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<typeofbuildLifecycle>;
 }
 
-functiongetStateExpiresAt(state: unknown): number|undefined{
-if(!state||typeofstate!=="object")returnundefined;
-constexpiresAt=(stateas{expiresAt?: unknown}).expiresAt;
-returntypeofexpiresAt==="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.
+ */
+exportfunctiongetStateExpiresAt(state: unknown): number|undefined{
+if(!state||typeofstate!=="object")returnundefined;
+constexpiresAt=(stateas{expiresAt?: unknown}).expiresAt;
+returntypeofexpiresAt==="number" ? expiresAt : undefined;
+}