diff --git a/changelog.d/unreleased/2951.fixed.md b/changelog.d/unreleased/2951.fixed.md
new file mode 100644
index 0000000000..3ec9306675
--- /dev/null
+++ b/changelog.d/unreleased/2951.fixed.md
@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 2951
+affected:
+  - src/CodeIndex/Cli/DbPathResolver.cs
+  - tests/CodeIndex.Tests/DbPathResolverTests.cs
+---
+
+## English
+
+- **DbPathResolver query tests now isolate active workspace state (#2951)** — internal query data-dir resolution tests can inject active-workspace state explicitly, so ambient user config no longer redirects the temporary project roots under test.
+
+## 日本語
+
+- **DbPathResolver の query test が active workspace state を隔離するようになりました (#2951)** — internal query data-dir resolution test が active-workspace state を明示的に注入できるようになり、ambient なユーザー設定でテスト用の一時 project root が別 DB に向かなくなりました。
diff --git a/src/CodeIndex/Cli/DbPathResolver.cs b/src/CodeIndex/Cli/DbPathResolver.cs
index 92ccc6531e..1124e54045 100644
--- a/src/CodeIndex/Cli/DbPathResolver.cs
+++ b/src/CodeIndex/Cli/DbPathResolver.cs
@@ -60,7 +60,12 @@ internal static DbPathResolution ResolveDataDir(string workspacePath, string? ex
         return BuildDataDirResolution(Path.Combine(fullWorkspacePath, ".cdidx"), DataDirSourceWorkspace);
     }
 
-    internal static DbPathResolution ResolveDataDirForQuery(string workspacePath, string? explicitDataDir, string? environmentDataDir, string? xdgDataHome)
+    internal static DbPathResolution ResolveDataDirForQuery(
+        string workspacePath,
+        string? explicitDataDir,
+        string? environmentDataDir,
+        string? xdgDataHome,
+        Func<ActiveWorkspaceState?>? activeWorkspaceLoader = null)
     {
         var fullWorkspacePath = Path.GetFullPath(workspacePath);
         if (!string.IsNullOrWhiteSpace(explicitDataDir))
@@ -69,7 +74,7 @@ internal static DbPathResolution ResolveDataDirForQuery(string workspacePath, st
         if (!string.IsNullOrWhiteSpace(environmentDataDir))
             return BuildDataDirResolution(environmentDataDir, DataDirSourceEnv);
 
-        var active = ActiveWorkspace.Load();
+        var active = (activeWorkspaceLoader ?? ActiveWorkspace.Load)();
         if (active != null)
             return new DbPathResolution(active.DbPath, Path.GetDirectoryName(active.DbPath), DataDirSourceActiveWorkspace);
 
diff --git a/tests/CodeIndex.Tests/DbPathResolverTests.cs b/tests/CodeIndex.Tests/DbPathResolverTests.cs
index 7e324c1629..69ac383f52 100644
--- a/tests/CodeIndex.Tests/DbPathResolverTests.cs
+++ b/tests/CodeIndex.Tests/DbPathResolverTests.cs
@@ -89,7 +89,12 @@ public void ResolveDataDirForQuery_WithXdgPrefersAncestorWorkspaceDataDir()
             var indexedRootResolution = DbPathResolver.ResolveDataDir(projectRoot, explicitDataDir: null, environmentDataDir: null, xdgDataHome: xdgDir);
             Directory.CreateDirectory(indexedRootResolution.DataDir!);
 
-            var resolved = DbPathResolver.ResolveDataDirForQuery(child, explicitDataDir: null, environmentDataDir: null, xdgDataHome: xdgDir);
+            var resolved = DbPathResolver.ResolveDataDirForQuery(
+                child,
+                explicitDataDir: null,
+                environmentDataDir: null,
+                xdgDataHome: xdgDir,
+                activeWorkspaceLoader: () => null);
 
             Assert.Equal(indexedRootResolution.DbPath, resolved.DbPath);
             Assert.Equal(indexedRootResolution.DataDir, resolved.DataDir);
@@ -113,7 +118,12 @@ public void ResolveDataDirForQuery_PrefersOutermostAncestorCdidx()
             Directory.CreateDirectory(Path.Combine(projectRoot, ".cdidx"));
             Directory.CreateDirectory(Path.Combine(projectRoot, "src", ".cdidx"));
 
-            var resolved = DbPathResolver.ResolveDataDirForQuery(child, explicitDataDir: null, environmentDataDir: null, xdgDataHome: null);
+            var resolved = DbPathResolver.ResolveDataDirForQuery(
+                child,
+                explicitDataDir: null,
+                environmentDataDir: null,
+                xdgDataHome: null,
+                activeWorkspaceLoader: () => null);
 
             Assert.Equal(Path.Combine(projectRoot, ".cdidx", "codeindex.db"), resolved.DbPath);
             Assert.Equal(DbPathResolver.DataDirSourceWorkspace, resolved.DataDirSource);
@@ -124,6 +134,36 @@ public void ResolveDataDirForQuery_PrefersOutermostAncestorCdidx()
         }
     }
 
+    [Fact]
+    public void ResolveDataDirForQuery_UsesInjectedActiveWorkspaceBeforeAncestorCdidx()
+    {
+        var projectRoot = TestProjectHelper.CreateTempProject("cdidx_query_active_workspace_project");
+        var activeRoot = TestProjectHelper.CreateTempProject("cdidx_query_active_workspace_state");
+        var activeDb = Path.Combine(activeRoot, ".cdidx", "codeindex.db");
+        try
+        {
+            var child = Path.Combine(projectRoot, "src", "App");
+            Directory.CreateDirectory(child);
+            Directory.CreateDirectory(Path.Combine(projectRoot, ".cdidx"));
+
+            var resolved = DbPathResolver.ResolveDataDirForQuery(
+                child,
+                explicitDataDir: null,
+                environmentDataDir: null,
+                xdgDataHome: null,
+                activeWorkspaceLoader: () => new ActiveWorkspaceState("test", activeRoot, activeDb));
+
+            Assert.Equal(Path.GetFullPath(activeDb), resolved.DbPath);
+            Assert.Equal(Path.GetDirectoryName(Path.GetFullPath(activeDb)), resolved.DataDir);
+            Assert.Equal(DbPathResolver.DataDirSourceActiveWorkspace, resolved.DataDirSource);
+        }
+        finally
+        {
+            TestProjectHelper.DeleteDirectory(projectRoot);
+            TestProjectHelper.DeleteDirectory(activeRoot);
+        }
+    }
+
     [Fact]
     public void ResolveDataDirForQuery_FallsBackToCurrentDirectoryWhenNoAncestorCdidxExists()
     {
@@ -133,7 +173,12 @@ public void ResolveDataDirForQuery_FallsBackToCurrentDirectoryWhenNoAncestorCdid
             var child = Path.Combine(projectRoot, "src", "App");
             Directory.CreateDirectory(child);
 
-            var resolved = DbPathResolver.ResolveDataDirForQuery(child, explicitDataDir: null, environmentDataDir: null, xdgDataHome: null);
+            var resolved = DbPathResolver.ResolveDataDirForQuery(
+                child,
+                explicitDataDir: null,
+                environmentDataDir: null,
+                xdgDataHome: null,
+                activeWorkspaceLoader: () => null);
 
             Assert.Equal(Path.Combine(child, ".cdidx", "codeindex.db"), resolved.DbPath);
             Assert.Equal(DbPathResolver.DataDirSourceWorkspace, resolved.DataDirSource);