diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/.gitattributes b/codex-rs/apply-patch/tests/fixtures/scenarios/.gitattributes
new file mode 100644
index 000000000..a42a20ddc
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/.gitattributes
@@ -0,0 +1 @@
+** text eol=lf
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/001_add_file/expected/bar.md b/codex-rs/apply-patch/tests/fixtures/scenarios/001_add_file/expected/bar.md
new file mode 100644
index 000000000..6dfa057f0
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/001_add_file/expected/bar.md
@@ -0,0 +1 @@
+This is a new file
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/001_add_file/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/001_add_file/patch.txt
new file mode 100644
index 000000000..37735b2a4
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/modify.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/modify.txt
new file mode 100644
index 000000000..1b2ee3e56
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/modify.txt
@@ -0,0 +1,2 @@
+line1
+changed
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/nested/new.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/nested/new.txt
new file mode 100644
index 000000000..315166639
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/expected/nested/new.txt
@@ -0,0 +1 @@
+created
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/delete.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/delete.txt
new file mode 100644
index 000000000..6e263abce
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/delete.txt
@@ -0,0 +1 @@
+obsolete
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/modify.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/modify.txt
new file mode 100644
index 000000000..c0d0fb45c
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/input/modify.txt
@@ -0,0 +1,2 @@
+line1
+line2
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/002_multiple_operations/patch.txt
new file mode 100644
index 000000000..673dec2f7
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/expected/multi.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/expected/multi.txt
new file mode 100644
index 000000000..9054a7291
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/expected/multi.txt
@@ -0,0 +1,4 @@
+line1
+changed2
+line3
+changed4
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/input/multi.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/input/multi.txt
new file mode 100644
index 000000000..84275f993
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/input/multi.txt
@@ -0,0 +1,4 @@
+line1
+line2
+line3
+line4
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/003_multiple_chunks/patch.txt
new file mode 100644
index 000000000..45733c714
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/old/other.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/old/other.txt
new file mode 100644
index 000000000..b61039d3d
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/old/other.txt
@@ -0,0 +1 @@
+unrelated file
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/renamed/dir/name.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/renamed/dir/name.txt
new file mode 100644
index 000000000..b66ba06d3
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/expected/renamed/dir/name.txt
@@ -0,0 +1 @@
+new content
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/name.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/name.txt
new file mode 100644
index 000000000..33194a0a6
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/name.txt
@@ -0,0 +1 @@
+old content
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/other.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/other.txt
new file mode 100644
index 000000000..b61039d3d
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/input/old/other.txt
@@ -0,0 +1 @@
+unrelated file
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/004_move_to_new_directory/patch.txt
new file mode 100644
index 000000000..5e2d723a2
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/005_rejects_empty_patch/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/005_rejects_empty_patch/patch.txt
new file mode 100644
index 000000000..4fcfecbbc
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/005_rejects_empty_patch/patch.txt
@@ -0,0 +1,2 @@
+*** Begin Patch
+*** End Patch
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/expected/modify.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/expected/modify.txt
new file mode 100644
index 000000000..c0d0fb45c
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/expected/modify.txt
@@ -0,0 +1,2 @@
+line1
+line2
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/input/modify.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/input/modify.txt
new file mode 100644
index 000000000..c0d0fb45c
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/input/modify.txt
@@ -0,0 +1,2 @@
+line1
+line2
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/006_rejects_missing_context/patch.txt
new file mode 100644
index 000000000..488438b12
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/007_rejects_missing_file_delete/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/007_rejects_missing_file_delete/patch.txt
new file mode 100644
index 000000000..6f95531db
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/008_rejects_empty_update_hunk/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/008_rejects_empty_update_hunk/patch.txt
new file mode 100644
index 000000000..d7596a362
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/009_requires_existing_file_for_update/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/009_requires_existing_file_for_update/patch.txt
new file mode 100644
index 000000000..a7de4f24c
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/old/other.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/old/other.txt
new file mode 100644
index 000000000..b61039d3d
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/old/other.txt
@@ -0,0 +1 @@
+unrelated file
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/renamed/dir/name.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/renamed/dir/name.txt
new file mode 100644
index 000000000..3e757656c
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/expected/renamed/dir/name.txt
@@ -0,0 +1 @@
+new
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/name.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/name.txt
new file mode 100644
index 000000000..3940df7cd
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/name.txt
@@ -0,0 +1 @@
+from
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/other.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/other.txt
new file mode 100644
index 000000000..b61039d3d
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/old/other.txt
@@ -0,0 +1 @@
+unrelated file
