ci(coverage): defer the KVM-runner diff-coverage gate

Split the self-hosted KVM runner setup out of this branch so main's CI
doesn't require a runner that isn't registered yet. The `coverage` job
runs on ubuntu-latest again and reports combined coverage informationally
— the hard diff-coverage gate (which needs the firecracker integration
suite, hence /dev/kvm + the provisioned pool) is deferred and moves to a
separate PR. The unit-coverage tests added alongside the gate stay.

See PRD 0069 / #348; the runner + gate re-land on the ci-runner branch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

.gitea/workflows/test.yml

@@ -71,45 +71,30 @@ jobs:
       - name: Run integration tests
         run: python3 -m unittest discover -t . -s tests/integration -v
 
-  # Combined unit+integration coverage + the diff-coverage gate (the hard
-  # gate: new/changed lines >= 90%). See docs/decisions/0004-coverage-policy.md.
+  # Combined unit+integration coverage report (informational). See
+  # docs/decisions/0004-coverage-policy.md.
   #
-  # This runs on a self-hosted KVM runner (label `kvm`), NOT ubuntu-latest,
-  # because the Firecracker backend's subprocess/VM orchestration
-  # (launch/boot/SSH/isolation-probe) is covered by the integration suite,
-  # and that suite needs `/dev/kvm` + the provisioned TAP/nft pool — which a
-  # container-based runner doesn't have. On such a runner the firecracker
-  # integration test skips and its ~230 orchestration lines read as
-  # uncovered, so the gate can't pass there.
-  #
-  # Runner prerequisites (provision once on the host; see the README
-  # "Firecracker on Linux" section): the `firecracker` binary on PATH,
-  # `/dev/kvm` accessible to the runner user, Docker, the cached guest
-  # kernel + static dropbear (BOT_BOTTLE_FC_KERNEL / BOT_BOTTLE_FC_DROPBEAR),
-  # and the network pool installed as the persistent systemd unit
-  # (`./cli.py backend setup --backend=firecracker`). The preflight step
-  # below fails fast with instructions if anything is missing.
+  # The hard diff-coverage gate (changed lines >= 90%) is DEFERRED: the
+  # Firecracker backend's VM/SSH orchestration is covered by the integration
+  # suite, which needs /dev/kvm + the provisioned TAP/nft pool — a
+  # container-based runner skips it and those lines read uncovered, so the
+  # gate can't pass here. Re-enabling it on a self-hosted KVM runner is
+  # tracked separately (see PRD 0069 / #348 and the ci-runner branch).
   coverage:
-    runs-on: [self-hosted, kvm]
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
 
-      - name: Preflight — Firecracker host is ready
-        run: |
-          command -v firecracker >/dev/null || {
-            echo "firecracker not on PATH — provision the runner (README: Firecracker on Linux)"; exit 1; }
-          test -e /dev/kvm || { echo "/dev/kvm missing — KVM not available on this runner"; exit 1; }
-          # `backend status` exits non-zero unless the TAP pool is up + no
-          # range overlap; it prints the exact `backend setup` fix.
-          python3 cli.py backend status --backend=firecracker
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
 
-      - name: Combined coverage (unit + integration, incl. firecracker)
+      - name: Install dev requirements
+        run: python3 -m pip install -r requirements-dev.txt
+
+      - name: Combined coverage report (unit + integration)
         run: PYTHON=python3 bash scripts/coverage.sh critical
-
-      - name: Diff-coverage gate (changed lines >= 90%)
-        run: |
-          git fetch --no-tags origin main:refs/remotes/origin/main
-          python3 scripts/diff_coverage.py --base origin/main --min 90