Put the tree on the screen

The pager could only step between attempts, and stepping has nothing to say
about the thing the tree exists for: taking a path the story moved past and
keeping both. Every attempt has been its own node since SP4, so a chip is a
node now, and "take this path" forks — or simply switches, when the turn is
still the tip and its attempts are leaves nobody has built on.

Beside it, a Branches panel: every line the story has taken, with where each
left its parent and where it ends, and switch, rename and delete-with-confirm.
It sits with Plot/Memory/Scripts/Insights rather than inventing a new place to
put a rail. An unnamed branch is drawn from its fork depth, never from its
position in the list — a position shifts the moment a branch above it goes.

A spatial per-node map was considered and deliberately not built. At the size
this has to be verified against it is a second windowing problem, and it can be
added later without a new endpoint, since the rail and a map read the same
GET /branches. VariantOut grows an id because a fork is addressed by the node
being taken, not by an ordinal in a group that renumbers.

Driven by hand against the 602-action fixture, which found one bug that no test
could: the panel refreshed on actions.length, and a fork swaps a 60-action
window for another 60-action window, so it went on drawing a one-branch tree
while the story was already on the second. It keys off the counter adoptWindow
bumps now.

The scroll path was driven at the same time — three prepends of ~16,200 px, the
same node holding viewport top 792 to 787, never thrown to the end. That closes
the standing gap in this project. Console clean.

396 tests, build clean, no new lint.

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

plan/STATUS.md

@@ -78,41 +78,43 @@ needed; nothing requires reading a row of anyone's story.
 
 ## Pick up here
 
-**`plan/14-phase-story-tree.md`, SP7 — the frontend.** SP0–SP6 are done and green
-(**381 tests**); **nothing is deployed yet**. The tree is complete everywhere except the
-screen: a retry writes a sibling node, continuing from a discarded attempt forks a branch,
-and a backup carries the whole thing (`ai-dnd-adventure-v2`, with the v1 reader kept so
-existing bundles still import). What is left is the frontend (SP7) and dropping the legacy
-columns (SP8).
+**`plan/14-phase-story-tree.md`, SP8 — drop the legacy columns.** SP0–SP7 are done and
+green (**396 tests**); **nothing is deployed yet**. The tree is complete and reachable: a
+retry writes a sibling node, continuing from a discarded attempt forks a branch, a backup
+carries the whole thing (`ai-dnd-adventure-v2`, v1 reader kept), and as of SP7 there is a
+Branches panel that switches, renames and deletes. What is left of the phase is SP8.
 
-**SP7 is the release gate, and it is unscoped.** `VariantPager` comes out, a spatial tree
-view replaces it, and branch management — switch, rename, delete-with-confirm — is a hard
-dependency rather than a nice-to-have, because nothing auto-prunes and storage otherwise
-grows without limit. `api.js` gains `GET /branches`, `POST /branches/{id}/switch` and
-`POST /actions/{id}/fork`, which SP5 built for exactly this.
+**SP8 is gated on the tree being proven live, and it is not.** It drops `index`,
+`variants`, `variant_index`, `variant_count`, the two legacy cursors and the two
+`*_before` snapshots. `variant_count` / `variant_index` are the ones to watch: SP7's
+attempt chips still read both, so SP8 has to move the chips onto the sibling group before
+it drops them. Everything else has been unread since SP3/SP4.
 
-**Drive the 600-action `--keep` fixture in a browser by hand.** That is SP7's own verify
-line and the standing open gap in this project: the scroll path has never been driven by
-hand and has already hidden one bug. A vitest + jsdom harness covers the prepend
-arithmetic, but jsdom has no layout, so scroll position still needs eyes.
+**Deploy before SP8, not after.** SP7 is a natural release: the phase is usable from the
+screen for the first time, and dropping columns is the one step that cannot be rolled
+back by redeploying the previous build.
 
 **The schema is live in code but not on production.** When this ships, the deploy needs
 one `VACUUM FULL actions;` on the direct (non-`-pooler`) endpoint afterwards — SP1's
 migration rewrites every row and SP4's rewrites it three times more, so **two vacuums are
-owed and one run settles both**. SP3's, SP5's and SP6's changes need none (SP5 and SP6 add
-no migration at all). See the 144 MB lesson at the top of this file.
+owed and one run settles both**. SP3's, SP5's, SP6's and SP7's changes need none (SP5 and
+SP6 add no migration; SP7's migration 61 touches `branches`, a handful of rows per
+adventure). See the 144 MB lesson at the top of this file.
 
