OTA: clean refusal report in ota_push.py; shorter signature error

The device refuses at the header and hangs up mid-transfer; the push
client now says so instead of crashing on the reset. The error fits a
Toast (47 characters).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

lib/ota/src/update_parser.cpp

@@ -30,7 +30,7 @@ void UpdateParser::parseHeader() {
     if (sigLen == 0 || sigLen > update::kMaxSignature) return fail("missing signature");
     uint8_t digest[32];
     Sha256::hash(h, update::kSignedBytes, digest);
-    if (!verifier_.verify(digest, h + 82, sigLen)) return fail("bad signature: not signed with this device's key");
+    if (!verifier_.verify(digest, h + 82, sigLen)) return fail("bad signature (wrong key)");
 
     downgrade_ = versionOlder(version_, installed_);
     if (!sink_.begin(imageSize_)) return fail("could not prepare the update slot");

scripts/ota_push.py

@@ -15,6 +15,18 @@ def main():
         sys.exit(__doc__)
     path, host = sys.argv[1:3]
     data = open(path, "rb").read()
+    try:
+        reply = push(data, host)
+    except (ConnectionResetError, BrokenPipeError):
+        # The device checks the header first and hangs up on a refused update mid-transfer.
+        print()
+        print("device: refused the update and closed the connection (the reason is on its screen)")
+        sys.exit(1)
+    print(f"device: {reply or '(no answer)'}")
+    sys.exit(0 if reply.startswith("OK") else 1)
+
+
+def push(data, host):
     with socket.create_connection((host, PORT), timeout=15) as s:
         s.settimeout(60)
         sent, last = 0, -1
@@ -44,9 +56,7 @@ def main():
                 break
             reply += part
     print()
-    reply = reply.decode(errors="replace").strip()
-    print(f"device: {reply or '(no answer)'}")
-    sys.exit(0 if reply.startswith("OK") else 1)
+    return reply.decode(errors="replace").strip()
 
 
 if __name__ == "__main__":