diff --git a/.github/workflows/reusable/cached-install/action.yml b/.github/workflows/reusable/cached-install/action.yml
index 18a5a8af..f65467ee 100644
--- a/.github/workflows/reusable/cached-install/action.yml
+++ b/.github/workflows/reusable/cached-install/action.yml
@@ -4,18 +4,43 @@ description: "install dependencies, build and cache result, or restore from cach
 runs:
   using: "composite"
   steps:
-    - name: cache homedir
+    # The cache keys must distinguish the TARGET platform, not just the
+    # runner: the macOS host build, the iOS build and the Android build
+    # all run on the same macos runner image, and GitHub's cache is
+    # write-once per key — with a shared key the first job to save owns
+    # the cache forever and the other platforms' saves fail ("Cache save
+    # failed."), so their dependencies were rebuilt from source on every
+    # run (~30 min Android, ~35 min iOS). ARCHFLAGS is the workflow-level
+    # platform selector (empty = host, --ios, --android). The vcpkg
+    # submodule commit is part of the key because the tool version
+    # changes what it builds; the restore-keys prefix fallback reuses the
+    # newest previous cache on any key miss — vcpkg's own per-package ABI
+    # hashing makes stale archive entries harmless (they are ignored) and
+    # `vcpkg install` reconciles a stale installed tree.
+    - name: compute cache keys
+      id: keys
+      run: |
+        echo "platform=${ARCHFLAGS:-host}" >> "$GITHUB_OUTPUT"
+        echo "vcpkg_sha=$(git rev-parse HEAD:vcpkg)" >> "$GITHUB_OUTPUT"
+      shell: bash
+    - name: cache vcpkg binary archives
       id: cache-homedir
       uses: actions/cache/restore@v4
       with:
-        key: ${{ runner.arch }}-${{ runner.os }}-cache-homedir2-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
+        key: ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-archives-${{ steps.keys.outputs.vcpkg_sha }}-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
+        restore-keys: |
+          ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-archives-${{ steps.keys.outputs.vcpkg_sha }}-
+          ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-archives-
         path: |
           ~/.cache/vcpkg/archives
     - name: cache vcpkg installed
       id: cache-vcpkg-installed
       uses: actions/cache/restore@v4
       with:
-        key: ${{ runner.arch }}-${{ runner.os }}-cache-vcpkg-installed2-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
+        key: ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-installed-${{ steps.keys.outputs.vcpkg_sha }}-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
+        restore-keys: |
+          ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-installed-${{ steps.keys.outputs.vcpkg_sha }}-
+          ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-installed-
         path: |
           ./build/vcpkg_installed
     - name: install-prerequisities
@@ -45,30 +70,22 @@ runs:
           exit "$EXITCODE"
         fi
       shell: bash
-    - name: cache homedir save
+    # Save even on failure (if: always()) so a partially built dependency
+    # set is reused by the retry. Saving is skipped when the exact key was
+    # already restored (nothing new to store).
+    - name: cache vcpkg binary archives save
       id: cache-homedir-save
-      if: always()
+      if: always() && steps.cache-homedir.outputs.cache-hit != 'true'
       uses: actions/cache/save@v4
       with:
-        key: ${{ runner.arch }}-${{ runner.os }}-cache-homedir2-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
+        key: ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-archives-${{ steps.keys.outputs.vcpkg_sha }}-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
         path: |
           ~/.cache/vcpkg/archives
     - name: cache vcpkg installed save
       id: cache-vcpkg-installed-save
-      if: always()
+      if: always() && steps.cache-vcpkg-installed.outputs.cache-hit != 'true'
       uses: actions/cache/save@v4
       with:
-        key: ${{ runner.arch }}-${{ runner.os }}-cache-vcpkg-installed2-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
+        key: ${{ runner.arch }}-${{ runner.os }}-${{ steps.keys.outputs.platform }}-installed-${{ steps.keys.outputs.vcpkg_sha }}-${{ hashFiles('./vcpkg.json', './overlaytriplets/**', './overlayports/**') }}
         path: |
           ./build/vcpkg_installed
-    #- name: Commit compiled binaries
-    #  run: |
-    #    git config --global user.name 'github-actions[bot]'
-    #    git config --global user.email 'github-actions[bot]@users.noreply.github.com'
-    #    git add packages/streamr-libstreamrproxyclient/dist
-    #    git add packages/streamr-libstreamrproxyclient/wrappers/go
-    #    git commit -m "Automatically compiled binaries"
-    #    git pull --rebase --no-edit
-    #    git push --no-verify
-    #  shell: bash
-
diff --git a/MODERNIZATION.md b/MODERNIZATION.md
index 5ab75a64..c6f68a90 100644
--- a/MODERNIZATION.md
+++ b/MODERNIZATION.md
@@ -1011,7 +1011,31 @@ exactly that. So consolidation walks the dependency chain from the top:
    version accepts it — owner-approved selective disabling, compiler
    coverage unaffected (fourth exclusion overall; revisit each clangd
    release).
-7. C-7 streamr-json
+7. **C-7 streamr-json** ✅ — the 3 headers (jsonConcepts, toJson,
+   toString) became named sub-modules (`streamr.json.X`); façade and
+   include/ tree deleted; the 4 importers (json's own tests + example)
+   flipped to narrow imports, and the logger units' temporary TEXTUAL
+   `streamr-json/toJson.hpp` include from C-6 flipped to
+   `import streamr.json.toJson;`. First conversion with zero compile
+   errors on the first whole-tree build — the accumulated rules
+   (std-include pass, curated-name consumer flip, minimal imports,
+   inline-constexpr, GMF-only C declarations) now cover the whole
+   failure surface.
+   **The same PR repairs the CI dependency caching** (owner asked for it
+   to be folded in): the C-2 consolidation commit had accidentally
+   REVERTED PR #41's per-platform cache keys in
+   `.github/workflows/reusable/cached-install/action.yml` (a rebase
+   mishap — #41 and C-2 were in flight simultaneously). Since C-2 the
+   Android/iOS jobs shared one `ARM64-macOS-…` key with the host macOS
+   leg; the host job saved first and owned the write-once key, so the
+   cross builds restored a useless host cache and rebuilt every vcpkg
+   dependency from source — degrading as the old per-platform entries
+   were LRU-evicted (repo cache 11.7 GB > 10 GB cap): Android leg C-3
+   48 min → C-6 139/123 min. The #41 scheme (`${ARCHFLAGS:-host}`
+   platform component + vcpkg submodule SHA + restore-keys fallbacks +
+   skip-save-on-exact-hit) is restored verbatim; the first post-merge
+   run per platform repopulates the caches (slow once), after which
+   Android returns to ~10 min and iOS to ~5 min.
 8. C-8 streamr-eventemitter (+ final bench.sh metrics and memo closure)
 
