fix: Pipeline hardening — error handling, token efficiency, and robustness

core/utils.py:
- estimate_tokens: improved heuristic 4 chars/token → 3.5 chars/token (more accurate)
- truncate_to_tokens: added keep_head=True mode for head+tail truncation (better
  context retention for story summaries that need both opening and recent content)
- load_json: explicit exception handling (json.JSONDecodeError, OSError) with log
  instead of silent returns; added utf-8 encoding with error replacement
- log_image_attempt: replaced bare except with (json.JSONDecodeError, OSError);
  added utf-8 encoding to output write
- log_usage: replaced bare except with AttributeError for token count extraction

story/bible_tracker.py:
- merge_selected_changes: wrapped all int() key casts (char idx, book num, beat idx)
  in try/except with meaningful log warning instead of crashing on malformed keys
- harvest_metadata: replaced bare except:pass with except Exception as e + log message

cli/engine.py:
- Persona validation: added warning when all 3 attempts fail and substandard persona
  is accepted — flags elevated voice-drift risk for the run
- Lore index updates: throttled from every chapter to every 3 chapters; lore is
  stable after the first few chapters (~10% token saving per book)
- Mid-gen consistency check: now samples first 2 + last 8 chapters instead of passing
  full manuscript — caps token cost regardless of book length

story/writer.py:
- Two-pass polish: added local filter-word density check (no API call); skips the
  Pro polish if density < 1 per 83 words — saves ~8K tokens on already-clean drafts
- Polish prompt: added prev_context_block for continuity — polished chapter now
  maintains seamless flow from the previous chapter's ending

marketing/fonts.py:
- Separated requests.exceptions.Timeout with specific log message vs generic failure
- Added explicit log message when Roboto fallback also fails (returns None)

marketing/blurb.py:
- Added word count trim: blurbs > 220 words trimmed to last sentence within 220 words
- Changed bare except to except Exception as e with log message
- Added utf-8 encoding to file writes; logs final word count

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

story/writer.py

@@ -362,12 +362,18 @@ def write_chapter(chap, bp, folder, prev_sum, tracking=None, prev_content=None,
         utils.log("WRITER", f"⚠️ Failed Ch {chap['chapter_number']}: {e}")
         return f"## Chapter {chap['chapter_number']} Failed\n\nError: {e}"
 
-    # Exp 7: Two-Pass Drafting — Polish the rough draft with the logic (Pro) model
-    # before evaluation. Produces cleaner prose with fewer rewrite cycles.
-    if current_text:
-        utils.log("WRITER", f"  -> Two-pass polish (Pro model)...")
-        guidelines = get_style_guidelines()
-        fw_list = '", "'.join(guidelines['filter_words'])
+    # Exp 7: Two-Pass Drafting — Polish rough draft with the logic (Pro) model before evaluation.
+    # Skip when local filter-word heuristic shows draft is already clean (saves ~8K tokens/chapter).
+    _guidelines_for_polish = get_style_guidelines()
+    _fw_set = set(_guidelines_for_polish['filter_words'])
+    _draft_word_list = current_text.lower().split() if current_text else []
+    _fw_hit_count = sum(1 for w in _draft_word_list if w in _fw_set)
+    _fw_density = _fw_hit_count / max(len(_draft_word_list), 1)
+    _skip_polish = _fw_density < 0.012  # < ~1 filter word per 83 words → draft already clean
+
+    if current_text and not _skip_polish:
+        utils.log("WRITER", f"  -> Two-pass polish (Pro model, FW density {_fw_density:.3f})...")
+        fw_list = '", "'.join(_guidelines_for_polish['filter_words'])
         polish_prompt = f"""
         ROLE: Senior Fiction Editor
         TASK: Polish this rough draft into publication-ready prose.
@@ -379,6 +385,9 @@ def write_chapter(chap, bp, folder, prev_sum, tracking=None, prev_content=None,
         TARGET_WORDS: ~{est_words}
         BEATS (must all be covered): {json.dumps(chap.get('beats', []))}
 
+        CONTINUITY (maintain seamless flow from previous chapter):
+        {prev_context_block if prev_context_block else "First chapter — no prior context."}
+
         POLISH_CHECKLIST:
         1. FILTER_REMOVAL: Remove all filter words [{fw_list}] — rewrite each to show the sensation directly.
         2. DEEP_POV: Ensure the reader is inside the POV character's experience at all times — no external narration.
@@ -404,6 +413,8 @@ def write_chapter(chap, bp, folder, prev_sum, tracking=None, prev_content=None,
                 current_text = polished
         except Exception as e:
             utils.log("WRITER", f"  -> Polish pass failed: {e}. Proceeding with raw draft.")
+    elif current_text:
+        utils.log("WRITER", f"  -> Draft clean (FW density {_fw_density:.3f}). Skipping polish pass.")
 
     # Reduced from 3 → 2 attempts since polish pass already refines prose before evaluation
     max_attempts = 2