Give every memory a node, and show only the ones on your path

A hand-written memory used to carry a NULL depth, described in the model as
"belongs to the adventure rather than to a path". That sounds harmless and
is not: a NULL is a coordinate no fork can cap, so a note typed on one line
followed the reader onto branches whose story it never described. It takes
the head now — the story you were reading when you wrote it — and obeys
exactly the rule a summarised memory obeys.

The unanchored escape clause in lineage.Path.clause existed for that single
case and is deleted rather than left unused. Its docstring argued that a
capped depth would drop a typed memory the moment its branch stopped being
the newest entry; anchoring answers the same worry better, because the
memory is not exempt from the path, it is on one.

The drawer now shows the path being read and nothing else, filtered by the
clause retrieval itself uses, so the bank you can see is the bank the model
can see. Nothing is stranded: a memory lives on a branch, switching to that
branch shows it, and deleting the branch deletes it. Pinning decides order,
the path decides existence.

Migration 62 lands existing NULL-depth memories at depth 0 of their branch
rather than at the tip. 0 is at or before every fork point, so every memory
stays visible from exactly the paths it is visible from today — nobody's
bank loses a row on deploy. The tip is the tidier-sounding choice and would
have emptied them out of every branch forked earlier than they were typed.

This supersedes the on_path flag and the "another branch" badge from
earlier today; anchoring makes them redundant, and they are removed.

Four tests changed because they asserted the old contract, not because
they broke. The one worth reading is the pair replacing
test_a_hand_written_memory_is_not_lost_at_the_first_fork: typed on shared
trunk it still survives a fork, and typed on ground the fork never
travelled it no longer follows you.

402 tests. Verified on tools/branch_fixture.py: each branch's drawer holds
its own memory and not the other's.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015H5qiyiR7gtFQaoDphHZ3g

backend/app/context/lineage.py

@@ -87,7 +87,6 @@ class Path:
         self,
         model=models.Action,
         count: int | None = None,
-        unanchored: bool = False,
     ):
         """The branch clause, over `model` (`Action` or `Memory`).
 
@@ -95,12 +94,12 @@ class Path:
         read. `None` is the whole lineage, which is what anything counting from
         the *oldest* end (a slice, a total) has to use.
 
-        `unanchored` keeps rows with no depth. Only memories ever have one: a
-        hand-written memory summarises no node, so it has a branch but no
-        depth, and a capped `depth <= n` would drop it the moment its branch
-        stopped being the newest entry — a memory vanishing at the first fork
-        after it was typed. An action with no depth is a pre-tree row that no
-        read should see, so actions never pass this.
+        Every row this reads has a depth. Memories used to be the exception —
+        a hand-written one had a branch and no depth, and needed an escape
+        clause here to survive being capped at a fork. SP7 anchors them at the
+        head instead (`tree.place_memory`), which is a better answer to the same
+        problem: the memory is not exempt from the path, it is *on* one. A row
+        with no depth is now a pre-tree leftover that no read should see.
 
         Actions also have to be *live* (SP4). A coordinate can hold several
         attempts at the same turn, and the story tells one of them; the losing
@@ -115,19 +114,16 @@ class Path:
         entries = self.entries if count is None else self.entries[:count]
         if not entries:
             return false()
-        on_path = or_(*[self._entry_clause(model, b, d, unanchored) for b, d in entries])
+        on_path = or_(*[self._entry_clause(model, b, d) for b, d in entries])
         if model is models.Action:
             return and_(on_path, models.Action.live.is_(True))
         return on_path
 
     @staticmethod
-    def _entry_clause(model, branch_id: int, max_depth: int | None, unanchored=False):
+    def _entry_clause(model, branch_id: int, max_depth: int | None):
         if max_depth is None:
             return model.branch_id == branch_id
-        within = model.depth <= max_depth
-        if unanchored:
-            within = or_(within, model.depth.is_(None))
-        return and_(model.branch_id == branch_id, within)
+        return and_(model.branch_id == branch_id, model.depth <= max_depth)
 
     # ------------------------------------------------------------- Python