Requested by Can · project thread

#What this changes

Two of the smaller bugs reported on GitHub (codician-team/diffinery#4):

• Merged pull requests showed 0 commits and 0 changed files. Commits, files and stats were always counted from the base branch's tip. After a merge commit (or an import of a PR merged that way on GitHub), the base contains the head, so nothing was left.
  • A merged pull request is now counted from where the base was when it merged. This is kept in a new pulls.merged_base column set by completeMerge, which covers direct merges, auto-merge and the merge queue.
  • Imported pull requests use GitHub's base.sha.
  • Pull requests merged before this change use their merge commit's first parent. Old fast-forward merges have nothing to go by and stay as before.
• /compare/main~1...main returned 404. resolve() now takes git's ancestry suffixes (~N, ^N, ~, ^) after any branch, tag, SHA or HEAD. Ref names can't contain ~ or ^, so nothing that resolved before changes. Compare, commits, contents and everything else that resolves refs get this.
• Docs: Pull requests (what a merged PR's tabs count from) and Browsing code (relative refs in compare).

#How it was tested

• e2e, run locally:
  • The GitHub import test now checks that the imported --no-ff merged PR #2 has 1 commit and 1 file, with the right SHA and filename. This fails on main.
  • The security test that merges with merge_method: "merge" now checks the PR still lists its two commits and both files.
  • The sizes test covers main~1...main, main^...main, main~...HEAD, <sha>...main~0 and commits/main~1, plus 404s for main~2 past the root and main^2 with no second parent.
• Typecheck is clean and the unit tests pass (1128).

#Checklist

• Docs updated
• No workflow files changed

🤖 Generated with Claude Code

https://claude.ai/code/session_015ALxdbMU5hpZXjGpL2jhC4