diff --git a/crates/path-cli/tests/support/mod.rs b/crates/path-cli/tests/support/mod.rs
index 578b5af1..b3ae4ae4 100644
--- a/crates/path-cli/tests/support/mod.rs
+++ b/crates/path-cli/tests/support/mod.rs
@@ -26,11 +26,20 @@ pub fn env_lock() -> std::sync::MutexGuard<'static, ()> {
         .unwrap_or_else(|e| e.into_inner())
 }
 
-/// RAII guard that pins `$HOME` and `$TOOLPATH_CONFIG_DIR` to a tempdir.
+/// RAII guard that pins `$HOME`, `$TOOLPATH_CONFIG_DIR`, and
+/// `$XDG_DATA_HOME` to a tempdir.
+///
+/// `$XDG_DATA_HOME` matters because the opencode `PathResolver` prefers it
+/// over `$HOME` when locating `opencode.db`. Without pinning it, a machine
+/// that sets `$XDG_DATA_HOME` (common on Linux; also set on this dev box)
+/// would send the opencode projector to the *real* user database — the
+/// test would fail with "table … already exists" and, worse, mutate the
+/// user's live opencode data. Pinning it keeps every harness sandboxed.
 pub struct ScopedHome {
     _td: tempfile::TempDir,
     prev_home: Option<OsString>,
     prev_config: Option<OsString>,
+    prev_xdg_data: Option<OsString>,
 }
 
 impl ScopedHome {
@@ -38,14 +47,17 @@ impl ScopedHome {
         let td = tempfile::tempdir().unwrap();
         let prev_home = std::env::var_os("HOME");
         let prev_config = std::env::var_os("TOOLPATH_CONFIG_DIR");
+        let prev_xdg_data = std::env::var_os("XDG_DATA_HOME");
         unsafe {
             std::env::set_var("HOME", td.path());
             std::env::set_var("TOOLPATH_CONFIG_DIR", td.path().join(".toolpath"));
+            std::env::set_var("XDG_DATA_HOME", td.path().join(".local/share"));
         }
         Self {
             _td: td,
             prev_home,
             prev_config,
+            prev_xdg_data,
         }
     }
 
@@ -65,6 +77,10 @@ impl Drop for ScopedHome {
                 Some(v) => std::env::set_var("TOOLPATH_CONFIG_DIR", v),
                 None => std::env::remove_var("TOOLPATH_CONFIG_DIR"),
             }
+            match &self.prev_xdg_data {
+                Some(v) => std::env::set_var("XDG_DATA_HOME", v),
+                None => std::env::remove_var("XDG_DATA_HOME"),
+            }
         }
     }
 }