Add plugboard process validate CLI command

Adds a new `validate` subcommand to the CLI that checks whether a process
defined in a YAML config file is valid. It builds the process and runs all
topology validation checks (connected inputs, event matching, cycle detection).
Exits with code 0 on success, code 1 with error details on failure.

Co-authored-by: toby-coleman <13170610+toby-coleman@users.noreply.github.com>

Author: Copilot

plugboard/cli/process/__init__.py

@@ -13,7 +13,7 @@
 
 from plugboard.diagram import MermaidDiagram
 from plugboard.process import Process, ProcessBuilder
-from plugboard.schemas import ConfigSpec
+from plugboard.schemas import ConfigSpec, validate_process
 from plugboard.tune import Tuner
 from plugboard.utils import add_sys_path, run_coro_sync
 
@@ -164,3 +164,31 @@ def diagram(
     diagram = MermaidDiagram.from_process(process)
     md = Markdown(f"```\n{diagram.diagram}\n```\n[Editable diagram]({diagram.url}) (external link)")
     print(md)
+
+
+@app.command()
+def validate(
+    config: Annotated[
+        Path,
+        typer.Argument(
+            exists=True,
+            file_okay=True,
+            dir_okay=False,
+            writable=False,
+            readable=True,
+            resolve_path=True,
+            help="Path to the YAML configuration file.",
+        ),
+    ],
+) -> None:
+    """Validate a Plugboard process configuration."""
+    config_spec = _read_yaml(config)
+    with add_sys_path(config.parent):
+        process = _build_process(config_spec)
+    errors = validate_process(process.dict())
+    if errors:
+        stderr.print("[red]Validation failed:[/red]")
+        for error in errors:
+            stderr.print(f"  • {error}")
+        raise typer.Exit(1)
+    print("[green]Validation passed[/green]")

tests/unit/test_cli.py

@@ -87,6 +87,23 @@ def test_cli_process_diagram() -> None:
     assert "flowchart" in result.stdout
 
 
+def test_cli_process_validate() -> None:
+    """Tests the process validate command."""
+    result = runner.invoke(app, ["process", "validate", "tests/data/minimal-process.yaml"])
+    # CLI must run without error for a valid config
+    assert result.exit_code == 0
+    assert "Validation passed" in result.stdout
+
+
+def test_cli_process_validate_invalid() -> None:
+    """Tests the process validate command with an invalid process."""
+    with patch("plugboard.cli.process.validate_process") as mock_validate:
+        mock_validate.return_value = ["Component 'x' has unconnected inputs: ['in_1']"]
+        result = runner.invoke(app, ["process", "validate", "tests/data/minimal-process.yaml"])
+        assert result.exit_code == 1
+        assert "Validation failed" in result.stderr
+
+
 def test_cli_server_discover(test_project_dir: Path) -> None:
     """Tests the server discover command."""
     with respx.mock: