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 A fact withdrawn by a manual correction is now named as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

planning/STORY-BRANCH-SEMANTICS.md

@@ -377,37 +377,69 @@ Therefore the system must:
 
 The system must not simply replace visible text while leaving stale state behind.
 
-## 14A. Editing In Place, Before §14-15 Are Implemented
+### How this is built (M5 corrective pass)
 
-§14 and §15 describe the finished behavior: a narrator edit becomes
-authoritative, the state it implies is re-evaluated, a new continuation is
-created, and the original narration and its future are retained. That
-requirement stands in full and is **not** weakened by this section.
+All five conditions are implemented. A narrator edit is not a write to the row
+being corrected — nothing on the line being left is written to at all. It is the
+same operation as playing the turn again from here, with the reader's words in
+place of a generated reply, and it reuses the fork, take, head and snapshot
+machinery M3 and M4 already provide rather than introducing a second history
+mechanism.
 
-It is not yet built. Re-evaluating the state implied by prose a user typed
-requires the authoritative narrative-state extraction that the genre-neutral
-state milestone introduces, so the finished behavior is completed there. What
-exists in the meantime is a plain correction: it changes the words of one turn
-and re-evaluates nothing.
+```text
+before                       after
 
-That correction is safe while everything descending from the turn is on screen,
-because the user can see what their change has to stay consistent with. It is
-not safe when a continuation descends from the turn and is **off screen** —
-undone and not yet redone, or left behind by a divergence — because the edit
-would then silently change the words that retained story was written from, and
-nothing on screen would show it. Retained history is not permitted to be made to
-disagree with itself in a way the user cannot see.
+parent                       parent
+└── original narrator        ├── original narrator ──> old future   [retained]
+    └── old future           └── corrected narrator                 [active]
+```
 
-Until §14-15 are implemented, the system must therefore **refuse** an in-place
-edit of a turn that has story descending from it which is not currently being
-shown, and say why. The user resolves it the same two ways as §10:
+Two shapes, chosen by whether anything was written after the turn:
 
-- **Redo**, bringing the later story back into view; or
-- **play the turn again from here**, which is the §13 shape — return to the
-  parent position, continue differently, and keep the old line as retained
-  history.
+- **Nothing below it.** The attempts at that turn are still leaves, so the
+  correction joins them as another take and the original stays beside it in the
+  pager. No branch is created, and the head does not move.
+- **A story below it**, on screen or not. That story was written as a
+  continuation of the words that are there now, so it keeps them: the correction
+  leaves the path just before the turn, and the departed line keeps its node,
+  its future and its live flag.
 
-Refusing is the minimum that keeps the invariant. It is not the destination.
+The state the correction implies is derived from the snapshot on the node
+*before* the edited turn — one row read, not a replay — and put through the same
+validation the model's own proposals face. The correction's node then carries
+that document as its own outcome, so the campaign's live state and the state
+stored at the head are the same document. That equality is the invariant:
+
+```text
+visible active transcript position == stored head == authoritative state
+```
+
+The M5 review found it broken by the interim implementation, which rewrote the
+row in place and rewound the campaign's live state to that position while the
+head stayed at the tip. The reader saw a full transcript over a state document
+describing an earlier moment, and the snapshots below the edit still described
+prose that no longer existed.
+
+## 14A. Editing In Place — Superseded for Narrator Output
+
+§§14-15 are implemented, and the refusal this section described no longer
+applies to narrator turns. It is kept because it explains why the current shape
+is the one it is.
+
+The refusal existed because an in-place edit rewrote the words that a
+descending, invisible story had been written from, and retained history is not
+permitted to be made to disagree with itself where the user cannot see it. A
+fork removes the premise: the off-screen future keeps the exact narration it
+descends from, so there is nothing left to refuse. What was the unsafe case is
+now an ordinary one.
+
+Two in-place edits remain, and neither can produce that disagreement:
+
+- **A player's own input** (§13) is still edited in place, and is still refused
+  while a story descends from it off screen. Bringing §13 onto the same footing
+  as §§14-15 is not yet done.
+- **A take the story is not telling** has no continuation of its own — keeping
+  one is what forking is for — so correcting its words contradicts nothing.
 
 ## 16. Manual State / Canon Correction