diff --git a/scripts/build.py b/scripts/build.py
index 6763520..e2fb518 100644
--- a/scripts/build.py
+++ b/scripts/build.py
@@ -212,11 +212,41 @@ def compress(src,out):
     subprocess.run(['zstd','-q','-f','-T1','-19',str(src),'-o',str(out)],check=True)
 
 
+def build_signature(source_revs, schema_path):
+    """Fingerprint inputs that can change the generated data, not wall-clock time."""
+    scripts_dir = Path(__file__).resolve().parent
+    h = hashlib.sha256()
+    # Include every Python importer/helper alongside the builder, as well as SQL schema.
+    inputs = sorted(scripts_dir.glob('*.py'))
+    inputs.append(schema_path.resolve())
+    for path in inputs:
+        if not path.is_file():
+            raise RuntimeError(f'Missing build input: {path}')
+        logical_name = 'schema.sql' if path == schema_path.resolve() else f'scripts/{path.name}'
+        h.update(logical_name.encode('utf-8') + b'\x00')
+        h.update(hashlib.sha256(path.read_bytes()).digest())
+    h.update(canonical(source_revs).encode('utf-8'))
+    return h.hexdigest()
+
+
+def existing_release_ok(output, manifest):
+    """Only skip if current release artifacts exist and match recorded hash."""
+    dbfile, packed = output / 'master.db', output / 'master.db.zst'
+    if not dbfile.is_file() or not packed.is_file() or not manifest.get('master_sha256'):
+        return False
+    h = hashlib.sha256()
+    with packed.open('rb') as stream:
+        for block in iter(lambda: stream.read(1024 * 1024), b''):
+            h.update(block)
+    return h.hexdigest() == manifest['master_sha256']
+
+
 def main():
     ap=argparse.ArgumentParser()
     ap.add_argument('--sources',type=Path,required=True)
     ap.add_argument('--output',type=Path,required=True)
     ap.add_argument('--schema',type=Path,default=Path(__file__).resolve().parents[1]/'sql/schema.sql')
+    ap.add_argument('--force', action='store_true', help='Force rebuild even when input signature is unchanged')
     args=ap.parse_args()
     args.output.mkdir(parents=True,exist_ok=True)
     active=[(p.name,p) for p in sorted(args.sources.iterdir()) if p.is_dir() and (p/'.git').exists()]
@@ -227,7 +257,22 @@ def main():
         if name not in [n for n,_ in active]:
             raise SystemExit(f'Missing core source: {name}')
     source_revs={name:get_git_revision(path) for name,path in active}
-    old_db=args.output/'master.db'
+    signature = build_signature(source_revs, args.schema)
+    manifest_path = args.output / 'manifest.json'
+    previous_manifest = None
+    if manifest_path.is_file():
+        try:
+            previous_manifest = json.loads(manifest_path.read_text(encoding='utf-8'))
+        except (ValueError, UnicodeError) as exc:
+            raise RuntimeError(f'Invalid existing manifest, refusing to overwrite: {exc}') from exc
+    if (not args.force and previous_manifest
+            and previous_manifest.get('build_signature') == signature
+            and existing_release_ok(args.output, previous_manifest)):
+        print(f"NO_CHANGES: version={previous_manifest['version']} inputs unchanged; master and delta retained", flush=True)
+        return
+    if not args.force and previous_manifest and previous_manifest.get('build_signature') == signature:
+        print('WARNING: unchanged inputs but missing/invalid release artifact; rebuilding', flush=True)
+    old_db=args.output/'master.db' 
     with tempfile.TemporaryDirectory(prefix='vuln-build-',dir=args.output) as td:
         tmp=Path(td); new=tmp/'master.db'; db=sqlite3.connect(new)
         db.executescript(args.schema.read_text(encoding='utf-8'))
@@ -253,6 +298,7 @@ def main():
         assert db.execute('PRAGMA integrity_check').fetchone()[0]=='ok'
         db.close()
         manifest={'version':version,'schema_version':1,'previous':old_version,'source_commits':source_revs,
+                  'build_signature':signature,
                   'indexed_documents':stats,'format':'sqlite+zstd','delta_format':'jsonl+zstd',
                   'note':'Only CVE/NVD/OSV indexed in v1; no complete version-matching engine'}
         compress(new,tmp/'master.db.zst')