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

plan/STATUS.md

@@ -166,15 +166,25 @@ That is now four bugs on this frontend found by exercising it rather than by tes
 two of them in paths that had just shipped. The pattern is not subtle any more: **this
 frontend has no test runner, so anything not driven by hand is unverified.**
 
-**The memory drawer now says what the model can see.** Retrieval has been path-scoped
-since SP3, but the drawer listed every memory alike — so on a fork you read "Fell down
-the cellar stairs" and reasonably concluded the AI knew it, when that memory is never
-retrieved on that branch. Rows off the current path are set back and labelled *another
-branch*, still fully editable and deletable. The flag comes from the predicate retrieval
-itself uses, so the badge cannot drift from the behaviour. Note the asymmetry before
-changing it: a fork borrows its ancestors, so a parent's memory *is* on the fork's path;
-the reverse never is. And a hand-written memory has no depth, so it survives the fork cap
-by design — see SP7's entry in `plan/14` for the one case where that surprises.
+**A memory is now attached to a node, always — migration 62.** Hand-written ones used to
+carry a NULL depth ("belongs to the adventure, not to a path"), which is a coordinate no
+fork can cap, so a note typed on one line followed you onto branches whose story it never
+described. They anchor at the head now, and the `unanchored` escape clause in
+`lineage.Path.clause` is deleted rather than left to rot.
+
+**And the drawer shows only the path being read**, filtered by the same clause retrieval
+uses: the bank you can see is the bank the model can see. Nothing is stranded — a memory
+lives on a branch, switching to it shows the memory, 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**, which is
+at or before every fork point, so nobody's bank loses a row on deploy. The tip would have
+been the tidier-sounding choice and would have emptied them out of every branch forked
+earlier than they were typed.
+
+An earlier pass this session shipped the other design — adventure-wide list, `on_path`
+flag, *another branch* badge. Anchoring made it redundant and it was removed. Worth
+knowing if the phrase turns up in an older commit message.
 
 **The scroll path is finally driven.** 602-action fixture, three prepends of ~16,200 px
 each: the same DOM node held viewport top 792 → 787, and the view stayed 48,174 px from