refactor(sandbox): extract getStateExpiresAt to its own SRP file

Per review: the inline helper in getSandboxReconnectHandler.ts is its
own concern (read epoch-ms expiresAt off a sandbox state) and belongs
in a dedicated file alongside the other state predicates.

Adds `lib/sandbox/getStateExpiresAt.ts` with a focused test (numeric
match, non-numeric reject, null/scalar guard). Reconnect handler now
imports from the new path; no behavior change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: sweetmantech

lib/sandbox/__tests__/getStateExpiresAt.test.ts

@@ -0,0 +1,22 @@
+import { describe, it, expect } from "vitest";
+import { getStateExpiresAt } from "@/lib/sandbox/getStateExpiresAt";
+
+describe("getStateExpiresAt", () => {
+  it("returns the numeric expiresAt when present", () => {
+    expect(getStateExpiresAt({ type: "vercel", expiresAt: 4_102_444_800_000 })).toBe(
+      4_102_444_800_000,
+    );
+  });
+
+  it("returns undefined when expiresAt is not a number", () => {
+    expect(getStateExpiresAt({ type: "vercel", expiresAt: "soon" })).toBeUndefined();
+    expect(getStateExpiresAt({ type: "vercel" })).toBeUndefined();
+  });
+
+  it("returns undefined for null / undefined / non-object inputs", () => {
+    expect(getStateExpiresAt(null)).toBeUndefined();
+    expect(getStateExpiresAt(undefined)).toBeUndefined();
+    expect(getStateExpiresAt("nope")).toBeUndefined();
+    expect(getStateExpiresAt(42)).toBeUndefined();
+  });
+});

lib/sandbox/getSandboxReconnectHandler.ts

@@ -4,6 +4,7 @@ import { buildLifecycle } from "@/lib/sandbox/buildLifecycle";
 import { clearUnavailableSandboxState } from "@/lib/sandbox/clearUnavailableSandboxState";
 import { connectSandbox } from "@/lib/sandbox/factory";
 import { getSandboxExpiresAtDate } from "@/lib/sandbox/getSandboxExpiresAtDate";
+import { getStateExpiresAt } from "@/lib/sandbox/getStateExpiresAt";
 import { hasRuntimeSandboxState } from "@/lib/sandbox/hasRuntimeSandboxState";
 import { isSandboxUnavailableError } from "@/lib/sandbox/isSandboxUnavailableError";
 import { noSandboxResponse } from "@/lib/sandbox/noSandboxResponse";
@@ -21,12 +22,6 @@ interface ReconnectBody {
   lifecycle: ReturnType<typeof buildLifecycle>;
 }
 
-function getStateExpiresAt(state: unknown): number | undefined {
-  if (!state || typeof state !== "object") return undefined;
-  const expiresAt = (state as { expiresAt?: unknown }).expiresAt;
-  return typeof expiresAt === "number" ? expiresAt : undefined;
-}
-
 /**
  * Handles `GET /api/sandbox/reconnect`. Live runtime probe — actually
  * runs a quick command inside the sandbox to verify it is reachable.

lib/sandbox/getStateExpiresAt.ts

@@ -0,0 +1,19 @@
+/**
+ * Reads the runtime `expiresAt` field (epoch ms) off a sandbox state.
+ * Returns undefined when the input is not an object or when
+ * `expiresAt` is missing or a non-number — so callers can treat the
+ * absence of an expiry as "unknown" without coercing to NaN/0.
+ *
+ * Distinct from `getSandboxExpiresAtDate`, which formats the same
+ * field as an ISO-8601 string for persistence to
+ * `sessions.sandbox_expires_at`.
+ *
+ * @param state - The `sandbox_state` JSON value, typically from
+ *   `sandbox.getState()` or the persisted session row.
+ * @returns Epoch ms expiry, or undefined.
+ */
+export function getStateExpiresAt(state: unknown): number | undefined {
+  if (!state || typeof state !== "object") return undefined;
+  const expiresAt = (state as { expiresAt?: unknown }).expiresAt;
+  return typeof expiresAt === "number" ? expiresAt : undefined;
+}