.CompletionItemKind.Constant,
+}
+COMMAND_KINDS = {
+    lsp.CompletionItemKind.Function,
+    lsp.CompletionItemKind.Method,
+    lsp.CompletionItemKind.Constructor,
+    lsp.CompletionItemKind.Keyword,
+}
+
+_VARIABLE_PREFIX_RE = re.compile(r"(?<!\\)\$(?:\{)?[A-Za-z0-9_:]*$")
+_COMMAND_PREFIX_RE = re.compile(r"(?:^|[;\[\{])\s*[^\s;\[\]\{\}]*$")
+
+
+def _codepoint_offset(line: str, utf16_offset: int) -> int:
+    """Translate an LSP UTF-16 character offset into a Python string offset."""
+    if utf16_offset <= 0:
+        return 0
+
+    units = 0
+    for offset, character in enumerate(line):
+        units += 2 if ord(character) > 0xFFFF else 1
+        if units >= utf16_offset:
+            return offset + 1
+    return len(line)
+
+
+def completion_context(
+    source_lines: Sequence[str], position: lsp.Position
+) -> CompletionContext:
+    if position.line < 0 or position.line >= len(source_lines):
+        return CompletionContext.GENERAL
+
+    line = source_lines[position.line]
+    prefix = line[: _codepoint_offset(line, position.character)]
+    if _VARIABLE_PREFIX_RE.search(prefix):
+        return CompletionContext.VARIABLE
+    if _COMMAND_PREFIX_RE.search(prefix):
+        return CompletionContext.COMMAND
+    return CompletionContext.GENERAL
+
+
+def _is_allowed(item: lsp.CompletionItem, context: CompletionContext) -> bool:
+    if context == CompletionContext.VARIABLE:
+        return item.kind in VARIABLE_KINDS
+    if context == CompletionContext.COMMAND:
+        return item.kind in COMMAND_KINDS
+    return True
+
+
+def ranked_completion_items(
+    candidates: Iterable[tuple[int, lsp.CompletionItem]],
+    context: CompletionContext,
+) -> list[lsp.CompletionItem]:
+    """Filter, de-duplicate, and rank completion candidates for one request."""
+    items = []
+    seen: set[tuple[str, lsp.CompletionItemKind | None]] = set()
+    for sequence, (priority, item) in enumerate(candidates):
+        if not _is_allowed(item, context):
+            continue
+
+        key = (item.label, item.kind)
+        if key in seen:
+            continue
+        seen.add(key)
+
+        ranked = copy.copy(item)
+        ranked.sort_text = f"{priority:03d}:{item.label.casefold()}:{sequence:06d}"
+        items.append(ranked)
+    return items
+
+
 class CompletionItems:
     def __init__(self):
         self._custom_functions: list[lsp.CompletionItem] = []
@@ -77,9 +164,17 @@ class CompletionCollector(Visitor):
         # Collect global variables declared with: global var1 var2 ...
         elif routine.contents == "global" and command.args:
             for arg in command.args:
-                if isinstance(arg, BareWord) and getattr(arg, "value", None):
-                    if arg.value not in BUILTIN_VAR_LABELS:
-                        self._append_unique(lsp.CompletionItem(label=arg.value, kind=lsp.CompletionItemKind.Variable))
+                if (
+                    isinstance(arg, BareWord)
+                    and getattr(arg, "value", None)
+                    and arg.value not in BUILTIN_VAR_LABELS
+                ):
+                    self._append_unique(
+                        lsp.CompletionItem(
+                            label=arg.value,
+                            kind=lsp.CompletionItemKind.Variable,
+                        )
+                    )
 
         # Collect variables set with explicit global namespace: set ::var_name ...
         elif routine.contents == "set" and command.args: