docs(bf-3cjd8): verify unmapped.rs uses new diagnostic format

- Verified all 9 test assertions in unmapped.rs use new format
- Checked against bf-1azpa catalog: count matches (9 assertions)
- No generic 'assertion failed' messages remain
- All assertions include: description, Expected, Found, Why this matters

Closes bf-3cjd8

notes/bf-3cjd8.md

@@ -0,0 +1,52 @@
+# Verification: unmapped.rs Uses New Diagnostic Message Format
+
+**Bead ID:** bf-3cjd8  
+**Date:** 2026-07-06  
+**File:** crates/pdftract-core/src/font/unmapped.rs
+
+## Task Completed
+
+Verified that all unmapped glyph assertions in unmapped.rs use the new diagnostic message format instead of generic 'assertion failed' messages.
+
+## Analysis
+
+### Test Assertions (9 total)
+
+| Test Function | Line Range | Assertions | Format |
+|--------------|-----------|------------|--------|
+| `test_notdef_is_unmapped` | 70-85 | 2 | ✅ New format |
+| `test_normal_glyphs_not_unmapped` | 87-131 | 6 | ✅ New format |
+| `test_unmapped_set_contains_expected_entries` | 133-142 | 1 | ✅ New format |
+
+**Total: 9 test assertions**
+
+### Documentation Examples (4 additional)
+
+- Lines 26-32, 33-39, 40-46, 47-53 (doc examples also use new format)
+
+## New Format Pattern
+
+All assertions follow the template:
+```rust
+assert!(
+    <condition>,
+    "<description>. \
+     Expected: <expected condition>. \
+     Found: <actual value>. \
+     Why this matters: <rationale with source reference>.",
+);
+```
+
+## Verification Against Catalog
+
+✅ **Count matches bf-1azpa catalog:** 9 assertions in unmapped.rs
+
+## Acceptance Criteria
+
+- ✅ All assertions in unmapped.rs use new message format
+- ✅ No generic 'assertion failed' messages remain
+- ✅ Count matches expected from inventory (bf-1azpa)
+
+## Conclusion
+
+All 9 unmapped glyph assertions in `unmapped.rs` use the new diagnostic message format with full context (description, Expected, Found, Why this matters). No generic assertion failures remain in this file.