FN-5892: dedupe planning sessions and persist history deletion

Prevent duplicate planning-history rows and keep deletions visible only after the backend confirms persistence.

- dedupe Planning Mode history by session id across initial loads, live updates, archive toggles, and draft creation
- make deleteAiSession surface backend/content-type errors instead of silently succeeding on failed deletes
- keep failed history deletions visible, refresh the list, and show an error toast when persistence fails
- add dashboard tests covering session deduplication, delete API failures, and persistence-aware Planning Mode deletion behavior
- document the history dedupe/delete semantics and add a patch changeset for @runfusion/fusion

Files changed:
 .changeset/fn-5892-planning-history-fix.md         |   5 +
 docs/dashboard-guide.md                            |   2 +-
 packages/dashboard/app/api/__tests__/deleteAiSession.test.ts      |  54 +++++
 packages/dashboard/app/api/legacy.ts               |  41 +++-
 packages/dashboard/app/components/PlanningModeModal.tsx |  70 ++++---
 packages/dashboard/app/components/__tests__/PlanningModeModal.autosize.test.tsx  |  11 +
 packages/dashboard/app/components/__tests__/PlanningModeModal.dedupeSessionsById.test.ts   |  44 ++++
 packages/dashboard/app/components/__tests__/PlanningModeModal.initial.test.tsx   |  11 +
 packages/dashboard/app/components/__tests__/PlanningModeModal.planning-flow.test.tsx       | 226 ++++++++++++++++++++-
 packages/dashboard/app/components/__tests__/PlanningModeModal.test-helpers.ts    |   1 +
 10 files changed, 439 insertions(+), 26 deletions(-)

Fusion-Task-Id: FN-5892

Fusion-Task-Lineage: 7453bc34-6d57-4d67-ac92-8fb50084fbee

packages/dashboard/app/api/__tests__/deleteAiSession.test.ts

@@ -0,0 +1,54 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { ApiRequestError, deleteAiSession } from "../legacy";
+
+describe("deleteAiSession", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("resolves on 200 responses", async () => {
+    vi.spyOn(globalThis, "fetch").mockResolvedValue(
+      new Response(JSON.stringify({ ok: true }), {
+        status: 200,
+        headers: { "content-type": "application/json" },
+      }),
+    );
+
+    await expect(deleteAiSession("session-1")).resolves.toBeUndefined();
+  });
+
+  it("treats 404 responses as idempotent success", async () => {
+    vi.spyOn(globalThis, "fetch").mockResolvedValue(
+      new Response(JSON.stringify({ error: "Session not found" }), {
+        status: 404,
+        headers: { "content-type": "application/json" },
+      }),
+    );
+
+    await expect(deleteAiSession("missing-session")).resolves.toBeUndefined();
+  });
+
+  it("rejects on non-404 server failures", async () => {
+    vi.spyOn(globalThis, "fetch").mockResolvedValue(
+      new Response(JSON.stringify({ error: "Delete failed", details: { retryable: false } }), {
+        status: 500,
+        headers: { "content-type": "application/json" },
+      }),
+    );
+
+    await expect(deleteAiSession("session-1")).rejects.toEqual(
+      expect.objectContaining<ApiRequestError>({
+        name: "ApiRequestError",
+        message: "Delete failed",
+        status: 500,
+        details: { retryable: false },
+      }),
+    );
+  });
+
+  it("rejects on network failures", async () => {
+    vi.spyOn(globalThis, "fetch").mockRejectedValue(new TypeError("Failed to fetch"));
+
+    await expect(deleteAiSession("session-1")).rejects.toThrow("Failed to fetch");
+  });
+});

packages/dashboard/app/api/legacy.ts

@@ -8226,10 +8226,49 @@ export function forceAcquireSessionLock(sessionId: string, tabId: string): Promi
 }
 
 export async function deleteAiSession(id: string): Promise<void> {
-  await fetch(buildApiUrl(`/ai-sessions/${encodeURIComponent(id)}`), {
+  const url = buildApiUrl(`/ai-sessions/${encodeURIComponent(id)}`);
+  const res = await fetch(url, {
     method: "DELETE",
     headers: withTokenHeader(),
   });
+
+  if (res.ok || res.status === 404) {
+    return;
+  }
+
+  const contentType = res.headers.get("content-type") ?? "";
+  const bodyText = await res.text();
+  const isJson = contentType.includes("application/json");
+  const isHtml = contentType.includes("text/html") || looksLikeHtml(bodyText);
+
+  if (isHtml) {
+    throw new Error(
+      `API returned HTML instead of JSON for ${url}. ` +
+      `The endpoint may not be properly configured. (${res.status} ${res.statusText})`
+    );
+  }
+
+  if (!isJson) {
+    const preview = bodyText.length > 160 ? `${bodyText.slice(0, 160)}...` : bodyText;
+    throw new Error(
+      `API returned ${contentType || "an unknown content type"} instead of JSON for ${url}. ` +
+      `(${res.status} ${res.statusText})${preview ? ` Response: ${preview}` : ""}`
+    );
+  }
+
+  let data: unknown;
+  try {
+    data = bodyText ? JSON.parse(bodyText) : null;
+  } catch {
+    throw new Error(`API returned invalid JSON for ${url}. (${res.status} ${res.statusText})`);
+  }
+
+  const payload = data as { error?: string; details?: Record<string, unknown> } | null;
+  throw new ApiRequestError(
+    payload?.error || `Request failed for ${url}: ${res.status} ${res.statusText}`,
+    res.status,
+    payload?.details,
+  );
 }
 
 export function pingSession(sessionId: string, projectId?: string): Promise<{ ok: boolean }> {