Display rebase progress in status buffer

[sei40kr]

Add a rebase-sequence section to the status buffer showing the progress of an in-progress rebase, matching Magit's display style.

Summary

This change adds comprehensive rebase progress tracking to the status buffer. When a rebase is in progress (either interactive or am-backend), a new "Rebasing X onto Y" section appears at the top, displaying:

• Pending commits (remaining todo lines, newest first)
• The commit where the rebase stopped (if any)
• Already-applied commits
• The base being rebased onto

Each row is a clickable commit section, allowing users to visit commits during a rebase.

Key changes

• Parser additions (git/parse.rs):

  • parse_hash_subject(): Extract commit hash and subject from git log output
  • parse_mail_patch(): Parse mailbox-format patch files from am-backend rebases
  • assemble_rebase_steps(): Assemble the display rows from sequencer state (todo, stop point, applied commits, base)

• Rebase detection and reading (git/client.rs):

  • read_rebase(): Detect and read rebase state from rebase-merge/ (interactive) or rebase-apply/ (am-backend) directories
  • apply_backend_pending(): Extract pending commits from numbered patch files
  • abbreviate_todo(): Batch-resolve full commit ids to short hashes for display

• Display types (git/types.rs):

  • SeqKind enum: Categorizes commits (Pending, Stop, Done, Onto)
  • SeqStep struct: One row of rebase progress
  • RebaseInfo struct: Complete rebase state for display

• UI rendering (ui/build.rs):

  • rebase_section(): Build the rebase-sequence section with color-coded step words
  • Integrated into status buffer, appearing before file lists

• Todo parsing (git/todo.rs):

  • parse_todo_display(): Lenient parser for display (skips unsupported instructions like exec, break, label)

• Theme (src/theme.rs):

  • Added sequence_stop, sequence_done, sequence_onto color roles for rebase step styling

• Tests:

  • Unit tests for parsers and step assembly
  • Integration test verifying rebase progress display with a real conflicted rebase

Implementation notes

• Rebase detection checks both rebase-merge/ (interactive) and rebase-apply/ (am-backend) directories
• Commit ids are matched by prefix to handle both full and abbreviated hashes from different sources
• The display is newest-first (like a log) so it reads top-to-bottom: pending, stop, done, base
• Applied commits are detected via git log onto..HEAD to avoid relying on sequencer state files
• The "onto" base is named after the branch it points to (via git name-rev) when possible, falling back to its short hash

https://claude.ai/code/session_014zsTaZna79VjjCAddF8BT1