diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 6d445b8b1..a6a3283c5 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -66,8 +66,19 @@ jobs:
   build:
     name: "ubuntu-${{ matrix.os }}-${{ matrix.arch }}, GHC: ${{ matrix.ghc }}"
     needs: maybe-release
+    permissions:
+      contents: write
+      packages: write
     env:
       apps: "smp-server xftp-server ntf-server xftp"
+      opt: ${{ github.event_name == 'pull_request' && 'O0' || 'O2' }}
+      ghc_options: ${{ github.event_name == 'pull_request' && '--ghc-options=-O0' || '' }}
+      release: ${{ startsWith(github.ref, 'refs/tags/v') }}
+      postgres_dist: ${{ startsWith(github.ref, 'refs/tags/v') && 'dist-newstyle' || 'dist-postgres' }}
+      branch: ${{ github.base_ref || github.ref_name }}
+      cache_o0: ${{ github.event_name == 'push' && (github.ref == 'refs/heads/master' || github.ref == 'refs/heads/stable') }}
+      image_cache: ghcr.io/simplex-chat/simplexmq-build-cache:${{ matrix.os }}-${{ matrix.arch }}-ghc${{ matrix.ghc }}
+      source_hashes: dist-newstyle/sources.sha256
     runs-on: ${{ matrix.runner }}
     services:
       postgres:
@@ -146,6 +157,18 @@ jobs:
           sudo apt update
           sudo apt -y install postgresql-client-15
 
+      - name: Log in to GitHub Container Registry
+        if: matrix.should_run == true && env.release != 'true'
+        shell: bash
+        env:
+          GHCR_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: echo "$GHCR_TOKEN" | docker login ghcr.io -u "${{ github.actor }}" --password-stdin
+
+      - name: Compute image cache week
+        id: week
+        if: matrix.should_run == true && env.release != 'true'
+        run: echo "week=$(date -u +%G-W%V)" >> "$GITHUB_OUTPUT"
+
       - name: Build and cache Docker image
         if: matrix.should_run == true
         uses: simplex-chat/docker-build-push-action@v6
@@ -157,20 +180,14 @@ jobs:
           build-args: |
             TAG=${{ matrix.os }}
             GHC=${{ matrix.ghc }}
-
-      - name: Cache dependencies
-        if: matrix.should_run == true
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cabal/store
-            dist-newstyle
-          key: ubuntu-${{ matrix.os }}-${{ matrix.arch }}-ghc${{ matrix.ghc }}-${{ hashFiles('cabal.project', 'simplexmq.cabal') }}
+          cache-from: ${{ env.release != 'true' && format('type=registry,ref={0}-{1}', env.image_cache, steps.week.outputs.week) || '' }}
+          cache-to: ${{ github.event_name == 'push' && github.ref == 'refs/heads/master' && format('type=registry,ref={0}-{1},mode=max,ignore-error=true', env.image_cache, steps.week.outputs.week) || '' }}
 
       - name: Start container
         if: matrix.should_run == true
         shell: bash
         run: |
+          mkdir -p ~/.cabal
           docker run -t -d \
             --device /dev/fuse \
             --cap-add SYS_ADMIN \
@@ -181,21 +198,66 @@ jobs:
             -v ${{ github.workspace }}:/project \
             build/${{ matrix.os }}:latest
 
