M5: genre-neutral authoritative narrative state, with review corrections

Replaces AI-DnD's RPG relative-delta world state with the genre-neutral typed
narrative state of ADR 010: explicit, absolute, allowlisted events proposed by
the model, validated by the application, applied to one authoritative document,
and snapshotted per position so restore stays a row read.

This commit includes the corrective pass that followed the independent review
in planning/reports/M5-IMPLEMENTATION-REPORT.md. The invariant it exists to
hold is:

    visible active transcript position == stored head == authoritative state

Narrator editing (D10, STORY-BRANCH-SEMANTICS §§14-15)

  A narrator edit no longer rewrites a row. It returns to the state before the
  turn, takes the reader's exact text as the accepted narration, re-derives the
  state that text implies, and becomes a new active continuation — while the
  original narration keeps its words, its live flag and its whole future as
  retained history. At the tip the correction is another take; with story below
  it, it forks. No new history machinery: this is the existing fork/take/head
  path with the reader's text in place of a generated reply. The §14A refusal
  is therefore gone for narrator turns, and remains only for player input.

Pre-M5 positions

  Migration 88 backfills the empty narrative document onto every action written
  before M5, and a missing snapshot now restores the empty document instead of
  leaving the previous position's state standing. Restoring to an old Save
  Point no longer leaves a later position's entities and facts on screen.

Narrator context

  Replayed history carries prose only; the machine-readable block is no longer
  reconstructed into past turns, where it contradicted the authoritative state
  in the same prompt. A fact withdrawn by a manual correction is now named as
  no longer true, with the reader's reason, rather than silently dropped.

Also

  - state_changes joins the action-list bulk read, removing one query per row.
  - Extraction takes only the application's own protocol payload: an ordinary
    ```json or ```python block in a story survives, and a mangled proposal
    still does not reach the reader.

Planning: ADR 013 records the authoritative document shape; §§14-15/14A, D10,
C04 and BUILD-MILESTONES are updated to describe what exists. Debt is recorded
against M8 (scenario editor UX) and M9 (export of the audit trail).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PWU4gTfLYY6Qq9U7aa9Qw2

