diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 325579a5b..fe0976228 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,6 +20,8 @@ jobs:
       with:
         fetch-depth: 0
     - uses: cachix/install-nix-action@v19
+      with:
+        install_url: https://releases.nixos.org/nix/nix-2.13.3/install
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
     - uses: cachix/cachix-action@v12
       if: needs.check_secrets.outputs.cachix == 'true'
@@ -59,6 +61,8 @@ jobs:
         fetch-depth: 0
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
     - uses: cachix/install-nix-action@v19
+      with:
+        install_url: https://releases.nixos.org/nix/nix-2.13.3/install
     - uses: cachix/cachix-action@v12
       with:
         name: '${{ env.CACHIX_NAME }}'
@@ -103,6 +107,8 @@ jobs:
       with:
         fetch-depth: 0
     - uses: cachix/install-nix-action@v19
+      with:
+        install_url: https://releases.nixos.org/nix/nix-2.13.3/install
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
     - run: echo NIX_VERSION="$(nix --experimental-features 'nix-command flakes' eval .\#default.version | tr -d \")" >> $GITHUB_ENV
     - uses: cachix/cachix-action@v12
diff --git a/.version b/.version
index 575a07b9f..c910885a0 100644
--- a/.version
+++ b/.version
@@ -1 +1 @@
-2.14.0
\ No newline at end of file
+2.15.0
\ No newline at end of file
diff --git a/Makefile b/Makefile
index 8675c9925..31e4961bc 100644
--- a/Makefile
+++ b/Makefile
@@ -2,13 +2,10 @@ makefiles = \
   mk/precompiled-headers.mk \
   local.mk \
   src/libutil/local.mk \
-  src/libutil/tests/local.mk \
   src/libstore/local.mk \
-  src/libstore/tests/local.mk \
   src/libfetchers/local.mk \
   src/libmain/local.mk \
   src/libexpr/local.mk \
-  src/libexpr/tests/local.mk \
   src/libcmd/local.mk \
   src/nix/local.mk \
   src/resolve-system-dependencies/local.mk \
@@ -19,12 +16,22 @@ makefiles = \
   misc/systemd/local.mk \
   misc/launchd/local.mk \
   misc/upstart/local.mk \
-  doc/manual/local.mk \
-  tests/local.mk \
-  tests/plugins/local.mk
+  doc/manual/local.mk
 
 -include Makefile.config
 
+ifeq ($(tests), yes)
+makefiles += \
+  src/libutil/tests/local.mk \
+  src/libstore/tests/local.mk \
+  src/libexpr/tests/local.mk \
+  tests/local.mk \
+  tests/plugins/local.mk
+else
+makefiles += \
+  mk/disable-tests.mk
+endif
+
 OPTIMIZE = 1
 
 ifeq ($(OPTIMIZE), 1)
diff --git a/Makefile.config.in b/Makefile.config.in
index 1c5405c6d..a6c84f2ad 100644
--- a/Makefile.config.in
+++ b/Makefile.config.in
@@ -45,3 +45,4 @@ sandbox_shell = @sandbox_shell@
 storedir = @storedir@
 sysconfdir = @sysconfdir@
 system = @system@
+tests = @tests@
diff --git a/configure.ac b/configure.ac
index 09b3651b9..36e119bed 100644
--- a/configure.ac
+++ b/configure.ac
@@ -145,6 +145,13 @@ if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
     LDFLAGS="-latomic $LDFLAGS"
 fi
 
+# Building without tests is useful for bootstrapping with a smaller footprint
+# or running the tests in a separate derivation. Otherwise, we do compile and
+# run them.
+AC_ARG_ENABLE(tests, AS_HELP_STRING([--disable-tests],[Do not build the tests]),
+  tests=$enableval, tests=yes)
+AC_SUBST(tests)
+
 # LTO is currently broken with clang for unknown reasons; ld segfaults in the llvm plugin
 AC_ARG_ENABLE(lto, AS_HELP_STRING([--enable-lto],[Enable LTO (only supported with GCC) [default=no]]),
   lto=$enableval, lto=no)
@@ -270,6 +277,8 @@ if test "$gc" = yes; then
 fi
 
