fix: reject invalid transport and port from environment

Self-review fixes on top of the stateless HTTP transport:

- argparse never checks `choices` against an env-supplied default, so a
  typo in MCP_TRANSPORT would silently fall back to stdio inside a
  container that expects an HTTP listener; validate it after parsing.
- A non-integer MCP_PORT now exits with a clean parser error instead of
  an unhandled ValueError traceback.
- Drop a redundant local `import os` (already imported at module level).
- Fix a stale README sentence claiming the server is not meant to run
  as a long-running HTTP service, which contradicted the new section.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U9zFxq8V4qxG4aMzJhGBFn

Author: claude

README.md

@@ -58,7 +58,7 @@ pip install -e .
 
 ## Use With An MCP Client
 
-This server runs over stdio, so it is meant to be launched by an MCP client rather than used as a long-running HTTP service.
+By default this server runs over stdio and is launched by an MCP client. It can also run as a stateless Streamable HTTP service — see [Run as a Stateless HTTP Server](#run-as-a-stateless-http-server).
 
 With `uvx` (recommended — no install needed):
 

src/commit_check_mcp/server.py

@@ -619,9 +619,12 @@ def main(argv: list[str] | None = None) -> None:
     this server it is simply true.
     """
     import argparse
-    import os
 
     parser = argparse.ArgumentParser(prog="commit-check-mcp")
+    try:
+        default_port = int(os.environ.get("MCP_PORT", "8000"))
+    except ValueError:
+        parser.error(f"MCP_PORT must be an integer, got {os.environ['MCP_PORT']!r}")
     parser.add_argument(
         "--transport",
         choices=["stdio", "http"],
@@ -636,11 +639,20 @@ def main(argv: list[str] | None = None) -> None:
     parser.add_argument(
         "--port",
         type=int,
-        default=int(os.environ.get("MCP_PORT", "8000")),
+        default=default_port,
         help="port for --transport http (default 8000)",
     )
     args = parser.parse_args(argv)
 
+    # argparse does not check `choices` against env-supplied defaults, and a
+    # typo in MCP_TRANSPORT must not silently fall back to stdio inside a
+    # container that expects an HTTP listener.
+    if args.transport not in ("stdio", "http"):
+        parser.error(
+            f"argument --transport: invalid choice: {args.transport!r}"
+            " (choose from 'stdio', 'http')"
+        )
+
     if args.transport == "http":
         mcp.run(
             transport="streamable-http",

tests/test_server.py

@@ -924,3 +924,23 @@ def test_transport_from_environment(self, monkeypatch: pytest.MonkeyPatch) -> No
     def test_rejects_unknown_transport(self) -> None:
         with pytest.raises(SystemExit):
             server.main(["--transport", "sse"])
+
+    def test_rejects_unknown_transport_from_environment(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """argparse skips `choices` for env-supplied defaults; a typo in
+        MCP_TRANSPORT must fail loudly, not silently serve stdio in a
+        container that expects an HTTP listener."""
+        monkeypatch.setenv("MCP_TRANSPORT", "htpp")
+        monkeypatch.setattr(
+            server.mcp, "run", lambda **kw: pytest.fail("server must not start")
+        )
+        with pytest.raises(SystemExit):
+            server.main([])
+
+    def test_rejects_non_integer_port_from_environment(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        monkeypatch.setenv("MCP_PORT", "eight thousand")
+        with pytest.raises(SystemExit):
+            server.main([])