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Production logs from the last 24 h show 60 Failed to send message part to Matrix errors with M_BAD_JSON: event content can't be over 64 KiB, across 5 accounts and 30 distinct LINE messages. The encrypted send requests were ~75 KB, so the plaintext content was around 55 KB. These messages are never bridged. Since they're never saved, the recent-message backfill re-queues them on every restart and they fail again.

Cause: convertLineMessage has no size limit. A long LINE text keeps the full text in body, and when it has mentions or inline sticons, the same text is copied again into formatted_body, together with m.mentions.

Change: after conversion, each part whose JSON-encoded content is over 40,000 bytes goes through a cutoff modeled on mautrix-whatsapp (whatsapp#988/#995). Ghost mentions are dropped. If a formatted body is present, the plain-text fallback is shortened to 500 bytes. If it's still too large, the formatted body (then the body) is cut at a rune and tag boundary, with a "[long message cut off]" marker. The cut point is found by binary search on the encoded size, because quotes, <, > and & expand when escaped. A warn line logs the LINE content type and the encoded size before and after the cut.

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• Indent Review Agent · No bugs found in the long-message cutoff.

Full results

Indent Review Agent

• Summary: No bugs found in the long-message cutoff.
• Last ran on commit: 4e3be785
• Latest result

  {
    "summary": "No bugs found in the long-message cutoff.",
    "findings": []
  }

[highesttt]

Size check uses raw bytes, but the limit is on the JSON-encoded event. Quote-heavy HTML can pass the check and still be too large. Measure the encoded size instead