docs(bf-2nn5x): verify unmapped_glyph_names config wiring to CMAP entry creation

Verify that the unmapped_glyph_names configuration is properly wired
through to the CMAP entry creation point in Type1 font encoding
differences parsing.

The configuration was already added in bf-4zgpr (commit 7660cfc8). This
bead confirms the wiring is complete:
- DifferencesOverlay stores unmapped_glyph_names as instance state
- Default initialization loads from global UNMAPPED_GLYPH_NAMES set
- Skip check at encoding.rs:227 filters unmapped glyphs before entry creation
- Custom configuration available via with_unmapped_glyph_names() constructor

Acceptance criteria:
- ✅ CMAP entry creation accepts unmapped_glyph_names (via self field)
- ✅ Configuration passes from defaults to entry creation
- ✅ Code compiles without errors

See notes/bf-2nn5x.md for detailed verification.

notes/bf-2nn5x.md

@@ -0,0 +1,133 @@
+# Verification: unmapped_glyph_names Config Wired to CMAP Entry Creation
+
+## Task
+Wire unmapped_glyph_names config to CMAP entry creation point.
+
+## Status: PASS
+
+The unmapped_glyph_names configuration was already wired to the CMAP entry creation point in a previous commit (7660cfc8: "feat(bf-4zgpr): add unmapped_glyph_names config field to CMAP generator"). This bead verifies the wiring is complete and functional.
+
+## Implementation
+
+### CMAP Entry Creation Point
+**Location:** `crates/pdftract-core/src/font/encoding.rs:220-230`
+
+The CMAP entry creation for Type1 font encoding differences occurs in `DifferencesOverlay::parse()`. This is where individual (code, glyph_name) pairs are added to the overlay.
+
+### Configuration Storage
+**Location:** `crates/pdftract-core/src/font/encoding.rs:129-146`
+
+The `DifferencesOverlay` struct stores the `unmapped_glyph_names` configuration:
+
+```rust
+pub struct DifferencesOverlay {
+    entries: Vec<(u8, Arc<str>)>,
+    unmapped_glyph_names: std::collections::HashSet<String>,
+}
+```
+
+### Configuration Initialization
+**Location:** `crates/pdftract-core/src/font/encoding.rs:140-168`
+
+The configuration is initialized with defaults from the global `UNMAPPED_GLYPH_NAMES` set:
+
+```rust
+pub fn new() -> Self {
+    Self {
+        entries: Vec::new(),
+        unmapped_glyph_names: Self::default_unmapped_glyph_names(),
+    }
+}
+
+fn default_unmapped_glyph_names() -> std::collections::HashSet<String> {
+    crate::font::unmapped::UNMAPPED_GLYPH_NAMES
+        .iter()
+        .map(|s| s.to_string())
+        .collect()
+}
+```
+
+### Skip Check at Entry Creation
+**Location:** `crates/pdftract-core/src/font/encoding.rs:223-230`
+
+The skip check prevents unmapped glyph names from being added as CMAP entries:
+
+```rust
+if cursor <= 255 {
+    // Skip unmapped glyph names (e.g., .notdef) to prevent them from
+    // appearing in text extraction output. These glyphs have no valid
+    // Unicode mapping and should emit GLYPH_UNMAPPED diagnostics instead.
+    if !overlay.is_unmapped_glyph_name(&name) {
+        overlay.entries.push((cursor as u8, Arc::clone(name)));
+    }
+}
+```
+
+### Accessor Methods
+**Locations:** `crates/pdftract-core/src/font/encoding.rs:148-158, 265-296`
+
+The configuration provides methods for customization and access:
+
+```rust
+// Custom constructor
+pub fn with_unmapped_glyph_names(unmapped_glyph_names: std::collections::HashSet<String>) -> Self
+
+// Membership check
+fn is_unmapped_glyph_name(&self, name: &str) -> bool
+
+// Getter
+pub fn unmapped_glyph_names(&self) -> &std::collections::HashSet<String>
+
+// Setter
+pub fn set_unmapped_glyph_names(&mut self, unmapped_glyph_names: std::collections::HashSet<String>)
+```
+
+## Call Chain
+
+Configuration flows from global constants to entry creation:
+
+1. **Global Definition:** `UNMAPPED_GLYPH_NAMES` in `unmapped.rs` (auto-generated from AGL)
+2. **Default Initialization:** `DifferencesOverlay::new()` loads global set
+3. **Parse Entry:** `DifferencesOverlay::parse()` creates overlay with defaults
+4. **Skip Check:** `is_unmapped_glyph_name(&name)` checks membership before adding
+5. **Entry Creation:** `overlay.entries.push()` executes only for mapped glyphs
+
+## Custom Configuration Path
+
+For custom configurations, users can:
+1. Create a `HashSet<String>` with desired glyph names
+2. Use `DifferencesOverlay::with_unmapped_glyph_names(custom_set)`
+3. Or use `set_unmapped_glyph_names()` on an existing overlay
+
+## Acceptance Criteria Status
+
+- ✅ CMAP entry creation point accepts unmapped_glyph_names (via `self` field)
+- ✅ Configuration is correctly passed from defaults through to entry creation
+- ✅ Code compiles without errors (`cargo check --package pdftract-core` passed)
+
+## Why This Design
+
+The `unmapped_glyph_names` configuration is stored as instance state in `DifferencesOverlay` rather than passed as a parameter to `add_mapping()` because:
+
+1. **Type1 Encoding Context:** The CMAP entry creation for Type1 fonts works with glyph names (e.g., ".notdef"), not byte codes
+2. **Semantic Fit:** The configuration belongs to the overlay that creates entries, not each individual entry
+3. **Flexibility:** Instance state allows custom configuration via constructor/setter without changing method signatures
+
+## Note on ToUnicode CMap
+
+The ToUnicode CMap parser (`cmap.rs`) does not use this configuration because:
+- ToUnicode CMaps map byte sequences → Unicode characters directly
+- There are no glyph names involved in ToUnicode mappings
+- The skip logic is specific to Type1 font encoding differences
+
+## Related Files
+
+- `crates/pdftract-core/src/font/encoding.rs` - CMAP entry creation and config
+- `crates/pdftract-core/src/font/unmapped.rs` - Global UNMAPPED_GLYPH_NAMES set
+- `crates/pdftract-core/src/font/cmap.rs` - ToUnicode CMap parser (different code path)
+
+## Related Beads
+
+- bf-4zgpr: Added unmapped_glyph_names config field to DifferencesOverlay
+- bf-6cvmz: Documented unmapped_glyph_names configuration structure
+- bf-o4nrq: Documented CMAP entry creation point