-Three things to carry into SP7:
+Three things to carry forward:
 
 - **The bundle is the one thing here a migration can never reach.** `app/bundle.py` owns
   both formats and nothing else knows either. Its rule — *carry what was chosen, never
-  what is derived* — is worth borrowing anywhere else state has to leave the database.
-- **`variant_count` and `variant_index` die with the pager.** SP4 left them as a
-  maintained cache of the sibling group's shape because the pager reads both for every
-  row of a page. They are dead the moment the tree view replaces it, and SP8 drops them.
-- **Nothing on the screen has ever seen a second branch.** Forking has no UI, which is
-  why the v1-export gap could be left open through SP5 — SP7 is the subphase that makes
-  a fork reachable, so it is also the one that makes every branch-shaped bug reachable.
+  what is derived* — decided SP7's naming too: `branches.name` is stored because a player
+  picked it, and an unnamed branch is drawn from its fork depth rather than given a
+  generated label that would go stale when a branch before it is deleted.
+- **A one-line subphase spec can hide a schema change.** SP7 read as "plus the UI for
+  switch/rename/delete"; two of those three had no backend at all. Check the routes exist
+  before believing a spec that says "frontend".
+- **The spatial node map was deliberately not built.** SP7 shipped a rail instead, on the
+  grounds that a per-node map is a second windowing problem at 600 nodes. It is a
+  standalone feature whenever it is wanted, and it needs no new endpoint — the rail and a
+  map both draw from `GET /branches`.
 
 And one known cost, not a bug: the two memory marks are a single pair on the adventure,
 so switching branches makes the mark on the branch being left unreadable from the new one
@@ -121,14 +123,46 @@ the safe direction. Per-branch cursors are the fix if it ever matters.
 
 **After any migration that rewrites `actions`:** one `VACUUM FULL actions;`. That is the
 lesson of the 144 MB above — a rewrite doubles the table and only a `VACUUM FULL` gives
-it back. Phase 14's migration rewrites every row.
+it back. SP8's migration rewrites every row.
 
-**There is a 600-action adventure to test against now** — `--keep`, below. The tree's
-frontend work lands on the same scroll path that has still never been driven by hand, so
-drive it before rewriting it.
+**The scroll gap is closed.** It was driven by hand on the 602-action `--keep` fixture
+during SP7 — three prepends, 5 px of drift, no throw-to-the-end. What is still missing is
+an automated version; see SP7's entry in `plan/14`.
 
 ---
 
+## What happened on 2026-08-18, part four — the tree, SP7
+
+The tree reached the screen. A Branches panel beside Plot/Memory/Scripts/Insights lists
+every line the story has taken and switches, renames or deletes one; under a retried turn
+the ‹ 2/3 › pager is gone, replaced by attempt chips and a **take this path** that forks
+when the story has already moved past. **396 tests green**, 15 new in
+`test_branch_management.py`. Branch `sp7-tree-ui`, migration 61, no vacuum owed by it.
+
+**Three mockups were built before a line of it was written**, because the spec was one
+paragraph and the choice was expensive: a per-node spatial map is a second windowing
+problem at 600 nodes. The rail won on the grounds that it does not delay the verification
+SP7 exists to do, and the map stays available as a later feature at no extra cost — both
+read the same `GET /branches`.
+
+**Two of the three operations SP7 "just needed UI for" did not exist.** `switch` did.
+`rename` had no column and no route; `delete` had no route. Migration 61 adds
+`branches.name`, and the two endpoints came with it.
+
+**One bug, and only a browser could have found it.** The panel refreshed on
+`actions.length`. Forking from the story column swaps a 60-action window for another
+60-action window, so the length never changes — the panel kept drawing a one-branch tree
+while the story was already being read on the second branch. The server was right the
+whole time and no test could see it. That is now three bugs on this frontend found by
+exercising it rather than by testing it, and the second found in a path that had just
+shipped.
+
+**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
+the bottom. PR #2's fix holds. Measuring note worth keeping — the fixture's prose repeats,
+so an anchor matched by *text* finds an older copy of the same sentence and reports a
+16,000 px jump that never happened. Hold the node.
+
 ## What happened on 2026-08-18, part three — the tree, SP6
 
 The backup learned the tree. `ai-dnd-adventure-v2` carries branches, the fork point each