build: optimize CI cache usage and add fast lint gate

This PR addresses cache storage approaching its 10GB limit by:

1. Cache optimization (saves ~2+ GB):
   - Remove Java version from cargo cache key (Rust target is JDK-independent)
   - Use actions/cache/restore + actions/cache/save pattern
   - Only save cache on main branch, not on PRs

2. Reduce Rust test matrix:
   - Consolidate from 2 jobs (Java 11 + Java 17) to 1 job (Java 17)
   - Rust code is JDK-independent, so no coverage lost

3. Add fast lint gate (~30 seconds):
   - New lint job runs cargo fmt --check before expensive builds
   - build-native and linux-test-rust depend on lint passing
   - Fail fast on formatting errors instead of waiting 5-10 minutes
   - macOS lint runs on ubuntu-latest for cost efficiency

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: andygrove

.github/actions/rust-test/action.yaml

@@ -21,11 +21,7 @@ description: "Run Rust tests"
 runs:
   using: "composite"
   steps:
-    - name: Check Cargo fmt
-      shell: bash
-      run: |
-        cd native
-        cargo fmt --all -- --check --color=never
+    # Note: cargo fmt check is now handled by the lint job that gates this workflow
 
     - name: Check Cargo clippy
       shell: bash

.github/workflows/pr_build_linux.yml

@@ -47,8 +47,23 @@ env:
 
 jobs:
 
+  # Fast lint check - gates all other jobs
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    container:
+      image: amd64/rust
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Check Rust formatting
+        run: |
+          rustup component add rustfmt
+          cd native && cargo fmt --all -- --check
+
   # Build native library once and share with all test jobs
   build-native:
+    needs: lint
     name: Build Native Library
     runs-on: ubuntu-latest
     container:
@@ -62,8 +77,8 @@ jobs:
           rust-version: ${{ env.RUST_VERSION }}
           jdk-version: 17  # JDK only needed for common module proto generation
 
-      - name: Cache Cargo
-        uses: actions/cache@v4
+      - name: Restore Cargo cache
+        uses: actions/cache/restore@v4
         with:
           path: |
             ~/.cargo/registry
@@ -87,15 +102,21 @@ jobs:
           path: native/target/ci/libcomet.so
           retention-days: 1
 
+      - name: Save Cargo cache
+        uses: actions/cache/save@v4
+        if: github.ref == 'refs/heads/main'
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            native/target
+          key: ${{ runner.os }}-cargo-ci-${{ hashFiles('native/**/Cargo.lock', 'native/**/Cargo.toml') }}
+
   # Run Rust tests (runs in parallel with build-native, uses debug builds)
   linux-test-rust:
-    strategy:
-      matrix:
-        os: [ubuntu-latest]
-        java_version: [11, 17]
-      fail-fast: false
-    name: ${{ matrix.os }}/java ${{ matrix.java_version }}-rust
-    runs-on: ${{ matrix.os }}
+    needs: lint
+    name: ubuntu-latest/rust-test
+    runs-on: ubuntu-latest
     container:
       image: amd64/rust
     steps:
@@ -105,22 +126,33 @@ jobs:
         uses: ./.github/actions/setup-builder
         with:
           rust-version: ${{ env.RUST_VERSION }}
-          jdk-version: ${{ matrix.java_version }}
+          jdk-version: 17
 
-      - name: Cache Cargo
-        uses: actions/cache@v4
+      - name: Restore Cargo cache
+        uses: actions/cache/restore@v4
         with:
           path: |
             ~/.cargo/registry
             ~/.cargo/git
             native/target
-          key: ${{ runner.os }}-cargo-debug-java${{ matrix.java_version }}-${{ hashFiles('native/**/Cargo.lock', 'native/**/Cargo.toml') }}
+          # Note: Java version intentionally excluded - Rust target is JDK-independent
+          key: ${{ runner.os }}-cargo-debug-${{ hashFiles('native/**/Cargo.lock', 'native/**/Cargo.toml') }}
           restore-keys: |
-            ${{ runner.os }}-cargo-debug-java${{ matrix.java_version }}-
+            ${{ runner.os }}-cargo-debug-
 
       - name: Rust test steps
         uses: ./.github/actions/rust-test
 
+      - name: Save Cargo cache
+        uses: actions/cache/save@v4
+        if: github.ref == 'refs/heads/main'
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            native/target
+          key: ${{ runner.os }}-cargo-debug-${{ hashFiles('native/**/Cargo.lock', 'native/**/Cargo.toml') }}
+
   linux-test:
     needs: build-native
     strategy:

.github/workflows/pr_build_macos.yml

@@ -47,8 +47,23 @@ env:
 
 jobs:
 
+  # Fast lint check - gates all other jobs (runs on Linux for cost efficiency)
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    container:
+      image: amd64/rust
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Check Rust formatting
+        run: |
+          rustup component add rustfmt
+          cd native && cargo fmt --all -- --check
+
   # Build native library once and share with all test jobs
   build-native:
+    needs: lint
     name: Build Native Library (macOS)
     runs-on: macos-14
     steps:
@@ -62,8 +77,8 @@ jobs:
           jdk-architecture: aarch64
           protoc-architecture: aarch_64
 
-      - name: Cache Cargo
-        uses: actions/cache@v4
+      - name: Restore Cargo cache
+        uses: actions/cache/restore@v4
         with:
           path: |
             ~/.cargo/registry
@@ -87,6 +102,16 @@ jobs:
           path: native/target/ci/libcomet.dylib
           retention-days: 1
 
+      - name: Save Cargo cache
+        uses: actions/cache/save@v4
+        if: github.ref == 'refs/heads/main'
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            native/target
+          key: ${{ runner.os }}-cargo-ci-${{ hashFiles('native/**/Cargo.lock', 'native/**/Cargo.toml') }}
+
   macos-aarch64-test:
     needs: build-native
     strategy:

.github/workflows/spark_sql_test.yml

@@ -68,8 +68,8 @@ jobs:
           rust-version: ${{ env.RUST_VERSION }}
           jdk-version: 17
 
-      - name: Cache Cargo
-        uses: actions/cache@v4
+      - name: Restore Cargo cache
+        uses: actions/cache/restore@v4
         with:
           path: |
             ~/.cargo/registry
@@ -91,6 +91,16 @@ jobs:
           path: native/target/ci/libcomet.so
           retention-days: 1
 
+      - name: Save Cargo cache
+        uses: actions/cache/save@v4
+        if: github.ref == 'refs/heads/main'
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            native/target
+          key: ${{ runner.os }}-cargo-ci-${{ hashFiles('native/**/Cargo.lock', 'native/**/Cargo.toml') }}
+
   spark-sql-auto-scan:
     needs: build-native
     strategy: