DisplaySyncManager had no tests at all — it appeared in the suite only as
a MagicMock() stand-in, so none of its framing, handshake, or socket
handling was ever exercised. Writing that coverage surfaced three bugs.
Both receive loops caught the generic Exception and immediately retried.
A socket left in a bad state raises on every call, so the thread spun at
100% CPU logging the same line; the reverted-code run of the new
regression test takes 24 seconds where the fixed one takes 0.2. Both now
back off briefly before retrying.
The follower dispatched on `data[:8] == _RAW_MAGIC or len(data) > 512`.
That size threshold is not part of either wire format: a control message
over 512 bytes — a hello_ack carrying a long incompatibility error, for
instance — went to the image decoder and was dropped, and a raw frame
under 512 bytes went to the JSON parser. Both formats are already
self-describing, so dispatch on the magic prefix and treat a JSON parse
failure as the legacy unmarked PNG, with the shared frame bookkeeping
factored into _handle_received_frame().
_oversized_frame_warned was created on first use through
getattr(self, ..., False) rather than in __init__, alone among the
instance attributes.
75 tests: role parsing, the hello compatibility matrix, watchdog
timeouts, both receive loops, the TCP image server's length and
dimension caps and decompression-bomb guard, status shape per role, and
one end-to-end loopback handshake so the wire format is exercised for
real and not only against mocks.
Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NohXi78cwsAKtN1sCfxjUh
