feat(FN-4400): complete Step 7 — add prompt-size api and dashboard sparkline

Fusion-Task-Id: FN-4400
Fusion-Task-Lineage: 0d4f9c48-5b8b-49eb-9cf3-d1d585ffe7fc

packages/dashboard/src/__tests__/routes-agent-prompt-sizes.test.ts

@@ -0,0 +1,98 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { EventEmitter } from "node:events";
+import { get } from "../test-request.js";
+import { createServer } from "../server.js";
+
+const {
+  mockInit,
+  mockGetAgent,
+  mockIsEphemeralAgent,
+  mockChatStoreInit,
+  mockAll,
+} = vi.hoisted(() => ({
+  mockInit: vi.fn().mockResolvedValue(undefined),
+  mockGetAgent: vi.fn(),
+  mockIsEphemeralAgent: vi.fn(),
+  mockChatStoreInit: vi.fn().mockResolvedValue(undefined),
+  mockAll: vi.fn(),
+}));
+
+vi.mock("@fusion/core", () => ({
+  AgentStore: class MockAgentStore {
+    init = mockInit;
+    getAgent = mockGetAgent;
+  },
+  isEphemeralAgent: mockIsEphemeralAgent,
+  ChatStore: class MockChatStore {
+    init = mockChatStoreInit;
+  },
+}));
+
+class MockStore extends EventEmitter {
+  getRootDir(): string {
+    return "/tmp/fn-4400-test";
+  }
+
+  getFusionDir(): string {
+    return "/tmp/fn-4400-test/.fusion";
+  }
+
+  getDatabase() {
+    return {
+      exec: vi.fn(),
+      prepare: vi.fn().mockReturnValue({
+        run: vi.fn().mockReturnValue({ changes: 0 }),
+        get: vi.fn(),
+        all: mockAll,
+      }),
+    };
+  }
+}
+
+describe("GET /api/agents/:id/prompt-sizes", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockGetAgent.mockResolvedValue({ id: "agent-001", role: "executor", metadata: {} });
+    mockIsEphemeralAgent.mockReturnValue(false);
+    mockAll.mockReturnValue([
+      {
+        runId: "run-1",
+        createdAt: "2026-05-14T00:00:00.000Z",
+        systemChars: 120,
+        execChars: 880,
+        totalChars: 1000,
+      },
+      {
+        runId: "run-2",
+        createdAt: "2026-05-13T23:00:00.000Z",
+        systemChars: 0,
+        execChars: 0,
+        totalChars: 0,
+      },
+    ]);
+  });
+
+  it("returns recent prompt size rows", async () => {
+    const app = createServer(new MockStore() as any);
+    const res = await get(app, "/api/agents/agent-001/prompt-sizes");
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual([
+      expect.objectContaining({ runId: "run-1", totalChars: 1000 }),
+      expect.objectContaining({ runId: "run-2", systemChars: 0, execChars: 0, totalChars: 0 }),
+    ]);
+  });
+
+  it("returns 404 when agent is missing", async () => {
+    mockGetAgent.mockResolvedValueOnce(null);
+    const app = createServer(new MockStore() as any);
+    const res = await get(app, "/api/agents/missing/prompt-sizes");
+    expect(res.status).toBe(404);
+  });
+
+  it("returns 400 for ephemeral agents", async () => {
+    mockIsEphemeralAgent.mockReturnValueOnce(true);
+    const app = createServer(new MockStore() as any);
+    const res = await get(app, "/api/agents/agent-001/prompt-sizes");
+    expect(res.status).toBe(400);
+  });
+});

packages/dashboard/src/routes/register-agent-runtime-routes.ts

@@ -631,6 +631,64 @@ export function registerAgentRuntimeRoutes(ctx: ApiRoutesContext, deps: AgentRun
     }
   });
 
+  /**
+   * GET /api/agents/:id/prompt-sizes
+   * Get recent prompt-size points for a permanent agent.
+   */
+  router.get("/agents/:id/prompt-sizes", async (req, res) => {
+    try {
+      const { store: scopedStore } = await getProjectContext(req);
+      const { AgentStore, isEphemeralAgent } = await import("@fusion/core");
+      const agentStore = new AgentStore({ rootDir: scopedStore.getFusionDir() });
+      await agentStore.init();
+
+      const agent = await agentStore.getAgent(req.params.id);
+      if (!agent) {
+        throw notFound("Agent not found");
+      }
+      if (isEphemeralAgent(agent)) {
+        throw badRequest("Prompt sizes are not available for ephemeral agents");
+      }
+
+      const rawLimit = typeof req.query.limit === "string" ? Number.parseInt(req.query.limit, 10) : 7;
+      if (!Number.isInteger(rawLimit) || rawLimit <= 0) {
+        throw badRequest("limit must be a positive integer");
+      }
+      const limit = Math.min(rawLimit, 30);
+
+      const rows = scopedStore.getDatabase().prepare(`
+        SELECT
+          id AS runId,
+          createdAt,
+          COALESCE(length(json_extract(data, '$.systemPrompt')), 0) AS systemChars,
+          COALESCE(length(json_extract(data, '$.executionPrompt')), 0) AS execChars,
+          COALESCE(length(json_extract(data, '$.systemPrompt')), 0)
+            + COALESCE(length(json_extract(data, '$.executionPrompt')), 0) AS totalChars
+        FROM agentRuns
+        WHERE json_extract(data, '$.agentId') = ?
+        ORDER BY createdAt DESC
+        LIMIT ?
+      `).all(req.params.id, limit) as Array<{
+        runId: string;
+        createdAt: string;
+        systemChars: number;
+        execChars: number;
+        totalChars: number;
+      }>;
+
+      res.json(rows);
+    } catch (err: unknown) {
+      if (err instanceof ApiError) {
+        throw err;
+      }
+      if ((err instanceof Error ? err.message : String(err)).includes("not found")) {
+        throw notFound(err instanceof Error ? err.message : String(err));
+      } else {
+        rethrowAsApiError(err);
+      }
+    }
+  });
+
   /**
    * GET /api/agents/:id/token-usage
    * Get cache/token usage summary windows for a permanent agent.