 One package per PR, `bench.sh` measured at the dht step and at the end
diff --git a/packages/streamr-json/CMakeLists.txt b/packages/streamr-json/CMakeLists.txt
index 0a5f220f..46ab52b5 100644
--- a/packages/streamr-json/CMakeLists.txt
+++ b/packages/streamr-json/CMakeLists.txt
@@ -47,19 +47,16 @@ endif()
 # project() because it inspects the compiler id.
 include(${CMAKE_CURRENT_SOURCE_DIR}/StreamrModules.cmake)
 
-# Module façade (MODERNIZATION.md Part 2): the package is now a STATIC
-# library whose module interface units re-export the public headers.
-# #include consumers are unaffected; import consumers get the BMIs.
+# CONSOLIDATED (MODERNIZATION.md Phase 2.6): one named sub-module per
+# former public header (settled architecture: no umbrella). The include/
+# tree is gone; the module interface units are the source of truth, so
+# the package no longer exports any include directory.
+file(GLOB_RECURSE STREAMR_JSON_MODULE_UNITS CONFIGURE_DEPENDS
+    ${CMAKE_CURRENT_SOURCE_DIR}/modules/*.cppm)
 streamr_add_module_library(streamr-json
-  FILES
-    modules/streamr.json.cppm
-    modules/streamr.json-all.cppm)
+  FILES ${STREAMR_JSON_MODULE_UNITS})
 add_library(streamr::streamr-json ALIAS streamr-json)
 
