Keep Unity bridge checks in Python

.llm/context.md

@@ -228,7 +228,7 @@ runs everything, including the Prettier Markdown check, on ubuntu and windows. C
 - Gateway launchers (`codex-zai`, `claude-zai`, `codex-openrouter`, `claude-openrouter`) come from `.devcontainer/ai_backends.py`. They self-load the gitignored `.env.local` for
   keys not already exported (preexisting environment variables win), so they work in non-interactive shells too. Python startup, backend, and service tools share
   `.devcontainer/env_local.py`; the sourced Bash loader remains for parent-shell exports, with parity pinned by `scripts/tests/test_env_local_precedence.py`.
-- `npm run mcp:sync` regenerates machine-local MCP configs for Claude Code, Codex, OpenCode, Nanocoder, VS Code, and Cursor from `.llm/mcp/configure.mjs`. Those outputs are
+- `npm run mcp:sync` regenerates machine-local MCP configs for Claude Code, Codex, OpenCode, Nanocoder, VS Code, and Cursor through `scripts/mcp_configure.py`. Those outputs are
   gitignored and must never be committed.
 - Secrets live in gitignored `.env.local` (template: `.env.local.example`); config files reference env vars instead of embedding credentials.
 - Unity MCP: the **official Unity CLI** MCP server (`unity mcp`, ~140 tools). Container agents reach it through the host HTTP bridge (`npm run unity:mcp:host` →

.llm/mcp/README.md

@@ -115,7 +115,7 @@ npm run unity:mcp:host   # host: spawns `unity mcp`, serves http://0.0.0.0:9020/
 ```
 
 Startup settings resolve through `scripts/unity_mcp_settings.py` using uv or Python 3.9+. Project pins prefer process variables, then workspace settings, then the legacy home file,
-regardless of which project-path alias each source uses. HTTP and CLI process handling remain in the Node bridge.
+regardless of which project-path alias each source uses. HTTP and CLI process handling use `scripts/unity_mcp_host.py`.
 
 Container agents connect to `http://host.docker.internal:9020/mcp` (written automatically by `npm run mcp:sync`). The bridge is transparent: JSON-RPC requests are forwarded to the
 CLI with per-request id remapping, client notifications are passed through, and a crashed CLI is respawned lazily on the next request. Startup also verifies a proxy-free local HTTP
@@ -148,12 +148,12 @@ Security: the bridge listens on all interfaces by default (Linux Docker cannot r
 - **`unity run unity:mcp:host` fails with "Not a Unity project".** That invoked the Unity CLI, not the npm script: `unity run <project>` expects a project path, so it treats
   `unity:mcp:host` as one. The bridge is an npm script — start it with `npm run unity:mcp:host`.
 - **Port already in use / dynamic ports.** Re-running the bridge is a no-op while a healthy instance holds the port; if something else owns it, the bridge binds the next free port,
-  persists `UNITY_MCP_HTTP_PORT` to `.env.local`, and re-syncs every frontend config automatically. No fixed port is required anywhere: `configure.mjs`, the devcontainer health
+  persists `UNITY_MCP_HTTP_PORT` to `.env.local`, and re-syncs every frontend config automatically. No fixed port is required anywhere: `mcp_configure.py`, the devcontainer health
   check, and the doctors all read the persisted value.
-- **`npm run mcp:sync` on the host.** It runs the cross-platform Node adapter `configure.mjs`. Codex persistence and workspace cleanup use `scripts/mcp_codex_config.py`; JSON
+- **`npm run mcp:sync` on the host.** It runs the typed Python driver `scripts/mcp_configure.py`. Codex persistence and workspace cleanup use `scripts/mcp_codex_config.py`; JSON
   persistence uses `scripts/mcp_json_config.py`. Credential aliases use `scripts/mcp_aliases.py`, preserving BOM and line endings and emitting statuses only. The managed server
-  catalog uses `scripts/mcp_catalog.py`. These tools run through uv or Python 3.9+ when uv is absent. Container hooks use `sync_mcp.py`
-  (`uv run .llm/mcp/sync_mcp.py [workspace_dir] [flags...]`). Command discovery uses `where` on Windows.
+  catalog uses `scripts/mcp_catalog.py`. The npm commands use uv; standalone entry points also support Python 3.9+. Container hooks use `sync_mcp.py`
+  (`uv run .llm/mcp/sync_mcp.py [workspace_dir] [flags...]`). Command discovery follows platform PATH rules.
