ORIGINAL INCIDENT:
Discord forum descriptions (the topic field on ForumChannel) were invisible
to the agent. When a user set project instructions in a forum's description
(e.g. tool-evaluations), threads created in that forum had no Channel Topic
in their session context. Discovered while evaluating per-forum auto-context
injection for web-tap-terminal development threads.
ISSUE IN THE CODE:
In gateway/platforms/discord.py, all three session entry points
(_handle_message, _build_slash_event, _dispatch_thread_session) read
chat_topic via getattr(channel, 'topic', None). Discord Thread objects
don't carry a topic — only the parent ForumChannel does. So chat_topic
was always None for forum threads, and the Channel Topic line was never
injected into build_session_context_prompt output. The infrastructure to
handle this was already in place — _is_forum_parent() detects forum
channels, _format_thread_chat_name() traverses to the parent, and
build_session_context_prompt() renders Channel Topic when present. The
forum parent was being identified; its topic just wasn't being read.
HOW THIS COMMIT FIXES IT:
Adds _get_effective_topic(channel, is_thread) helper that reads
channel.topic first, then falls back to the parent forum's topic when
the channel is a thread inside a forum. All three session entry points
now call this helper instead of inlining getattr(channel, 'topic', None).
Existing tests pass unchanged.
Co-authored-by: dhabibi <9087935+dhabibi@users.noreply.github.com>
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