workspace-server/internal/handlers/delegation.go

@@ -747,6 +747,14 @@ func (h *DelegationHandler) listDelegationsFromLedger(ctx context.Context, works
 			entry["response_preview"] = textutil.TruncateBytes(resultPreview.String, 300)
 		}
 		if errorDetail.Valid && errorDetail.String != "" {
+			// Emit both keys: `error_detail` is the canonical field the
+			// Python poll-mode consumer (a2a_tools_delegation.py:184)
+			// reads from /delegations rows — without it, poll-mode
+			// silently loses the failure reason and falls through to
+			// the generic "delegation failed" string. `error` is kept
+			// for back-compat with existing UI surfaces that read the
+			// shorter name.
+			entry["error_detail"] = errorDetail.String
 			entry["error"] = errorDetail.String
 		}
 		if lastHeartbeat != nil {
@@ -808,6 +816,8 @@ func (h *DelegationHandler) listDelegationsFromActivityLogs(ctx context.Context,
 			entry["delegation_id"] = delegationID
 		}
 		if errorDetail != "" {
+			// Emit both keys per the rename: see listDelegationsFromLedger.
+			entry["error_detail"] = errorDetail
 			entry["error"] = errorDetail
 		}
 		if responseBody != "" {

workspace-server/internal/handlers/delegation_test.go

@@ -1546,6 +1546,71 @@ func TestListDelegations_LedgerEmptyFallsBackToActivityLogs(t *testing.T) {
 	}
 }
 
+// ---------- ListDelegations: activity_logs failed row emits BOTH error + error_detail ----------
+
+// Field-rename pin (P1 #348 / RFC #2829 PR-2 follow-up): the legacy
+// activity_logs fallback path must also emit `error_detail` alongside
+// the historical `error` key. Without this, poll-mode (which reads
+// `error_detail`) silently loses the failure reason when the ledger
+// is empty and the handler falls back to activity_logs.
+func TestListDelegations_ActivityLogsFailedEmitsBothErrorKeys(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	wh := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+	dh := NewDelegationHandler(wh, broadcaster)
+
+	// Ledger empty → fall back to activity_logs.
+	mock.ExpectQuery("SELECT d.delegation_id, d.caller_id, d.callee_id, d.task_preview").
+		WithArgs("ws-source").
+		WillReturnRows(sqlmock.NewRows([]string{
+			"delegation_id", "caller_id", "callee_id", "task_preview",
+			"status", "result_preview", "error_detail", "last_heartbeat",
+			"deadline", "created_at", "updated_at",
+		}))
+
+	now := time.Now()
+	activityRows := sqlmock.NewRows([]string{
+		"id", "activity_type", "source_id", "target_id",
+		"summary", "status", "error_detail", "response_body",
+		"delegation_id", "created_at",
+	}).AddRow(
+		"act-failed", "delegate_result", "ws-source", "ws-target",
+		"Delegation failed", "error", "codex runtime timed out", "",
+		"del-failed-002", now,
+	)
+	mock.ExpectQuery("SELECT id, activity_type").
+		WithArgs("ws-source").
+		WillReturnRows(activityRows)
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: "ws-source"}}
+	c.Request = httptest.NewRequest("GET", "/workspaces/ws-source/delegations", nil)
+
+	dh.ListDelegations(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	var resp []map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("failed to parse response: %v", err)
+	}
+	if len(resp) != 1 {
+		t.Fatalf("expected 1 row, got %d", len(resp))
+	}
+	if resp[0]["error"] != "codex runtime timed out" {
+		t.Errorf("expected `error` field set, got %v", resp[0]["error"])
+	}
+	if resp[0]["error_detail"] != "codex runtime timed out" {
+		t.Errorf("expected `error_detail` field set (poll-mode contract), got %v", resp[0]["error_detail"])
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet sqlmock expectations: %v", err)
+	}
+}
+
 // ---------- ListDelegations: both ledger and activity_logs empty → [] ----------
 
 func TestListDelegations_BothEmptyReturnsEmptyArray(t *testing.T) {
@@ -1744,7 +1809,15 @@ func TestListDelegations_LedgerFailedIncludesErrorDetail(t *testing.T) {
 		t.Errorf("expected status 'failed', got %v", resp[0]["status"])
 	}
 	if resp[0]["error"] != "Callee workspace not reachable" {
-		t.Errorf("expected error detail, got %v", resp[0]["error"])
+		t.Errorf("expected error detail under `error`, got %v", resp[0]["error"])
+	}
+	// Field-rename pin (P1 #348 / RFC #2829 PR-2 follow-up): the
+	// Python poll-mode consumer in a2a_tools_delegation.py:184 reads
+	// `error_detail`, not `error`. Both keys MUST be present so polling
+	// surfaces the real failure reason instead of falling through to
+	// the generic "delegation failed" string.
+	if resp[0]["error_detail"] != "Callee workspace not reachable" {
+		t.Errorf("expected error detail under `error_detail`, got %v", resp[0]["error_detail"])
 	}
 	if err := mock.ExpectationsWereMet(); err != nil {
 		t.Errorf("unmet sqlmock expectations: %v", err)