 
+if test "$tests" = yes; then
+
 # Look for gtest.
 PKG_CHECK_MODULES([GTEST], [gtest_main])
 
@@ -282,6 +291,7 @@ dnl No good for C++ libs with mangled symbols
 dnl AC_CHECK_LIB([rapidcheck], [])
 AC_LANG_POP(C++)
 
+fi
 
 # Look for nlohmann/json.
 PKG_CHECK_MODULES([NLOHMANN_JSON], [nlohmann_json >= 3.9])
diff --git a/doc/manual/src/installation/prerequisites-source.md b/doc/manual/src/installation/prerequisites-source.md
index 6f4eb3008..5a708f11b 100644
--- a/doc/manual/src/installation/prerequisites-source.md
+++ b/doc/manual/src/installation/prerequisites-source.md
@@ -71,3 +71,8 @@
     <http://libcpuid.sourceforge.net>.
     This is an optional dependency and can be disabled
     by providing a `--disable-cpuid` to the `configure` script.
+
+  - Unless `./configure --disable-tests` is specified, GoogleTest (GTest) and
+    RapidCheck are required, which are available at
+    <https://google.github.io/googletest/> and
+    <https://github.com/emil-e/rapidcheck> respectively.
diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md
index dbd2e88f7..c78b20eed 100644
--- a/doc/manual/src/release-notes/rl-next.md
+++ b/doc/manual/src/release-notes/rl-next.md
@@ -3,3 +3,20 @@
 * Commands which take installables on the command line can now read them from the standard input if
   passed the `--stdin` flag. This is primarily useful when you have a large amount of paths which
   exceed the OS arg limit.
+
+* The special handling of an [installable](../command-ref/new-cli/nix.md#installables) with `.drv` suffix being interpreted as all of the given [store derivation](../glossary.md#gloss-store-derivation)'s output paths is removed, and instead taken as the literal store path that it represents.
+
+  The new `^` syntax for store paths introduced in Nix 2.13 allows explicitly referencing output paths of a derivation.
+  Using this is better and more clear than relying on the now-removed `.drv` special handling.
+
+  For example,
+  ```shell-session
+  $ nix path-info /nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv
+  ```
+
+  now gives info about the derivation itself, while
+
+  ```shell-session
+  $ nix path-info /nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^*
+  ```
+  provides information about each of its outputs.
\ No newline at end of file
diff --git a/flake.nix b/flake.nix
index 563a46d65..5e0504a59 100644
--- a/flake.nix
+++ b/flake.nix
@@ -89,9 +89,7 @@
         });
 
         configureFlags =
-          [
-            "CXXFLAGS=-I${lib.getDev rapidcheck}/extras/gtest/include"
-          ] ++ lib.optionals stdenv.isLinux [
+          lib.optionals stdenv.isLinux [
             "--with-boost=${boost}/lib"
             "--with-sandbox-shell=${sh}/bin/busybox"
           ]
@@ -99,6 +97,10 @@
             "LDFLAGS=-fuse-ld=gold"
           ];
 
+        testConfigureFlags = [
+          "CXXFLAGS=-I${lib.getDev rapidcheck}/extras/gtest/include"
+        ];
+
         nativeBuildDeps =
           [
             buildPackages.bison
@@ -124,13 +126,16 @@
             libarchive
             boost
             lowdown-nix
-            gtest
-            rapidcheck
           ]
           ++ lib.optionals stdenv.isLinux [libseccomp]
           ++ lib.optional (stdenv.isLinux || stdenv.isDarwin) libsodium
           ++ lib.optional stdenv.hostPlatform.isx86_64 libcpuid;
 
