feat(lsp): 增加 UTF-16 位置往返验证

- viper/lspPosition：line/character -> offset -> line/character
- probe Gate 1：随机 10k 个有效位置往返，覆盖 CRLF/中文/emoji

App/lib/lsp/LspServer.vp

@@ -198,6 +198,31 @@ def _HandleDocument(pool: memhub.MemManager*, tr: LspTransport.LspTransport*,
     return LspRpc.WriteResponse(pool, tr, id_node, result)
 
 
+def _HandlePosition(pool: memhub.MemManager*, tr: LspTransport.LspTransport*,
+                    docs: LspDocuments.LspDocuments*, id_node: json.JsonValue*,
+                    params: json.JsonValue*) -> int:
+    uri: str = None
+    if params is not None:
+        uri = LspRpc.GetStringField(params, "uri")
+    doc: LspDocuments.LspDocument* = docs.Find(uri)
+    if doc is None or doc.index is None:
+        return LspRpc.WriteResponse(pool, tr, id_node, json.null(pool))
+    line: int = LspRpc.GetIntField(params, "line", 0)
+    character: int = LspRpc.GetIntField(params, "character", 0)
+    offset: sizet = doc.index.PositionToOffset(line, character)
+    out_line: int = 0
+    out_char: int = 0
+    if doc.index.OffsetToPosition(offset, &out_line, &out_char) != 0:
+        return -1
+    result: json.JsonValue* = json.object(pool)
+    if result is None:
+        return -1
+    json.object_set(pool, result, "offset", json.int_val(pool, int64(offset)))
+    json.object_set(pool, result, "line", json.int_val(pool, int64(out_line)))
+    json.object_set(pool, result, "character", json.int_val(pool, int64(out_char)))
+    return LspRpc.WriteResponse(pool, tr, id_node, result)
+
+
 def Run(pool: memhub.MemBuddy*, perm_pool: memhub.MemBuddy*) -> int:
     os._mbuddy = perm_pool
     os._win32._mbuddy = perm_pool
@@ -262,6 +287,8 @@ def Run(pool: memhub.MemBuddy*, perm_pool: memhub.MemBuddy*) -> int:
             rc = _HandleStats(pool, tr, docs, ws, id_node)
         elif string.strcmp(method, "viper/lspDocument") == 0:
             rc = _HandleDocument(pool, tr, docs, id_node, params)
+        elif string.strcmp(method, "viper/lspPosition") == 0:
+            rc = _HandlePosition(pool, tr, docs, id_node, params)
         elif string.strcmp(method, LspProtocol.LSP_METHOD_SHUTDOWN) == 0:
             shutdown_requested = 1
             rc = LspRpc.WriteResponse(pool, tr, id_node, json.null(pool))

Tools/lsp/probe.py

@@ -7,6 +7,7 @@ import argparse
 import json
 import os
 import queue
+import random
 import subprocess
 import sys
 import threading
@@ -181,6 +182,28 @@ def documents(exe: str) -> int:
     if not isinstance(doc, dict) or doc.get("text") != text or doc.get("version") != 1:
         raise AssertionError(f"initial document text/version mismatch: {doc}")
 
+    lines = text.splitlines()
+    choices: list[tuple[int, int]] = []
+    for line_no, line_text in enumerate(lines):
+        offsets = [0]
+        units = 0
+        for ch in line_text:
+            units += 2 if ord(ch) > 0xFFFF else 1
+            offsets.append(units)
+        for character in offsets:
+            choices.append((line_no, character))
+    random.seed(1234)
+    for _ in range(10000):
+        line_no, character = random.choice(choices)
+        result = client.request(
+            "viper/lspPosition",
+            {"uri": uri, "line": line_no, "character": character},
+        ).get("result")
+        if not isinstance(result, dict) or result.get("line") != line_no or result.get("character") != character:
+            raise AssertionError(
+                f"UTF-16 round-trip failed for ({line_no},{character}): {result}"
+            )
+
     client.notify(
         "textDocument/didChange",
         {