docs(pregate): gstack remote-gate example and the small-machine pregate row

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

CONTRIBUTING.md

@@ -187,6 +187,7 @@ the new defaults.
 | Run one free test file while repairing | `bun test <file>` | Free, seconds | Never bare `bun test` for the suite |
 | Run full free acceptance before publishing | `bun run test` | Free, a few minutes | Bun 1.4.2 |
 | Run the full free suite from a small machine | `bun run test:ubicloud` | Free suite on a billed 16-vCPU VM, about 5 minutes | `UBICLOUD_API_KEY` |
+| Clear pregate's test tier on a machine under 8 cores ([remote gate](docs/pregate.md#remote-gate)) | `gstack-pregate --stage tests --remote --spend-cap 2 --timeout 2700 --allow-repo-commands` (same command keyed or keyless) | Keyed: one billed 16-vCPU VM, worst case $0.38; keyless: free, the selected files run locally in parallel shards | Keyed: `UBICLOUD_API_KEY`; keyless: nothing |
 | Run the curated Windows-safe subset | `bun run test:windows` (CI: six `windows-latest` jobs) | Free | Windows, Git Bash |
 | Refresh the Windows duration seed | `gh workflow run windows-free-tests.yml --ref <branch> -f record_durations=true`, then commit the `free-test-durations-windows` artifact | Free CI runners | Pushed branch, `gh` with workflow rights |
 | Run a native Windows or Dia qualification campaign | `gh workflow run native-qualification.yml --ref <branch> -f mode=<mode>` ([modes](docs/TESTING_INTERNALS.md#windows-free-lane)) | Free CI runners | Pushed branch, `gh` with workflow rights |

docs/pregate.md

@@ -238,6 +238,24 @@ the supervision above. Close the obligation one of two ways:
   `spent, reserved, unknown`: a gate that prints no `spent=` is `unknown`,
   counted at the cap.
 
+gstack's own example: `.gstack/pregate.json` declares
+`"remote_gate": "bash scripts/ubicloud/pregate-remote.sh"`. With
+`UBICLOUD_API_KEY` set the script runs the selected files on one Ubicloud VM
+with `bun run test:ubicloud`'s environment, refuses before creating the VM when
+the cap cannot buy a 20-minute run at the size's list price (`UBI_SIZE`,
+default `standard-16`), checks the tree and the planned file set on the VM
+before any test runs, and reports `spent=` from billed minutes. Without a key
+it runs the same files locally in parallel shards
+(`test-free-shards.ts --files-from`) and reports `spent=0`. The command is the
+same either way (`--remote` always needs a cap; the keyless path spends
+nothing). `--timeout 2700` keeps pregate's default 600 s deadline from cutting
+off a slow VM run inside its 45-minute wall (the VM's teardown runs in its own
+session, so a pregate timeout never strands it):
+
+```bash
+gstack-pregate --stage tests --remote --spend-cap 2 --timeout 2700 --allow-repo-commands
+```
+
 <a id="guards"></a>
 ## Guards and the lane-done rule