+        checkDeps = [
+          gtest
+          rapidcheck
+        ];
+
         awsDeps = lib.optional (stdenv.isLinux || stdenv.isDarwin)
           (aws-sdk-cpp.override {
             apis = ["s3" "transfer"];
@@ -200,7 +205,7 @@
         VERSION_SUFFIX = versionSuffix;
 
         nativeBuildInputs = nativeBuildDeps;
-        buildInputs = buildDeps ++ awsDeps;
+        buildInputs = buildDeps ++ awsDeps ++ checkDeps;
         propagatedBuildInputs = propagatedDeps;
 
         enableParallelBuilding = true;
@@ -305,7 +310,7 @@
           };
           let
             canRunInstalled = currentStdenv.buildPlatform.canExecute currentStdenv.hostPlatform;
-          in currentStdenv.mkDerivation {
+          in currentStdenv.mkDerivation (finalAttrs: {
             name = "nix-${version}";
             inherit version;
 
@@ -318,7 +323,8 @@
             nativeBuildInputs = nativeBuildDeps;
             buildInputs = buildDeps
               # There have been issues building these dependencies
-              ++ lib.optionals (currentStdenv.hostPlatform == currentStdenv.buildPlatform) awsDeps;
+              ++ lib.optionals (currentStdenv.hostPlatform == currentStdenv.buildPlatform) awsDeps
+              ++ lib.optionals finalAttrs.doCheck checkDeps;
 
             propagatedBuildInputs = propagatedDeps;
 
@@ -348,6 +354,8 @@
             configureFlags = configureFlags ++
               [ "--sysconfdir=/etc" ] ++
               lib.optional stdenv.hostPlatform.isStatic "--enable-embedded-sandbox-shell" ++
+              [ (lib.enableFeature finalAttrs.doCheck "tests") ] ++
+              lib.optionals finalAttrs.doCheck testConfigureFlags ++
               lib.optional (!canRunInstalled) "--disable-doc-gen";
 
             enableParallelBuilding = true;
@@ -369,7 +377,7 @@
               ''}
             '';
 
-            doInstallCheck = true;
+            doInstallCheck = finalAttrs.doCheck;
             installCheckFlags = "sysconfdir=$(out)/etc";
 
             separateDebugInfo = !currentStdenv.hostPlatform.isStatic;
@@ -411,7 +419,7 @@
             });
 
             meta.platforms = lib.platforms.unix;
-          };
+          });
 
           lowdown-nix = with final; currentStdenv.mkDerivation rec {
             name = "lowdown-0.9.0";
@@ -462,6 +470,14 @@
 
         buildNoGc = forAllSystems (system: self.packages.${system}.nix.overrideAttrs (a: { configureFlags = (a.configureFlags or []) ++ ["--enable-gc=no"];}));
 
+        buildNoTests = forAllSystems (system:
+          self.packages.${system}.nix.overrideAttrs (a: {
+            doCheck =
+              assert ! a?dontCheck;
+              false;
+          })
+        );
+
         # Perl bindings for various platforms.
         perlBindings = forAllSystems (system: nixpkgsFor.${system}.native.nix.perl-bindings);
 
@@ -634,9 +650,9 @@
             nativeBuildInputs = nativeBuildDeps
                                 ++ (lib.optionals stdenv.cc.isClang [ pkgs.bear pkgs.clang-tools ]);
 
-            buildInputs = buildDeps ++ propagatedDeps ++ awsDeps;
+            buildInputs = buildDeps ++ propagatedDeps ++ awsDeps ++ checkDeps;
 
-            inherit configureFlags;
+            configureFlags = configureFlags ++ testConfigureFlags;
 
             enableParallelBuilding = true;
 
diff --git a/maintainers/release-process.md b/maintainers/release-process.md
index b52d218f5..ec9e96489 100644
--- a/maintainers/release-process.md
+++ b/maintainers/release-process.md
@@ -123,6 +123,7 @@ release:
   `/home/eelco/Dev/nixpkgs-pristine`.
 
