fix apply patch when user has no git

QUICKSTART.md

@@ -177,6 +177,7 @@ pipeline:
       type: patch_apply
       mode: apply
       output: patch-apply-output.txt
+      on_fail: implement
 
     - id: test
       type: command

README.md

@@ -161,6 +161,7 @@ pipeline:
       type: patch_apply
       mode: apply
       output: patch-apply-output.txt
+      on_fail: implement
 
     - id: test
       type: command

docs/tutorial/01-intro.md

@@ -167,6 +167,7 @@ In `nightshift.yaml`:
   type: patch_apply
   mode: dry_run
   output: patch-apply-output.txt
+  on_fail: implement
 ```
 
 Run one task:
@@ -199,6 +200,7 @@ If the dry run looks good, switch to apply mode:
   type: patch_apply
   mode: apply
   output: patch-apply-output.txt
+  on_fail: implement
 ```
 
 Run again:

examples/quickstart-lisp/nightshift.yaml

@@ -67,6 +67,7 @@ pipeline:
       type: patch_apply
       mode: apply
       output: patch-apply-output.txt
+      on_fail: implement
 
     - id: test
       type: command

nightshift/patches.py

@@ -81,6 +81,8 @@ def validate_patch(
 
     for path_text in files:
         _validate_patch_path(path_text, root, scoped_roots, forbidden_paths)
+    _validate_hunk_lines(patch)
+    _validate_file_states(patch, root)
     return PatchValidationResult(files=tuple(sorted(files)), changed_lines=changed_lines)
 
 
@@ -174,6 +176,57 @@ def _patch_files(patch: str) -> set[str]:
     return {path for path in files if path}
 
 
+def _validate_hunk_lines(patch: str) -> None:
+    in_hunk = False
+    for line_number, line in enumerate(patch.splitlines(), start=1):
+        if line.startswith("diff --git "):
+            in_hunk = False
+            continue
+        if line.startswith("@@"):
+            in_hunk = True
+            continue
+        if not in_hunk:
+            continue
+        if line.startswith(("+", "-", " ", "\\")):
+            continue
+        raise PipelineError(
+            "Patch validation failed: malformed hunk line "
+            f"{line_number}; expected ' ', '+', '-', or '\\'."
+        )
+
+
+def _validate_file_states(patch: str, root: Path) -> None:
+    current_path: str | None = None
+    current_is_new = False
+    current_is_deleted = False
+
+    def flush() -> None:
+        if not current_path:
+            return
+        target = root / current_path
+        if current_is_new and target.exists():
+            raise PipelineError(
+                f"Patch validation failed: patch creates existing file `{current_path}`."
+            )
+        if current_is_deleted and not target.exists():
+            raise PipelineError(
+                f"Patch validation failed: patch deletes missing file `{current_path}`."
+            )
+
+    for line in patch.splitlines():
+        if line.startswith("diff --git "):
+            flush()
+            parts = line.split()
+            current_path = _strip_prefix(parts[3]) if len(parts) >= 4 else None
+            current_is_new = False
+            current_is_deleted = False
+        elif line.startswith("new file mode "):
+            current_is_new = True
+        elif line.startswith("deleted file mode "):
+            current_is_deleted = True
+    flush()
+
+
 def _changed_line_count(patch: str) -> int:
     count = 0
     for line in patch.splitlines():

tests/test_patches.py

@@ -52,6 +52,50 @@ class PatchTests(unittest.TestCase):
             with self.assertRaisesRegex(PipelineError, "forbidden path"):
                 validate_patch(patch, root, safety)
 
+    def test_validate_patch_rejects_malformed_hunk_line(self) -> None:
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            (root / "src").mkdir()
+            safety = SafetyConfig(
+                require_clean_worktree=False,
+                scoped_paths=("src",),
+                allowed_commands=(),
+                forbidden_commands=(),
+            )
+            patch = """diff --git a/src/app.py b/src/app.py
+--- a/src/app.py
++++ b/src/app.py
+@@ -1 +1,2 @@
+-old
++new
+bare line
+"""
+
+            with self.assertRaisesRegex(PipelineError, "malformed hunk line"):
+                validate_patch(patch, root, safety)
+
+    def test_validate_patch_rejects_new_file_when_target_exists(self) -> None:
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            (root / "src").mkdir()
+            (root / "src" / "app.py").write_text("old\n", encoding="utf-8")
+            safety = SafetyConfig(
+                require_clean_worktree=False,
+                scoped_paths=("src",),
+                allowed_commands=(),
+                forbidden_commands=(),
+            )
+            patch = """diff --git a/src/app.py b/src/app.py
+new file mode 100644
+--- /dev/null
++++ b/src/app.py
+@@ -0,0 +1 @@
++new
+"""
+
+            with self.assertRaisesRegex(PipelineError, "creates existing file"):
+                validate_patch(patch, root, safety)
+
 
 if __name__ == "__main__":
     unittest.main()