docs(bf-682zv): add sync blocker report for GitHub large file issue

notes/bf-682zv.md

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+# GitHub Sync Attempt - Blocker Report
+
+## Task
+Sync GitHub main to match forgejo/main (84 commits behind)
+
+## Current State
+- **Forgejo/main**: 02bfffef docs(bf-1o0la): document Forgejo push mirror configuration and status
+- **GitHub/main**: 88b4f0da fix(pdftract-2rc4): fix CI schema gate script and add verification note
+- **Commits behind**: 160 (updated from initial 84 estimate)
+
+## Blocker: Large File in Git History
+
+GitHub rejected the push due to large file(s) in git history:
+
+```
+remote: warning: File test_parse_simple is 60.74 MB; this is larger than GitHub's recommended maximum file size of 50.00 MB
+remote: error: File --1.ppm is 235.13 MB; this exceeds GitHub's file size limit of 100.00 MB
+remote: error: GH001: Large files detected.
+```
+
+### Problem Details
+
+1. **Large file**: `--1.ppm` (235.13 MB PPM image file)
+   - Added in: `1c6f26ec` fix(bf-4mkhv): clean up unused imports in hash.rs
+   - Removed in: `007439e7` chore(bf-8031): remove tracked debug/scratch artifacts and compiled binaries
+   - Both commits are in the sync range
+
+2. **GitHub's behavior**: GitHub checks all objects being pushed, even if the large file was later removed from the working tree. The file still exists in the git object database.
+
+3. **Result**: Pre-receive hook declined - sync cannot complete
+
+## Acceptance Criteria Status
+
+- **FAIL**: GitHub main commit SHA does not equal forgejo/main (blocker: large file)
+- **PASS**: No commits exist on GitHub main that are not on forgejo main
+- **PASS**: Merge strategy was used (attempted fast-forward merge)
+- **WARN**: Automatic sync triggered by Forgejo mirror did not resolve this
+
+## Resolution Options
+
+### Option 1: Git LFS (Recommended)
+Set up Git LFS for large files:
+```bash
+git lfs install
+git lfs track "*.ppm" "*.pdf" "*.bin"
+git add .gitattributes
+git commit -m "chore: enable git-lfs for large files"
+```
+
+### Option 2: History Rewrite (Not Recommended)
+Use git filter-branch or BFG to remove large file from history:
+```bash
+git filter-branch --force --index-filter \
+  "git rm --cached --ignore-unmatch --1.ppm" \
+  --prune-empty --tag-name-filter cat -- --all
+```
+This would diverge forgejo/main from GitHub main.
+
+### Option 3: Manual Intervention
+Manually exclude the problematic commit from sync and re-implement the change without the large file.
+
+## Recommendation
+
+**Setup Git LFS** on both repositories (Forgejo and GitHub) before re-attempting sync. The large file `--1.ppm` was a temporary scratch file that should have been handled by git-lfs from the start.
+
+## Status
+**BLOCKED** - Requires git-lfs setup or history cleanup before sync can proceed.