[rigel-mintaka]

What does this PR do?

A Discord forum send that carries media now names the new post from its caption. Before, the media path sent the text as caption with an empty message, so the post was titled "New Post". This happened to Nemo's #health check-in on 2026-11-08.

Related Issue

RIG-8690 (Linear).

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• plugins/platforms/discord/adapter.py _standalone_send: the forum branch derives the thread name from caption or message, the same text it already uses for the starter content.
• tests/tools/test_discord_send_message_caption.py: forum media send with a caption, and with message text only, both name the post from the first line.

How to Test

1. The new caption case failed before the fix ('New Post' == 'Health check-in: Sun Nov 8') and passes after.
2. 61 Discord test files at -j 2: 570 passed, 2 skipped, 0 failed. Ruff clean.

Checklist

Code

• Conventional Commits
• Only this fix
• Regression test fails before and passes after

Documentation & Housekeeping

• Documentation: N/A

For New Skills

N/A.

Screenshots / Logs

N/A.

Refs RIG-8690

Co-authored-by: Matt Wilkinson matt@rigel.build

[linear-code]

RIG-8690

[rigel-mintaka]

Review (single pass, trivial diff): one-line fix plus regression test; the forum starter content already used caption or message, the thread name now matches it. Other _derive_forum_thread_name calls have no caption in scope. All-clear on 4cc681a2.

[rigel-mintaka]

Submit rebased onto rigel-release; same two-file diff. All-clear on d6a676a, CI SUCCESS.