diff --git a/.gitea/actions/setup/action.yml b/.gitea/actions/setup/action.yml
index cc3cb6b..2317dd8 100644
--- a/.gitea/actions/setup/action.yml
+++ b/.gitea/actions/setup/action.yml
@@ -1,27 +1,69 @@
 name: Rust plugin toolchain
-description: Native checks and optional Windows GNU cross-compilation in Node's Debian container
+description: >-
+  Native checks and optional Windows GNU cross-compilation in Node's Debian
+  container. Restores the Rust toolchain, Cargo registry, and the caller's
+  build directories from the runner cache, and saves them after the job.
 inputs:
   windows:
     description: Install the Windows cross compiler
     default: "false"
+  cache-name:
+    description: Distinguishes build-directory caches of different jobs
+    required: true
+  target-paths:
+    description: Build directories to cache, one per line, relative to the workspace
+    default: target
 runs:
   using: composite
   steps:
+    - name: Cache keys
+      id: keys
+      shell: bash
+      run: |
+        # A new ISO week starts fresh caches, so stale build output cannot grow forever
+        # and the stable toolchain is refreshed regularly.
+        echo "week=$(date -u +%G-%V)" >> "$GITHUB_OUTPUT"
+    - name: Restore Rust toolchain and Cargo registry
+      uses: https://github.com/actions/cache@v4
+      with:
+        path: |
+          .cargo-ci/bin
+          .cargo-ci/registry/index
+          .cargo-ci/registry/cache
+          .cargo-ci/git/db
+          .rustup-ci
+        key: rust-${{ inputs.windows }}-${{ steps.keys.outputs.week }}-${{ hashFiles('Cargo.lock', 'plugins/*/plugin/Cargo.lock', 'tools/editor-check/Cargo.lock') }}
+        restore-keys: |
+          rust-${{ inputs.windows }}-${{ steps.keys.outputs.week }}-
+    - name: Restore build directories
+      uses: https://github.com/actions/cache@v4
+      with:
+        path: ${{ inputs.target-paths }}
+        # One entry per job, week, and dependency set: compiled dependencies are
+        # reused, and only this repository's crates rebuild on each push.
+        key: build-${{ inputs.cache-name }}-${{ steps.keys.outputs.week }}-${{ hashFiles('Cargo.lock', 'plugins/*/plugin/Cargo.lock', 'tools/editor-check/Cargo.lock') }}
+        restore-keys: |
+          build-${{ inputs.cache-name }}-${{ steps.keys.outputs.week }}-
     - name: Install build prerequisites
       shell: bash
       run: |
         apt-get update
         apt-get install -y --no-install-recommends python3 curl ca-certificates pkg-config libgl1-mesa-dev libx11-dev libxcursor-dev libx11-xcb-dev libxcb1-dev libxcb-dri2-0-dev libxcb-icccm4-dev libxkbcommon-x11-dev
+        if [ "${{ inputs.windows }}" = "true" ]; then
+          apt-get install -y --no-install-recommends gcc-mingw-w64-x86-64
+        fi
     - name: Install Rust
       shell: bash
       run: |
-        curl --proto '=https' --tlsv1.2 -fsSL https://sh.rustup.rs -o /tmp/rustup-init.sh
-        sh /tmp/rustup-init.sh -y --profile minimal --default-toolchain stable
+        if [ ! -x "$CARGO_HOME/bin/rustup" ]; then
+          curl --proto '=https' --tlsv1.2 -fsSL https://sh.rustup.rs -o /tmp/rustup-init.sh
+          sh /tmp/rustup-init.sh -y --profile minimal --default-toolchain none --no-modify-path
+        fi
         echo "$CARGO_HOME/bin" >> "$GITHUB_PATH"
-        "$CARGO_HOME/bin/rustup" component add rustfmt clippy
-    - name: Install Windows target
-      if: inputs.windows == 'true'
-      shell: bash
-      run: |
-        apt-get install -y --no-install-recommends gcc-mingw-w64-x86-64
-        rustup target add x86_64-pc-windows-gnu
+        # No-op when the restored toolchain is already current.
+        "$CARGO_HOME/bin/rustup" toolchain install stable --profile minimal -c rustfmt -c clippy
+        "$CARGO_HOME/bin/rustup" default stable
+        if [ "${{ inputs.windows }}" = "true" ]; then
+          "$CARGO_HOME/bin/rustup" target add x86_64-pc-windows-gnu
+        fi
+        "$CARGO_HOME/bin/rustc" --version
diff --git a/.gitea/workflows/check.yml b/.gitea/workflows/check.yml
index 36c7c3b..afa031a 100644
--- a/.gitea/workflows/check.yml
+++ b/.gitea/workflows/check.yml
@@ -10,7 +10,10 @@ permissions:
 
