reply API throws "guid.startsWith" on text containing literal mc-prefix-double-underscore patterns

[rancur]

Summary

The BlueBubbles server's /api/v1/message text endpoint throws undefined is not an object (evaluating 'guid.startsWith') when the message text contains certain double-underscore patterns (e.g. an identifier-shaped token with __ separators). Short messages and messages without the pattern send successfully.

Repro

1. POST /api/v1/message/text with a body whose message field contains a literal identifier of the shape prefix__middle__suffix (two underscores around the middle segment).
2. Server returns error: undefined is not an object (evaluating 'guid.startsWith').
3. Same body with single-underscore (prefix_middle_suffix) sends successfully.

Expected

Message sends as plain text — double underscores have no special meaning in iMessage and should be treated as literal characters in the message body.

Actual

Error is thrown server-side; the message is dropped silently from the user's perspective (no delivery, no client-side error indication beyond the API response).

Workaround

On the client side, replace __ with _ or another separator (e.g. /) in outgoing text before sending.

Likely cause

The text appears to be parsed as if it contained an identifier or reference pattern; a downstream code path then dereferences a guid that comes back undefined when the pattern doesn't resolve to a real object. The guid.startsWith call site is the symptom — the upstream parse/lookup is the bug.

Environment

• BlueBubbles server: latest (please confirm by version checked at the time of triage)
• macOS host: 26.2 (build 25C56)
• Client: REST API consumer over HTTP

Happy to provide a more precise server version on request — wanted to file the repro while it was fresh.