diff --git a/App/lib/lsp/LspWorkspace.vp b/App/lib/lsp/LspWorkspace.vp
index 0ece618..6902ebf 100644
--- a/App/lib/lsp/LspWorkspace.vp
+++ b/App/lib/lsp/LspWorkspace.vp
@@ -136,8 +136,6 @@ def DecodeUri(pool: memhub.MemManager*, uri: str) -> str:
     p: str = uri
     if string.strncmp(uri, "file://", 7) == 0:
         p = uri + 7
-        if p[0] == '/' and len(p) >= 3 and p[2] == ':':
-            p = p + 1
     n: sizet = string.strlen(p)
     out: bytes = pool.alloc(n + 1)
     if out is None:
@@ -158,6 +156,10 @@ def DecodeUri(pool: memhub.MemManager*, uri: str) -> str:
         o += 1
         i += 1
     out[o] = 0
+    # VS Code sends the drive colon percent-encoded (file:///d%3A/...), so the leading
+    # separator must be dropped after decoding, not before.
+    if string.strncmp(uri, "file://", 7) == 0 and o >= 3 and out[0] == '/' and out[2] == ':':
+        return str(out + 1)
     return str(out)
 
 
diff --git a/Tools/lsp/probe.py b/Tools/lsp/probe.py
index 86ec566..5b60f70 100644
--- a/Tools/lsp/probe.py
+++ b/Tools/lsp/probe.py
@@ -1765,6 +1765,50 @@ def gate10(exe: str) -> int:
     code = client.close()
     if code != 0:
         raise AssertionError(f"exit code is {code}, expected 0")
+
+    # VS Code's URI serializer percent-encodes the drive colon (file:///d%3A/...). A decoded
+    # path starting with "/" prevents project adoption and leaves the index roots empty.
+    def vscode_uri(path: Path) -> str:
+        p = path.resolve().as_posix()
+        if len(p) >= 2 and p[1] == ":":
+            p = p[0].lower() + "%3A" + p[2:]
+        return "file:///" + p
+
+    enc_client = Client(exe)
+    enc_init = enc_client.request(
+        "initialize",
+        {"processId": os.getpid(), "rootUri": vscode_uri(workspace), "capabilities": {}},
+    )
+    if not isinstance(enc_init.get("result"), dict):
+        raise AssertionError(f"encoded-URI initialize failed: {enc_init}")
+    enc_client.notify("initialized", {})
+    enc_client.notify(
+        "textDocument/didOpen",
+        {"textDocument": {"uri": vscode_uri(use_path), "languageId": "viper",
+                          "version": 1, "text": text}},
+    )
+    enc_client.wait_notification("textDocument/publishDiagnostics")
+    enc_stats = enc_client.request("viper/lspStats").get("result") or {}
+    enc_source = str(enc_stats.get("sourceDir") or "")
+    if enc_source.startswith("/"):
+        raise AssertionError(f"encoded URI root was not decoded: {enc_stats}")
+    if Path(enc_source).resolve() != workspace.resolve():
+        raise AssertionError(f"encoded URI sourceDir mismatch: {enc_stats}")
+    enc_sem = enc_client.request(
+        "textDocument/semanticTokens/full", {"textDocument": {"uri": vscode_uri(use_path)}},
+        timeout=120.0,
+    ).get("result")
+    if not isinstance(enc_sem, dict):
+        raise AssertionError(f"encoded URI semanticTokens failed: {enc_sem}")
+    enc_tokens = _decode_tokens(enc_sem.get("data", []))
+    enc_pos = _position(text, "s.value")
+    enc_pos["character"] += 2
+    if not _find_token(enc_tokens, enc_pos["line"], enc_pos["character"], sem_types.index("property")):
+        raise AssertionError(f"encoded URI lost cross-file member token: {enc_pos}")
+    enc_client.request("shutdown")
+    if enc_client.close() != 0:
+        raise AssertionError("encoded URI client did not exit cleanly")
+
     shutil.rmtree(workspace, ignore_errors=True)
     print("member-annotations: OK")
     print("member-module-chain: OK")