fix(chat): états vides explicites et reroutage vers le fil actif quand Work state signale un agent busy — #238

ConversationViewer remplace « Aucun tour pour le moment » par un diagnostic
differentié (agent actif sans tour affichable, transcript non synchronisé,
activité sur un autre fil) avec action « Ouvrir le fil actif ». Le panneau
Work state affiche le résumé du fil du ticket actif et ProjectsView/WebWorkspace
câblent onOpenConversation.

frontend/src/features/conversations/ConversationViewer.tsx

@@ -10,7 +10,14 @@
 
 import { useMemo, useState } from "react";
 
-import type { TurnSource, TurnView } from "@/domain";
+import type {
+  AgentWorkState,
+  BackgroundCompletion,
+  ConversationWorkSummary,
+  ProjectWorkState,
+  TurnSource,
+  TurnView,
+} from "@/domain";
 import { Button, Spinner, cn } from "@/shared";
 import { useProjectWorkState } from "@/features/workstate";
 import { useConversationThread } from "./useConversationThread";
@@ -19,6 +26,7 @@ export interface ConversationViewerProps {
   projectId: string;
   conversationId: string;
   onClose: () => void;
+  onOpenConversation?: (conversationId: string) => void;
 }
 
 function shortId(id: string): string {
@@ -50,6 +58,118 @@ function roleLabel(role: TurnView["role"]): string {
   }
 }
 
+interface ConversationActivity {
+  conversationId: string;
+  label: string;
+  priority: number;
+}
+
+interface EmptyThreadState {
+  message: string;
+  detail?: string;
+  action?: {
+    conversationId: string;
+    label: string;
+  };
+}
+
+function taskIsActive(status: BackgroundCompletion["status"]): boolean {
+  return status === "running" || status === "pending" || status === "cancelling";
+}
+
+function agentLabel(agent: AgentWorkState): string {
+  return agent.name.trim() || `Agent ${shortId(agent.agentId)}`;
+}
+
+function summaryHasVisibleContent(summary: ConversationWorkSummary): boolean {
+  return Boolean(
+    summary.objectivePreview ||
+      summary.summaryPreview ||
+      (summary.recentTurns ?? []).length > 0,
+  );
+}
+
+function activeConversations(state: ProjectWorkState | null): ConversationActivity[] {
+  const out: ConversationActivity[] = [];
+  for (const agent of state?.agents ?? []) {
+    for (const ticket of agent.tickets ?? []) {
+      out.push({
+        conversationId: ticket.conversationId,
+        label: `${agentLabel(agent)} · ${ticket.taskPreview || "ticket actif"}`,
+        priority: ticket.status === "inProgress" ? 0 : 1,
+      });
+    }
+    for (const task of agent.backgroundTasks ?? []) {
+      if (!task.conversationId || !taskIsActive(task.status)) continue;
+      out.push({
+        conversationId: task.conversationId,
+        label: `${agentLabel(agent)} · ${task.kind}`,
+        priority: 2,
+      });
+    }
+  }
+  return out.sort(
+    (a, b) =>
+      a.priority - b.priority ||
+      a.conversationId.localeCompare(b.conversationId),
+  );
+}
+
+function emptyThreadState(
+  conversationId: string,
+  state: ProjectWorkState | null,
+): EmptyThreadState {
+  const summaries = state?.conversations ?? [];
+  const currentSummary = summaries.find(
+    (summary) => summary.conversationId === conversationId,
+  );
+  const activities = activeConversations(state);
+  const currentActivity = activities.find(
+    (activity) => activity.conversationId === conversationId,
+  );
+  if (currentActivity) {
+    return {
+      message: "Agent actif, aucun message visible pour le moment.",
+      detail:
+        "Le fil est bien celui de l'activité en cours, mais le transcript n'a pas encore livré de tour affichable.",
+    };
+  }
+  if (currentSummary && summaryHasVisibleContent(currentSummary)) {
+    return {
+      message: "Activité détectée, transcript pas encore synchronisé.",
+      detail:
+        "Le résumé Work state connaît ce fil, mais la lecture paginée ne renvoie encore aucun tour.",
+    };
+  }
+
+  const otherActivity = activities.find(
+    (activity) => activity.conversationId !== conversationId,
+  );
+  if (otherActivity) {
+    return {
+      message: "Aucun tour sur ce fil.",
+      detail: `L'activité en cours semble être sur un autre fil: ${otherActivity.label}.`,
+      action: {
+        conversationId: otherActivity.conversationId,
+        label: "Ouvrir le fil actif",
+      },
+    };
+  }
+
+  const busyAgent = (state?.agents ?? []).find(
+    (agent) => agent.busy?.state === "busy",
+  );
+  if (busyAgent) {
+    return {
+      message: "Agent actif sans message visible.",
+      detail:
+        "Work state signale une activité, mais aucun ticket ou fil actif n'est encore associé au snapshot courant.",
+    };
+  }
+
+  return { message: "Aucun tour pour le moment." };
+}
+
 /** One collapsible tool-activity turn (dimmed, folded by default). */
 function ToolTurn({ turn, sideClass }: { turn: TurnView; sideClass: string }) {
   const [open, setOpen] = useState(false);
@@ -87,6 +207,7 @@ export function ConversationViewer({
   projectId,
   conversationId,
   onClose,
+  onOpenConversation,
 }: ConversationViewerProps) {
   const vm = useConversationThread(projectId, conversationId);
   // Reuse the already-loaded work-state inventory to resolve agent names.
@@ -126,6 +247,11 @@ export function ConversationViewer({
     return "Conversation";
   }, [parties]);
 
+  const emptyState = useMemo(
+    () => emptyThreadState(conversationId, work.state),
+    [conversationId, work.state],
+  );
+
   function sideOf(source: TurnSource): "left" | "right" {
     return parties.meta.get(partyKey(source))?.side ?? "left";
   }
@@ -191,7 +317,24 @@ export function ConversationViewer({
             <span>Chargement du fil…</span>
           </div>
         ) : vm.turns.length === 0 ? (
-          <p className="text-sm text-muted">Aucun tour pour le moment.</p>
+          <div className="max-w-xl text-sm text-muted">
+            <p>{emptyState.message}</p>
+            {emptyState.detail && (
+              <p className="mt-1 text-xs text-faint">{emptyState.detail}</p>
+            )}
+            {emptyState.action && onOpenConversation && (
+              <Button
+                size="sm"
+                variant="ghost"
+                className="mt-2"
+                onClick={() =>
+                  onOpenConversation(emptyState.action!.conversationId)
+                }
+              >
+                {emptyState.action.label}
+              </Button>
+            )}
+          </div>
         ) : (
           vm.turns.map((turn) => {
             const side = sideOf(turn.source);