Projects live at URLs, have owners, and are edited together live

A project is only ever at /p/<id>/<slug>; / is the index of the projects
you own or edit. Every project has an owner, who can name editors;
anyone with the link can view. Every edit saves itself, one request in
flight at a time, as a patch of the leaves that changed, and a websocket
(channels + daphne) carries presence and each committed write to
everyone else in the project. The first write to a leaf wins, and the
loser is told.

Undo is per person: a step undoes only if the leaves it touched still
hold what it left, so it never takes a collaborator's work with it.
Named snapshots replace saving, and restore as an ordinary write.

An empty symbol now survives the leaf round trip with `:nodes {}`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

clips/models.py

@@ -24,7 +24,9 @@ without parsing its leaves: which footage, which analysis, which blocks.
 """
 import uuid
 
+from django.conf import settings
 from django.db import models
+from django.utils import timezone
 
 
 class Blob(models.Model):
@@ -201,10 +203,19 @@ class Project(models.Model):
 
     `schema_version` identifies the stored document format. `seq` counts writes
     to this particular project; it is not a format version. Every write bumps
-    `seq`, and a client that sees `seq > local + 1` refetches once broadcasts exist.
+    `seq`, and a client that sees `seq > local + 1` refetches.
+
+    ANYONE WITH THE LINK CAN VIEW; the owner and the editors can write. Every
+    project has an owner.
     """
 
     id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    owner = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="projects",
+    )
+    editors = models.ManyToManyField(
+        settings.AUTH_USER_MODEL, blank=True, related_name="shared_projects",
+    )
     name = models.CharField(max_length=200, default="untitled")
     schema_version = models.PositiveIntegerField(default=2)
     seq = models.PositiveBigIntegerField(default=0)
@@ -219,10 +230,19 @@ class Project(models.Model):
         return f"{self.name} ({self.id})"
 
     def bump(self):
-        self.seq += 1
-        self.save(update_fields=["seq", "updated"])
+        """The next seq, taken with an UPDATE so that inside a transaction it is
+        also the write lock: two concurrent saves cannot both get the same one."""
+        Project.objects.filter(id=self.id).update(
+            seq=models.F("seq") + 1, updated=timezone.now()
+        )
+        self.refresh_from_db(fields=["seq", "updated"])
         return self.seq
 
+    def can_edit(self, user):
+        return user.is_authenticated and (
+            user.id == self.owner_id or self.editors.filter(id=user.id).exists()
+        )
+
 
 class Clip(models.Model):
     """Tier 1: the unit of work, and the thing leaf paths are scoped by.
@@ -271,6 +291,9 @@ class Leaf(models.Model):
     path = models.CharField(max_length=300)
     value = models.JSONField()
     version = models.PositiveBigIntegerField(default=1)
+    seq = models.PositiveBigIntegerField(
+        default=0, help_text="the project seq of the write that last changed it",
+    )
     updated = models.DateTimeField(auto_now=True)
 
     class Meta:
@@ -288,7 +311,9 @@ class Leaf(models.Model):
 
 
 class Revision(models.Model):
-    """Tier 1: a snapshot of the authored layer, with a user and a summary.
+    """Tier 1: a snapshot of the authored layer, with a user and a summary — a
+    named snapshot, which is how a person marks a version now that every edit
+    saves itself.
 
     ON AN EXPLICIT TRIGGER, not on every save. tl snapshots a small annotation
     layer; arthur's tier 1 will contain cel polygons, so a snapshot per save bloats
@@ -302,6 +327,9 @@ class Revision(models.Model):
     author = models.CharField(max_length=200, blank=True)
     summary = models.CharField(max_length=500, blank=True)
     document = models.JSONField(help_text="every leaf of the project, by path")
+    blocks = models.JSONField(
+        default=dict, help_text="each clip's tier-2 block keys, by cid, so a restore can name them",
+    )
     created = models.DateTimeField(auto_now_add=True)
 
     class Meta: