Answer the review, and keep the opening node's bank

Nine findings from a review of the phase-14 stack. The one about a retry
withdrawing a memory is not a bug — a memory anchored to a node describes that
node, and it goes when the node goes. The root is the exception, and it is the
only one: migration 62 parked every memory written before memories had
coordinates on depth 0, so withdrawing the opening node would retire a whole
bank nobody attached there. A memory with no source range covers no story and
now stays; a summary that genuinely ends there is still withdrawn.

The rest are repairs.

* The adventure list quoted whichever attempt was written last rather than the
  one the story tells, so switching back left the index disagreeing with the
  page.
* A v1 import gave a typed memory no depth, rebuilding the NULL the migration
  exists to remove — invisible until the imported adventure forked.
* The action cap counted a v1 file's turns, and a turn expands into a row per
  saved attempt, so a file inside the cap could write a multiple of it.
* Forking a live node on a borrowed ancestor promoted a sibling on a branch the
  caller never named. It is a branch switch, and now says so.
* Switching attempts left the state, status and memory panels reading the
  previous take: the story does not change length, so nothing keyed on its
  length noticed. Same class as the branch-switch bug this phase already fixed.
* A retry after switching back numbered the new attempt into the middle of the
  group instead of the end.
* The cursor backfill numbered every action in the table once per adventure;
  correlated to the adventure being updated, it is an index lookup instead.
* Renaming a branch answered own_actions=0.

And one behaviour change recorded rather than repaired: script-visible history
and actionCount no longer count blank-text rows. That is the right shape and
there is no reading compatible with both, so plan/14 says so.

409 tests.

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

backend/app/context/lineage.py

@@ -41,6 +41,14 @@ from .. import models
 # separately so a read never has to import the write half.
 NO_DEPTH = -1
 
+# The opening node of an adventure. Depth 0 exists only on the root branch — a
+# fork starts its own nodes after the depth it forked at — so this names one
+# node per adventure, not one per branch. It is also where migration 62 parked
+# every memory written before memories had coordinates, which is why the two
+# places that can retire a memory (`memorybank.forget_node`, and a v1 import
+# with no depth to read) both have to say something about it.
+ROOT_DEPTH = 0
+
 
 def entries_of(branch: models.Branch) -> list[tuple[int, int | None]]:
     """`branch.lineage` as (branch_id, max_depth) pairs, newest first.