+      - name: Compute cache key prefixes
+        id: keys
+        if: matrix.should_run == true && env.release != 'true'
+        run: |
+          toolchain=$(docker exec builder dpkg-query -W -f '${db:Status-Status} ${binary:Package} ${Version}\n' 'binutils*' 'cpp*' 'gcc*' '*-dev' | grep '^installed ' | sha256sum | cut -c1-16)
+          target=${{ matrix.os }}-${{ matrix.arch }}-ghc${{ matrix.ghc }}-$toolchain
+          echo "deps=deps-$target" >> "$GITHUB_OUTPUT"
+          echo "dist=dist-$target" >> "$GITHUB_OUTPUT"
+
+      - name: Restore dependencies from cache
+        id: restore-deps
+        if: matrix.should_run == true && env.release != 'true'
+        uses: actions/cache/restore@v4
+        with:
+          path: ~/.cabal/store
+          key: ${{ steps.keys.outputs.deps }}-${{ env.branch }}-${{ github.sha }}
+          restore-keys: |
+            ${{ steps.keys.outputs.deps }}-${{ env.branch }}-
+            ${{ steps.keys.outputs.deps }}-
+
+      - name: Warn if dependencies not in cache
+        if: matrix.should_run == true && env.release != 'true' && steps.restore-deps.outputs.cache-matched-key == ''
+        run: echo "::warning title=Cache miss::${{ steps.keys.outputs.deps }}-${{ env.branch }}"
+
+      - name: Restore build directories from cache
+        id: restore-build
+        if: matrix.should_run == true && env.release != 'true'
+        uses: actions/cache/restore@v4
+        with:
+          path: |
+            dist-newstyle
+            dist-postgres
+          key: ${{ steps.keys.outputs.dist }}-${{ env.opt }}-${{ env.branch }}-${{ github.sha }}
+          restore-keys: |
+            ${{ steps.keys.outputs.dist }}-${{ env.opt }}-${{ env.branch }}-
+            ${{ steps.keys.outputs.dist }}-${{ env.opt }}-
+
+      - name: Warn if build directories not in cache
+        if: matrix.should_run == true && env.release != 'true' && steps.restore-build.outputs.cache-matched-key == ''
+        run: echo "::warning title=Cache miss::${{ steps.keys.outputs.dist }}-${{ env.opt }}-${{ env.branch }}"
+
+      - name: Set old timestamps on unchanged sources (GHC 8.10.7)
+        if: matrix.ghc == '8.10.7' && steps.restore-build.outputs.cache-matched-key != '' && hashFiles(env.source_hashes) != ''
+        run: scripts/ci/source-timestamps.sh restore ${{ env.source_hashes }}
+
       - name: Build smp-server, xftp-server (postgresql) and tests
         if: matrix.should_run == true
         shell: docker exec -t builder sh -eu {0}
         run: |
-          chmod -fR 777 ~/.cabal ./dist-newstyle || :; git config --global --add safe.directory '*'
-          cabal clean
+          chmod -fR 777 ~/.cabal ./dist-newstyle ./dist-postgres || :; git config --global --add safe.directory '*'
+          scripts/ci/prune-old-builds.sh dist-newstyle dist-postgres
           cabal update
-          cabal build --jobs=$(nproc) --enable-tests -fserver_postgres
+          cabal build --builddir=${{ env.postgres_dist }} --jobs=$(nproc) --enable-tests -fserver_postgres ${{ env.ghc_options }}
           mkdir -p /out
-          for i in smp-server xftp-server simplexmq-test; do
-            bin=$(find /project/dist-newstyle -name "$i" -type f -executable)
+          for i in smp-server xftp-server ntf-server simplexmq-test; do
+            bin=$(find /project/${{ env.postgres_dist }} -name "$i" -type f -executable)
             chmod +x "$bin"
-            mv "$bin" /out/
+            cp "$bin" /out/
           done
-          strip /out/smp-server /out/xftp-server
+          strip /out/smp-server /out/xftp-server /out/ntf-server
 
       - name: Copy simplexmq-test from container
         if: matrix.should_run == true
@@ -228,16 +290,17 @@ jobs:
           cat hashes.output >> "$GITHUB_OUTPUT"
 
       - name: Build everything else (standard)
+        id: build-standard
         if: matrix.should_run == true
         shell: docker exec -t builder sh -eu {0}
         run: |
-          cabal build --jobs=$(nproc)
+          cabal build --jobs=$(nproc) ${{ env.ghc_options }}
           mkdir -p /out
-          for i in ${{ env.apps }}; do
+          for i in smp-server xftp-server xftp; do
             bin=$(find /project/dist-newstyle -name "$i" -type f -executable)
             strip "$bin"
             chmod +x "$bin"
-            mv "$bin" /out/
+            cp "$bin" /out/
           done
 
       - name: Copy binaries from container and prepare them
@@ -282,6 +345,33 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: Record source hashes (GHC 8.10.7)
+        if: matrix.should_run == true && matrix.ghc == '8.10.7'
+        shell: docker exec -t builder sh -eu {0}
+        run: scripts/ci/source-timestamps.sh record ${{ env.source_hashes }}
+
+      - name: Compute dependency cache key
+        id: hash-deps
+        if: matrix.should_run == true && env.release != 'true'
+        shell: bash
+        run: echo "hash=$(ls ~/.cabal/store/ghc-*/ | sha256sum | cut -c1-16)" >> "$GITHUB_OUTPUT"
+
+      - name: Save dependencies to cache
+        if: matrix.should_run == true && env.release != 'true' && steps.restore-deps.outputs.cache-matched-key != format('{0}-{1}-{2}', steps.keys.outputs.deps, env.branch, steps.hash-deps.outputs.hash)
+        uses: actions/cache/save@v4
+        with:
+          path: ~/.cabal/store
+          key: ${{ steps.keys.outputs.deps }}-${{ env.branch }}-${{ steps.hash-deps.outputs.hash }}
+
+      - name: Save build directories to cache
+        if: matrix.should_run == true && env.release != 'true' && steps.restore-build.outputs.cache-hit != 'true'
+        uses: actions/cache/save@v4
+        with:
+          path: |
+            dist-newstyle
+            dist-postgres
+          key: ${{ steps.keys.outputs.dist }}-${{ env.opt }}-${{ env.branch }}-${{ github.sha }}
+
       - name: Test
         if: matrix.should_run == true && matrix.arch == 'x86-64'
         timeout-minutes: 120
@@ -306,6 +396,52 @@ jobs:
             exit 1
           fi
 
