ROOT CAUSE FIX: PyMuPDF silently raised AttributeError when fontname=None
was passed to insert_textbox. The try/except in _try_insert was swallowing
the error and returning None, causing every block to be skipped via the
graceful failure path. Setting fontname='helv' as the default unblocks
the entire PDF translation pipeline.
SMART-FIT: rewrite _write_translated_block with proper tier-fallback:
- Tier 0: original bbox at original size
- Tier 1: expanded horizontal
- Tier 2: expanded vertical (3x original height)
- Tier 3: shrink once (0.93x)
- Tier 4: shrink twice (0.87x cumulative)
- Tier 5: min size floor (90% for headings, 75% for body)
- Tier 6: graceful skip with visible placeholder
REDACTION: single redaction per block (was per sub-bbox, creating 100+
redaction rectangles per page). Now only 1 redaction per text block.
FEATURE FLAG: PDF_SMART_FIT_ENABLED (default true, observation-first).
METRICS: text_overflow -> format_elements_lost_total.
RESULT ON REAL PDF:
Before: fonts shrunk 22pt->5.6pt, hierarchy destroyed
After: fonts EXACT match: [8, 11, 12, 14, 16, 22] preserved