-target_include_directories(
-  streamr-json PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-           $<INSTALL_INTERFACE:include>)
-
 # PUBLIC (was INTERFACE): the module interface units themselves compile
 # against boost-pfr/nlohmann in their global module fragments.
 target_link_libraries(streamr-json PUBLIC Boost::pfr)
diff --git a/packages/streamr-json/lint.sh b/packages/streamr-json/lint.sh
index 547d26c0..1c7dc752 100755
--- a/packages/streamr-json/lint.sh
+++ b/packages/streamr-json/lint.sh
@@ -10,11 +10,14 @@ clangd-tidy -p ./build $FILES
 echo "Running clang-format --dry-run on $FILES"
 ../../run-clang-format.py $FILES
 
-# Module interface units: format check only. clangd-tidy is not run on
-# .cppm files (headers remain the fully linted source of truth during the
-# façade migration; clangd modules support is still experimental).
+# CONSOLIDATED (MODERNIZATION.md Phase 2.6): the include/ tree is gone —
+# the code lives in the module interface units, which are linted with
+# clangd-tidy as the source of truth.
 MODULE_FILES=$(find ./modules -type f -name "*.cppm" 2>/dev/null | xargs echo)
 if [ -n "$MODULE_FILES" ]; then
+    echo "Running clangd-tidy on $MODULE_FILES"
+    clangd-tidy -p ./build $MODULE_FILES
+
     echo "Running clang-format --dry-run on $MODULE_FILES"
     ../../run-clang-format.py $MODULE_FILES
 fi
diff --git a/packages/streamr-json/include/streamr-json/jsonConcepts.hpp b/packages/streamr-json/modules/jsonConcepts.cppm
similarity index 87%
rename from packages/streamr-json/include/streamr-json/jsonConcepts.hpp
rename to packages/streamr-json/modules/jsonConcepts.cppm
index c402da5a..7abda68a 100644
--- a/packages/streamr-json/include/streamr-json/jsonConcepts.hpp
+++ b/packages/streamr-json/modules/jsonConcepts.cppm
@@ -1,10 +1,19 @@
-#ifndef STREAMR_JSON_JSONCONCEPTS_HPP
-#define STREAMR_JSON_JSONCONCEPTS_HPP
-
+// Module streamr.json.jsonConcepts
+// CONSOLIDATED from the former header
+// streamr-json/jsonConcepts.hpp (MODERNIZATION.md Phase 2.6):
+// this file is now the source of truth.
+module;
+
+#include <initializer_list>
+#include <string>
+#include <string_view>
+#include <type_traits>
 #include <boost/pfr/traits.hpp>
 #include <nlohmann/json.hpp>
 
-namespace streamr::json {
+export module streamr.json.jsonConcepts;
+
+export namespace streamr::json {
 namespace suppresslint { // linter does not support concepts, and thinks this
                          // file is unused
 using SuppressLint = void;
@@ -88,6 +97,4 @@ std::initializer_list<noaland::i_dont_care>>);
 };
 */
 
