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/models.py

@@ -2,6 +2,7 @@ import uuid
 
 from django.db import models
 from django.urls import reverse
+from django.utils import timezone
 
 
 class Post(models.Model):
@@ -38,3 +39,64 @@ class Line(models.Model):
 
     def __str__(self):
         return self.text
+
+
+class Brief(models.Model):
+    """A slide-down notification record. Owner = whose attention; post = where
+    FYI navigates (and where mark-read happens on GET); line = the specific
+    appended Line that triggered it (so the banner can surface its text).
+
+    `kind` discriminates the affordances the banner renders. NOTE_UNLOCK
+    Briefs get a clickable square that jumps direct to my_notes.html;
+    SHARE_INVITE Briefs render the invitation copy; USER_POST is the legacy
+    user-authored compose flow.
+
+    Magic-link confirmation + invalid-link banners use the same Gaussian-glass
+    visual styling but ride no Brief row (transient one-shot).
+    """
+    KIND_NOTE_UNLOCK   = "note_unlock"
+    KIND_USER_POST     = "user_post"
+    KIND_SHARE_INVITE  = "share_invite"
+    KIND_CHOICES = [
+        (KIND_NOTE_UNLOCK,  "Note unlock"),
+        (KIND_USER_POST,    "User post"),
+        (KIND_SHARE_INVITE, "Share invite"),
+    ]
+
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    owner = models.ForeignKey(
+        "lyric.User",
+        related_name="briefs",
+        on_delete=models.CASCADE,
+    )
+    post = models.ForeignKey(
+        Post,
+        related_name="briefs",
+        on_delete=models.CASCADE,
+    )
+    # Line is nullable because a share_invite-style Brief can race ahead of its
+    # async-appended Line write; the post FK alone is enough to navigate.
+    line = models.ForeignKey(
+        Line,
+        related_name="briefs",
+        on_delete=models.CASCADE,
+        null=True,
+        blank=True,
+    )
+    is_unread = models.BooleanField(default=True)
+    kind = models.CharField(
+        max_length=32,
+        choices=KIND_CHOICES,
+        default=KIND_USER_POST,
+    )
+    title = models.CharField(max_length=255, blank=True)
+    created_at = models.DateTimeField(default=timezone.now)
+
+    class Meta:
+        ordering = ["-created_at"]
+
+    def __str__(self):
+        return (
+            f"Brief({self.kind}, {self.owner.email}, "
+            f"unread={self.is_unread})"
+        )