ci: Remove sccache from GitHub workflows (#75)

Remove all sccache-related configuration and replace with simple cargo
home directory caching. This simplifies the CI workflow by caching only
the cargo registry, git dependencies, and binaries, avoiding the
complexity and size issues of target directory caching.

Co-authored-by: Claude <noreply@anthropic.com>

Author: CSRessel

.github/workflows/rust-ci.yml

@@ -14,7 +14,6 @@ jobs:
         working-directory: codex-rs
     env:
       CARGO_INCREMENTAL: "0"
-      SCCACHE_CACHE_SIZE: 10G
 
     strategy:
       fail-fast: false
@@ -44,8 +43,7 @@ jobs:
           echo "hash=$(sha256sum Cargo.lock | cut -d' ' -f1)" >> "$GITHUB_OUTPUT"
           echo "toolchain_hash=$(sha256sum rust-toolchain.toml | cut -d' ' -f1)" >> "$GITHUB_OUTPUT"
 
-      # Explicit cache restore: split cargo home vs target, so we can
-      # avoid caching the large target dir on the gnu-dev job.
+      # Cache cargo home directory (registry, git deps, etc.)
       - name: Restore cargo home cache
         id: cache_cargo_home_restore
         uses: actions/cache/restore@v4
@@ -59,41 +57,6 @@ jobs:
           restore-keys: |
             cargo-home-${{ matrix.runner }}-${{ matrix.target }}-${{ matrix.profile }}-
 
-      # Install and restore sccache cache
-      - name: Install sccache
-        if: ${{ env.USE_SCCACHE == 'true' }}
-        uses: taiki-e/install-action@44c6d64aa62cd779e873306675c7a58e86d6d532 # v2
-        with:
-          tool: sccache
-          version: 0.7.5
-
-      - name: Configure sccache backend
-        shell: bash
-        run: |
-          set -euo pipefail
-          if [[ -n "${ACTIONS_CACHE_URL:-}" && -n "${ACTIONS_RUNTIME_TOKEN:-}" ]]; then
-            echo "SCCACHE_GHA_ENABLED=true" >> "$GITHUB_ENV"
-            echo "Using sccache GitHub backend"
-          else
-            echo "SCCACHE_GHA_ENABLED=false" >> "$GITHUB_ENV"
-            echo "SCCACHE_DIR=${{ github.workspace }}/.sccache" >> "$GITHUB_ENV"
-            echo "Using sccache local disk fallback"
-          fi
-
-      - name: Enable sccache wrapper
-        shell: bash
-        run: echo "RUSTC_WRAPPER=sccache" >> "$GITHUB_ENV"
-
-      - name: Restore sccache cache (fallback)
-        if: ${{ env.SCCACHE_GHA_ENABLED != 'true' }}
-        uses: actions/cache/restore@v4
-        with:
-          path: ${{ github.workspace }}/.sccache/
-          key: sccache-${{ matrix.runner }}-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}-${{ github.run_id }}
-          restore-keys: |
-            sccache-${{ matrix.runner }}-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}-
-            sccache-${{ matrix.runner }}-${{ matrix.target }}-
-
       # CI checks
       - name: cargo check
         run: cargo check --target ${{ matrix.target }} --all-features
@@ -108,16 +71,14 @@ jobs:
         continue-on-error: true  # TODO: Fix pre-existing test failures in codex-app-server
         run: cargo test --target ${{ matrix.target }} --all-features
 
-      # Save sccache
-      - name: Save sccache cache (fallback)
-        if: always() && !cancelled() && env.SCCACHE_GHA_ENABLED != 'true'
-        continue-on-error: true
+      # Save cargo home cache
+      - name: Save cargo home cache
+        if: always() && !cancelled()
         uses: actions/cache/save@v4
         with:
-          path: ${{ github.workspace }}/.sccache/
-          key: sccache-${{ matrix.runner }}-${{ matrix.target }}-${{ hashFiles('**/Cargo.lock') }}-${{ github.run_id }}
-
-      - name: sccache stats
-        if: always()
-        continue-on-error: true
-        run: sccache --show-stats || true
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+          key: cargo-home-${{ matrix.runner }}-${{ matrix.target }}-${{ matrix.profile }}-${{ steps.lockhash.outputs.hash }}-${{ steps.lockhash.outputs.toolchain_hash }}