Git history lab — expected observations / 预期结果
All history, authors, dates and incident wording are synthetic teaching fixtures.
Requires Git 2.29+, Python 3.9+, no packages or network.

History (oldest first):
ce4c0cfdc66b0cc0f2eb40ac8439ed75e49465ad baseline
e87088e01edc8b803d103d2e3922b5ffcbcc3ac5 fix-positive-lines
7d41ebcff562a3e75e396667aa6f6f3562d40f52 rename-module
27a0dc5716e1128dfe486074b7a7c2cef6ee98f4 format-spacing

git blame -L 3,3 HEAD -- source_lines.py
  Attributes line 3 to format-spacing (27a0dc57).

git blame -w -L 3,4 HEAD -- source_lines.py
  Attributes both lines to fix-positive-lines (e87088e0), path line_reader.py.

git blame --ignore-rev format-spacing -L 3,3 HEAD -- source_lines.py
  Attributes line 3 to fix-positive-lines.

git log --format='%h %s' -p -S 'line number must be positive' HEAD -- '*.py'
  Only fix-positive-lines, showing addition of the guard and error.

git log --format='%h %s' -p -S 'line_number < 1' HEAD -- '*.py'
  format-spacing, then fix-positive-lines (exact string removed, then added).

git log --follow --format='%h %s' -p -S 'line number must be positive' HEAD -- source_lines.py
  Reaches fix-positive-lines at the previous path.

git log --format='%h %s' -L 3,4:source_lines.py HEAD
  format-spacing, then fix-positive-lines.
  The unchanged block at the rename has no separate patch.

git log --format='%h %s' -L :read_line:source_lines.py HEAD
git log --format='%h %s' -L 1,7:source_lines.py HEAD
  format-spacing, fix-positive-lines, baseline.

Behavior for ['alpha', 'omega']:
  baseline: line 0 -> 'omega'; line -1 -> 'alpha'
  fixed and later: both raise ValueError

Verification:
  baseline's committed suite: 3 tests OK
  fix's regression suite against baseline source: 5 tests, 2 EXPECTED failures
  fix-positive-lines's suite: 5 tests OK
  rename-module's suite: 5 tests OK
  format-spacing's suite: 5 tests OK
  rename-module preserves source bytes
  format-spacing preserves Python AST
  git diff --check baseline HEAD: no whitespace errors
  git fsck --full: succeeds
  working tree stays clean; no remote is configured

The two baseline failures are intentional and checked by the verifier. Any other
failure stops verification. Full hashes are fixed by the generator; abbreviated
hash lengths and human-readable formatting can vary with Git versions/settings.
The script isolates its Git subprocesses from global/system configuration.
Commands you type directly use your own configuration, which can affect display.

The diff and tests demonstrate behavior for the tested inputs. The synthetic
commit message does not prove that a production incident happened. No real
application callers, UI integration, or non-integer input validation are modeled.