diff --git a/.github/workflows/gate.yml b/.github/workflows/gate.yml
index 0a946f9..8bd7046 100644
--- a/.github/workflows/gate.yml
+++ b/.github/workflows/gate.yml
@@ -83,6 +83,11 @@ on:
         type: boolean
         required: false
         default: true
+      sccache:
+        description: "Also cache the workspace crates' compiled libraries (which rust-cache leaves out) with sccache in the GitHub Actions cache. It writes where the dependency cache is saved (pushes to the default branch, opted-in manual runs); other runs read those entries. SCCACHE_GHA_RW_MODE in `env` overrides that. Test executables are never cached. Its cache starts afresh when cache-version, a Cargo.toml or a build.rs changes; bump cache-version when files a procedural macro reads change (see the README)"
+        type: boolean
+        required: false
+        default: false
       cache-version:
         description: "Bump to start the dependency cache afresh"
         type: string
@@ -279,6 +284,33 @@ jobs:
           save-if: ${{ github.event_name != 'pull_request' && (github.ref_name == github.event.repository.default_branch || (inputs.cache-save-on-dispatch && github.event_name == 'workflow_dispatch')) }}
           cache-on-failure: true
 
+      # After rust-cache, so its key does not depend on RUSTC_WRAPPER.
+      - name: Install sccache
+        if: inputs.sccache
+        uses: Mozilla-Actions/sccache-action@fc920bf0ec8de6ee65d409111f7ec508035751ba # v0.0.11
+        with:
+          version: v0.18.0
+
+      - name: Use sccache
+        if: inputs.sccache
+        shell: bash
+        env:
+          WRITES: ${{ github.event_name != 'pull_request' && (github.ref_name == github.event.repository.default_branch || (inputs.cache-save-on-dispatch && github.event_name == 'workflow_dispatch')) }}
+          # sccache leaves `--check-cfg` out of its key, so after a change to the expected cfgs a
+          # cached compile would replay its old `unexpected_cfgs` warnings. A change to the files
+          # that declare them (Cargo.toml lints, build scripts), or to cache-version, starts a
+          # fresh sccache cache instead.
+          VERSION: ${{ inputs.cache-version }}-${{ hashFiles('**/Cargo.toml', '**/build.rs') }}
+        run: |
+          echo "SCCACHE_GHA_ENABLED=true" >> "$GITHUB_ENV"
+          echo "RUSTC_WRAPPER=sccache" >> "$GITHUB_ENV"
+          if [ -z "${SCCACHE_GHA_VERSION:-}" ]; then
+            echo "SCCACHE_GHA_VERSION=$VERSION" >> "$GITHUB_ENV"
+          fi
+          if [ -z "${SCCACHE_GHA_RW_MODE:-}" ] && [ "$WRITES" != true ]; then
+            echo "SCCACHE_GHA_RW_MODE=READ_ONLY" >> "$GITHUB_ENV"
+          fi
+
       - name: Caller setup
         if: inputs.setup-command != ''
         shell: bash
diff --git a/.github/workflows/sonarcloud.yml b/.github/workflows/sonarcloud.yml
index 3e23760..89995be 100644
--- a/.github/workflows/sonarcloud.yml
+++ b/.github/workflows/sonarcloud.yml
@@ -235,8 +235,10 @@ jobs:
         run: |
           echo "CRAFT_FONTS_DIR=$CRAFT_FONTS_PATH" >> "$GITHUB_ENV"
           echo "CRAFT_FONTS_REQUIRED=1" >> "$GITHUB_ENV"
+      # In the background, as in gate.yml: the space is free before the build needs it.
       - name: Free disk space
-        run: sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc /opt/hostedtoolcache/CodeQL
+        run: |
+          nohup sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc /opt/hostedtoolcache/CodeQL </dev/null >/dev/null 2>&1 &
       - name: Install Linux build dependencies
         uses: storytold/craft-common-actions/actions/install-apt-packages@main
         with:
diff --git a/README.md b/README.md
index 45ff022..61f66fa 100644
--- a/README.md
+++ b/README.md
@@ -527,7 +527,17 @@ The quality gate for an app's pull requests and pushes to main. It runs `command
   `cache-save-on-dispatch: true`. The restore prefix includes the canonical root `[profile]`
   table; dependency, version and comment edits do not discard reusable dependency artifacts.
   rust-cache still keys on lockfiles, member manifests, toolchain and build environment, and
-  Cargo validates restored fingerprints. Bump `cache-version` to start afresh.
+  Cargo validates restored fingerprints. Bump `cache-version` to start afresh;
+- with `sccache: true`, sccache (through the GitHub Actions cache) for the workspace's own
+  library crates, which rust-cache doesn't keep. It writes where the dependency cache saves and
+  only reads elsewhere; set `SCCACHE_GHA_RW_MODE` in `env` to choose. Test, binary and
+  proc-macro crates aren't cacheable, so it mainly helps workspaces with many library crates.
+  sccache's cache starts afresh when `cache-version` or any `Cargo.toml` or `build.rs` changes,
+  because its key leaves out `--check-cfg`: a cached compile would replay its old
+  `unexpected_cfgs` warnings after the expected cfgs change. It also can't see files a procedural
+  macro reads without rustc tracking them (some asset-embedding macros): don't opt in while
+  such files change often, or bump `cache-version` when they do. `SCCACHE_GHA_VERSION` in
+  `env` sets the cache's version instead;
 
 After the gate, the job fails if `Cargo.lock` changed. Legs run with `fail-fast: false`; each has
 `timeout-minutes` (default 60). A job only some apps need, such as a web build or a Windows-only
@@ -923,7 +933,8 @@ Ordinary test failures still allow coverage and static analysis to upload, but t
 fail the scan job. Missing shard status also fails closed; a green analysis job
 must not conceal failed tests. The single-shard Rust path is unchanged.
 
-The scan job frees unused runner SDKs before either Rust coverage path. Sharded
+The scan job frees unused runner SDKs before either Rust coverage path. The archive build
+frees them in the background, so the build starts at once. Sharded
 coverage merges and removes the shard profiles before extracting the test archive, then
 releases the compressed archive and temporary binaries as they are consumed.
 Disk-space snapshots in the logs show headroom before cleanup and aggregation.