From 4ffbc854117a44bb63a70b4f31f1e709e9d58fc4 Mon Sep 17 00:00:00 2001
From: Kevin Veen-Birkenbach <kevin@veen.world>
Date: Tue, 3 Nov 2026 21:11:34 +0100
Subject: [PATCH] fix(kvb-git-commit-next): renumber kept hunks in
 stage_hunks.py

git apply --unidiff-zero places an add-only hunk, which has no context to match, at its new-side start line. That line counts every earlier hunk of the diff, so each hunk select() dropped shifted the later add-only hunks down by its size: on the real README a staged node landed in the wrong Mermaid subgraph. renumber() rewrites each kept header from the old start plus the net lines of the hunks kept before it (+1 for a pure insertion, -1 for a pure deletion), with counts that match the kept lines. A new test drops an early hunk and a line of a mixed one and compares the whole staged file; against the previous script it fails with the line one place too low.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../kvb-git-commit-next/scripts/stage_hunks.py | 18 +++++++++++++++++-
 tests/test_stage_hunks.py                      | 10 ++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/skills/kvb-git-commit-next/scripts/stage_hunks.py b/skills/kvb-git-commit-next/scripts/stage_hunks.py
index 72d2060..1594135 100755
--- a/skills/kvb-git-commit-next/scripts/stage_hunks.py
+++ b/skills/kvb-git-commit-next/scripts/stage_hunks.py
@@ -21,6 +21,22 @@ import subprocess
 import sys
 from pathlib import Path
 
+HEADER = re.compile(r"^@@ -(\d+)(?:,(\d+))? \+\d+(?:,\d+)? @@(.*)$")
+
+
+def renumber(hunks: list[list[str]]) -> list[list[str]]:
+    offset = 0
+    out = []
+    for hunk in hunks:
+        match = HEADER.match(hunk[0])
+        start, count = int(match.group(1)), int(match.group(2) or 1)
+        added = sum(line.startswith("+") for line in hunk[1:])
+        removed = sum(line.startswith("-") for line in hunk[1:])
+        new_start = start + offset + (1 if count == 0 else 0) - (1 if added == 0 else 0)
+        out.append([f"@@ -{start},{count} +{new_start},{added} @@{match.group(3)}", *hunk[1:]])
+        offset += added - removed
+    return out
+
 
 def fail(message: str) -> None:
     print(f"stage_hunks: {message}", file=sys.stderr)
@@ -78,7 +94,7 @@ def main() -> int:
     except re.error as error:
         fail(f"--match: {error}")
     header, hunks = split(git(repo, "diff", "--no-color", "-U0", "--", args.file))
-    kept = select(hunks, pattern)
+    kept = renumber(select(hunks, pattern))
     if not kept:
         print(f"stage_hunks: no change in {args.file} matches {args.match!r}", file=sys.stderr)
         return 1
diff --git a/tests/test_stage_hunks.py b/tests/test_stage_hunks.py
index de579bf..d52af3b 100644
--- a/tests/test_stage_hunks.py
+++ b/tests/test_stage_hunks.py
@@ -55,6 +55,16 @@ class TestStageHunks(unittest.TestCase):
         unstaged = [line for line in self._git("diff", "-U0").splitlines() if line.startswith("+") and not line.startswith("+++")]
         self.assertEqual(unstaged, ["+beta one", "+beta two"])
 
+    def test_kept_lines_land_where_they_stand_after_dropped_hunks(self):
+        self.file.write_text(
+            "one\nbeta one\ntwo\nthree\nalpha three\nbeta three\nfour\nfive\nalpha five\n", encoding="utf-8"
+        )
+        result = self._run("alpha")
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(
+            self._git("show", ":notes.txt"), "one\ntwo\nthree\nalpha three\nfour\nfive\nalpha five\n"
+        )
+
     def test_no_match_exits_1_and_bad_pattern_exits_2(self):
         self.assertEqual(self._run("gamma").returncode, 1)
         self.assertEqual(self._run("(").returncode, 2)