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/renamed/dir/name.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/renamed/dir/name.txt
new file mode 100644
index 000000000..cbaf024e5
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/input/renamed/dir/name.txt
@@ -0,0 +1 @@
+existing
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/010_move_overwrites_existing_destination/patch.txt
new file mode 100644
index 000000000..c45ce6d78
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/expected/duplicate.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/expected/duplicate.txt
new file mode 100644
index 000000000..b66ba06d3
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/expected/duplicate.txt
@@ -0,0 +1 @@
+new content
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/input/duplicate.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/input/duplicate.txt
new file mode 100644
index 000000000..33194a0a6
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/input/duplicate.txt
@@ -0,0 +1 @@
+old content
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/011_add_overwrites_existing_file/patch.txt
new file mode 100644
index 000000000..bad9cf3fd
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/012_delete_directory_fails/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/012_delete_directory_fails/patch.txt
new file mode 100644
index 000000000..a10bcd9ea
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/012_delete_directory_fails/patch.txt
@@ -0,0 +1,3 @@
+*** Begin Patch
+*** Delete File: dir
+*** End Patch
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/013_rejects_invalid_hunk_header/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/013_rejects_invalid_hunk_header/patch.txt
new file mode 100644
index 000000000..b35d7207d
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/expected/no_newline.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/expected/no_newline.txt
new file mode 100644
index 000000000..06fcdd77c
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/input/no_newline.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/input/no_newline.txt
new file mode 100644
index 000000000..a6e09874b
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/input/no_newline.txt
@@ -0,0 +1 @@
+no newline at end
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/014_update_file_appends_trailing_newline/patch.txt
new file mode 100644
index 000000000..4ed5818eb
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/015_failure_after_partial_success_leaves_changes/expected/created.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/015_failure_after_partial_success_leaves_changes/expected/created.txt
new file mode 100644
index 000000000..ce0136250
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/015_failure_after_partial_success_leaves_changes/expected/created.txt
@@ -0,0 +1 @@
+hello
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/015_failure_after_partial_success_leaves_changes/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/015_failure_after_partial_success_leaves_changes/patch.txt
new file mode 100644
index 000000000..a6e9709d1
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/expected/input.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/expected/input.txt
new file mode 100644
index 000000000..f6d6f0bef
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/input/input.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/input/input.txt
new file mode 100644
index 000000000..c0d0fb45c
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/input/input.txt
@@ -0,0 +1,2 @@
+line1
+line2
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/016_pure_addition_update_chunk/patch.txt
new file mode 100644
index 000000000..56337549f
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/expected/foo.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/expected/foo.txt
new file mode 100644
index 000000000..3e757656c
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/expected/foo.txt
@@ -0,0 +1 @@
+new
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/input/foo.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/input/foo.txt
new file mode 100644
index 000000000..3367afdbb
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/input/foo.txt
@@ -0,0 +1 @@
+old
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/017_whitespace_padded_hunk_header/patch.txt
new file mode 100644
index 000000000..21e6c1958
--- /dev/null
+++ b/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
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/expected/file.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/expected/file.txt
new file mode 100644
index 000000000..f719efd43
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/expected/file.txt
@@ -0,0 +1 @@
+two
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/input/file.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/input/file.txt
new file mode 100644
index 000000000..5626abf0f
--- /dev/null
+++ b/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/input/file.txt
@@ -0,0 +1 @@
+one
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/patch.txt b/codex-rs/apply-patch/tests/fixtures/scenarios/018_whitespace_padded_patch_markers/patch.txt
new file mode 100644
index 000000000..264872179
--- /dev/null
+++ b/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 
diff --git a/codex-rs/apply-patch/tests/fixtures/scenarios/README.md b/codex-rs/apply-patch/tests/fixtures/scenarios/README.md
new file mode 100644
index 000000000..65d1fbe2e
--- /dev/null
+++ b/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
+```
diff --git a/codex-rs/apply-patch/tests/suite/mod.rs b/codex-rs/apply-patch/tests/suite/mod.rs
index 882c5a6ff..7d54de85a 100644
--- a/codex-rs/apply-patch/tests/suite/mod.rs
+++ b/codex-rs/apply-patch/tests/suite/mod.rs
@@ -1,3 +1,4 @@
 mod cli;
+mod scenarios;
 #[cfg(not(target_os = "windows"))]
 mod tool;
diff --git a/codex-rs/apply-patch/tests/suite/scenarios.rs b/codex-rs/apply-patch/tests/suite/scenarios.rs
new file mode 100644
index 000000000..4b3eb3c84
--- /dev/null
+++ b/codex-rs/apply-patch/tests/suite/scenarios.rs
@@ -0,0 +1,114 @@
+use assert_cmd::prelude::*;
+use pretty_assertions::assert_eq;
+use std::collections::BTreeMap;
+use std::fs;
+use std::path::Path;
+use std::path::PathBuf;
+use std::process::Command;
+use tempfile::tempdir;
+
+#[test]
+fn test_apply_patch_scenarios() -> anyhow::Result<()> {
+    for scenario in fs::read_dir("tests/fixtures/scenarios")? {
+        let scenario = scenario?;
+        let path = scenario.path();
+        if path.is_dir() {
+            run_apply_patch_scenario(&path)?;
+        }
+    }
+    Ok(())
+}
+
+/// Reads a scenario directory, copies the input files to a temporary directory, runs apply-patch,
+/// and asserts that the final state matches the expected state exactly.
