Add guarded dev restart handling

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/__tests__/dev-server-status.test.ts

@@ -0,0 +1,66 @@
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { readPersistedDevServerStatus, toDevServerHealthStatus } from "../dev-server-status.js";
+
+const tempDirs = [];
+
+function createTempStatusFile(payload: unknown) {
+  const dir = mkdtempSync(path.join(os.tmpdir(), "paperclip-dev-status-"));
+  tempDirs.push(dir);
+  const filePath = path.join(dir, "dev-server-status.json");
+  writeFileSync(filePath, `${JSON.stringify(payload)}\n`, "utf8");
+  return filePath;
+}
+
+afterEach(() => {
+  for (const dir of tempDirs.splice(0)) {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});
+
+describe("dev server status helpers", () => {
+  it("reads and normalizes persisted supervisor state", () => {
+    const filePath = createTempStatusFile({
+      dirty: true,
+      lastChangedAt: "2026-03-20T12:00:00.000Z",
+      changedPathCount: 4,
+      changedPathsSample: ["server/src/app.ts", "packages/shared/src/index.ts"],
+      pendingMigrations: ["0040_restart_banner.sql"],
+      lastRestartAt: "2026-03-20T11:30:00.000Z",
+    });
+
+    expect(readPersistedDevServerStatus({ PAPERCLIP_DEV_SERVER_STATUS_FILE: filePath })).toEqual({
+      dirty: true,
+      lastChangedAt: "2026-03-20T12:00:00.000Z",
+      changedPathCount: 4,
+      changedPathsSample: ["server/src/app.ts", "packages/shared/src/index.ts"],
+      pendingMigrations: ["0040_restart_banner.sql"],
+      lastRestartAt: "2026-03-20T11:30:00.000Z",
+    });
+  });
+
+  it("derives waiting-for-idle health state", () => {
+    const health = toDevServerHealthStatus(
+      {
+        dirty: true,
+        lastChangedAt: "2026-03-20T12:00:00.000Z",
+        changedPathCount: 2,
+        changedPathsSample: ["server/src/app.ts"],
+        pendingMigrations: [],
+        lastRestartAt: "2026-03-20T11:30:00.000Z",
+      },
+      { autoRestartEnabled: true, activeRunCount: 3 },
+    );
+
+    expect(health).toMatchObject({
+      enabled: true,
+      restartRequired: true,
+      reason: "backend_changes",
+      autoRestartEnabled: true,
+      activeRunCount: 3,
+      waitingForIdle: true,
+    });
+  });
+});