ci: make Omarchy rebuild explicit

Author: quanru

.github/workflows/midscene-experimental.yml

@@ -4,8 +4,9 @@ on:
   push:
     branches: [ci/midscene-e2e]
     paths:
-      - ".github/workflows/midscene-experimental.yml"
-      - "tests/midscene/**"
+      # The VM install is deliberately expensive. Push this marker only when
+      # the pinned Omarchy ISO or installer harness needs to be revalidated.
+      - "tests/midscene/.rebuild-omarchy-vm"
   workflow_dispatch:
 
 permissions:
@@ -36,4 +37,3 @@ jobs:
           path: .midscene-omarchy/omarchy-iso/test-runs/**/runs/**
           if-no-files-found: warn
           retention-days: 3
-

tests/midscene/README.md

@@ -8,6 +8,19 @@ official Omarchy ISO in a headless QEMU/KVM VM. It reuses Omarchy's own ISO
 acceptance harness and saves installer screenshots and logs as short-lived
 artifacts. It does not upload the VM disk or its temporary SSH key.
 
+The full Omarchy install is intentionally not triggered by ordinary pushes.
+During development on this branch, deliberately add/update
+`tests/midscene/.rebuild-omarchy-vm` only when the pinned ISO or installer
+harness changes. Once this workflow exists on the default branch, it can also
+be started with `workflow_dispatch`. GitHub-hosted runners are ephemeral, so
+every such full rebuild downloads the pinned ISO again; routine Ubuntu
+Midscene tests do not need the ISO.
+
+Omarchy 4.0.3 was installed successfully on a GitHub-hosted runner in
+[Actions run 34866563731](https://github.com/quanru/doubao-say/actions/runs/34866563731).
+The run took 13 minutes 41 seconds, including about 55 seconds to transfer the
+ISO.
+
 After that probe is stable, the next stages are:
 
 1. Boot a throwaway overlay from the installed base image.