fix: pre-landing review fixes (name the full reattach key; destroy the old VM when a rerun does not reattach)

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

docs/pregate.md

@@ -615,11 +615,16 @@ prints the VM's name and the exact
 `bash scripts/ubicloud/ubi-runner.sh down <name>` line to destroy it.
 
 A run killed before its teardown line leaves its VM running. A machine restart
-kills a background pregate this way. Don't destroy the VM: rerun the same
-`gstack-pregate` command on the same tree. It reattaches to that VM
-(`reattaching to VM <name>`), finishes the run, and bills from the VM's
-original create. Use the `down` line only when you are giving up on the run
-or the tree has changed. A reattach whose billed minutes leave the cap no room
+kills a background pregate this way. Don't destroy the VM first: rerun the same
+`gstack-pregate` command before anything it depends on changes. The run key
+covers the tree, the planned file set, the commit `origin/HEAD` points at (a
+`git fetch` that moves it counts), `UBI_LOCATION`, the size, the environment
+and the gstack version. When the rerun prints `reattaching to VM <name>` with
+the name from the create line, it finishes the run on that VM and bills from
+the VM's original create. When it creates a new VM instead (the key changed,
+or the restart came before the runner recorded the VM), destroy the old one
+with the `down` line from its create line. Use the same line when you give up
+on the run. A reattach whose billed minutes leave the cap no room
 refuses (`PREGATE_REMOTE_CAP_SPENT`) and prints both choices: destroy the VM,
 or rerun with a higher `--spend-cap`. The whole script is parsed before it
 runs, so editing it during a run changes nothing. `--timeout 2700` gives a

scripts/ubicloud/pregate-remote.sh

@@ -248,7 +248,7 @@ while :; do
   rm -f "$log.pid" "$log.timedout" "$log.left"
   t0=$(date +%s)
   vm_name="ubirun-$(bash "$here/ubi-runner.sh" owner)-$(date +%s)-$(head -c4 /dev/urandom | od -An -tx1 | tr -d ' \n')-t$(( (stop_after + 900 + 3599) / 3600 ))"
-  [ -n "$prior_vm" ] || say "VM $vm_name; if this run is killed before its teardown line, rerun the same command to reattach; to give up on it, destroy it with: bash scripts/ubicloud/ubi-runner.sh down $vm_name"
+  [ -n "$prior_vm" ] || say "VM $vm_name; if this run is killed before its teardown line, rerun the same command to reattach; if the rerun does not reattach to it, or you give up, destroy it with: bash scripts/ubicloud/ubi-runner.sh down $vm_name"
   UBI_LEFT_FILE="$log.left" python3 -c 'import os, sys; os.setsid(); os.execvp(sys.argv[1], sys.argv[1:])' \
     bash -c "$vm_session" pregate-remote-vm "$stop_after" "$log" "$stream" "$here/ubi-runner.sh" "${args[@]}" -n "$vm_name" &
   vmrun=$!

test/ubicloud-pregate-remote.test.ts

@@ -272,7 +272,7 @@ describe('pregate-remote.sh keyed path (stub ubi-runner)', () => {
     expect(create.exit, create.out).toBe(4);
     expect(create.out).toContain('PREGATE_REMOTE_INFRA: infrastructure failure (ubi-runner exit 1): ubi-runner: create failed');
     expect(create.out).toMatch(/VM: eu-central-h1\/(ubirun-stub-\d+-[0-9a-f]{8}-t1); ubi-runner: gone: eu-central-h1\/\1 \(never existed or already destroyed\)/);
-    expect(create.out).toMatch(/VM (ubirun-stub-\d+-[0-9a-f]{8}-t1); if this run is killed before its teardown line, rerun the same command to reattach; to give up on it, destroy it with: bash scripts\/ubicloud\/ubi-runner\.sh down \1\n/);
+    expect(create.out).toMatch(/VM (ubirun-stub-\d+-[0-9a-f]{8}-t1); if this run is killed before its teardown line, rerun the same command to reattach; if the rerun does not reattach to it, or you give up, destroy it with: bash scripts\/ubicloud\/ubi-runner\.sh down \1\n/);
     expect(create.out).toMatch(/log: \S+\/\.context\/pregate-remote\/\S+\/run\.log/);
     expect(create.out).toContain('spent=0.00 (0 billed min on standard-16)');
     const setup = gate(fixture(), ['test/alpha.test.ts'], { ...KEY, STUB_SETUP_FAIL: '1' });