diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e27cadf4b..99300a356 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,9 +5,10 @@ on:
     branches: [main]
   pull_request:
 
+# The runner images are pinned to the platforms thirdshift supports.
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v7
       - uses: dtolnay/rust-toolchain@stable
@@ -17,5 +18,13 @@ jobs:
       - run: cargo fmt --check
       - run: cargo clippy --all-targets -- -D warnings
       # The tests run the binary against real git and fake gh and claude
-      # (Python scripts in tests/fakes), all present on ubuntu-latest.
+      # (Python scripts in tests/fakes), all present on the runner image.
+      - run: cargo test
+
+  test-macos:
+    runs-on: macos-26
+    steps:
+      - uses: actions/checkout@v7
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
       - run: cargo test
diff --git a/tests/support/mod.rs b/tests/support/mod.rs
index 684c1f6b8..3ceb21cc6 100644
--- a/tests/support/mod.rs
+++ b/tests/support/mod.rs
@@ -33,7 +33,11 @@ pub const OWNER: &str = "acme";
 pub const REPO: &str = "widgets";
 
 pub struct Scenario {
-    root: TempDir,
+    /// Deletes the temp root when the scenario is dropped.
+    _temp_dir: TempDir,
+    /// The temp root's path with symlinks resolved, as git reports it: on
+    /// macOS the temp directory is under `/var`, a symlink to `/private/var`.
+    root: PathBuf,
 }
 
 pub struct RunResult {
@@ -56,8 +60,12 @@ impl Scenario {
     /// An origin with one commit on `main`, a launch clone of it with `main`
     /// checked out, and an open issue #7.
     pub fn new() -> Self {
-        let root = TempDir::new().unwrap();
-        let scenario = Scenario { root };
+        let temp_dir = TempDir::new().unwrap();
+        let root = temp_dir.path().canonicalize().unwrap();
+        let scenario = Scenario {
+            _temp_dir: temp_dir,
+            root,
+        };
         for dir in ["home", "bin", "tmp", "work"] {
             fs::create_dir_all(scenario.path(dir)).unwrap();
         }
@@ -97,7 +105,7 @@ impl Scenario {
     }
 
     pub fn path(&self, relative: &str) -> PathBuf {
-        self.root.path().join(relative)
+        self.root.join(relative)
     }
 
     pub fn launch_dir(&self) -> PathBuf {