+      - name: Remove -O2 build directories
+        id: remove-o2
+        if: env.cache_o0 == 'true' && !cancelled() && steps.build-standard.outcome == 'success'
+        shell: docker exec -t builder sh -eu {0}
+        run: rm -rf dist-newstyle dist-postgres
+
+      - name: Restore -O0 build directories from cache
+        id: restore-build-o0
+        if: ${{ !cancelled() && steps.remove-o2.outcome == 'success' }}
+        uses: actions/cache/restore@v4
+        with:
+          path: |
+            dist-newstyle
+            dist-postgres
+          key: ${{ steps.keys.outputs.dist }}-O0-${{ env.branch }}-${{ github.sha }}
+          restore-keys: |
+            ${{ steps.keys.outputs.dist }}-O0-${{ env.branch }}-
+            ${{ steps.keys.outputs.dist }}-O0-
+
+      - name: Set old timestamps on unchanged sources for -O0 build (GHC 8.10.7)
+        if: ${{ !cancelled() && matrix.ghc == '8.10.7' && steps.restore-build-o0.outputs.cache-matched-key != '' && hashFiles(env.source_hashes) != '' }}
+        run: scripts/ci/source-timestamps.sh restore ${{ env.source_hashes }}
+
+      - name: Build at -O0 for pull request caches
+        id: build-o0
+        if: ${{ !cancelled() && steps.remove-o2.outcome == 'success' }}
+        shell: docker exec -t builder sh -eu {0}
+        run: |
+          scripts/ci/prune-old-builds.sh dist-newstyle dist-postgres
+          cabal build --builddir=dist-postgres --jobs=$(nproc) --enable-tests -fserver_postgres --ghc-options=-O0
+          cabal build --jobs=$(nproc) --ghc-options=-O0
+
+      - name: Record source hashes for -O0 build (GHC 8.10.7)
+        if: ${{ !cancelled() && matrix.ghc == '8.10.7' && steps.build-o0.outcome == 'success' }}
+        shell: docker exec -t builder sh -eu {0}
+        run: scripts/ci/source-timestamps.sh record ${{ env.source_hashes }}
+
+      - name: Save -O0 build directories to cache
+        if: ${{ !cancelled() && steps.build-o0.outcome == 'success' && steps.restore-build-o0.outputs.cache-hit != 'true' }}
+        uses: actions/cache/save@v4
+        with:
+          path: |
+            dist-newstyle
+            dist-postgres
+          key: ${{ steps.keys.outputs.dist }}-O0-${{ env.branch }}-${{ github.sha }}
+
 # =============================
 #      Resolver test job
 # =============================
diff --git a/scripts/ci/prune-old-builds.sh b/scripts/ci/prune-old-builds.sh
new file mode 100755
index 000000000..c122ed338
--- /dev/null
+++ b/scripts/ci/prune-old-builds.sh
@@ -0,0 +1,9 @@
+#!/bin/sh
+set -eu
+
+version=$(awk '/^version:/ {print $2}' simplexmq.cabal)
+for dir in "$@"; do
+  if [ -d "$dir/build" ]; then
+    find "$dir/build" -mindepth 3 -maxdepth 3 -type d -name 'simplexmq-*' ! -name "simplexmq-$version" -exec rm -rf {} +
+  fi
+done
diff --git a/scripts/ci/source-timestamps.sh b/scripts/ci/source-timestamps.sh
new file mode 100755
index 000000000..e8bc8b1ce
--- /dev/null
+++ b/scripts/ci/source-timestamps.sh
@@ -0,0 +1,27 @@
+#!/bin/sh
+set -eu
+
+command=$1
+hashes=$2
+
+sources() {
+  git ls-files -z '*.hs' '*.hsc'
+}
+
+case "$command" in
+  record)
+    sources | xargs -0 sha256sum > "$hashes"
+    ;;
+  restore)
+    sources | xargs -0 touch
+    while read -r hash file; do
+      if [ -f "$file" ] && [ "$(sha256sum "$file" | cut -d' ' -f1)" = "$hash" ]; then
+        touch -d 2000-01-01 "$file"
+      fi
+    done < "$hashes"
+    ;;
+  *)
+    echo "usage: $0 record|restore <hashes file>" >&2
+    exit 1
+    ;;
+esac
diff --git a/tests/Util.hs b/tests/Util.hs
index 9a4049d68..eaa670f06 100644
--- a/tests/Util.hs
+++ b/tests/Util.hs
@@ -56,7 +56,7 @@ instance Example a => Example (TestWrapper a) where
     ci <- envCI
     runTest `E.catches` [E.Handler (onTestFailure ci), E.Handler (onTestException ci)]
     where
-      tt = 120
+      tt = 300
       runTest =
         timeout (tt * 1000000) (evaluateExample action params hooks state) `finally` callCommand "sync" >>= \case
           Just r -> pure r