fix(mcp): pin mcp below 2 and say when the installed mcp is unsupported

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Install
         run: |
           python -m pip install --upgrade pip
-          pip install -e "cli[dev]" ruff
+          pip install -e "cli[dev,mcp]" ruff
 
       - name: Ruff
         run: ruff check cli/src

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## Unreleased
+
+### Fixed
+- **`prescale mcp` works on a fresh install again.** `pip install 'prescale[mcp]'` picked up the new
+  mcp 2.x, which renamed the server class PreScale uses, so the MCP server wouldn't start and told
+  you to install the extra you already had. The extra now installs mcp 1.x, and if an unsupported
+  mcp is already installed, `prescale mcp` says so and shows the command that fixes it.
+
 ## 1.1.3 — 2026-10-22
 
 ### Added

cli/pyproject.toml

@@ -35,7 +35,7 @@ dependencies = [
 
 [project.optional-dependencies]
 mcp = [
-    "mcp>=1.0",
+    "mcp>=1.0,<2",  # 2.x renamed FastMCP; see mcp_server.py
 ]
 dev = [
     "pytest>=7.0.0",

cli/src/prescale_cli/commands/mcp.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import importlib.util
 import os
 
 import click
@@ -28,7 +29,14 @@ def mcp(allow_hosts: tuple[str, ...]) -> None:
     """
     try:
         from prescale_cli.mcp_server import serve
-    except ImportError:
+    except ImportError as exc:
+        if importlib.util.find_spec("mcp") is not None:
+            # Installed, but a version we can't use (mcp 2.x renamed FastMCP).
+            err.print("[red]Error:[/red] the installed mcp package isn't supported:")
+            err.print(f"    {exc}", markup=False)
+            err.print("Install a supported version with:")
+            err.print("    pip install 'mcp>=1.0,<2'", markup=False)
+            raise SystemExit(1)
         err.print("[red]Error:[/red] MCP support needs the optional extra. Install it with:")
         err.print("    pip install 'prescale[mcp]'", markup=False)
         raise SystemExit(1)

cli/tests/test_mcp.py

@@ -135,7 +135,25 @@ def test_mcp_command_without_extra_gives_correct_install_hint(monkeypatch):
 
     # simulate the optional extra not being installed
     monkeypatch.setitem(sys.modules, "prescale_cli.mcp_server", None)
+    monkeypatch.setattr("importlib.util.find_spec", lambda name: None)
     res = CliRunner().invoke(cli, ["mcp"])
     assert res.exit_code == 1
     # the [mcp] must survive (rich must not eat it as markup)
     assert "prescale[mcp]" in res.stderr
+
+
+def test_mcp_command_with_unsupported_mcp_says_so(monkeypatch):
+    import importlib.util
+    import sys
+
+    from click.testing import CliRunner
+
+    from prescale_cli.main import cli
+
+    # mcp is installed, but importing the server fails (e.g. mcp 2.x renamed FastMCP)
+    monkeypatch.setitem(sys.modules, "prescale_cli.mcp_server", None)
+    monkeypatch.setattr(importlib.util, "find_spec", lambda name: object())
+    res = CliRunner().invoke(cli, ["mcp"])
+    assert res.exit_code == 1
+    assert "isn't supported" in res.stderr
+    assert "mcp>=1.0,<2" in res.stderr