ci: stop archiving every dependency's unpacked source in each cache (#5566)

The four consolidated ci keys plus the build keys still do not fit the
repository's fixed 10GB Actions cache quota, so LRU keeps evicting them:
measured demand is ci-dev 2331MB + ci-feat-proto 2310MB + ci-feat-rio 1951MB +
ci-uring 1317MB + two build legs at ~1429MB + cargo-deny 844MB, and main pushes
add two more build legs. That is roughly 14.4GB against 10.24GB. The symptom is
misleading: Cache Warm reports every job successful and the restores log "full
match: true", yet ci-feat-rio and ci-uring disappear from the cache list between
runs.

cache-all-crates was the wrong default for this repository. With it set to true,
rust-cache's cleanup returns before pruning ~/.cargo/registry/src and its config
archives the whole registry, so every cache carried the unpacked source tree of
every dependency — not, as the name suggests, just a few extra crates.

Setting it to false is rust-cache's own default and loses no coverage: the
package set comes from `cargo metadata --all-features`, a strict superset of any
single lane's feature closure; -sys crates are explicitly exempt from pruning,
since their source timestamps would otherwise trigger rebuilds; and everything
pruned is re-unpacked from the .crate files still in registry/cache, whose
mtimes crates.io normalises, so cargo fingerprints stay valid.

Applied to the setup composite and to audit.yml's own rust-cache. Cache Warm
now also reports the sizes of registry/src, registry/cache, registry/index,
~/.cargo/git and target/ to the step summary, immediately before rust-cache's
post step archives them, so the size of the effect is measured rather than
assumed.

The new sizes only appear once the cache key next rotates, since rust-cache
skips the save entirely on an exact key hit. Deliberately not forcing that by
bumping prefix-key: it would invalidate every family at once and produce a
repository-wide cold build.

Refs: rustfs/backlog#1598, rustfs/backlog#1600

.github/workflows/audit.yml

@@ -100,7 +100,9 @@ jobs:
       - name: Setup Rust cache
         uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2
         with:
-          cache-all-crates: true
+          # Same reasoning as the setup composite: true archives every
+          # dependency's unpacked source tree.
+          cache-all-crates: false
           cache-on-failure: true
           shared-key: rustfs-cargo-deny
           save-if: ${{ github.ref == 'refs/heads/main' }}

.github/workflows/cache-warm.yml

@@ -107,10 +107,6 @@ jobs:
           cache-save-if: 'true'
           install-build-packaging-tools: 'false'
 
-      # --all-targets covers the test binaries nextest builds, including
-      # e2e_test, which test-and-lint's own run excludes. The second build adds
-      # the e2e-test-hooks feature resolution that build-rustfs-debug-binary uses
-      # and that no lint lane enables.
       # rustfs/backlog#1601 gate. sccache can only cache compilation units whose
       # --emit includes link, so it covers workspace rlibs and nothing else:
       # clippy is metadata-only, and the ~100 test binaries, the rustfs bin and
@@ -138,6 +134,10 @@ jobs:
           retention-days: 30
           if-no-files-found: error
 
+      # --all-targets covers the test binaries nextest builds, including
+      # e2e_test, which test-and-lint's own run excludes. The second build adds
+      # the e2e-test-hooks feature resolution that build-rustfs-debug-binary uses
+      # and that no lint lane enables.
       - name: Build ci-dev superset
         env:
           # Same limit ci.yml puts on its nextest step: this builds the same
@@ -148,6 +148,21 @@ jobs:
           cargo build --workspace --all-targets
           cargo build -p rustfs --bins --features e2e-test-hooks
 
+      # Runs before rust-cache's post step, so these are the sizes it is about
+      # to archive. Reported so the cache-all-crates decision stays evidence-led:
+      # registry/src is what that flag prunes, registry/cache is what the pruned
+      # sources are re-unpacked from. See rustfs/backlog#1600.
+      - name: Report cache input sizes
+        if: always()
+        run: |
+          {
+            echo "### Cache input sizes (ci-dev)"
+            echo '```'
+            du -sh ~/.cargo/registry/src ~/.cargo/registry/cache ~/.cargo/registry/index \
+                   ~/.cargo/git target 2>/dev/null || true
+            echo '```'
+          } >> "$GITHUB_STEP_SUMMARY"
+
   # Readers: test-and-lint-rio-v2, build-rustfs-debug-binary-rio-v2.
   warm-ci-feat-rio:
     name: Warm ci-feat-rio

.github/workflows/runner-hygiene.yml

@@ -0,0 +1,81 @@
+# Copyright 2026 RustFS Team
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Asserts that the self-hosted runners are still ephemeral — one job per pod.
+#
+# This repository is public and its pull_request jobs run on those runners,
+# executing the PR's own build.rs, proc-macros and tests. The only thing keeping
+# that code from reaching a later job is that each ARC pod handles exactly one
+# job and is then destroyed. That guarantee lives in the ARC scale-set
+# configuration, outside this repository, where it can be changed without any PR
+# — so it is asserted here from the outside, against real run data, instead of
+# being assumed.
+#
+# Monthly rather than per-PR: the property changes only when someone
+# reconfigures the scale set, and the check costs a few dozen API calls.
+# See docs/ci/runners.md and rustfs/backlog#1602.
+
+name: Runner Hygiene
+
+on:
+  schedule:
+    - cron: "0 6 1 * *" # Monthly, 1st at 06:00 UTC (after the daily audit cron)
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: runner-hygiene
+  cancel-in-progress: false
+
+jobs:
+  check-ephemerality:
+    name: Check runner ephemerality
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
+        with:
+          persist-credentials: false
+
+      # Exit 2 (inconclusive / broken) is deliberately not a pass: a window
+      # where every sm-* job was still queued would otherwise look identical to
+      # a clean bill of health.
+      - name: Assert one job per self-hosted runner
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: ./scripts/ci/check_runner_ephemerality.sh 40
+
+  alert-on-failure:
+    name: Alert on scheduled failure
+    needs: [check-ephemerality]
+    # Same ci-8 mechanism as coverage.yml, audit.yml and the nightly lanes:
+    # scheduled runs file a tracking issue, manual dispatch stays quiet so
+    # debugging never produces a spurious alert.
+    if: always() && github.event_name == 'schedule' && contains(needs.*.result, 'failure')
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    permissions:
+      contents: read
+      issues: write
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
+        with:
+          persist-credentials: false
+      - name: Open or update failure-tracking issue
+        uses: ./.github/actions/schedule-failure-issue
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}