fix(sandbox): set source.prebuilt:true when restoring from org snapshot

Caught during the hit-case smoke test against a real recoupable org
repo: with a snapshot found and `baseSnapshotId` plumbed in, the
sandbox boot still fell through to a fresh `git clone`, which then
failed with exit 128. Reason: I'd dropped the `prebuilt` source flag
from the port, calling it "informational." It is not.

Reading lib/sandbox/vercel/sandbox/VercelSandbox.ts, the flag switches
between two distinct boot paths:

- `source && baseSnapshotId && !source.prebuilt` → fresh clone on top
  of snapshot (often fails for private repos and defeats the warm-boot
  benefit)
- `source?.prebuilt && baseSnapshotId` → `git fetch` + `git reset --hard`
  against the repo that's already inside the snapshot (the fast path)

Setting `prebuilt: !!orgSnapshotId` matches open-agents' behavior and
unlocks the actual ~75s warm-boot win this PR exists to enable.

Tests updated: existing assertions for hit-case extended to also
verify `source.prebuilt === true` when a snapshot is found, and
`source.prebuilt === false` when the lookup misses.

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

Author: sweetmantech

lib/sandbox/__tests__/createSandboxHandler.test.ts

@@ -186,7 +186,10 @@ describe("createSandboxHandler", () => {
     expect(findOrgSnapshot).toHaveBeenCalledWith("org-acme-xyz");
     const arg = vi.mocked(connectSandbox).mock.calls[0]?.[0];
     if (!arg || !("options" in arg)) throw new Error("expected new-API config shape");
+    if (!("state" in arg)) throw new Error("expected new-API state shape");
     expect(arg.options?.baseSnapshotId).toBe("snap_abc123");
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect((arg.state as any).source.prebuilt).toBe(true);
   });
 
   it("skips the snapshot lookup entirely for non-recoupable repos", async () => {
@@ -221,7 +224,10 @@ describe("createSandboxHandler", () => {
     expect(findOrgSnapshot).toHaveBeenCalledWith("org-no-snap-yet");
     const arg = vi.mocked(connectSandbox).mock.calls[0]?.[0];
     if (!arg || !("options" in arg)) throw new Error("expected new-API config shape");
+    if (!("state" in arg)) throw new Error("expected new-API state shape");
     expect(arg.options?.baseSnapshotId).toBeUndefined();
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect((arg.state as any).source.prebuilt).toBe(false);
   });
 
   it("does not attempt skill installation when no sessionId is provided", async () => {

lib/sandbox/createSandboxHandler.ts

@@ -75,7 +75,13 @@ export async function createSandboxHandler(request: NextRequest): Promise<NextRe
       state: {
         type: "vercel",
         ...(sandboxName ? { sandboxName } : {}),
-        source: { repo: body.repoUrl },
+        // `prebuilt: true` when restoring from an org snapshot tells the
+        // Vercel sandbox runtime to skip the fresh `git clone` and instead
+        // `git fetch` + `git reset --hard` the repo that's already inside
+        // the snapshot. Without this flag, Vercel treats the snapshot as a
+        // base image and tries to clone fresh on top — which often fails
+        // for private repos and definitely defeats the warm-boot benefit.
+        source: { repo: body.repoUrl, prebuilt: !!orgSnapshotId },
       },
       options: {
         timeout: DEFAULT_TIMEOUT_MS,