docs(bf-4zhtc): verify profile_yaml fuzz harness source code

- Validated fuzz/fuzz_targets/profile_yaml.rs exists and has correct structure
- Verified imports match working fuzz target patterns
- Confirmed load_profile_yaml function exists in pdftract-core
- Checked Cargo.toml configuration for libfuzzer-sys and profiles feature
- All acceptance criteria PASS

Closes bf-4zhtc

notes/bf-4zhtc.md

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+# bf-4zhtc: Validate profile_yaml fuzz harness source code
+
+**Date:** 2026-07-06
+**Status:** PASS
+
+## Acceptance Criteria Validation
+
+### ✓ fuzz/fuzz_targets/profile_yaml.rs exists and is readable
+- File exists at `/home/coding/pdftract/fuzz/fuzz_targets/profile_yaml.rs`
+- File size: 766 bytes
+- Readable and properly formatted
+
+### ✓ File contains valid Rust code structure
+- Correct `#![no_main]` attribute for fuzz targets
+- Proper `use libfuzzer_sys::fuzz_target;` import
+- Valid `fuzz_target!(|data: &[u8]| { ... });` macro usage
+- Expected rustc error about `libfuzzer_sys` is normal for fuzz-only dependencies
+
+### ✓ No obvious syntax errors when viewing the file
+- Proper UTF-8 handling with early return on invalid UTF-8
+- Clean closure structure
+- Well-documented with INV-8 (no panic at public boundary) reference
+
+### ✓ Imports match patterns used in other working fuzz targets
+- Pattern matches other targets (content.rs, cmap_parser.rs, stream_decoder.rs)
+- Uses same `libfuzzer_sys::fuzz_target` pattern
+- Follows same documentation style with INV-8 reference
+
+### ✓ Target function exists
+- Verified `pdftract_core::profiles::load_profile_yaml` exists in `crates/pdftract-core/src/profiles/loader.rs`
+- Function signature: `pub fn load_profile_yaml(content: &str) -> Result<Value, ProfileLoadError>`
+
+### ✓ Cargo.toml configuration
+- `libfuzzer-sys = { version = "0.4", features = ["arbitrary-derive"] }` properly configured
+- `pdftract-core = { path = "../crates/pdftract-core", features = ["profiles"] }` includes profiles feature
+- `[[bin]]` target for `profile_yaml` properly registered (lines 43-45)
+
+## Conclusion
+The profile_yaml fuzz harness source code is valid and properly configured. No issues found. Ready for build testing.