ci: optimize Go and Docker layer caching across CI workflows

- Fix apps/testapp/Dockerfile: copy go.mod/go.sum before source so
  the go mod download layer is stable across code-only changes
- Add cache-from/cache-to GHA cache to docker-build-push.yml with
  per-app scopes to prevent cache eviction between parallel builds
- Add cache-dependency-path: "**/go.sum" to all actions/setup-go
  steps in test.yml, docker-tests.yml, and lint.yml so the module
  cache key covers all go.sum files in the multi-module repo
- Add explicit scope to the e2e Docker build cache in test.yml to
  align with the docker-build-push.yml scope naming

Closes #3196

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tac0turtle

.github/workflows/docker-build-push.yml

@@ -48,3 +48,5 @@ jobs:
           push: true
           platforms: linux/amd64,linux/arm64
           tags: ghcr.io/${{ github.repository_owner }}/${{ matrix.app.name }}:${{ inputs.image-tag }}
+          cache-from: type=gha,scope=${{ matrix.app.name }}
+          cache-to: type=gha,mode=max,scope=${{ matrix.app.name }}

.github/workflows/docker-tests.yml

@@ -27,6 +27,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./test/docker-e2e/go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Install just
         uses: extractions/setup-just@v3
       - name: Run Docker E2E Tests
@@ -46,6 +47,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./test/docker-e2e/go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Install just
         uses: extractions/setup-just@v3
       - name: Run Docker Upgrade E2E Tests
@@ -65,6 +67,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./test/docker-e2e/go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Install just
         uses: extractions/setup-just@v3
       - name: Run Docker Compat E2E Tests

.github/workflows/lint.yml

@@ -16,6 +16,7 @@ jobs:
       - uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./go.mod
+          cache-dependency-path: "**/go.sum"
       # This steps sets the GIT_DIFF environment variable to true
       # if files defined in PATTERS changed
       - uses: technote-space/get-diff-action@v6.1.2

.github/workflows/test.yml

@@ -17,6 +17,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Install just
         uses: extractions/setup-just@v3
       - name: Build all ev-node binaries
@@ -30,6 +31,7 @@ jobs:
       - uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./go.mod
+          cache-dependency-path: "**/go.sum"
       - uses: extractions/setup-just@v3
       - run: just deps
       - name: check for diff
@@ -47,6 +49,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Install just
         uses: extractions/setup-just@v3
       - name: Run unit test
@@ -66,6 +69,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Install just
         uses: extractions/setup-just@v3
       - name: Run integration test
@@ -89,6 +93,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v4
       - name: Build evstack:local-dev (cached)
@@ -98,8 +103,8 @@ jobs:
           file: apps/testapp/Dockerfile
           load: true
           tags: evstack:local-dev
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+          cache-from: type=gha,scope=ev-node-testapp
+          cache-to: type=gha,mode=max,scope=ev-node-testapp
       - name: Install just
         uses: extractions/setup-just@v3
       - name: E2E Tests
@@ -115,6 +120,7 @@ jobs:
         uses: actions/setup-go@v6.3.0
         with:
           go-version-file: ./go.mod
+          cache-dependency-path: "**/go.sum"
       - name: Install just
         uses: extractions/setup-just@v3
       - name: EVM Tests

apps/testapp/Dockerfile

@@ -17,11 +17,14 @@ FROM base AS builder
 
 WORKDIR /ev-node
 
-# Copy all source code first
-COPY . .
+# Copy module files first to leverage Docker layer caching.
+# Dependencies are only re-downloaded when go.mod or go.sum change.
+COPY go.mod go.sum ./
+RUN go mod download
 
-# Now download dependencies and build
-RUN go mod download && cd apps/testapp && go install .
+# Copy the rest of the source and build.
+COPY . .
+RUN cd apps/testapp && go install .
 
 ## prep the final image.
 #