   TODO: trigger nixos.org netlify: https://docs.netlify.com/configure-builds/build-hooks/
+
 * Prepare for the next point release by editing `.version` to
   e.g.
 
@@ -152,7 +153,7 @@ release:
   from the previous milestone, and close the previous milestone. Set
   the date for the next milestone 6 weeks from now.
 
-* Create a backport label
+* Create a backport label.
 
 * Post an [announcement on Discourse](https://discourse.nixos.org/c/announcements/8), including the contents of
   `rl-$VERSION.md`.
diff --git a/mk/disable-tests.mk b/mk/disable-tests.mk
new file mode 100644
index 000000000..f72f84412
--- /dev/null
+++ b/mk/disable-tests.mk
@@ -0,0 +1,12 @@
+# This file is only active for `./configure --disable-tests`.
+# Running `make check` or `make installcheck` would indicate a mistake in the
+# caller.
+
+installcheck:
+	@echo "Tests are disabled. Configure without '--disable-tests', or avoid calling 'make installcheck'."
+	@exit 1
+
+# This currently has little effect.
+check:
+	@echo "Tests are disabled. Configure without '--disable-tests', or avoid calling 'make check'."
+	@exit 1
diff --git a/scripts/nix-profile-daemon.sh.in b/scripts/nix-profile-daemon.sh.in
index 80774f1f2..8cfd3149e 100644
--- a/scripts/nix-profile-daemon.sh.in
+++ b/scripts/nix-profile-daemon.sh.in
@@ -8,7 +8,7 @@ if [ -n "${XDG_STATE_HOME-}" ]; then
 else
     NIX_LINK_NEW=$HOME/.local/state/nix/profile
 fi
-if ! [ -e "$NIX_LINK" ]; then
+if [ -e "$NIX_LINK_NEW" ]; then
     NIX_LINK="$NIX_LINK_NEW"
 else
     if [ -t 2 ] && [ -e "$NIX_LINK_NEW" ]; then
diff --git a/scripts/nix-profile.sh.in b/scripts/nix-profile.sh.in
index e8af91211..c4d60cf37 100644
--- a/scripts/nix-profile.sh.in
+++ b/scripts/nix-profile.sh.in
@@ -8,7 +8,7 @@ if [ -n "$HOME" ] && [ -n "$USER" ]; then
     else
         NIX_LINK_NEW="$HOME/.local/state/nix/profile"
     fi
-    if ! [ -e "$NIX_LINK" ]; then
+    if [ -e "$NIX_LINK_NEW" ]; then
         NIX_LINK="$NIX_LINK_NEW"
     else
         if [ -t 2 ] && [ -e "$NIX_LINK_NEW" ]; then
diff --git a/src/libcmd/installable-derived-path.cc b/src/libcmd/installable-derived-path.cc
index a9921b901..729dc7d31 100644
--- a/src/libcmd/installable-derived-path.cc
+++ b/src/libcmd/installable-derived-path.cc
@@ -31,27 +31,24 @@ InstallableDerivedPath InstallableDerivedPath::parse(
     ExtendedOutputsSpec extendedOutputsSpec)
 {
     auto derivedPath = std::visit(overloaded {
-        // If the user did not use ^, we treat the output more liberally.
+        // If the user did not use ^, we treat the output more
+        // liberally: we accept a symlink chain or an actual
+        // store path.
         [&](const ExtendedOutputsSpec::Default &) -> DerivedPath {
-            // First, we accept a symlink chain or an actual store path.
             auto storePath = store->followLinksToStorePath(prefix);
-            // Second, we see if the store path ends in `.drv` to decide what sort
-            // of derived path they want.
-            //
-            // This handling predates the `^` syntax. The `^*` in
-            // `/nix/store/hash-foo.drv^*` unambiguously means "do the
-            // `DerivedPath::Built` case", so plain `/nix/store/hash-foo.drv` could
-            // also unambiguously mean "do the DerivedPath::Opaque` case".
-            //
-            // Issue #7261 tracks reconsidering this `.drv` dispatching.
-            return storePath.isDerivation()
-                ? (DerivedPath) DerivedPath::Built {
-                    .drvPath = std::move(storePath),
-                    .outputs = OutputsSpec::All {},
-                }
-                : (DerivedPath) DerivedPath::Opaque {
-                    .path = std::move(storePath),
+            // Remove this prior to stabilizing the new CLI.
+            if (storePath.isDerivation()) {
+                auto oldDerivedPath = DerivedPath::Built {
+                    .drvPath = storePath,
+                    .outputs = OutputsSpec::All { },
                 };
+                warn(
+                    "The interpretation of store paths arguments ending in `.drv` recently changed. If this command is now failing try again with '%s'",
+                    oldDerivedPath.to_string(*store));
+            };
+            return DerivedPath::Opaque {
+                .path = std::move(storePath),
+            };
         },
         // If the user did use ^, we just do exactly what is written.
         [&](const ExtendedOutputsSpec::Explicit & outputSpec) -> DerivedPath {
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index a67841bb6..7d444aac0 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -677,9 +677,12 @@ StorePathSet Installable::toDerivations(
         for (const auto & b : i->toDerivedPaths())
             std::visit(overloaded {
                 [&](const DerivedPath::Opaque & bo) {
-                    if (!useDeriver)
-                        throw Error("argument '%s' did not evaluate to a derivation", i->what());
-                    drvPaths.insert(getDeriver(store, *i, bo.path));
+                    drvPaths.insert(
+                        bo.path.isDerivation()
+                            ? bo.path
+                        : useDeriver
+                            ? getDeriver(store, *i, bo.path)
+                        : throw Error("argument '%s' did not evaluate to a derivation", i->what()));
                 },
                 [&](const DerivedPath::Built & bfd) {
                     drvPaths.insert(bfd.drvPath);
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index 17da37f47..95c0f5974 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -63,6 +63,11 @@ public:
        one that contains a commit hash or content hash. */
     bool isLocked() const { return locked; }
 
