diff --git a/.cargo/config.toml b/.cargo/config.toml
new file mode 100644
index 00000000..5d8c2cd4
--- /dev/null
+++ b/.cargo/config.toml
@@ -0,0 +1,14 @@
+# Windows MSVC: bump the main-thread stack from the default 1 MiB to 8 MiB.
+#
+# Rust debug builds produce very large async state machines (no optimisation
+# collapses them), and `#[tokio::main]` polls the top-level future on the main
+# thread. The compile path nests many async fns whose combined Future state
+# easily exceeds 1 MiB, crashing with `thread 'main' has overflowed its stack`
+# on a stock `cargo build` + `target\debug\ado-aw.exe compile <fixture>` run.
+#
+# 8 MiB matches the Linux default and is what the binary already gets on
+# Linux/macOS, so applying it on Windows just restores parity rather than
+# introducing a platform-specific quirk. Release builds work either way; this
+# only matters in practice for debug/test builds.
+[target.'cfg(all(windows, target_env = "msvc"))']
+rustflags = ["-C", "link-arg=/STACK:8388608"]
diff --git a/tests/compiler_tests.rs b/tests/compiler_tests.rs
index 78d350a7..85de086e 100644
--- a/tests/compiler_tests.rs
+++ b/tests/compiler_tests.rs
@@ -851,11 +851,17 @@ fn test_1es_compiled_output_no_unreplaced_markers() {
     ));
     fs::create_dir_all(&temp_dir).expect("Failed to create temp directory");
 
-    let fixture_path = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+    let fixture_src = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
         .join("tests")
         .join("fixtures")
         .join("1es-test-agent.md");
 
+    // Copy the fixture into the temp dir before compiling so codemods
+    // (e.g. pool_object_form) can never rewrite the source tree, and
+    // parallel test runs cannot race on the same input file.
+    let fixture_path = temp_dir.join("1es-test-agent.md");
+    fs::copy(&fixture_src, &fixture_path).expect("Failed to copy 1ES fixture into temp dir");
+
     let output_path = temp_dir.join("1es-test-agent.yml");
 
     // Run the compiler binary
@@ -3520,11 +3526,20 @@ fn compile_fixture_with_flags(fixture_name: &str, extra_flags: &[&str]) -> Strin
     ));
     fs::create_dir_all(&temp_dir).expect("Failed to create temp directory");
 
-    let fixture_path = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+    let fixture_src = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
         .join("tests")
         .join("fixtures")
         .join(fixture_name);
 
+    // Copy the fixture into the temp dir before compiling. Codemods
+    // (e.g. pool_object_form) may rewrite the source on disk; copying
+    // keeps the canonical fixture under tests/fixtures pristine and
+    // prevents parallel tests that target the same fixture from
+    // racing on the lost-update guard in compile.
+    let fixture_path = temp_dir.join(fixture_name);
+    fs::copy(&fixture_src, &fixture_path)
+        .unwrap_or_else(|e| panic!("Failed to copy fixture {fixture_name} into temp dir: {e}"));
+
     let output_path = temp_dir.join(fixture_name.replace(".md", ".yml"));
 
     let binary_path = PathBuf::from(env!("CARGO_BIN_EXE_ado-aw"));