diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 27a4ca8..a2f3326 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,40 +14,49 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
+# Every job runs on spark-1 (aarch64, 20 cores). Two reasons, and the second
+# outlives the first:
+#
+#  1. GitHub-hosted runners are currently unavailable on this account for
+#     billing reasons. Public repos get them free, so this may be temporary.
+#  2. aarch64 is the deployment target — Oracle Cloud's Ampere A1. Testing on
+#     the architecture we ship is worth more than testing on x86 and hoping.
+#
+# An x86_64 job is worth adding back once hosted runners work, to catch
+# endianness- and width-dependent bugs. Tracked in ROADMAP.md.
+#
+# ⚠️ Do NOT add Swatinem/rust-cache to these jobs. On a self-hosted runner its
+# post-step prunes ~/.cargo — which here is a real, persistent toolchain, not a
+# disposable one. It silently deleted the rustup binary and every subsequent
+# job failed with exit 127. The toolchain now lives at /opt/rust (wired via the
+# runner's .env and .path) partly to put it out of reach, but do not re-add the
+# action. The runner keeps its target dir between runs anyway, so caching buys
+# nothing here.
+
 jobs:
   check:
     name: check · test · clippy · fmt
-    runs-on: ubuntu-latest
+    runs-on: [self-hosted, Linux, ARM64, spark-1]
     steps:
       - uses: actions/checkout@v5
-      - uses: dtolnay/rust-toolchain@stable
-        with:
-          components: rustfmt, clippy
-      - uses: Swatinem/rust-cache@v2
       - run: cargo fmt --all --check
       - run: cargo clippy --workspace --all-targets --all-features
       - run: cargo test --workspace --all-features
 
   licences:
     name: licence policy (ADR 0002)
-    runs-on: ubuntu-latest
+    runs-on: [self-hosted, Linux, ARM64, spark-1]
     steps:
       - uses: actions/checkout@v5
-      - uses: EmbarkStudios/cargo-deny-action@v2
-        with:
-          command: check licenses bans sources advisories
+      - run: cargo deny check licenses bans sources advisories
 
-  # Native aarch64 build on spark-1. Oracle Cloud's free tier is Ampere A1
-  # (aarch64), so the release artefact must be aarch64 — and spark-1 (GB10,
-  # 20 cores, 121 GB) builds it natively rather than cross-compiling.
-  aarch64:
-    name: release build · aarch64 (spark-1)
+  release:
+    name: release build · aarch64
     runs-on: [self-hosted, Linux, ARM64, spark-1]
     if: github.ref == 'refs/heads/main' || github.event_name == 'workflow_dispatch'
     steps:
       - uses: actions/checkout@v5
-      - uses: Swatinem/rust-cache@v2
-      - run: cargo build --release --workspace
+      - run: cargo build --release --workspace --locked
       - uses: actions/upload-artifact@v4
         with:
           name: openmail-aarch64