chore(apply-patch) scenarios for e2e testing (#7567)

## Summary
This PR introduces an End to End test suite for apply-patch, so we can
easily validate behavior against other implementations as well.

## Testing
- [x] These are tests

codex-rs/apply-patch/tests/fixtures/scenarios/.gitattributes

@@ -0,0 +1 @@
+** text eol=lf

codex-rs/apply-patch/tests/fixtures/scenarios/001_add_file/expected/bar.md

@@ -0,0 +1 @@
+This is a new file

codex-rs/apply-patch/tests/fixtures/scenarios/001_add_file/patch.txt

@@ -0,0 +1,4 @@
+*** Begin Patch
+*** Add File: bar.md
++This is a new file
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/modify.txt

@@ -0,0 +1,2 @@
+line1
+changed

codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/nested/new.txt

@@ -0,0 +1 @@
+created

codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/delete.txt

@@ -0,0 +1 @@
+obsolete

codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/modify.txt

@@ -0,0 +1,2 @@
+line1
+line2

codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/patch.txt

@@ -0,0 +1,9 @@
+*** Begin Patch
+*** Add File: nested/new.txt
++created
+*** Delete File: delete.txt
+*** Update File: modify.txt
+@@
+-line2
++changed
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/expected/multi.txt

@@ -0,0 +1,4 @@
+line1
+changed2
+line3
+changed4

codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/input/multi.txt

@@ -0,0 +1,4 @@
+line1
+line2
+line3
+line4

codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/patch.txt

@@ -0,0 +1,9 @@
+*** Begin Patch
+*** Update File: multi.txt
+@@
+-line2
++changed2
+@@
+-line4
++changed4
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/old/other.txt

@@ -0,0 +1 @@
+unrelated file

codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/renamed/dir/name.txt

@@ -0,0 +1 @@
+new content

codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/name.txt

@@ -0,0 +1 @@
+old content

codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/other.txt

@@ -0,0 +1 @@
+unrelated file

codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/patch.txt

@@ -0,0 +1,7 @@
+*** Begin Patch
+*** Update File: old/name.txt
+*** Move to: renamed/dir/name.txt
+@@
+-old content
++new content
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/005_rejects_empty_patch/patch.txt

@@ -0,0 +1,2 @@
+*** Begin Patch
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/expected/modify.txt

@@ -0,0 +1,2 @@
+line1
+line2

codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/input/modify.txt

@@ -0,0 +1,2 @@
+line1
+line2

codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/patch.txt

@@ -0,0 +1,6 @@
+*** Begin Patch
+*** Update File: modify.txt
+@@
+-missing
++changed
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/007_rejects_missing_file_delete/patch.txt

@@ -0,0 +1,3 @@
+*** Begin Patch
+*** Delete File: missing.txt
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/008_rejects_empty_update_hunk/patch.txt

@@ -0,0 +1,3 @@
+*** Begin Patch
+*** Update File: foo.txt
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/009_requires_existing_file_for_update/patch.txt

@@ -0,0 +1,6 @@
+*** Begin Patch
+*** Update File: missing.txt
+@@
+-old
++new
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/old/other.txt

@@ -0,0 +1 @@
+unrelated file

codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/renamed/dir/name.txt

@@ -0,0 +1 @@
+new

codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/name.txt

@@ -0,0 +1 @@
+from

codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/other.txt

@@ -0,0 +1 @@
+unrelated file

codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/renamed/dir/name.txt

@@ -0,0 +1 @@
+existing

codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/patch.txt

@@ -0,0 +1,7 @@
+*** Begin Patch
+*** Update File: old/name.txt
+*** Move to: renamed/dir/name.txt
+@@
+-from
++new
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/expected/duplicate.txt

@@ -0,0 +1 @@
+new content

codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/input/duplicate.txt

@@ -0,0 +1 @@
+old content

codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/patch.txt

@@ -0,0 +1,4 @@
+*** Begin Patch
+*** Add File: duplicate.txt
++new content
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/012_delete_directory_fails/patch.txt

@@ -0,0 +1,3 @@
+*** Begin Patch
+*** Delete File: dir
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/013_rejects_invalid_hunk_header/patch.txt

@@ -0,0 +1,3 @@
+*** Begin Patch
+*** Frobnicate File: foo
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/expected/no_newline.txt

@@ -0,0 +1,2 @@
+first line
+second line

codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/input/no_newline.txt

@@ -0,0 +1 @@
+no newline at end

codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/patch.txt

@@ -0,0 +1,7 @@
+*** Begin Patch
+*** Update File: no_newline.txt
+@@
+-no newline at end
++first line
++second line
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/015_failure_after_partial_success_leaves_changes/expected/created.txt

@@ -0,0 +1 @@
+hello

codex-rs/apply-patch/tests/fixtures/scenarios/015_failure_after_partial_success_leaves_changes/patch.txt

@@ -0,0 +1,8 @@
+*** Begin Patch
+*** Add File: created.txt
++hello
+*** Update File: missing.txt
+@@
+-old
++new
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/expected/input.txt

@@ -0,0 +1,4 @@
+line1
+line2
+added line 1
+added line 2

codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/input/input.txt

@@ -0,0 +1,2 @@
+line1
+line2

codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/patch.txt

@@ -0,0 +1,6 @@
+*** Begin Patch
+*** Update File: input.txt
+@@
++added line 1
++added line 2
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/expected/foo.txt

@@ -0,0 +1 @@
+new

codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/input/foo.txt

@@ -0,0 +1 @@
+old

codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/patch.txt

@@ -0,0 +1,6 @@
+*** Begin Patch
+  *** Update File: foo.txt
+@@
+-old
++new
+*** End Patch

codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/expected/file.txt

@@ -0,0 +1 @@
+two

codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/input/file.txt

@@ -0,0 +1 @@
+one

codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/patch.txt

@@ -0,0 +1,6 @@
+ *** Begin Patch
+*** Update File: file.txt
+@@
+-one
++two
+*** End Patch 

codex-rs/apply-patch/tests/fixtures/scenarios/README.md

@@ -0,0 +1,18 @@
+# Overview
+This directory is a collection of end to end tests for the apply-patch specification, meant to be easily portable to other languages or platforms.
+
+
+# Specification
+Each test case is one directory, composed of input state (input/), the patch operation (patch.txt), and the expected final state (expected/). This structure is designed to keep tests simple (i.e. test exactly one patch at a time) while still providing enough flexibility to test any given operation across files.
+
+Here's what this would look like for a simple test apply-patch test case to create a new file:
+
+```
+001_add/
+  input/
+    foo.md
+  expected/
+    foo.md
+    bar.md
+  patch.txt
+```