docs(bf-632yt): add verification note

Add verification note documenting validation script implementation
and test results against grep-corpus.

notes/bf-632yt.md

@@ -0,0 +1,53 @@
+# bf-632yt: Create corpus validation script
+
+## Summary
+
+Created `scripts/validate-corpus.sh` to verify corpus integrity against `manifest.csv`.
+
+## Implementation
+
+The script validates all 5 required manifest fields:
+1. **File existence** - Verifies all files listed in manifest.csv exist
+2. **File size** - Checks file sizes match manifest
+3. **SHA256 checksums** - Validates checksums using `sha256sum`
+4. **License information** - Verifies license field is present and valid
+5. **Counts** - Reports total files, pages, and size
+
+## Testing Results
+
+Ran validation against `tests/fixtures/grep-corpus`:
+
+- **Total files in manifest:** 1,260
+- **Valid files:** 603 (with known licenses)
+- **Missing files:** 0
+- **Size mismatches:** 0
+- **Checksum mismatches:** 0
+- **Missing licenses:** 657 (PDFium test files with "unknown" license)
+
+The 657 files with "unknown" licenses are from the PDFium test corpus, which is expected behavior. These files correctly fail the license validation check as designed.
+
+## Exit Codes
+
+- `0` - Validation passed (all files valid)
+- `1` - Validation failed (errors found)
+- `2` - Usage error or manifest not found
+
+## Usage
+
+```bash
+./scripts/validate-corpus.sh [corpus_directory]
+```
+
+Default corpus directory: `tests/fixtures/grep-corpus`
+
+## Acceptance Criteria Status
+
+- ✅ scripts/validate-corpus.sh exists and is executable (chmod +x)
+- ✅ Script validates all 5 manifest fields (existence, size, checksum, count, license)
+- ✅ Returns 0 on success, non-zero on validation failure
+- ✅ Outputs summary: total files, total pages, total size, validation status
+
+## Commit
+
+- Commit: `c189bfd2`
+- Files changed: `scripts/validate-corpus.sh` (1 file, 114 insertions, 147 deletions)