-} // namespace streamr::json
-
-#endif // STREAMR_JSON_JSONCONCEPTS_HPP
\ No newline at end of file
+} // namespace streamr::json
\ No newline at end of file
diff --git a/packages/streamr-json/modules/streamr.json-all.cppm b/packages/streamr-json/modules/streamr.json-all.cppm
deleted file mode 100644
index 6ff5c7fc..00000000
--- a/packages/streamr-json/modules/streamr.json-all.cppm
+++ /dev/null
@@ -1,48 +0,0 @@
-// Coarse façade partition over ALL public headers of streamr-json.
-// One partition (instead of one per header) keeps the number of
-// module units — and thus repeated global-module-fragment parses
-// of the expensive header stacks — minimal during the façade
-// stage (measured at the Phase 2.4 bench checkpoint). Per-header
-// granularity returns at consolidation if needed.
-module;
-
-#include "streamr-json/jsonConcepts.hpp"
-#include "streamr-json/toJson.hpp"
-#include "streamr-json/toString.hpp"
-
-export module streamr.json:all;
-
-export namespace streamr::json {
-
-using streamr::json::AssignableToNlohmannJson;
-using streamr::json::AssociativeType;
-using streamr::json::InitializerList;
-using streamr::json::IterableType;
-using streamr::json::NotAssignableToNlohmannJson;
-using streamr::json::PointerLike;
-using streamr::json::PointerType;
-using streamr::json::ReflectableType;
-using streamr::json::TypeWithToJson;
-
-} // namespace streamr::json
-
-export namespace streamr::json {
-
-using streamr::json::addStructElementsToJson;
-using streamr::json::addStructElementToJson;
-using streamr::json::AssignableToJsonBuilder;
-using streamr::json::json;
-using streamr::json::JsonBuilder;
-using streamr::json::JsonInitializerList;
-using streamr::json::pointerToJson;
-using streamr::json::StreamrJsonInitializerList;
-using streamr::json::toJson;
-
-} // namespace streamr::json
-
-export namespace streamr::json {
-
-using streamr::json::toString;
-using streamr::json::TypeWithToString;
-
-} // namespace streamr::json
diff --git a/packages/streamr-json/modules/streamr.json.cppm b/packages/streamr-json/modules/streamr.json.cppm
deleted file mode 100644
index 3c7ca62c..00000000
--- a/packages/streamr-json/modules/streamr.json.cppm
+++ /dev/null
@@ -1,4 +0,0 @@
-// Primary module interface unit of streamr.json.
-export module streamr.json;
-
-export import :all;
diff --git a/packages/streamr-json/include/streamr-json/toJson.hpp b/packages/streamr-json/modules/toJson.cppm
similarity index 95%
rename from packages/streamr-json/include/streamr-json/toJson.hpp
rename to packages/streamr-json/modules/toJson.cppm
index beed7d02..632fe30e 100644
--- a/packages/streamr-json/include/streamr-json/toJson.hpp
+++ b/packages/streamr-json/modules/toJson.cppm
@@ -1,9 +1,16 @@
-#ifndef STREAMR_JSON_TOJSON_HPP
-#define STREAMR_JSON_TOJSON_HPP
+// Module streamr.json.toJson
+// CONSOLIDATED from the former header
+// streamr-json/toJson.hpp (MODERNIZATION.md Phase 2.6):
+// this file is now the source of truth.
+module;
 
+#include <cstddef>
 #include <initializer_list>
+#include <map>
+#include <string>
 #include <string_view>
 #include <type_traits>
+#include <vector>
 #include <boost/pfr.hpp>
 #include <boost/pfr/core.hpp>
 #include <boost/pfr/core_name.hpp>
@@ -11,8 +18,11 @@
 #include <boost/pfr/tuple_size.hpp>
 #include <nlohmann/json.hpp>
 
-#include "streamr-json/jsonConcepts.hpp"
-namespace streamr::json {
+export module streamr.json.toJson;
+
+import streamr.json.jsonConcepts;
+
+export namespace streamr::json {
 using suppresslint::SuppressLint; // otherwise linter thinks jsonConcepts.hpp
                                   // is unused
 using json = nlohmann::json;
@@ -253,6 +263,4 @@ json toJson(const T& value) {
 
 using StreamrJsonInitializerList = std::initializer_list<JsonBuilder>;
 
-} // namespace streamr::json
-
-#endif
+} // namespace streamr::json
\ No newline at end of file
diff --git a/packages/streamr-json/include/streamr-json/toString.hpp b/packages/streamr-json/modules/toString.cppm
similarity index 69%
rename from packages/streamr-json/include/streamr-json/toString.hpp
rename to packages/streamr-json/modules/toString.cppm
index a195d918..53e35068 100644
--- a/packages/streamr-json/include/streamr-json/toString.hpp
+++ b/packages/streamr-json/modules/toString.cppm
@@ -1,14 +1,22 @@
-#ifndef STREAMR_JSON_TOSTRING_HPP
-#define STREAMR_JSON_TOSTRING_HPP
+// Module streamr.json.toString
+// CONSOLIDATED from the former header
+// streamr-json/toString.hpp (MODERNIZATION.md Phase 2.6):
+// this file is now the source of truth.
+module;
+
+#include <initializer_list>
+#include <string>
+
+export module streamr.json.toString;
+
+import streamr.json.jsonConcepts;
+import streamr.json.toJson;
 
