diff --git a/internal/server/pi_agent_datadir_test.go b/internal/server/pi_agent_datadir_test.go
new file mode 100644
index 00000000..02cd9b58
--- /dev/null
+++ b/internal/server/pi_agent_datadir_test.go
@@ -0,0 +1,54 @@
+package server_test
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestResolvePiAgentSharedDataDir_PrefersRepoRootDevOverPackageLocal(t *testing.T) {
+	root := t.TempDir()
+	mustMkdirAll(t, filepath.Join(root, "data", "dev", "workspaces"))
+	mustWrite(t, filepath.Join(root, "go.mod"), "module example\n")
+
+	pkgLocal := filepath.Join(root, "internal", "server", "data", "test", "workspaces")
+	mustMkdirAll(t, pkgLocal)
+
+	cwd := filepath.Join(root, "internal", "server")
+	got := resolvePiAgentSharedDataDir(cwd, "")
+	want := filepath.Join(root, "data", "dev")
+	if got != want {
+		t.Fatalf("got %q want repo-root %q (must not pick package-local %q)", got, want, filepath.Join(root, "internal", "server", "data", "test"))
+	}
+	if strings.Contains(filepath.ToSlash(got), "/internal/") {
+		t.Fatalf("resolved path must not be under internal/: %q", got)
+	}
+}
+
+func TestResolvePiAgentSharedDataDir_EnvOverrides(t *testing.T) {
+	root := t.TempDir()
+	mustMkdirAll(t, filepath.Join(root, "data", "dev", "workspaces"))
+	mustWrite(t, filepath.Join(root, "go.mod"), "module example\n")
+	override := filepath.Join(root, "custom-data")
+	mustMkdirAll(t, filepath.Join(override, "workspaces"))
+
+	got := resolvePiAgentSharedDataDir(filepath.Join(root, "internal", "server"), override)
+	if got != override {
+		t.Fatalf("got %q want env override %q", got, override)
+	}
+}
+
+func mustMkdirAll(t *testing.T, path string) {
+	t.Helper()
+	if err := os.MkdirAll(path, 0o755); err != nil {
+		t.Fatalf("mkdir %s: %v", path, err)
+	}
+}
+
+func mustWrite(t *testing.T, path, body string) {
+	t.Helper()
+	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
+		t.Fatalf("write %s: %v", path, err)
+	}
+}
diff --git a/internal/server/test_helpers_test.go b/internal/server/test_helpers_test.go
index 9259c862..8747388d 100644
--- a/internal/server/test_helpers_test.go
+++ b/internal/server/test_helpers_test.go
@@ -118,24 +118,42 @@ func envOr(key, fallback string) string {
 	return fallback
 }
 
-func piAgentSharedDataDir(t *testing.T) string {
-	t.Helper()
-	if d := strings.TrimSpace(os.Getenv("DATA_DIR")); d != "" {
+// resolvePiAgentSharedDataDir picks the host DATA_DIR that the pi-agent runner
+// bind-mounts (compose: ./data/<env>/workspaces → /app/data/workspaces).
+// Prefer DATA_DIR env, then repo-root data/dev|test via go.mod walk — never the
+// package-local internal/server/data/* tree, which the runner cannot see.
+func resolvePiAgentSharedDataDir(cwd, envDataDir string) string {
+	if d := strings.TrimSpace(envDataDir); d != "" {
 		return d
 	}
+	dir := filepath.Clean(cwd)
+	for i := 0; i < 8; i++ {
+		if _, err := os.Stat(filepath.Join(dir, "go.mod")); err == nil {
+			for _, envName := range []string{"dev", "test"} {
+				candidate := filepath.Join(dir, "data", envName)
+				if st, err := os.Stat(filepath.Join(candidate, "workspaces")); err == nil && st.IsDir() {
+					return candidate
+				}
+			}
+			return ""
+		}
+		parent := filepath.Dir(dir)
+		if parent == dir {
+			break
+		}
+		dir = parent
+	}
+	return ""
+}
+
+func piAgentSharedDataDir(t *testing.T) string {
+	t.Helper()
 	cwd, err := os.Getwd()
 	if err != nil {
 		t.Fatalf("getwd: %v", err)
 	}
-	for _, rel := range []string{".", "..", "../..", "../../.."} {
-		base := filepath.Clean(filepath.Join(cwd, rel))
-		for _, envName := range []string{"dev", "test"} {
-			candidate := filepath.Join(base, "data", envName)
-			ws := filepath.Join(candidate, "workspaces")
-			if st, statErr := os.Stat(ws); statErr == nil && st.IsDir() {
-				return candidate
-			}
-		}
+	if d := resolvePiAgentSharedDataDir(cwd, os.Getenv("DATA_DIR")); d != "" {
+		return d
 	}
 	t.Skip("shared pi-agent DATA_DIR not found (mount data/test/workspaces or data/dev/workspaces)")
 	return ""
diff --git a/scripts/run-nightly-real-pi.sh b/scripts/run-nightly-real-pi.sh
index d3ddc169..011ffe86 100755
--- a/scripts/run-nightly-real-pi.sh
+++ b/scripts/run-nightly-real-pi.sh
@@ -127,6 +127,10 @@ export RUNNER_AUTH_TOKEN="${TOKEN}"
 export PI_AGENT_MODEL="${MODEL_ID}"
 export RUN_PI_E2E=1
 export KB_REQUIRE_ONLINE="${KB_REQUIRE_ONLINE:-1}"
+# Host Go tests must write workspaces into the same tree the runner mounts
+# (docker-compose.dev.yml: ./data/dev/workspaces → /app/data/workspaces).
+export DATA_DIR="${DATA_DIR:-${ROOT}/data/dev}"
+echo "==> DATA_DIR=${DATA_DIR}"
 
 # Shared KB preflight (host :5432). Fail closed unless KB_ALLOW_OFFLINE=1.
 preflight_shared_kb() {