diff --git a/tools/engine.py b/tools/engine.py
index b3dafff..89052d9 100644
--- a/tools/engine.py
+++ b/tools/engine.py
@@ -5,6 +5,7 @@ import random
 import re
 import sys
 from datetime import datetime
+from difflib import SequenceMatcher
 from pathlib import Path
 
 from engine_lib.models import TurnResult
@@ -117,8 +118,14 @@ class GameEngine:
                     if text:
                         book_log = (book_log + "\n\n" + text) if book_log else text
                 elif name == "finalize_turn":
-                    if args.get("ambience"):
-                        ambience = args["ambience"]
+                    raw = (args.get("ambience") or "").strip().lower()
+                    if raw:
+                        valid = state.get_valid_ambiences()
+                        if raw in valid:
+                            ambience = raw
+                        else:
+                            state.append_llm_log(f"\n[WARN] invalid ambience '{raw}'")
+                            ambience = None
                     if args.get("log_entry"):
                         log_entry = args["log_entry"]
                 elif name == "player_roll":
@@ -126,6 +133,25 @@ class GameEngine:
                 elif name not in ("roll",):
                     state_changes.append(tc)
 
+            # Duplicate check — reject if narrative is 80%+ similar to last book entry
+            if book_log:
+                prev = state.read_recent_book(1)
+                if prev and prev not in ("*No prior story.*",):
+                    prev_text = re.sub(r"^## Turn \d+\n\n", "", prev, flags=re.MULTILINE).strip()
+                    ratio = SequenceMatcher(None, book_log, prev_text).ratio()
+                    if ratio >= 0.8:
+                        state.append_llm_log(f"\n[TURN DUPLICATE] {ratio:.0%} match with previous turn")
+                        if attempt < MAX_RETRIES:
+                            feedback = "The narrative is nearly identical to the previous turn. Generate something new and different."
+                            state.append_llm_log(f"\n[TURN REGENERATE] (duplicate) attempt {attempt + 2}")
+                            continue
+                        state.append_llm_log(f"\n[TURN DUPLICATE EXCEEDED] cannot generate unique narrative")
+                        return TurnResult(
+                            book_log="",
+                            log_entry="Your action was rejected — could not generate a unique narrative.",
+                            user_prompt=f"*Your action:\n\t\"{player_action}\"\nwas rejected:\nengine failed to produce unique narrative*",
+                        )
+
             # Validate the generated turn
             if on_action:
                 on_action("DM is validating the response")
@@ -181,8 +207,6 @@ class GameEngine:
 
             if name == "narrative":
                 pass
-            elif name == "finalize_turn":
-                pass
             elif name == "player_roll" and on_player_roll:
                 dice = args.get("dice", "1d6")
                 reason = args.get("reason", "a check")
diff --git a/tools/engine_lib/state.py b/tools/engine_lib/state.py
index 125f066..2ab8be9 100644
--- a/tools/engine_lib/state.py
+++ b/tools/engine_lib/state.py
@@ -112,8 +112,6 @@ def validate_update_size(name: str, new_content: str, path: Path) -> bool:
 
 def apply_state(result: TurnResult) -> None:
     """Write state changes from a TurnResult to disk."""
-    if result.ambience:
-        AMBIENCE_PATH.write_text(result.ambience.strip().lower() + "\n")
     if result.changes:
         CHANGES_PATH.write_text("\n".join(result.changes) + "\n")
     else:
diff --git a/tools/engine_lib/tools_handler.py b/tools/engine_lib/tools_handler.py
index 1d3343f..6a52987 100644
--- a/tools/engine_lib/tools_handler.py
+++ b/tools/engine_lib/tools_handler.py
@@ -4,8 +4,8 @@ import json
 import random
 import re
 
-from .paths import CHAR_PATH, WORLD_PATH
-from .state import read_file, validate_update_size, update_journal, append_llm_log
+from .paths import AMBIENCE_PATH, CHAR_PATH, WORLD_PATH
+from .state import read_file, validate_update_size, update_journal, append_llm_log, get_valid_ambiences
 
 
 TOOL_REGISTRY: dict[str, dict] = {
@@ -168,6 +168,20 @@ def tool_journal_update(args: dict) -> str:
     return "Journal updated."
 
 
+def tool_finalize_turn(args: dict) -> str:
+    """Validate ambience and write to AMBIENCE_PATH."""
+    raw = (args or {}).get("ambience", "").strip().lower()
+    if not raw:
+        AMBIENCE_PATH.write_text("silence\n")
+        return "Ambience set to silence."
+    valid = get_valid_ambiences()
+    if raw not in valid:
+        append_llm_log(f"\n[WARN] invalid ambience '{raw}', allowed: {sorted(valid)}")
+        return f"**Error:** invalid ambience '{raw}'. Allowed: {', '.join(sorted(valid))}."
+    AMBIENCE_PATH.write_text(raw + "\n")
+    return f"Ambience set to {raw}."
+
+
 def execute_tool(tool_name: str, args: dict) -> str:
     """Execute a tool by name. Returns result string."""
     fn_map = {
@@ -181,6 +195,7 @@ def execute_tool(tool_name: str, args: dict) -> str:
         "replace_note": tool_replace_note,
         "world_update": tool_world_update,
         "journal_update": tool_journal_update,
+        "finalize_turn": tool_finalize_turn,
     }
     fn = fn_map.get(tool_name)
     if not fn:
@@ -227,6 +242,9 @@ def describe_change(tool_name: str, args: dict) -> str:
         for d in args.get("done", []):
             parts.append(f"✅ {d}")
         return "; ".join(parts) if parts else ""
+    elif tool_name == "finalize_turn":
+        a = args.get("ambience", "")
+        return f"♫ {a}" if a else ""
     return ""