Feature: Show unread status on threads you're participating in

[staticpayload]

Summary

Fixes #71

The Problem

In the threads view, it's hard to know which threads have unread comments. The regular room unread logic (based on timestamp) doesn't work for threads because you could have read everything in a recent thread but have unread comments in an older thread.

The Solution

Made the "Last reply [timestamp]" bold and black when there's unread activity in a thread for participating users.

Implementation

1. Thread Model (app/models/rooms/thread.rb)

Added two methods:

participating?(user) - Returns true if user:

• Created the parent message (original message being threaded)
• Created the thread (first commenter)
• Has a visible membership (not "invisible" involvement)
• Was mentioned (which gives them a membership)

unread_for_participating?(user) - Checks if the user's membership has unread messages based on unread_at timestamp.

2. Threads View (app/views/messages/_threads.html.erb)

<% is_participating = thread.participating?(Current.user) %>
<% has_unread = is_participating && thread.unread_for_participating?(Current.user) %>

<% timestamp_class = has_unread ? "txt-primary fw-800" : "txt-muted" %>
<span class="<%= timestamp_class %>">Last reply <%= local_datetime_tag ... %></span>

3. Utility CSS (app/assets/stylesheets/application/utilities.css)

Added .fw-800 { font-weight: 800; } to match sidebar bold styling.

Visual Result

State	Appearance
Unread (participating)	Last reply 2 hours ago (bold, black)
Read (participating)	Last reply 2 hours ago (muted, gray)
Non-participating	Last reply 2 hours ago (muted, gray)

Testing

• Participating user sees bold timestamp for unread threads
• Participating user sees muted timestamp for read threads
• Non-participating user always sees muted timestamp
• Participation correctly detected (parent creator, thread creator, membership)

AI Disclosure

This PR was developed with AI assistance:

• Opus 4.5 for planning and code review
• GLM 4.7 for code execution
• GitHub PR review for quality assurance