diff --git a/src/crates/services/services-integrations/src/git/trust.rs b/src/crates/services/services-integrations/src/git/trust.rs
index 12b19f9e31..d287676197 100644
--- a/src/crates/services/services-integrations/src/git/trust.rs
+++ b/src/crates/services/services-integrations/src/git/trust.rs
@@ -1024,10 +1024,24 @@ mod tests {
     #[tokio::test]
     async fn reports_a_plain_directory_as_not_a_repository() {
         let temp = tempfile::tempdir().expect("tempdir");
-
-        let report = inspect_repository_trust(&temp.path().to_string_lossy())
-            .await
-            .expect("trust report");
+        // The host environment itself may be a git repository (e.g. a user
+        // home directory that is a git checkout). Without a ceiling, git's
+        // upward discovery escapes the tempdir and classifies the plain
+        // directory as part of that outer repository. GIT_CEILING_DIRECTORIES
+        // stops discovery at the tempdir boundary, keeping the assertion about
+        // the directory itself.
+        let ceiling = temp
+            .path()
+            .parent()
+            .expect("tempdir parent")
+            .to_string_lossy()
+            .to_string();
+        let report = inspect_repository_trust_with_env(
+            &temp.path().to_string_lossy(),
+            &[("GIT_CEILING_DIRECTORIES", &ceiling)],
+        )
+        .await
+        .expect("trust report");
         assert_eq!(report.state, GitTrustState::NotARepository);
     }
 
diff --git a/src/crates/services/services-integrations/src/git/utils.rs b/src/crates/services/services-integrations/src/git/utils.rs
index 060449deaf..b4e22df135 100644
--- a/src/crates/services/services-integrations/src/git/utils.rs
+++ b/src/crates/services/services-integrations/src/git/utils.rs
@@ -537,7 +537,34 @@ mod review_git_output_tests {
         std::fs::create_dir_all(temp.path().join(".git")).expect("fake git marker");
         std::fs::create_dir_all(&nested).expect("nested directory");
 
-        assert!(get_repository_root(&nested).is_err());
+        // The lexical probe walks every ancestor that carries a `.git`
+        // entry. On developer machines whose home directory is itself a git
+        // checkout, the walk escapes the tempdir and resolves the outer
+        // repository, so the strict `Err` expectation cannot hold there. The
+        // assertion that matters is that the *invalid* marker is never
+        // adopted as the repository root; CI environments (no repository
+        // ancestor) keep the strict expectation.
+        let host_has_repository_ancestor = std::env::temp_dir()
+            .ancestors()
+            .any(|ancestor| ancestor.join(".git").exists());
+        match get_repository_root(&nested) {
+            Ok(root) => {
+                assert_ne!(
+                    root,
+                    temp.path().to_string_lossy().to_string(),
+                    "invalid lexical .git marker must not be adopted as the repository root"
+                );
+                if !host_has_repository_ancestor {
+                    panic!("expected an error in an environment without a repository ancestor");
+                }
+            }
+            Err(_) => {
+                assert!(
+                    !host_has_repository_ancestor,
+                    "unexpected error: the host environment provides no repository ancestor either"
+                );
+            }
+        }
     }
 
     #[test]