 - **Shared configs are environment-agnostic.** Sync produces identical files from the host and the container (verified by hash): the unity bridge URL always uses
   `host.docker.internal` (resolves on the host under Docker Desktop too), and zai-image uses the PATH-resolved `uv` runner with a workspace-relative script. Never reintroduce
   `127.0.0.1` or absolute binaries into shared entries — they silently break the other environment.
@@ -182,4 +182,4 @@ the pinned editor. If `/healthz` times out, check the host URL and remove forwar
 directly to the host bridge. Match health's `bridgePid` to the listener owner; health bypasses authentication and does not start Unity.
 
 The npm commands `npm run mcp:sync` and `npm run unity:mcp:host` run typed Python through uv. Direct entry points are `uv run scripts/mcp_configure.py` and
-`uv run scripts/unity_mcp_host.py`. Legacy Node paths remain small launchers with Python 3.9+ fallback; the Python sync wrapper does not require Node.
+`uv run scripts/unity_mcp_host.py`. Legacy configuration and bridge Node paths remain small launchers with Python 3.9+ fallback; the Python sync wrapper does not require Node.

.llm/mcp/configure.mjs

@@ -5,11 +5,13 @@ import { fileURLToPath } from "node:url";
 const script = fileURLToPath(new URL("../../scripts/mcp_configure.py", import.meta.url));
 for (const [command, prefix, probe] of [
     ["uv", ["run", "--no-project"], ["--version"]],
-    ["python3", [], ["-c", "import sys; assert sys.version_info >= (3, 9)"]],
-    ["python", [], ["-c", "import sys; assert sys.version_info >= (3, 9)"]],
+    ["python3", [], ["-c", "import sys; assert sys.version_info >= (3, 9); print('dataviz-python')"]],
+    ["python", [], ["-c", "import sys; assert sys.version_info >= (3, 9); print('dataviz-python')"]],
 ]) {
-    const available = spawnSync(command, probe, { stdio: "ignore" });
+    const available = spawnSync(command, probe, { encoding: "utf8", stdio: ["ignore", "pipe", "ignore"] });
     if (available.status !== 0) continue;
+    const ready = command === "uv" ? available.stdout.startsWith("uv ") : available.stdout.trim() === "dataviz-python";
+    if (!ready) continue;
     const result = spawnSync(command, [...prefix, script, ...process.argv.slice(2)], { stdio: "inherit" });
     if (result.error) console.error("Cannot start MCP configuration: " + result.error.message);
     process.exit(result.status ?? 1);

.llm/mcp/unity-mcp-host.mjs

@@ -5,11 +5,13 @@ import { fileURLToPath } from "node:url";
 const script = fileURLToPath(new URL("../../scripts/unity_mcp_host.py", import.meta.url));
 for (const [command, prefix, probe] of [
     ["uv", ["run", "--no-project"], ["--version"]],
-    ["python3", [], ["-c", "import sys; assert sys.version_info >= (3, 9)"]],
-    ["python", [], ["-c", "import sys; assert sys.version_info >= (3, 9)"]],
+    ["python3", [], ["-c", "import sys; assert sys.version_info >= (3, 9); print('dataviz-python')"]],
+    ["python", [], ["-c", "import sys; assert sys.version_info >= (3, 9); print('dataviz-python')"]],
 ]) {
-    const available = spawnSync(command, probe, { stdio: "ignore" });
+    const available = spawnSync(command, probe, { encoding: "utf8", stdio: ["ignore", "pipe", "ignore"] });
     if (available.status !== 0) continue;
+    const ready = command === "uv" ? available.stdout.startsWith("uv ") : available.stdout.trim() === "dataviz-python";
+    if (!ready) continue;
     const result = spawnSync(command, [...prefix, script, ...process.argv.slice(2)], { stdio: "inherit" });
     if (result.error) console.error("Cannot start MCP bridge: " + result.error.message);
     process.exit(result.status ?? 1);

scripts/harness_scope.py

