docs: capture pdf domain language and deferred ingestion backlog

Co-authored-by: Cursor <cursoragent@cursor.com>

backlog/scanned-pdf-ocr.md

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+# Scanned PDF OCR (v1.1+)
+
+## Why deferred
+
+v1 only accepts Text PDFs and applies a Text-layer Gate: Scanned PDFs are hard-rejected at upload (not stored, not processed). OCR is a second product surface: noisy text poisons every Strategy equally and makes Experiment comparisons misleading.
+
+## Trigger
+
+Pick this up when:
+
+1. Text PDF path is trusted on real docs
+2. You have ~10–20 labeled Scanned PDFs + question JSONs matching chatbot traffic
+3. Production coverage of those docs matters more than clean benchmarks alone
+
+## Approach to try
+
+1. Detect empty / near-empty text layer at upload (same gate as v1 rejection)
+2. Run OCR as an **explicit pre-step** that still emits `ParseResult` (markdown + DocumentTree)
+3. Tag source as `ocr` so Experiments can filter Text PDF vs Scanned PDF runs
+4. Reuse Heading Reconstruction heuristics on OCR text (expect more false positives)
+
+## Success criteria
+
+- OCR’d markdown is readable enough that recursive Strategy headings aren’t nonsense
+- Side-by-side Experiment: Text PDF original vs OCR of a scan of the same doc — score delta understood, not mysterious