feat(shell): initial decnet_behave_shell spec + tests

Shell-session behavioral observation registry layered on core.
SPDX: GPL-3.0-or-later (code) / CC-BY-SA-4.0 (attribution-recipes.md).

BEHAVE-SHELL/scripts/generate_schema.py

@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+"""Regenerate ``json/observation.schema.json`` from the Pydantic source of truth.
+
+Idempotent. CI can gate on ``git diff --quiet json/observation.schema.json`` after
+running this — a non-empty diff means someone changed the model without
+regenerating the JSON Schema artifact.
+"""
+
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+
+# Allow running this script directly without installing the package.
+_REPO_ROOT = Path(__file__).resolve().parent.parent
+if str(_REPO_ROOT) not in sys.path:
+    sys.path.insert(0, str(_REPO_ROOT))
+
+from decnet_behave_shell.spec.envelope import OBSERVATION_SCHEMA_VERSION, Observation  # noqa: E402
+
+
+def build_schema() -> dict:
+    schema = Observation.model_json_schema()
+    schema["$id"] = (
+        f"https://behave.local/schema/observation/v{OBSERVATION_SCHEMA_VERSION}.json"
+    )
+    schema["$schema"] = "https://json-schema.org/draft/2020-12/schema"
+    return schema
+
+
+def main() -> int:
+    schema = build_schema()
+    out = _REPO_ROOT / "json" / "observation.schema.json"
+    out.parent.mkdir(parents=True, exist_ok=True)
+    out.write_text(json.dumps(schema, indent=2, sort_keys=True) + "\n")
+    print(f"wrote {out}")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())