diff --git a/.github/workflows/sourceos-contract-sync.yml b/.github/workflows/sourceos-contract-sync.yml
new file mode 100644
index 0000000..ecfbb58
--- /dev/null
+++ b/.github/workflows/sourceos-contract-sync.yml
@@ -0,0 +1,33 @@
+name: SourceOS Contract Sync
+
+on:
+  pull_request:
+    branches: ["main"]
+    paths:
+      - "src/agent_term/contracts/sourceos/generated/sourceos_interaction_event.py"
+      - "tools/sync_sourceos_contracts.py"
+      - ".github/workflows/sourceos-contract-sync.yml"
+  push:
+    branches: ["main", "work/sourceos-contract-sync"]
+    paths:
+      - "src/agent_term/contracts/sourceos/generated/sourceos_interaction_event.py"
+      - "tools/sync_sourceos_contracts.py"
+      - ".github/workflows/sourceos-contract-sync.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  check-sourceos-contract-sync:
+    name: Check SourceOS contract sync
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Check vendored SourceOS contracts
+        run: python tools/sync_sourceos_contracts.py --check
diff --git a/tools/sync_sourceos_contracts.py b/tools/sync_sourceos_contracts.py
new file mode 100644
index 0000000..f550fb6
--- /dev/null
+++ b/tools/sync_sourceos_contracts.py
@@ -0,0 +1,71 @@
+#!/usr/bin/env python3
+"""Sync vendored SourceOS contract artifacts from sourceos-spec."""
+
+from __future__ import annotations
+
+import argparse
+import sys
+import urllib.request
+from pathlib import Path
+
+SOURCEOS_SPEC_REF = "c7f8c2d9e42a56e1127c2f9b85649cbea0f0a9fa"
+SOURCE_PATH = "generated/python/sourceos_interaction_event.py"
+TARGET_PATH = Path("src/agent_term/contracts/sourceos/generated/sourceos_interaction_event.py")
+SOURCE_URL = (
+    "https://raw.githubusercontent.com/SourceOS-Linux/sourceos-spec/"
+    f"{SOURCEOS_SPEC_REF}/{SOURCE_PATH}"
+)
+HEADER = (
+    "# Generated from schemas/SourceOSInteractionEvent.json.\n"
+    f"# Do not edit by hand. Source: SourceOS-Linux/sourceos-spec {SOURCE_PATH}\n"
+    f"# Pinned sourceos-spec commit: {SOURCEOS_SPEC_REF}\n\n"
+)
+UPSTREAM_HEADER = (
+    "# Generated from schemas/SourceOSInteractionEvent.json.\n"
+    "# Do not edit by hand. Run: python tools/generate_sourceos_interaction_types.py\n\n"
+)
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--check", action="store_true", help="Fail if vendored contracts are stale.")
+    parser.add_argument("--write", action="store_true", help="Write vendored contracts from upstream.")
+    args = parser.parse_args(argv)
+
+    if args.check == args.write:
+        parser.error("choose exactly one of --check or --write")
+
+    expected = normalize(fetch_text(SOURCE_URL))
+
+    if args.write:
+        TARGET_PATH.parent.mkdir(parents=True, exist_ok=True)
+        TARGET_PATH.write_text(expected, encoding="utf-8")
+        print(f"synced {TARGET_PATH} from {SOURCE_URL}")
+        return 0
+
+    if not TARGET_PATH.exists():
+        print(f"missing vendored contract: {TARGET_PATH}", file=sys.stderr)
+        return 1
+
+    current = TARGET_PATH.read_text(encoding="utf-8")
+    if current != expected:
+        print(f"vendored SourceOS contract is stale: {TARGET_PATH}", file=sys.stderr)
+        print(f"source: {SOURCE_URL}", file=sys.stderr)
+        print("run: python tools/sync_sourceos_contracts.py --write", file=sys.stderr)
+        return 1
+
+    print(f"SourceOS contracts are current at {SOURCEOS_SPEC_REF}")
+    return 0
+
+
+def fetch_text(url: str) -> str:
+    with urllib.request.urlopen(url, timeout=30) as response:  # noqa: S310 - pinned public source file
+        return response.read().decode("utf-8")
+
+
+def normalize(content: str) -> str:
+    return HEADER + content.removeprefix(UPSTREAM_HEADER)
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())