Keep world-state emit reliable across turns

The AI would sometimes stop emitting the `state` delta block once it missed
a turn. Two compounding causes: the emit rule sat only in the system block
(far from where the model generates), and the block was stripped before
storage — so every replayed history turn looked blockless, biasing the model
by imitation to stop emitting too.

- EMIT_REMINDER: a one-line reminder appended last in the prompt (strongest
  recency slot), gated on has_ws and counted against the token budget.
- render_delta_block + _history_text: re-attach each past AI turn's own delta
  block in replayed history (reconstructed from the stored snapshot delta), so
  the model always sees its emit format. Action.text stays clean, so UI,
  embeddings, and card/NPC trigger-matching are unaffected. History budgeting
  counts the augmented text so it can't overflow.

Undo/retry untouched (read the separate world_state_before column). 46 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UWVyFKvqJGjfbXdibLgkMe

backend/app/context/builder.py

@@ -56,6 +56,24 @@ def _script_memory(adventure: models.Adventure) -> dict:
     return memory if isinstance(memory, dict) else {}
 
 
+def _history_text(action: models.Action) -> str:
+    """An AI turn as the model should see it in replayed history: its narration
+    with the state block it emitted re-appended (reconstructed from the stored
+    delta). The block is stripped before storage/UI, so without this every past
+    AI turn would look like one that emitted nothing — biasing the model, by
+    imitation, to stop emitting too. Player turns and blockless turns are
+    returned unchanged."""
+    text = action.text
+    snap = action.context_snapshot if isinstance(action.context_snapshot, dict) else None
+    if snap:
+        ws = snap.get("world_state")
+        if isinstance(ws, dict):
+            block = worldstate.render_delta_block(ws.get("delta") or {})
+            if block:
+                text = f"{text}\n{block}"
+    return text
+
+
 def _visible_npcs(adventure: models.Adventure, stat_schema: dict) -> dict[str, str]:
     """Defined NPCs whose trigger words appear in the recent story — the ones
     "in scene", so only their stats get injected. Maps npc id -> display name."""
@@ -99,7 +117,8 @@ def build_context(
 
     # RPG world state (Phase 12): current stats/milestones + how to report changes.
     stat_schema = adventure.scenario.stat_schema if adventure.scenario else None
-    if worldstate.has_schema(stat_schema):
+    has_ws = worldstate.has_schema(stat_schema)
+    if has_ws:
         guide = worldstate.render_reference(stat_schema)
         if guide:
             system_sections.append(Section("world_state_guide", guide))
@@ -139,6 +158,7 @@ def build_context(
         sum(s.tokens for s in system_sections)
         + count_tokens(authors_note)
         + count_tokens(front_memory)
+        + (count_tokens(worldstate.EMIT_REMINDER) if has_ws else 0)
     )
     available = max(256, settings.context_token_budget - reserved)
 
@@ -171,7 +191,10 @@ def build_context(
     spent = 0
     oldest_truncated = False
     for action in reversed(actions):
-        tokens = count_tokens(action.text) + count_tokens(SEPARATOR)
+        # Budget on the text as it will actually appear — with the re-attached
+        # state block (B) when this adventure tracks world state.
+        rendered = _history_text(action) if has_ws else action.text
+        tokens = count_tokens(rendered) + count_tokens(SEPARATOR)
         if spent + tokens > history_budget:
             if not included_actions:
                 # Even the newest action alone is over budget: hard-truncate it.
@@ -189,7 +212,9 @@ def build_context(
     included_actions.reverse()
 
     # ----- Assemble story text with author's note near the end -----
-    texts = [a.text for a in included_actions]
+    # Re-attach each AI turn's state block (stripped before storage) so recent
+    # history shows the model its own emit pattern to imitate.
+    texts = [_history_text(a) if has_ws else a.text for a in included_actions]
     note_sections: list[Section] = []
     if authors_note:
         pos = max(0, len(texts) - AUTHORS_NOTE_DEPTH)
@@ -202,6 +227,10 @@ def build_context(
         note_sections.append(Section("history", SEPARATOR.join(texts)))
     if front_memory:
         note_sections.append(Section("front_memory", front_memory))
+    if has_ws:
+        # Terminal reminder: the emit rule sits up in the system block, far from
+        # where the model generates; repeat it last, in the strongest recency slot.
+        note_sections.append(Section("world_state_reminder", worldstate.EMIT_REMINDER))
 
     story_sections = [s for s in note_sections if s.text]
     system_text = SEPARATOR.join(s.text for s in system_sections if s.text)