test(handlers): add rows.Err() + query-error coverage for admin_delegations.go

Issue #1286.

Three previously-untested error-returning paths in the AdminDelegations
HTTP handlers:

- TestAdminDelegations_List_RowsErr_PartialResults:
  RowError(1) fires after Next() advances to row index 1 but before Scan,
  so rows.Err() is set but row 0 is already in `out`. Verifies the
  non-fatal contract: 200 returned with partial results.

- TestAdminDelegations_Stats_QueryError_Returns500:
  mock query fails with "connection refused". Verifies 500 returned.

- TestAdminDelegations_Stats_RowsErr_PartialResults:
  Same RowError injection pattern as List. Verifies 200 with partial
  stats on rows.Err(). Non-fatal contract documented in handler comment.

All 13 admin_delegations tests pass; full suite unchanged at 69.1%.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/handlers/admin_delegations_test.go

@@ -2,6 +2,7 @@ package handlers
 
 import (
 	"encoding/json"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -304,6 +305,110 @@ func TestAdminDelegations_Stats_EmptyTable(t *testing.T) {
 	}
 }
 
+// ---------- rows.Err() + query-error paths ----------
+
+// TestAdminDelegations_List_RowsErr_PartialResults verifies that a mid-scan
+// database error sets rows.Err() but List still returns 200 with the rows
+// successfully scanned before the error. This is the documented non-fatal
+// contract: delegation rows already in `out` are returned; the error is
+// logged only.
+func TestAdminDelegations_List_RowsErr_PartialResults(t *testing.T) {
+	mock := setupTestDB(t)
+	h := NewAdminDelegationsHandler(nil)
+
+	now := time.Now()
+	// Row 0 scans OK; Row 1 triggers the error before Scan.
+	// RowError(1, err) fires after Next() advances to row index 1 but
+	// before Scan is called on it, so rows.Err() is set but row 0 is in `out`.
+	mock.ExpectQuery(`SELECT delegation_id`).
+		WithArgs("queued", "dispatched", "in_progress", 100).
+		WillReturnRows(sqlmock.NewRows([]string{
+			"delegation_id", "caller_id", "callee_id", "task_preview",
+			"status", "last_heartbeat", "deadline", "result_preview", "error_detail",
+			"retry_count", "created_at", "updated_at",
+		}).
+			AddRow("deleg-ok", "caller-1", "callee-1", "task ok",
+				"queued", now, now.Add(2*time.Hour), nil, nil,
+				0, now.Add(-1*time.Minute), now.Add(-1*time.Minute)).
+			RowError(1, errors.New("storage engine fault")))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("GET", "/admin/delegations", nil)
+	h.List(c)
+
+	// Non-fatal: partial results returned.
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200 (partial results), got %d: %s", w.Code, w.Body.String())
+	}
+	var body map[string]any
+	if err := json.Unmarshal(w.Body.Bytes(), &body); err != nil {
+		t.Fatalf("body parse: %v", err)
+	}
+	if got := body["count"]; got != float64(1) {
+		t.Errorf("count: expected 1 (row 0 only), got %v", got)
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet: %v", err)
+	}
+}
+
+// TestAdminDelegations_Stats_QueryError_Returns500 verifies that a DB query
+// failure in Stats returns 500 with a JSON error body.
+func TestAdminDelegations_Stats_QueryError_Returns500(t *testing.T) {
+	mock := setupTestDB(t)
+	h := NewAdminDelegationsHandler(nil)
+
+	mock.ExpectQuery(`SELECT status, COUNT\(\*\) FROM delegations GROUP BY status`).
+		WillReturnError(errors.New("connection refused"))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("GET", "/admin/delegations/stats", nil)
+	h.Stats(c)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500 on query error, got %d", w.Code)
+	}
+}
+
+// TestAdminDelegations_Stats_RowsErr_PartialResults verifies that a mid-scan
+// database error sets rows.Err() but Stats still returns 200 with the
+// counts successfully scanned before the error. The documented non-fatal
+// contract: partial stats are returned; the error is logged only.
+func TestAdminDelegations_Stats_RowsErr_PartialResults(t *testing.T) {
+	mock := setupTestDB(t)
+	h := NewAdminDelegationsHandler(nil)
+
+	// Row 0 scans OK; Row 1 triggers the error.
+	// RowError(1, err) fires after Next() advances to row index 1 but before
+	// Scan is called, so rows.Err() is set but row 0 is already in `stats`.
+	mock.ExpectQuery(`SELECT status, COUNT\(\*\) FROM delegations GROUP BY status`).
+		WillReturnRows(sqlmock.NewRows([]string{"status", "count"}).
+			AddRow("in_progress", 7).
+			RowError(1, errors.New("storage engine fault")))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("GET", "/admin/delegations/stats", nil)
+	h.Stats(c)
+
+	// Non-fatal: partial results returned.
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200 (partial results), got %d: %s", w.Code, w.Body.String())
+	}
+	var stats map[string]int
+	if err := json.Unmarshal(w.Body.Bytes(), &stats); err != nil {
+		t.Fatalf("body parse: %v", err)
+	}
+	if stats["in_progress"] != 7 {
+		t.Errorf("in_progress count: expected 7, got %d", stats["in_progress"])
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet: %v", err)
+	}
+}
+
 // statusFilters is a contract surface — every key here is documented in
 // the endpoint comment + accepted by the validator. Pin it.
 func TestStatusFiltersTableShape(t *testing.T) {