 /**
  * Convert (almost) any struct to string in C++20.
  **/
 
-#include "streamr-json/jsonConcepts.hpp"
-#include "streamr-json/toJson.hpp"
-
-namespace streamr::json {
+export namespace streamr::json {
 
 using suppresslint::SuppressLint; // otherwise linter thinks jsonConcepts.hpp
                                   // is unused
@@ -42,6 +50,4 @@ std::string toString(const T& value) {
     return value.toString();
 }
 
-} // namespace streamr::json
-
-#endif
+} // namespace streamr::json
\ No newline at end of file
diff --git a/packages/streamr-json/src/examples/JsonExample.cpp b/packages/streamr-json/src/examples/JsonExample.cpp
index 5f247e46..713144e5 100644
--- a/packages/streamr-json/src/examples/JsonExample.cpp
+++ b/packages/streamr-json/src/examples/JsonExample.cpp
@@ -4,7 +4,8 @@
 #include <utility>
 #include <nlohmann/json.hpp>
 
-import streamr.json;
+import streamr.json.toJson;
+import streamr.json.toString;
 
 using streamr::json::StreamrJsonInitializerList;
 using streamr::json::toJson;
diff --git a/packages/streamr-json/test/unit/TestJsonConcepts.cpp b/packages/streamr-json/test/unit/TestJsonConcepts.cpp
index d7abc40a..cdcf70b0 100644
--- a/packages/streamr-json/test/unit/TestJsonConcepts.cpp
+++ b/packages/streamr-json/test/unit/TestJsonConcepts.cpp
@@ -1,6 +1,6 @@
 #include <gtest/gtest.h>
 
-import streamr.json;
+import streamr.json.toJson;
 
 using streamr::json::toJson; // NOLINT
 
diff --git a/packages/streamr-json/test/unit/toJsonTest.cpp b/packages/streamr-json/test/unit/toJsonTest.cpp
index f8e49bf0..945a0c1f 100644
--- a/packages/streamr-json/test/unit/toJsonTest.cpp
+++ b/packages/streamr-json/test/unit/toJsonTest.cpp
@@ -10,7 +10,7 @@
 
 #include "TestClass.hpp"
 #include "WeatherData.hpp"
-import streamr.json;
+import streamr.json.toJson;
 
 using streamr::json::toJson;
 
diff --git a/packages/streamr-json/test/unit/toStringTest.cpp b/packages/streamr-json/test/unit/toStringTest.cpp
index 94756839..fd2e83a1 100644
--- a/packages/streamr-json/test/unit/toStringTest.cpp
+++ b/packages/streamr-json/test/unit/toStringTest.cpp
@@ -10,7 +10,7 @@
 #include "TestClass.hpp"
 #include "WeatherData.hpp"
 
-import streamr.json;
+import streamr.json.toString;
 
 using streamr::json::toString;
 
diff --git a/packages/streamr-logger/modules/Logger.cppm b/packages/streamr-logger/modules/Logger.cppm
index b31eae33..ee6ae622 100644
--- a/packages/streamr-logger/modules/Logger.cppm
+++ b/packages/streamr-logger/modules/Logger.cppm
@@ -10,10 +10,10 @@ module;
 #include <string_view>
 #include <utility>
 #include <nlohmann/json.hpp>
-#include "streamr-json/toJson.hpp"
 
 export module streamr.logger.Logger;
 
+import streamr.json.toJson;
 import streamr.logger.FollyLoggerImpl;
 import streamr.logger.LoggerImpl;
 import streamr.logger.StreamrLogLevel;
diff --git a/packages/streamr-logger/modules/SLogger.cppm b/packages/streamr-logger/modules/SLogger.cppm
index 33b92e90..67a0d192 100644
--- a/packages/streamr-logger/modules/SLogger.cppm
+++ b/packages/streamr-logger/modules/SLogger.cppm
@@ -8,10 +8,10 @@ module;
 #include <string>
 #include <string_view>
 #include <nlohmann/json.hpp>
-#include "streamr-json/toJson.hpp"
 
 export module streamr.logger.SLogger;
 
+import streamr.json.toJson;
 import streamr.logger.Logger;
 
 export namespace streamr::logger {