+fn run_apply_patch_scenario(dir: &Path) -> anyhow::Result<()> {
+    let tmp = tempdir()?;
+
+    // Copy the input files to the temporary directory
+    let input_dir = dir.join("input");
+    if input_dir.is_dir() {
+        copy_dir_recursive(&input_dir, tmp.path())?;
+    }
+
+    // Read the patch.txt file
+    let patch = fs::read_to_string(dir.join("patch.txt"))?;
+
+    // Run apply_patch in the temporary directory. We intentionally do not assert
+    // on the exit status here; the scenarios are specified purely in terms of
+    // final filesystem state, which we compare below.
+    Command::cargo_bin("apply_patch")?
+        .arg(patch)
+        .current_dir(tmp.path())
+        .output()?;
+
+    // Assert that the final state matches the expected state exactly
+    let expected_dir = dir.join("expected");
+    let expected_snapshot = snapshot_dir(&expected_dir)?;
+    let actual_snapshot = snapshot_dir(tmp.path())?;
+
+    assert_eq!(
+        actual_snapshot,
+        expected_snapshot,
+        "Scenario {} did not match expected final state",
+        dir.display()
+    );
+
+    Ok(())
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+enum Entry {
+    File(Vec<u8>),
+    Dir,
+}
+
+fn snapshot_dir(root: &Path) -> anyhow::Result<BTreeMap<PathBuf, Entry>> {
+    let mut entries = BTreeMap::new();
+    if root.is_dir() {
+        snapshot_dir_recursive(root, root, &mut entries)?;
+    }
+    Ok(entries)
+}
+
+fn snapshot_dir_recursive(
+    base: &Path,
+    dir: &Path,
+    entries: &mut BTreeMap<PathBuf, Entry>,
+) -> anyhow::Result<()> {
+    for entry in fs::read_dir(dir)? {
+        let entry = entry?;
+        let path = entry.path();
+        let Some(stripped) = path.strip_prefix(base).ok() else {
+            continue;
+        };
+        let rel = stripped.to_path_buf();
+        let file_type = entry.file_type()?;
+        if file_type.is_dir() {
+            entries.insert(rel.clone(), Entry::Dir);
+            snapshot_dir_recursive(base, &path, entries)?;
+        } else if file_type.is_file() {
+            let contents = fs::read(&path)?;
+            entries.insert(rel, Entry::File(contents));
+        }
+    }
+    Ok(())
+}
+
+fn copy_dir_recursive(src: &Path, dst: &Path) -> anyhow::Result<()> {
+    for entry in fs::read_dir(src)? {
+        let entry = entry?;
+        let path = entry.path();
+        let file_type = entry.file_type()?;
+        let dest_path = dst.join(entry.file_name());
+        if file_type.is_dir() {
+            fs::create_dir_all(&dest_path)?;
+            copy_dir_recursive(&path, &dest_path)?;
+        } else if file_type.is_file() {
+            if let Some(parent) = dest_path.parent() {
+                fs::create_dir_all(parent)?;
+            }
+            fs::copy(&path, &dest_path)?;
+        }
+    }
+    Ok(())
+}