Raise the actionable ninja message when the package itself is missing

esphome/arduino8266/framework.py

@@ -208,7 +208,13 @@ def _find_ninja() -> Path:
     """
     if binary := shutil.which("ninja"):
         return Path(binary)
-    import ninja
+    try:
+        import ninja
+    except ImportError as err:
+        raise EsphomeError(
+            "ninja not found on PATH or in the ninja package; reinstall the "
+            "esphome Python environment"
+        ) from err
 
     binary = Path(ninja.BIN_DIR) / ("ninja.exe" if os.name == "nt" else "ninja")
     if not binary.is_file():

tests/unit_tests/test_arduino8266_framework.py

@@ -237,6 +237,16 @@ def test_find_ninja_falls_back_to_wheel(tmp_path: Path) -> None:
         assert framework._find_ninja() == tmp_path / binary_name
 
 
+def test_find_ninja_package_not_installed() -> None:
+    """A missing ninja package raises the actionable message, not ImportError."""
+    with (
+        patch("shutil.which", return_value=None),
+        patch.dict(sys.modules, {"ninja": None}),
+        pytest.raises(EsphomeError, match="ninja not found"),
+    ):
+        framework._find_ninja()
+
+
 def test_find_ninja_missing_everywhere(tmp_path: Path) -> None:
     wheel = MagicMock(BIN_DIR=str(tmp_path))
     with (