fix(git-extension): limit commit_style parsing to first match in config

Address Copilot review feedback on PR #3413: grep '^commit_style:' without
-m1 could concatenate values if a config file accidentally contains
multiple commit_style lines (e.g. from a bad merge/manual edit), causing
an unexpected fallback to 'fixed'. Limit to the first match and add a
regression test covering duplicate commit_style lines.

Assisted-by: GitHub Copilot (model: claude-sonnet-5, autonomous)
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: dhruv-15-03

extensions/git/scripts/bash/auto-commit.sh

@@ -55,7 +55,7 @@ _commit_style="fixed"
 
 if [ -f "$_config_file" ]; then
     # Top-level scalar key: commit_style (fixed | conventional)
-    _style_val=$(grep '^commit_style:' "$_config_file" 2>/dev/null | sed 's/^commit_style:[[:space:]]*//' | sed 's/[[:space:]]\{1,\}#.*$//' | sed 's/[[:space:]]*$//' | sed 's/^["'\'']//' | sed 's/["'\'']*$//' | tr -d '[:space:]' | tr '[:upper:]' '[:lower:]')
+    _style_val=$(grep -m1 '^commit_style:' "$_config_file" 2>/dev/null | sed 's/^commit_style:[[:space:]]*//' | sed 's/[[:space:]]\{1,\}#.*$//' | sed 's/[[:space:]]*$//' | sed 's/^["'\'']//' | sed 's/["'\'']*$//' | tr -d '[:space:]' | tr '[:upper:]' '[:lower:]')
     if [ -n "$_style_val" ]; then
         case "$_style_val" in
             fixed|conventional)

tests/extensions/git/test_git_extension.py

@@ -1222,6 +1222,32 @@ def test_unknown_commit_style_defaults_to_fixed(self, tmp_path: Path):
         )
         assert "[Spec Kit] Add specification" in log.stdout
 
+    def test_duplicate_commit_style_lines_use_first_match(self, tmp_path: Path):
+        """A config with multiple `commit_style:` lines (e.g. from a bad merge) uses only
+        the first match instead of concatenating values into an unrecognized style."""
+        project = _setup_project(tmp_path)
+        _write_config(project, (
+            "commit_style: conventional\n"
+            "commit_style: fixed\n"
+            "auto_commit:\n"
+            "  default: false\n"
+            "  after_specify:\n"
+            "    enabled: true\n"
+            '    message: "[Spec Kit] Add specification"\n'
+        ))
+        (project / "new-file.txt").write_text("content")
+        result = _run_bash(
+            "auto-commit.sh", project, "after_specify", "feat: add OAuth specification"
+        )
+        assert result.returncode == 0
+        assert "unknown commit_style" not in result.stderr.lower()
+        log = subprocess.run(
+            ["git", "log", "--oneline", "-1"],
+            cwd=project, capture_output=True, text=True,
+        )
+        assert "feat: add OAuth specification" in log.stdout
+        assert "[Spec Kit] Add specification" not in log.stdout
+
 
 @pytest.mark.skipif(not HAS_PWSH, reason="pwsh not available")
 class TestAutoCommitPowerShell: