fix: avoid injecting unsupported --variant flag into kicad-cli

src/kicad_mcp/discovery.py

@@ -54,6 +54,7 @@ class CliCapabilities:
     supports_allegro_import: bool = False
     supports_pads_import: bool = False
     supports_geda_import: bool = False
+    supports_cli_variant: bool = False
 
 
 def _candidate_cli_paths() -> list[Path]:
@@ -195,6 +196,7 @@ def get_cli_capabilities(cli_path: Path) -> CliCapabilities:
         supports_allegro_import="allegro" in blob,
         supports_pads_import="pads" in blob,
         supports_geda_import="geda" in blob,
+        supports_cli_variant="--variant" in blob,
     )
     _CLI_CAPABILITIES_CACHE[cache_key] = capabilities
     return capabilities

src/kicad_mcp/tools/export.py

@@ -100,11 +100,31 @@ def _with_low_level_export_notice(message: str) -> str:
 
 def _active_variant_args(variant_name: str | None = None) -> list[str]:
     try:
-        return variant_apply_to_kicad_cli_args(variant_name)
+        args = variant_apply_to_kicad_cli_args(variant_name)
     except ValueError:
         if variant_name:
             raise
         return []
+    if not args:
+        return args
+    # ``--variant`` was added to ``kicad-cli`` in KiCad 10.  Earlier CLIs (9.x
+    # and below) reject it as ``Unknown argument`` and abort the export.  The
+    # ``default`` variant is a synthetic no-op baseline that adds no overrides,
+    # so suppress it unconditionally; for explicit non-default variants, gate
+    # on the local CLI's advertised capability.
+    if args == ["--variant", "default"]:
+        return []
+    try:
+        caps = get_cli_capabilities(get_config().kicad_cli)
+    except Exception:
+        return args
+    if not caps.supports_cli_variant:
+        raise ValueError(
+            f"The detected kicad-cli does not support --variant. "
+            f"Cannot apply variant '{args[1]}'. Upgrade to KiCad 10+ "
+            f"or run variant_set_active('default') to clear the override."
+        )
+    return args
 
 
 async def _report_progress(
@@ -389,7 +409,7 @@ def _export_sch_pdf() -> str:
         out_dir = _ensure_output_dir()
         out_file = out_dir / "schematic.pdf"
         variant_args = _active_variant_args()
-        code, _, stderr = _run_cli_variants(
+        code, stdout, stderr = _run_cli_variants(
             [
                 ["sch", "export", "pdf", *variant_args, "--output", str(out_file), str(sch_file)],
                 [
@@ -405,7 +425,7 @@ def _export_sch_pdf() -> str:
             ]
         )
         if code != 0:
-            return f"Schematic PDF export failed: {stderr or 'unknown error'}"
+            return f"Schematic PDF export failed: {stderr or stdout or 'unknown error'}"
         return f"Schematic PDF exported to {out_file}"
 
     @headless_compatible

tests/integration/test_export_tools.py

@@ -227,6 +227,7 @@ class Result:
             supports_render=True,
             supports_3d_pdf=True,
             supports_spice_netlist=True,
+            supports_cli_variant=True,
         ),
     )
 

tests/unit/test_release_hardening.py

@@ -533,6 +533,7 @@ def fake_run_cli_variants(variants: list[list[str]]) -> tuple[int, str, str]:
             drill_command="drill",
             position_command="pos",
             supports_ipc2581=True,
+            supports_cli_variant=True,
         ),
     )
 

tests/unit/test_variant_helpers.py

@@ -104,6 +104,75 @@ def test_variant_apply_to_kicad_cli_args_returns_empty_when_project_has_no_activ
     assert variant_apply_to_kicad_cli_args() == []
 
 
+class _FakeConfig:
+    kicad_cli = None
+
+
+def _patch_variant_args_dependencies(
+    monkeypatch: pytest.MonkeyPatch,
+    variant_args: list[str],
+    *,
+    supports_cli_variant: bool,
+) -> None:
+    from kicad_mcp.discovery import CliCapabilities
+
+    monkeypatch.setattr(
+        "kicad_mcp.tools.export.variant_apply_to_kicad_cli_args",
+        lambda variant_name=None: list(variant_args),
+    )
+    monkeypatch.setattr("kicad_mcp.tools.export.get_config", lambda: _FakeConfig())
+    monkeypatch.setattr(
+        "kicad_mcp.tools.export.get_cli_capabilities",
+        lambda _cli: CliCapabilities(
+            version="KiCad 9.0.7", supports_cli_variant=supports_cli_variant
+        ),
+    )
+
+
+def test_active_variant_args_raises_when_cli_lacks_variant_support(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Explicit non-default variants must fail loudly on pre-KiCad-10 CLIs.
+
+    Silently dropping the flag would cause a requested variant (e.g. ``lite``)
+    to manufacture as the default board, which is a correctness footgun.
+    """
+    from kicad_mcp.tools.export import _active_variant_args
+
+    _patch_variant_args_dependencies(
+        monkeypatch, ["--variant", "lite"], supports_cli_variant=False
+    )
+
+    with pytest.raises(ValueError, match="does not support --variant"):
+        _active_variant_args()
+
+
+def test_active_variant_args_suppresses_synthetic_default_on_old_cli(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The synthetic ``default`` variant adds no overrides, so dropping it is safe."""
+    from kicad_mcp.tools.export import _active_variant_args
+
+    _patch_variant_args_dependencies(
+        monkeypatch, ["--variant", "default"], supports_cli_variant=False
+    )
+
+    assert _active_variant_args() == []
+
+
+def test_active_variant_args_forwards_variant_on_new_cli(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """KiCad-10 CLIs accept ``--variant``, so the flag must pass through."""
+    from kicad_mcp.tools.export import _active_variant_args
+
+    _patch_variant_args_dependencies(
+        monkeypatch, ["--variant", "lite"], supports_cli_variant=True
+    )
+
+    assert _active_variant_args() == ["--variant", "lite"]
+
+
 def test_render_variant_components_merges_unknown_override_reference(
     sample_project,
     monkeypatch: pytest.MonkeyPatch,