+    /* Check whether the input carries all necessary info required
+       for cache insertion and substitution.
+       These fields are used to uniquely identify cached trees
+       within the "tarball TTL" window without necessarily
+       indicating that the input's origin is unchanged. */
     bool hasAllInfo() const;
 
     bool operator ==(const Input & other) const;
diff --git a/src/libstore/builtins/buildenv.cc b/src/libstore/builtins/buildenv.cc
index b1fbda13d..7bba33fb9 100644
--- a/src/libstore/builtins/buildenv.cc
+++ b/src/libstore/builtins/buildenv.cc
@@ -92,13 +92,11 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
                 if (S_ISLNK(dstSt.st_mode)) {
                     auto prevPriority = state.priorities[dstFile];
                     if (prevPriority == priority)
-                        throw Error(
-                                "files '%1%' and '%2%' have the same priority %3%; "
-                                "use 'nix-env --set-flag priority NUMBER INSTALLED_PKGNAME' "
-                                "or type 'nix profile install --help' if using 'nix profile' to find out how "
-                                "to change the priority of one of the conflicting packages"
-                                " (0 being the highest priority)",
-                                srcFile, readLink(dstFile), priority);
+                        throw BuildEnvFileConflictError(
+                            readLink(dstFile),
+                            srcFile,
+                            priority
+                        );
                     if (prevPriority < priority)
                         continue;
                     if (unlink(dstFile.c_str()) == -1)
diff --git a/src/libstore/builtins/buildenv.hh b/src/libstore/builtins/buildenv.hh
index 73c0f5f7f..a018de3af 100644
--- a/src/libstore/builtins/buildenv.hh
+++ b/src/libstore/builtins/buildenv.hh
@@ -12,6 +12,32 @@ struct Package {
     Package(const Path & path, bool active, int priority) : path{path}, active{active}, priority{priority} {}
 };
 
