diff --git a/src/crates/adapters/opencode-adapter/src/instruction_source.rs b/src/crates/adapters/opencode-adapter/src/instruction_source.rs
index 816962db89..5f18d1c656 100644
--- a/src/crates/adapters/opencode-adapter/src/instruction_source.rs
+++ b/src/crates/adapters/opencode-adapter/src/instruction_source.rs
@@ -448,6 +448,7 @@ mod tests {
         let config_dir = temp.path().join("config");
         let workspace = temp.path().join("workspace");
         std::fs::create_dir_all(&config_dir).expect("config directory");
+        std::fs::create_dir_all(workspace.join(".git")).expect("workspace git boundary");
         std::fs::create_dir_all(&workspace).expect("workspace directory");
         std::fs::write(workspace.join("file.md"), "file\n").expect("file instruction");
         std::fs::write(workspace.join("inline.md"), "inline\n").expect("inline instruction");
@@ -477,6 +478,7 @@ mod tests {
         let config_dir = temp.path().join("config");
         let workspace = temp.path().join("workspace");
         std::fs::create_dir_all(&config_dir).expect("config directory");
+        std::fs::create_dir_all(workspace.join(".git")).expect("workspace git boundary");
         std::fs::create_dir_all(&workspace).expect("workspace directory");
         for name in ["legacy.md", "global.md", "shared.md", "project.md"] {
             std::fs::write(workspace.join(name), format!("{name}\n")).expect("instruction");
@@ -573,6 +575,7 @@ mod tests {
         let outside = temp.path().join("explicit.md");
         std::fs::create_dir_all(&config_dir).expect("config directory");
         std::fs::create_dir_all(&home_dir).expect("home directory");
+        std::fs::create_dir_all(workspace.join(".git")).expect("workspace git boundary");
         std::fs::create_dir_all(workspace.join("rules/nested")).expect("rules directory");
         std::fs::write(workspace.join("rules/b.md"), "b\n").expect("b rule");
         std::fs::write(workspace.join("rules/a.md"), "a\n").expect("a rule");
@@ -732,6 +735,7 @@ mod tests {
         let config_dir = temp.path().join("config");
         let workspace = temp.path().join("workspace");
         std::fs::create_dir_all(&config_dir).expect("config directory");
+        std::fs::create_dir_all(workspace.join(".git")).expect("workspace git boundary");
         std::fs::create_dir_all(&workspace).expect("workspace directory");
         std::fs::write(workspace.join("root.md"), "root\n").expect("root rule");
         let mut unrelated = workspace.join("unrelated");
@@ -758,6 +762,7 @@ mod tests {
         let config_dir = temp.path().join("config");
         let workspace = temp.path().join("workspace");
         std::fs::create_dir_all(&config_dir).expect("config directory");
+        std::fs::create_dir_all(workspace.join(".git")).expect("workspace git boundary");
         std::fs::create_dir_all(workspace.join("team-alpha")).expect("matching directory");
         std::fs::write(workspace.join("team-alpha/rule.md"), "matching\n").expect("matching rule");
         let unrelated = workspace.join("vendor");
@@ -785,6 +790,7 @@ mod tests {
         let config_dir = temp.path().join("config");
         let workspace = temp.path().join("workspace");
         std::fs::create_dir_all(&config_dir).expect("config directory");
+        std::fs::create_dir_all(workspace.join(".git")).expect("workspace git boundary");
         std::fs::write(config_dir.join("AGENTS.md"), "global\n").expect("global rule");
         let mut too_deep = workspace.join("docs");
         for index in 0..33 {
@@ -810,6 +816,7 @@ mod tests {
         let config_dir = temp.path().join("config");
         let workspace = temp.path().join("workspace");
         std::fs::create_dir_all(&config_dir).expect("config directory");
+        std::fs::create_dir_all(workspace.join(".git")).expect("workspace git boundary");
         std::fs::create_dir_all(&workspace).expect("workspace directory");
         for index in 0..257 {
             let name = format!("rules/{index:03}.md");
diff --git a/src/crates/adapters/opencode-adapter/tests/tool_source_contracts.rs b/src/crates/adapters/opencode-adapter/tests/tool_source_contracts.rs
index d4b601e277..46523e2cb1 100644
--- a/src/crates/adapters/opencode-adapter/tests/tool_source_contracts.rs
+++ b/src/crates/adapters/opencode-adapter/tests/tool_source_contracts.rs
@@ -198,6 +198,12 @@ fn explicit_config_directory_is_appended_to_the_default_global_directory() {
         project_config_enabled: false,
     });
 
+    // Anchor the project boundary at the workspace so the host environment's
+    // own git repository (e.g. a user home directory that is a git checkout)
+    // cannot leak into find_project_root and reclassify the explicit global
+    // directory as workspace-local.
+    fs::create_dir_all(temp.path().join("workspace/.git")).unwrap();
+
     let snapshot = provider
         .discover(&context(temp.path().join("workspace")))
         .unwrap();