feat: support multi-module Go development in CI and update developer documentation

.github/workflows/go.yml

@@ -19,33 +19,87 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  discover:
+    runs-on: ubuntu-latest
+    outputs:
+      modules: ${{ steps.set-modules.outputs.modules }}
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+      - id: set-modules
+        run: |
+          MODULES=$(find . -not -path '*/\.git/*' -name go.mod -exec dirname {} \; | sort | jq -R -s -c 'split("\n")[:-1]')
+          echo "modules=$MODULES" >> $GITHUB_OUTPUT
+
   test:
+    needs: discover
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        module: ${{ fromJson(needs.discover.outputs.modules) }}
     steps:
     - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
     - name: Setup
       uses: ./.github/actions/setup
 
-    - name: Tidy
+    - name: Initialize workspace
+      run: go work init && go work use -r .
+
+    - name: Tidy Check
+      working-directory: ${{ matrix.module }}
       run: go mod tidy -diff
 
     - name: Build
+      working-directory: ${{ matrix.module }}
       run: go build -mod=readonly -v ./...
 
     - name: Test
+      working-directory: ${{ matrix.module }}
       run: go test -race -mod=readonly -v -count=1 -shuffle=on ./...
 
   lint:
+    needs: discover
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        module: ${{ fromJson(needs.discover.outputs.modules) }}
     steps:
     - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
     - name: Setup
       uses: ./.github/actions/setup
+
+    - name: Initialize workspace
+      run: go work init && go work use -r .
 
     - name: Lint
       uses: golangci/golangci-lint-action@1e7e51e771db61008b38414a730f564565cf7c20  # v9.2.0
       with:
+        working-directory: ${{ matrix.module }}
         install-mode: goinstall
         version: 5256574b81bcedfbcae9099f745f6aee9335da10 # v2.3.1
+
+  guardrail:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+
+    - name: Setup
+      uses: ./.github/actions/setup
+
+    - name: Check root go.mod against internal modules
+      run: |
+        ROOT_REQS=$(go mod edit -json | jq -r '.Require // [] | .[] | .Path')
+
+        FAIL=0
+        while IFS= read -r -d '' dir; do
+          MOD_PATH=$(cd "$dir" && go mod edit -json | jq -r '.Module.Path')
+          if [ -n "$MOD_PATH" ] && echo "$ROOT_REQS" | grep -F -x -q "$MOD_PATH"; then
+            echo "ERROR: Root go.mod requires internal submodule $MOD_PATH"
+            FAIL=1
+          fi
+        done < <(find . -mindepth 2 -not -path '*/\.git/*' -name go.mod -printf '%h\0')
+
+        exit $FAIL

.github/workflows/nightly.yml

@@ -7,19 +7,42 @@ on:
   workflow_dispatch:
 
 jobs:
+  discover:
+    runs-on: ubuntu-latest
+    outputs:
+      modules: ${{ steps.set-modules.outputs.modules }}
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+      - id: set-modules
+        run: |
+          MODULES=$(find . -not -path '*/\.git/*' -name go.mod -exec dirname {} \; | sort | jq -R -s -c 'split("\n")[:-1]')
+          echo "modules=$MODULES" >> $GITHUB_OUTPUT
+
   test:
+    needs: discover
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        module: ${{ fromJson(needs.discover.outputs.modules) }}
     steps:
     - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
     - name: Setup
       uses: ./.github/actions/setup
 
+
     - name: Nightly Test
+      working-directory: ${{ matrix.module }}
       run: go test -race -mod=readonly -v -count=1 -shuffle=on ./...
 
   vulncheck:
+    needs: discover
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        module: ${{ fromJson(needs.discover.outputs.modules) }}
     steps:
     - name: Run govulncheck
       # NOTE: pinned to master HEAD instead of a tag. The latest release (v1.0.4)
@@ -28,5 +51,6 @@ jobs:
       # TODO: re-pin to a tagged release once upstream tags one past v1.0.4.
       uses: golang/govulncheck-action@31f7c5463448f83528bd771c2d978d940080c9fd # master, post-v1.0.4 (Node 24)
       with:
-           go-version-file: go.mod
+           go-version-file: ${{ matrix.module }}/go.mod
+           work-dir: ${{ matrix.module }}
            repo-checkout: true

AGENTS.md

@@ -23,6 +23,8 @@ Run from the repo root. These match what CI enforces (CI also passes `-v`):
 - Tidy check:  `go mod tidy -diff`   (must print nothing)
 - Format:      `golangci-lint fmt`   (applies gofumpt + goimports per config)
 
+**Local Development**: Contributors should use `go work init && go work use -r .` to set up their local workspaces.
+
 ## Definition of done
 
 A change is complete only when all of these pass locally:
@@ -104,6 +106,10 @@ See `examples/quickstart` for a full runnable program.
 - **Add cross-cutting behavior:** register a `plugin.New(plugin.Config{...})`
   hook (`Before*`/`After*` for run/agent/model/tool) instead of editing the loop.
 
+## Multi-Module Development
+
+See the [Multi-Module Development](CONTRIBUTING.md#multi-module-development) section in `CONTRIBUTING.md` for policy, steps to add a new module, and release tagging information.
+
 ## Testing
 
 - Tests run **offline by default**: LLM HTTP traffic is replayed from

CONTRIBUTING.md

@@ -4,6 +4,7 @@ We'd love to accept your patches and contributions to this project.
 
 -   [How to contribute](#how-to-contribute)
 -   [Branches](#branches)
+-   [Multi-Module Development](#multi-module-development)
 -   [Before you begin](#before-you-begin)
     -   [Sign our Contributor License Agreement](#sign-our-contributor-license-agreement)
     -   [Review our community guidelines](#review-our-community-guidelines)
@@ -43,6 +44,31 @@ To work on a 1.x fix, base your branch on `v1`:
 git switch -c my-fix origin/v1
 ```
 
+## Multi-Module Development
+
+**Policy**: New integrations with heavy or optional dependencies must be created as separate Go modules.
+
+**Local Development**: Contributors should use `go work init && go work use -r .` to set up their local workspaces.
+
+**Steps to Add a New Module (e.g., `plugin/myplugin`)**:
+1. Navigate into the directory: `cd <module_directory_path>`
+2. Initialize the module: `go mod init google.golang.org/adk/<module_directory_path>`
+3. Add your Go code, dependencies, and tests.
+4. Tidy the module: `go mod tidy`
+5. Return to the repo root.
+6. Tidy the root module: `go mod tidy`
+7. Add the module to your workspace: `go work use ./<module_directory_path>`
+8. Verify everything builds and tests from the root: `go build work && go test work`. The CI will automatically pick up the new module on the PR.
+
+**Release Tagging**:
+- **Core Module**: Tags remain `vX.Y.Z` (e.g., `v2.1.0`).
+- **Submodules**: Tags are prefixed with the full module path directory, e.g., `plugin/agentanalytics/v0.1.0`. This is the standard Go way to version modules not at the repo root.
+- **go get / go install**: Consumers will use:
+  - `go get google.golang.org/adk/v2@v2.1.0`
+  - `go get google.golang.org/adk/plugin/agentanalytics@v0.1.0`
+- **Version Coupling**: Each submodule's `go.mod` will specify the minimum version of `google.golang.org/adk/v2` it depends on. Submodules can be released independently of the core module and each other.
+- **go.work Impact**: `go.work` is for local development only and does not affect how modules are versioned, tagged, or fetched by consumers.
+
 ## Before you begin
 
 ### Sign our Contributor License Agreement