+class BuildEnvFileConflictError : public Error
+{
+public:
+    const Path fileA;
+    const Path fileB;
+    int priority;
+
+    BuildEnvFileConflictError(
+        const Path fileA,
+        const Path fileB,
+        int priority
+    )
+        : Error(
+            "Unable to build profile. There is a conflict for the following files:\n"
+            "\n"
+            "  %1%\n"
+            "  %2%",
+            fileA,
+            fileB
+        )
+        , fileA(fileA)
+        , fileB(fileB)
+        , priority(priority)
+    {}
+};
+
 typedef std::vector<Package> Packages;
 
 void buildProfile(const Path & out, Packages && pkgs);
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 1c8676a59..6a4778d1f 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -88,6 +88,10 @@ struct curlFileTransfer : public FileTransfer
                 {request.uri}, request.parentAct)
             , callback(std::move(callback))
             , finalSink([this](std::string_view data) {
+                if (errorSink) {
+                    (*errorSink)(data);
+                }
+
                 if (this->request.dataCallback) {
                     auto httpStatus = getHTTPStatus();
 
@@ -163,8 +167,6 @@ struct curlFileTransfer : public FileTransfer
                     }
                 }
 
-                if (errorSink)
-                    (*errorSink)({(char *) contents, realSize});
                 (*decompressionSink)({(char *) contents, realSize});
 
                 return realSize;
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 11d089cd2..8cd7cc822 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -38,8 +38,6 @@ class RemoteStore : public virtual RemoteStoreConfig,
 {
 public:
 
-    virtual bool sameMachine() = 0;
-
     RemoteStore(const Params & params);
 
     /* Implementations of abstract store API methods. */
diff --git a/src/libstore/ssh-store.cc b/src/libstore/ssh-store.cc
index a1d4daafd..cfa063803 100644
--- a/src/libstore/ssh-store.cc
+++ b/src/libstore/ssh-store.cc
@@ -49,9 +49,6 @@ public:
         return *uriSchemes().begin() + "://" + host;
     }
 
-    bool sameMachine() override
-    { return false; }
-
     // FIXME extend daemon protocol, move implementation to RemoteStore
     std::optional<std::string> getBuildLogExact(const StorePath & path) override
     { unsupported("getBuildLogExact"); }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 601efa1cc..f32c2d30c 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -855,6 +855,7 @@ json Store::pathInfoToJSON(const StorePathSet & storePaths,
             auto info = queryPathInfo(storePath);
 
             jsonPath["path"] = printStorePath(info->path);
+            jsonPath["valid"] = true;
             jsonPath["narHash"] = info->narHash.to_string(hashBase, true);
             jsonPath["narSize"] = info->narSize;
 
diff --git a/src/libstore/uds-remote-store.hh b/src/libstore/uds-remote-store.hh
index f8dfcca70..d31a4d592 100644
--- a/src/libstore/uds-remote-store.hh
+++ b/src/libstore/uds-remote-store.hh
@@ -29,9 +29,6 @@ public:
     static std::set<std::string> uriSchemes()
     { return {"unix"}; }
 
-    bool sameMachine() override
-    { return true; }
-
     ref<FSAccessor> getFSAccessor() override
     { return LocalFSStore::getFSAccessor(); }
 
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 904ba6ebe..56bdaf87a 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -32,7 +32,8 @@ void Logger::warn(const std::string & msg)
 
 void Logger::writeToStdout(std::string_view s)
 {
-    std::cout << s << "\n";
+    writeFull(STDOUT_FILENO, s);
+    writeFull(STDOUT_FILENO, "\n");
 }
 
 class SimpleLogger : public Logger
@@ -84,7 +85,7 @@ public:
 
     void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
         const std::string & s, const Fields & fields, ActivityId parent)
-    override
+        override
     {
         if (lvl <= verbosity && !s.empty())
             log(lvl, s + "...");
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index 4642c49f7..a68edd15a 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -102,11 +102,9 @@ public:
     virtual void writeToStdout(std::string_view s);
 
