Give every new guest an adventure that is already played

An empty account gives a visitor nothing to read, and the daily demo turns are
limited, so learning what the app does cost one of them. `app/starter.py` now
copies a shipped export bundle into each new guest at the point the row is
created. The bundle is two exchanges of the Pokemon demo, which ends on a
knockout and shows an applied change, a refused one, and a milestone.

The guest row is committed before the copy is attempted, so a failure there
still leaves them with an account, and the copy runs inside a savepoint.

The row building that `POST /adventures/import` did inline moved into
`bundle.materialize`, which both callers use. The rate and size checks stayed
in the endpoint: the starter writes a file the server ships, so it has no
untrusted list to cap.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PacdRuPXSkQQy4ZYdH32hF

backend/app/routers/adventures.py

@@ -1824,56 +1824,7 @@ def import_adventure(
         branches=story["branches"],
     )
 
-    # A raw-dict import bypasses the schemas, so truncate strings bound for
-    # VARCHAR columns. Postgres enforces the widths. See `schemas.py`.
-    adventure = models.Adventure(
-        user_id=user.id,
-        title=str(payload.get("title") or "Imported Adventure")[:schemas.NAME_MAX],
-        memory=str(payload.get("memory") or ""),
-        authors_note=str(payload.get("authorsNote") or ""),
-        ai_instructions=str(payload.get("aiInstructions") or ""),
-        story_summary=str(payload.get("storySummary") or ""),
-        script_state=payload.get("scriptState") or {},
-        world_state=payload.get("worldState") or {},
-        auto_summarize=bool(payload.get("autoSummarize", False)),
-        memory_bank_enabled=bool(payload.get("memoryBankEnabled", False)),
-    )
-    db.add(adventure)
-    db.flush()
-
-    for card in payload.get("storyCards") or []:
-        if isinstance(card, dict):
-            db.add(models.StoryCard(
-                adventure_id=adventure.id,
-                type=str(card.get("type") or "")[:schemas.CARD_TYPE_MAX],
-                name=str(card.get("name") or "")[:schemas.NAME_MAX],
-                keys=str(card.get("keys") or ""),
-                entry=str(card.get("entry") or ""),
-                notes=str(card.get("notes") or ""),
-            ))
-
-    for i, s in enumerate(payload.get("scripts") or []):
-        if isinstance(s, dict):
-            db.add(models.AdventureScript(
-                adventure_id=adventure.id,
-                position=int(s.get("position", i)),
-                enabled=bool(s.get("enabled", True)),
-                name=str(s.get("name") or "Imported Script")[:schemas.NAME_MAX],
-                description=str(s.get("description") or ""),
-                library_js=str(s.get("library") or ""),
-                input_js=str(s.get("input") or ""),
-                context_js=str(s.get("context") or ""),
-                output_js=str(s.get("output") or ""),
-            ))
-
-    bundle.write(db, adventure, story)
-
-    # The anchors and the legacy counts describe the same boundary in two
-    # coordinate systems. Aligning them requires the actions to be queryable,
-    # and this is the only point where both exist.
-    db.flush()
-    db.expire(adventure, ["actions"])
-    bundle.settle(db, adventure, story)
+    adventure = bundle.materialize(db, payload, story, user.id)
 
     db.commit()
     db.refresh(adventure)