brief sprint C2: introduce billboard.Brief notification model + view_post marks-read on GET — TDD

Brief is the slide-down-banner record that connects an event (a Line freshly appended to a Post) to a user who needs to see it. It's the C3 attachment point for note-unlock + share-invite + future event sources; the banner JS (C3) reads the Brief shape to render kind-specific affordances. C2 lays the schema + the FYI-read contract; C3 hooks the senders.

Schema (billboard.Brief):
- owner FK→lyric.User (related_name='briefs') — required; whose attention this is for
- post  FK→billboard.Post (related_name='briefs') — required; where FYI navigates
- line  FK→billboard.Line (related_name='briefs', null=True) — the appended Line that triggered the Brief; nullable for share-invite-style flows where the Line write races behind the Brief
- is_unread BooleanField default=True — flips on view_post GET
- kind CharField (note_unlock | user_post | share_invite, default=user_post) — drives banner-side affordances
- title CharField (blank=True) — banner display title
- created_at DateTimeField (default=timezone.now) — Meta.ordering='-created_at'

view_post (the post-detail GET) now bulk-updates is_unread=False on every Brief where owner == request.user AND post == our_post AND is_unread=True. POST (the compose-a-new-Line path) intentionally does NOT mark read — the user is authoring, not reviewing.

Tests: BriefModelTest (7) covers defaults, kind choices include all three values, line nullability, owner+post requiredness, title field, __str__ shape. ViewPostMarksReadTest (5) covers the GET flips owner's unread Brief to read; doesn't flip other users' Briefs on the same post; doesn't flip Briefs on unrelated posts; idempotent for already-read; POST request does NOT mark read.

Auto migration billboard/0002_brief creates the table. 801-test IT regression green (789 + 12 new).

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Sonnet 4.6 <noreply@anthropic.com>

src/apps/billboard/views.py

@@ -9,7 +9,7 @@ from django.shortcuts import redirect, render
 
 from apps.applets.utils import applet_context, apply_applet_toggle
 from apps.billboard.forms import ExistingPostLineForm, LineForm
-from apps.billboard.models import Post
+from apps.billboard.models import Brief, Post
 from apps.dashboard.views import _PALETTE_DEFS
 from apps.drama.models import GameEvent, Note, ScrollPosition
 from apps.epic.models import Room
@@ -253,6 +253,14 @@ def view_post(request, post_id):
         if form.is_valid():
             form.save()
             return redirect(our_post)
+
+    # GET render is the FYI-read contract — flip every unread Brief on this
+    # post for the requesting user. POST (compose) is intentionally excluded
+    # because the user is authoring, not reviewing the new Line.
+    if request.user.is_authenticated:
+        Brief.objects.filter(
+            owner=request.user, post=our_post, is_unread=True,
+        ).update(is_unread=False)
     return render(request, "apps/billboard/post.html", {"post": our_post, "form": form})