Lazily import jsonschema in contract helpers

Author: mdheller

src/agent_machine/contracts.py

@@ -6,17 +6,20 @@
 from pathlib import Path
 from typing import Any
 
-try:
-    import jsonschema
-    from jsonschema.validators import validator_for
-except ImportError as exc:  # pragma: no cover - exercised in environments without deps
-    raise RuntimeError(
-        "Missing dependency: jsonschema. Install with `python -m pip install -r requirements-dev.txt`."
-    ) from exc
-
 from agent_machine.paths import repo_root_from_file
 
 
+def jsonschema_validator_for() -> Any:
+    """Import jsonschema lazily so non-validation commands stay dependency-light."""
+    try:
+        from jsonschema.validators import validator_for
+    except ImportError as exc:  # pragma: no cover - exercised in environments without deps
+        raise RuntimeError(
+            "Missing dependency: jsonschema. Install with `python -m pip install -r requirements-dev.txt`."
+        ) from exc
+    return validator_for
+
+
 def repo_root() -> Path:
     """Return the repository root for the current checkout/package context."""
     return repo_root_from_file(__file__)
@@ -59,15 +62,15 @@ def iter_json_files(directory: Path) -> list[Path]:
 
 def check_schema(path: Path) -> dict[str, Any]:
     schema = load_json(path)
-    validator_cls = validator_for(schema)
+    validator_cls = jsonschema_validator_for()(schema)
     validator_cls.check_schema(schema)
     return schema
 
 
 def validate_instance(instance_path: Path, schema_path: Path) -> None:
     schema = load_json(schema_path)
     instance = load_json(instance_path)
-    validator_cls = validator_for(schema)
+    validator_cls = jsonschema_validator_for()(schema)
     validator_cls.check_schema(schema)
     validator = validator_cls(schema)
     errors = sorted(validator.iter_errors(instance), key=lambda err: list(err.path))