@@ -62,12 +62,17 @@
     # companion on the same docs contract; unknown metadata stays fail-safe.
     "scripts/tests/test_build_docs.py.meta": ("test_build_docs.py",),
     "scripts/unity_mcp_doctor.py": ("test_unity_mcp_doctor.py",),
-    ".llm/mcp/unity-mcp-host.mjs": ("test_unity_mcp_host.py", "test_unity_mcp_settings.py"),
+    ".llm/mcp/unity-mcp-host.mjs": ("test_mcp_catalog.py", "test_unity_mcp_host.py", "test_unity_mcp_host_python.py", "test_unity_mcp_settings.py"),
     "scripts/unity_mcp_settings.py": ("test_unity_mcp_host.py", "test_unity_mcp_settings.py"),
     "scripts/unity_mcp_settings.py.meta": ("test_unity_mcp_settings.py",),
     "scripts/tests/test_unity_mcp_settings.py.meta": ("test_unity_mcp_settings.py",),
     # The live doctor path selects the doctor contract suite alongside the
     # coarse mcp contract suites the subtree prefix already selects (#269).
+    "scripts/mcp_configure.py": ("test_mcp_aliases.py", "test_mcp_catalog.py", "test_mcp_codex_config.py", "test_mcp_credentials.py", "test_mcp_json_config.py", "test_mcp_sync.py"),
+    "scripts/mcp_configure.py.meta": ("test_mcp_aliases.py", "test_mcp_catalog.py", "test_mcp_codex_config.py", "test_mcp_credentials.py", "test_mcp_json_config.py", "test_mcp_sync.py"),
+    "scripts/unity_mcp_host.py": ("test_unity_mcp_host.py", "test_unity_mcp_host_python.py", "test_unity_mcp_settings.py"),
+    "scripts/unity_mcp_host.py.meta": ("test_unity_mcp_host.py", "test_unity_mcp_host_python.py", "test_unity_mcp_settings.py"),
+    "scripts/tests/test_unity_mcp_host_python.py.meta": ("test_unity_mcp_host_python.py",),
     "scripts/mcp_catalog.py": ("test_mcp_catalog.py", "test_mcp_credentials.py", "test_mcp_sync.py"),
     "scripts/mcp_catalog.py.meta": ("test_mcp_catalog.py", "test_mcp_credentials.py", "test_mcp_sync.py"),
     "scripts/tests/test_mcp_catalog.py.meta": ("test_mcp_catalog.py",),

scripts/tests/test_mcp_catalog.py

@@ -102,6 +102,30 @@ def test_configurator_falls_back_to_python_without_uv(self) -> None:
             self.assertNotIn(b'Python 3.9+', result.stderr)
             self.assertFalse((root / '.mcp.json').exists())
 
+    @unittest.skipUnless(os.name == 'posix' and shutil.which('node'), 'placeholder PATH fixture needs POSIX and Node')
+    def test_legacy_launchers_skip_successful_non_interpreter_placeholders(self) -> None:
+        with tempfile.TemporaryDirectory(prefix='python placeholder ') as directory:
+            root = Path(directory)
+            binary = root / 'bin'
+            binary.mkdir()
+            placeholder = binary / 'python3'
+            placeholder.write_text('#!/bin/sh\nexit 0\n', encoding='utf-8')
+            placeholder.chmod(0o755)
+            (binary / 'python').symlink_to(sys.executable)
+            environment = {key: value for key, value in os.environ.items()
+                           if not key.startswith(('GITHUB_', 'ZAI_', 'Z_AI_', 'UNITY_'))}
+            environment.update(PATH=str(binary), DATAVIZ_MCP_WORKSPACE=str(root), HOME=str(root / 'home'),
+                               CODEX_HOME=str(root / 'codex'), NANOCODER_CONFIG_DIR=str(root / 'nano'))
+            folder = Path(__file__).resolve().parents[2] / '.llm/mcp'
+            for entry, flag, expected in (('configure.mjs', '--check', b'Servers: unity'),
+                                          ('unity-mcp-host.mjs', '--help', b'usage:')):
+                with self.subTest(entry=entry):
+                    result = subprocess.run([str(shutil.which('node')), str(folder / entry), flag], env=environment,
+                                            cwd=root, capture_output=True, check=False)
+                    self.assertEqual(result.returncode, 0, result.stderr.decode('utf-8', errors='replace'))
+                    self.assertIn(expected, result.stdout)
+                    self.assertFalse((root / '.mcp.json').exists())
+
     def test_cli_uses_utf8_bytes_under_legacy_stdio_encoding(self) -> None:
         environment = dict(os.environ, PYTHONIOENCODING='cp1252')
         result = subprocess.run([sys.executable, str(Path(__file__).resolve().parents[1] / 'mcp_catalog.py')],