ci: cache libwaku, gate go mod tidy, rename LMN_DIR

- Rename LMN_DIR -> LOGOS_DELIVERY_DIR across the PR-gate and nightly
  workflows, the waku Makefile, and the build docs.
- Cache the built logos-delivery kernel keyed on its upstream HEAD SHA,
  skipping the clone + libwaku build while that commit is unchanged.
- Add a "go mod tidy is clean" step that fails if go.mod/go.sum drift.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/CI.yml

@@ -46,9 +46,9 @@ jobs:
 
       - name: Build waku bindings
         run: |
-          export LMN_DIR=$(pwd)/vendor/logos-delivery
-          export CGO_CFLAGS="-I${LMN_DIR}/library/"
-          export CGO_LDFLAGS="-L${LMN_DIR}/build/ -lwaku -Wl,-rpath,${LMN_DIR}/build/" 
+          export LOGOS_DELIVERY_DIR=$(pwd)/vendor/logos-delivery
+          export CGO_CFLAGS="-I${LOGOS_DELIVERY_DIR}/library/"
+          export CGO_LDFLAGS="-L${LOGOS_DELIVERY_DIR}/build/ -lwaku -Wl,-rpath,${LOGOS_DELIVERY_DIR}/build/" 
           make -C waku build
 
       - name: Increase ulimit
@@ -58,9 +58,9 @@ jobs:
         run: |
           set -euo pipefail
           cd waku
-          export LMN_DIR=$(pwd)/vendor/logos-delivery
-          export CGO_CFLAGS="-I${LMN_DIR}/library/"
-          export CGO_LDFLAGS="-L${LMN_DIR}/build/ -lwaku -Wl,-rpath,${LMN_DIR}/build/"
+          export LOGOS_DELIVERY_DIR=$(pwd)/vendor/logos-delivery
+          export CGO_CFLAGS="-I${LOGOS_DELIVERY_DIR}/library/"
+          export CGO_LDFLAGS="-L${LOGOS_DELIVERY_DIR}/build/ -lwaku -Wl,-rpath,${LOGOS_DELIVERY_DIR}/build/"
           go test -count=10 -p=1 -v -timeout=360m . | tee ../testlogs.log
 
       - name: Upload daily test logs

.github/workflows/pr.yml

@@ -16,7 +16,7 @@ jobs:
     env:
       # Clone the logos-delivery checkout OUTSIDE the module tree: a directory
       # named `vendor/` at the module root would put Go into vendor mode.
-      LMN_DIR: ${{ github.workspace }}/.logos-delivery
+      LOGOS_DELIVERY_DIR: ${{ github.workspace }}/.logos-delivery
       # libwaku (kernel) is required at compile time for the cgo packages.
       # Updated to also include liblogosdelivery once the messaging package lands.
       CGO_CFLAGS: -I${{ github.workspace }}/.logos-delivery/library/
@@ -35,11 +35,29 @@ jobs:
         with:
           go-version: "1.24"
 
+      - name: Resolve logos-delivery commit
+        # Cache the built kernel keyed on the exact upstream commit, so the
+        # expensive clone + build is skipped while logos-delivery's HEAD is
+        # unchanged. ls-remote gives us the SHA before we clone.
+        id: logos-delivery-rev
+        run: |
+          rev=$(git ls-remote https://github.com/logos-messaging/logos-delivery.git HEAD | cut -f1)
+          echo "rev=$rev" >> "$GITHUB_OUTPUT"
+
+      - name: Cache logos-delivery build
+        id: logos-delivery-cache
+        uses: actions/cache@v4
+        with:
+          path: ${{ env.LOGOS_DELIVERY_DIR }}
+          key: logos-delivery-${{ runner.os }}-${{ steps.logos-delivery-rev.outputs.rev }}
+
       - name: Clone logos-delivery
-        run: git clone --depth 1 https://github.com/logos-messaging/logos-delivery.git "$LMN_DIR"
+        if: steps.logos-delivery-cache.outputs.cache-hit != 'true'
+        run: git clone --depth 1 https://github.com/logos-messaging/logos-delivery.git "$LOGOS_DELIVERY_DIR"
 
       - name: Build libwaku
-        run: make -C "$LMN_DIR" libwaku -j
+        if: steps.logos-delivery-cache.outputs.cache-hit != 'true'
+        run: make -C "$LOGOS_DELIVERY_DIR" libwaku -j
 
       - name: go build
         run: go build ./...
@@ -47,6 +65,14 @@ jobs:
       - name: go vet
         run: go vet ./...
 
+      - name: go mod tidy is clean
+        # `go mod tidy` must be a no-op on a well-maintained module. If it
+        # changes go.mod/go.sum the PR left them out of sync — fail and show
+        # the diff so the author can commit the tidied result.
+        run: |
+          go mod tidy
+          git diff --exit-code go.mod go.sum
+
       - name: Ensure base ref is available for lint
         # golangci-lint's new-from-merge-base needs origin/master present.
         run: git fetch --no-tags origin master

README.md

@@ -18,9 +18,9 @@ If you have `logos-delivery` checked out, point the build to it:
 
 ```bash
 # path to your existing logos-delivery clone
-export LMN_DIR=/absolute/path/to/logos-delivery
-export CGO_CFLAGS="-I${LMN_DIR}/library"
-export CGO_LDFLAGS="-L${LMN_DIR}/build -lwaku -Wl,-rpath,${LMN_DIR}/build"
+export LOGOS_DELIVERY_DIR=/absolute/path/to/logos-delivery
+export CGO_CFLAGS="-I${LOGOS_DELIVERY_DIR}/library"
+export CGO_LDFLAGS="-L${LOGOS_DELIVERY_DIR}/build -lwaku -Wl,-rpath,${LOGOS_DELIVERY_DIR}/build"
 
 # compile all packages
 make -C waku build

waku/Makefile

@@ -1,17 +1,17 @@
 # Makefile for Waku Go Bindings
 
 # Path to logos-delivery submodule
-export LMN_DIR ?= $(shell pwd)/../vendor/logos-delivery
+export LOGOS_DELIVERY_DIR ?= $(shell pwd)/../vendor/logos-delivery
 
 # Debugging output
 print-paths:
-	@echo "LMN_DIR: $(LMN_DIR)"
+	@echo "LOGOS_DELIVERY_DIR: $(LOGOS_DELIVERY_DIR)"
 	@echo "HEADER_PATH: $(LIBWAKU_HEADER_PATH)"
 	@echo "LIB_PATH: $(LIBWAKU_LIB_PATH)"
 
 # Default paths for libwaku library and headers (can be overridden)
-export LIBWAKU_HEADER_PATH ?= $(LMN_DIR)/library
-export LIBWAKU_LIB_PATH ?= $(LMN_DIR)/build
+export LIBWAKU_HEADER_PATH ?= $(LOGOS_DELIVERY_DIR)/library
+export LIBWAKU_LIB_PATH ?= $(LOGOS_DELIVERY_DIR)/build
 
 export CGO_CFLAGS := -I$(LIBWAKU_HEADER_PATH)/
 export CGO_LDFLAGS := -L$(LIBWAKU_LIB_PATH)/ -lwaku -Wl,-rpath,$(LIBWAKU_LIB_PATH)/