Document shallow clone issue causing apparent missing PR history

[Copilot]

Repository was cloned with --depth=1, making full git history unavailable. After git fetch --unshallow, verified all merged PRs exist in history.

Investigation Results

Last 6 merged PRs: #77, #78, #79, #80, #83, #84 - all present in git history with verified commit SHAs.

PR #81 and #82: Never created (GitHub API returns 404).

Root cause: Shallow clone contained only 1 commit; git log showed "(grafted)" indicator. After unshallowing, retrieved 1,459 commits.

Deliverables

• PR_INVESTIGATION_FINDINGS.md - Full technical analysis, evidence, and recommendations for CI/CD systems
• SHALLOW_CLONE_ISSUE.md - Quick reference guide with TL;DR and fix instructions
• scripts/verify_pr_history.sh - Automated tool to detect shallow clones and verify PR commits exist

Verification

# Check for shallow clone
[ -f .git/shallow ] && echo "Shallow clone detected"

# Fix
git fetch --unshallow

# Verify PRs
./scripts/verify_pr_history.sh

All merge commits verified present via git cat-file -t <sha>. No data loss or history corruption detected.

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