Build a fixture that can witness what a tree changes

The stress fixture is sized from production and exists to weigh bytes, so it
leaves every column it does not weigh at its default. Checked against a freshly
built one, that is exactly the set phase 14 has to migrate: state_before and
world_state_before NULL on all 600 rows, no scenario and so no RPG layer, no
adventure scripts, both cursors 0, and a hundred retry histories whose two
attempts carry byte-identical text with variant_index pinned at 0.

That last one matters most. "Which attempt is live?" is the question SP4's
migration answers when it decides which sibling node becomes the head of a
turn, and against that fixture the question had no observable answer -- a
migration that picked wrong would have looked correct.

--rich fills in those columns and no others. A real RPG scenario read from the
seed data rather than invented, with a world state played forward so hp
declines and flags flip; monotonic per-action state snapshots, so a rollback
that does not happen reads as a wrong number instead of as nothing; a gold
script, story cards, non-zero cursors, pinned and forgotten memories; retry
attempts with distinct texts, counts of two and three, and a live attempt that
is often not the last written. Plus a second adventure, because a branch clause
that forgot its adventure still looks right on a database holding one.

The invariant SP4 reads -- text mirrors variants[variant_index] -- is asserted
at build time rather than assumed.

The plain fixture is untouched and re-measured unchanged at 1.8 kB, so the
egress ceilings stay comparable. All six shapes run clean on --rich, including
the turn path with the RPG layer and script pipeline now live. 283 tests pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Dvvqn9ZDR4ixeFPHNbww7

plan/14-phase-story-tree.md

@@ -178,6 +178,42 @@ A pre-migration (**schema 45**) fixture is needed too, built by a script rather
 committed as a binary — but its only consumer is the SP1 migration test, so it lands
 there.
 
+#### `--rich`: a correctness fixture beside the scale one
+
+The measuring fixture is sized from production and leaves every column it does not weigh
+at its default. Checked against a freshly built one, that is exactly the set of columns a
+tree has to migrate: `state_before`/`world_state_before` NULL on all 600 rows, no
+scenario and so no RPG layer, no adventure scripts, both cursors 0, and 100 retry
+histories whose two attempts carry **byte-identical text with `variant_index` always 0** —
+so "which attempt is live?", the one question SP4's migration answers, had no observable
+answer.
+
+`tools.stress_session --rich` fills in precisely those and nothing else:
+
+```
+cd backend
+.venv/Scripts/python.exe -m tools.stress_session --rich --actions 30 --memories 12
+```
+
+An RPG scenario built from the real seed schema with a world state played forward (hp
+100 → 71, flags flipping partway); per-action `state_before`/`world_state_before`
+snapshots that are monotonic, so a bad rollback reads as a wrong number rather than as
+nothing; a gold script on the adventure; story cards; non-zero memory and summary
+cursors with a real `story_summary`; pinned and forgotten memories; retry attempts with
+distinct texts, counts of 2 *and* 3, and a live attempt that is **often not the last one
+written**; and a second adventure, so "does this leak across adventures?" is answerable —
+a branch clause that forgot its adventure would still look correct on a database holding
+exactly one.
+
+It is a correctness fixture, so prefer it small: what it is for is variety per row, not
+rows. **Its byte figures are not comparable to a plain run** and it does not replace the
+scale fixture — the plain one still holds the egress ceilings, and was re-measured
+unchanged (1.8 kB, actions 1.7 kB) after `--rich` was added.
+
+The invariant `text == variants[variant_index]["text"]` holds on every retried row, and
+is asserted when the fixture is built. SP4's migration reads exactly that to decide which
+sibling becomes the head.
+
 ### SP1 — Schema and migration *(no behaviour change)*
 
 | File | Change |