NameetP/pdfmux

Correctness patch

No defaults change. Every existing flag and CLI invocation behaves identically. Confidence numbers are now correct on documents where they were previously inflated.

The bug

`audit.compute_document_confidence` was returning 1.0 on documents with empty extractions. The function did a content-weighted average of the per-page `confidence` value the extractor wrote at yield time — always `1.0` with the comment audit will reassess. The reassessment never happened, so:

• Blank pages → confidence 1.0
• HTML files renamed to `.pdf` → confidence 1.0
• Single-character bodies → confidence 1.0
• Image-only pages with no OCR → confidence 1.0

This is the bug behind the silent failures in our 433-PDF batch retro. `--strict --min-confidence 0.20` shipped in 1.6.1 could not catch the eleven silent failures because the audit didn't know the pages were empty.

The fix (5 lines in `audit.py`)

• Re-score every page with `score_page(p.text, p.image_count)` before averaging.
• Stop flooring per-page weight at `1`. Blank pages now register zero weight in the denominator.

Also added: `eval/` calibration harness

The instrument that surfaced the bug. Self-contained, three composable steps:

```bash
python eval/build_fixtures.py # generates 50 labeled PDFs
python eval/run_eval.py # runs pdfmux on each
python eval/calibrate.py # ROC + threshold recommendations
```

The first calibration run produced precision flat at 0.683 across every threshold from 0.0 to 0.95 — the smoking gun. After the fix, threshold `0.75` produces precision `1.00`, recall `0.71` on the 50-fixture set.

Calibration headline

| Threshold | Precision | Recall | F1 |
|---:|---:|---:|---:|
| 0.50 | 0.821 | 0.821 | 0.821 |
| 0.75 | 1.000 | 0.714 | 0.833 |

`0.75` is the recommended default for `--min-confidence` when 1.7 ships breaking-default-strict on `pdfmux convert ` (target: 2026-05-08).

Tests

670 passing, 3 skipped. No regressions.

Install: `pip install -U pdfmux`