 env:
   CARGO_HOME: ${{ gitea.workspace }}/.cargo-ci
+  RUSTUP_HOME: ${{ gitea.workspace }}/.rustup-ci
   CARGO_TERM_COLOR: always
+  # Incremental data is not reused between CI runs; it only inflates the cache.
+  CARGO_INCREMENTAL: "0"
 
 jobs:
   check:
@@ -26,6 +29,11 @@ jobs:
           token: ${{ secrets.GITEA_TOKEN }}
           persist-credentials: false
       - uses: ./.gitea/actions/setup
+        with:
+          cache-name: check-${{ matrix.plugin }}
+          target-paths: |
+            target
+            plugins/${{ matrix.plugin }}/plugin/target
       - run: python3 -m unittest discover -s scripts/tests -v
       - run: python3 scripts/check-plugin.py --plugin "${{ matrix.plugin }}"
 
@@ -38,6 +46,9 @@ jobs:
           token: ${{ secrets.GITEA_TOKEN }}
           persist-credentials: false
       - uses: ./.gitea/actions/setup
+        with:
+          cache-name: previews
+          target-paths: tools/editor-check/target
       - run: |
           cargo fmt --all -- --check
           cargo fmt --manifest-path tools/editor-check/Cargo.toml -- --check
@@ -65,6 +76,8 @@ jobs:
       - uses: ./.gitea/actions/setup
         with:
           windows: "true"
+          cache-name: windows-preview
+          target-paths: target/windows
       - run: |
           python3 scripts/build-plugin.py --plugin rivet --target x86_64-pc-windows-gnu
           python3 scripts/build-plugin.py --plugin patina --target x86_64-pc-windows-gnu
diff --git a/.gitea/workflows/release.yml b/.gitea/workflows/release.yml
index d499f1a..57d5903 100644
--- a/.gitea/workflows/release.yml
+++ b/.gitea/workflows/release.yml
@@ -8,7 +8,9 @@ permissions:
 
 env:
   CARGO_HOME: ${{ gitea.workspace }}/.cargo-ci
+  RUSTUP_HOME: ${{ gitea.workspace }}/.rustup-ci
   CARGO_TERM_COLOR: always
+  CARGO_INCREMENTAL: "0"
   RELEASE_REF: ${{ gitea.ref }}
 
 jobs:
@@ -44,6 +46,10 @@ jobs:
       - uses: ./.gitea/actions/setup
         with:
           windows: "true"
+          # CARGO_TARGET_DIR holds both the native checks and the Windows build.
+          # Kept apart from branch builds; a release never reuses preview output.
+          cache-name: release-${{ needs.plan.outputs.plugin }}
+          target-paths: target/windows
       - run: |
           python3 -m unittest discover -s scripts/tests -v
           python3 scripts/check-plugin.py --plugin "$PLUGIN"
diff --git a/docs/releases.md b/docs/releases.md
index 4fe90e0..5779a2a 100644
--- a/docs/releases.md
+++ b/docs/releases.md
@@ -64,6 +64,24 @@ Node runtime, and a local composite action installs Rust and build dependencies.
 Windows binaries are cross-compiled with MinGW; no Windows runner or Linux release
 binary is required.
 
+### Build cache
+
+Every Rust job restores two caches through the runner's cache server
+(`actions/cache@v4`, run from the setup composite action):
+
+- **Toolchain:** rustup's stable toolchain, Cargo's binaries, and the registry and
+  git sources, keyed by ISO week, Windows target, and all three `Cargo.lock` files.
+- **Build directories:** each job's target directories (check per plugin,
+  previews, Windows preview, release per plugin), keyed the same way.
+
+A new week or a changed lockfile starts a fresh entry, so stale build output does
+not accumulate and the stable toolchain refreshes weekly. Within a week, pushes
+reuse compiled dependencies and rebuild only this repository's crates. Release
+jobs use their own entries and never reuse branch build output. A cache miss only
+costs time. The runner's cache server must be enabled (`cache.enabled` in
+`act_runner`'s config, the default) and must support post steps of actions
+inside composite actions (current `act_runner` releases do).
+
 The workflows use explicit action URLs and the v3-compatible artifact protocol.
 Only the publish job requests `contents: write`. It authenticates against the
 same Gitea instance using the automatic `secrets.GITEA_TOKEN`; no personal access