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>

marketing/fonts.py

@@ -42,14 +42,20 @@ def download_font(font_name):
         base_url = f"https://github.com/google/fonts/raw/main/{license_type}/{clean_name}"
         for pattern in patterns:
             try:
-                r = requests.get(f"{base_url}/{pattern}", headers=headers, timeout=5)
+                r = requests.get(f"{base_url}/{pattern}", headers=headers, timeout=6)
                 if r.status_code == 200 and len(r.content) > 1000:
-                    with open(font_path, 'wb') as f: f.write(r.content)
+                    with open(font_path, 'wb') as f:
+                        f.write(r.content)
                     utils.log("ASSETS", f"✅ Downloaded {font_name} to {font_path}")
                     return font_path
-            except Exception: continue
+            except requests.exceptions.Timeout:
+                utils.log("ASSETS", f"  Font download timeout for {font_name} ({pattern}). Trying next...")
+                continue
+            except Exception:
+                continue
 
     if clean_name != "roboto":
-        utils.log("ASSETS", f"⚠️ Font '{font_name}' not found. Falling back to Roboto.")
+        utils.log("ASSETS", f"⚠️ Font '{font_name}' not found on Google Fonts. Falling back to Roboto.")
         return download_font("Roboto")
+    utils.log("ASSETS", "⚠️ Roboto fallback also failed. PIL will use built-in default font.")
     return None