backend/app/narrative/store.py

@@ -0,0 +1,195 @@
+"""M5: writing accepted state, atomically with the turn that caused it.
+
+This is the only module in the package that touches the database, and the only
+place authoritative narrative state is written.
+
+## The atomicity rule (L01)
+
+Everything a turn establishes goes in one transaction: the narration, the head
+movement, the accepted events, the resulting snapshot, and the provenance. This
+function *adds* to the caller's session and never commits — the turn engine's
+single `db.commit()` remains the one commit point, so a failure anywhere before
+it rolls the whole turn back rather than leaving narration accepted with half its
+state written.
+
+That ordering is deliberate and load-bearing. `L01` forbids a head position that
+implies an accepted reply whose state commit did not complete, and the cheapest
+way to guarantee that is to never have two commits to get out of step.
+
+## What is not here
+
+No reconstruction. Nothing in this module reads `state_events` to rebuild a
+document — the snapshot on the node is the restore path
+(`TECHNICAL-DESIGN.md` §10.4). The events are the audit trail, and an audit
+trail that the system depends on for correctness stops being an audit trail and
+becomes a replay engine.
+"""
+
+from __future__ import annotations
+
+import copy
+
+from sqlalchemy.orm import Session
+
+from .. import models
+from . import apply as apply_module
+from . import model
+
+
+def current(adventure: models.Adventure) -> dict:
+    """The campaign's authoritative state right now, as a document.
+
+    Normalised on the way out, so every caller gets the same shape whatever a
+    hand-edited row or an older snapshot contains.
+    """
+    return model.normalize(adventure.narrative_state)
+
+
+def set_current(adventure: models.Adventure, state: dict) -> None:
+    adventure.narrative_state = model.normalize(state)
+
+
+def canon_of(adventure: models.Adventure) -> dict:
+    """The campaign's own rules, which outrank anything a narration proposes.
+
+    Configuration rather than code (C01, J03): the campaign says what it forbids,
+    and `validate` enforces it without knowing what the rule means.
+    """
+    canon = adventure.campaign_canon
+    return canon if isinstance(canon, dict) else {}
+
+
+def record(
+    db: Session,
+    adventure: models.Adventure,
+    *,
+    review,
+    raw_block: str = "",
+    parsed=None,
+    action: models.Action | None = None,
+    branch_id: int | None = None,
+    depth: int | None = None,
+    model_name: str = "",
+    source: str = "accepted_story",
+) -> tuple[dict, models.StateProposal]:
+    """Applies a reviewed proposal and records everything about it.
+
+    Returns `(new_state, proposal_row)`. The caller is responsible for putting
+    the new state where it belongs — on the campaign, and on the node's snapshot
+    — because only the caller knows whether this is a turn, a retry or a
+    correction.
+
+    Nothing is committed here. See the module docstring.
+    """
+    before = current(adventure)
+    after = apply_module.apply_events(
+        before, review.accepted, branch_id=branch_id, depth=depth, source=source
+    )
+
+    proposal = models.StateProposal(
+        adventure_id=adventure.id,
+        action_id=action.id if action is not None else None,
+        branch_id=branch_id,
+        depth=depth,
+        model_name=model_name or "",
+        source=source,
+        status=review.status,
+        raw_output=raw_block or "",
+        detail={
+            "parsed": parsed,
+            "accepted": review.accepted,
+            "rejected": [r.as_dict() for r in review.rejected],
+        },
+    )
+    db.add(proposal)
+    # The proposal needs an id before its events can point at it, and the
+    # session does not autoflush. This is a flush, not a commit: still one
+    # transaction, still all-or-nothing.
+    db.flush()
+
+    for sequence, event in enumerate(review.accepted):
+        db.add(models.StateEvent(
+            adventure_id=adventure.id,
+            proposal_id=proposal.id,
+            action_id=action.id if action is not None else None,
+            branch_id=branch_id,
+            depth=depth,
+            sequence=sequence,
+            event_type=event.get("type", ""),
+            payload=copy.deepcopy(event),
+            before=_before_value(before, event),
+            source=source,
+        ))
+    return after, proposal
+
+
+def _before_value(state: dict, event: dict) -> dict | None:
+    """What the value this event changes was, immediately beforehand.
+
+    Recorded per event so §8's "what was the previous value" is answerable
+    without replaying anything. Only the slice the event touches: a whole
+    document per event would duplicate the snapshot for no extra answer.
+    """
+    kind = event.get("type")
+    if kind in ("set_entity_status", "set_entity_attribute",
+                "set_entity_conditions", "set_current_location"):
+        entity = model.entity(state, event.get("entity", ""))
+        if entity is None:
+            return None
+        if kind == "set_entity_status":
+            return {"status": entity.get("status")}
+        if kind == "set_entity_attribute":
+            attribute = event.get("attribute")
+            return {"attribute": attribute,
+                    "value": (entity.get("attributes") or {}).get(attribute)}
+        if kind == "set_entity_conditions":
+            return {"conditions": list(entity.get("conditions") or [])}
+        return {"location": entity.get("location")}
+    if kind in ("set_possession", "clear_possession"):
+        return {"owner": model.owner_of(state, event.get("item", ""))}
+    if kind == "invalidate_fact":
+        for fact in state.get("facts") or []:
+            if fact.get("id") == event.get("fact_id"):
+                return {"status": fact.get("status"), "predicate": fact.get("predicate")}
+        return None
+    if kind == "resolve_story_thread":
+        thread = (state.get("threads") or {}).get(event.get("thread", ""))
+        return {"status": thread.get("status")} if isinstance(thread, dict) else None
+    if kind == "end_relationship":
+        return {"status": "active"}
+    return None
+
+
+# ------------------------------------------------------------------ reading
+
+def events_for(
+    db: Session, adventure: models.Adventure, action_id: int
+) -> list[models.StateEvent]:
+    """The accepted events one node's narration produced, in order."""
+    return (
+        db.query(models.StateEvent)
+        .filter(
+            models.StateEvent.adventure_id == adventure.id,
+            models.StateEvent.action_id == action_id,
+        )
+        .order_by(models.StateEvent.sequence, models.StateEvent.id)
+        .all()
+    )
+
+
+def history(
+    db: Session, adventure: models.Adventure, limit: int = 200
+) -> list[models.StateEvent]:
+    """The campaign's accepted state events, newest first.
+
+    Bounded by default: this is an audit view, and an unbounded read of a long
+    campaign's every event is the kind of query this project keeps a regression
+    test about.
+    """
+    return (
+        db.query(models.StateEvent)
+        .filter(models.StateEvent.adventure_id == adventure.id)
+        .order_by(models.StateEvent.id.desc())
+        .limit(limit)
+        .all()
+    )