     template<typename... Args>
-    inline void cout(const std::string & fs, const Args & ... args)
+    inline void cout(const Args & ... args)
     {
-        boost::format f(fs);
-        formatHelper(f, args...);
-        writeToStdout(f.str());
+        writeToStdout(fmt(args...));
     }
 
     virtual std::optional<char> ask(std::string_view s)
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 12b22d999..f4f2ec81d 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -139,11 +139,11 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
             for (auto & buildable : buildables) {
                 std::visit(overloaded {
                     [&](const BuiltPath::Opaque & bo) {
-                        std::cout << store->printStorePath(bo.path) << std::endl;
+                        logger->cout(store->printStorePath(bo.path));
                     },
                     [&](const BuiltPath::Built & bfd) {
                         for (auto & output : bfd.outputs) {
-                            std::cout << store->printStorePath(output.second) << std::endl;
+                            logger->cout(store->printStorePath(output.second));
                         }
                     },
                 }, buildable.path.raw());
diff --git a/src/nix/cat.cc b/src/nix/cat.cc
index 6420a0f79..60aa66ce0 100644
--- a/src/nix/cat.cc
+++ b/src/nix/cat.cc
@@ -17,7 +17,7 @@ struct MixCat : virtual Args
         if (st.type != FSAccessor::Type::tRegular)
             throw Error("path '%1%' is not a regular file", path);
 
-        std::cout << accessor->readFile(path);
+        writeFull(STDOUT_FILENO, accessor->readFile(path));
     }
 };
 
diff --git a/src/nix/describe-stores.cc b/src/nix/describe-stores.cc
index 1dd384c0e..eafcedd1f 100644
--- a/src/nix/describe-stores.cc
+++ b/src/nix/describe-stores.cc
@@ -25,7 +25,7 @@ struct CmdDescribeStores : Command, MixJSON
             res[storeName] = storeConfig->toJSON();
         }
         if (json) {
-            std::cout << res;
+            logger->cout("%s", res);
         } else {
             for (auto & [storeName, storeConfig] : res.items()) {
                 std::cout << "## " << storeName << std::endl << std::endl;
diff --git a/src/nix/diff-closures.cc b/src/nix/diff-closures.cc
index 3489cc132..c7c37b66f 100644
--- a/src/nix/diff-closures.cc
+++ b/src/nix/diff-closures.cc
@@ -97,7 +97,7 @@ void printClosureDiff(
                 items.push_back(fmt("%s → %s", showVersions(removed), showVersions(added)));
             if (showDelta)
                 items.push_back(fmt("%s%+.1f KiB" ANSI_NORMAL, sizeDelta > 0 ? ANSI_RED : ANSI_GREEN, sizeDelta / 1024.0));
-            std::cout << fmt("%s%s: %s\n", indent, name, concatStringsSep(", ", items));
+            logger->cout("%s%s: %s", indent, name, concatStringsSep(", ", items));
         }
     }
 }
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index a579213fd..209fd3ed2 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -112,11 +112,11 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
 
         else if (raw) {
             stopProgressBar();
-            std::cout << *state->coerceToString(noPos, *v, context, "while generating the eval command output");
+            writeFull(STDOUT_FILENO, *state->coerceToString(noPos, *v, context, "while generating the eval command output"));
         }
 
         else if (json) {
-            std::cout << printValueAsJSON(*state, true, *v, pos, context, false).dump() << std::endl;
+            logger->cout("%s", printValueAsJSON(*state, true, *v, pos, context, false));
         }
 
         else {
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 053a9c9e1..3fe093fc7 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -952,7 +952,7 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
                 {"path", store->printStorePath(flake.flake.sourceInfo->storePath)},
                 {"inputs", traverse(*flake.lockFile.root)},
             };
-            std::cout << jsonRoot.dump() << std::endl;
+            logger->cout("%s", jsonRoot);
         } else {
             traverse(*flake.lockFile.root);
         }
diff --git a/src/nix/log.cc b/src/nix/log.cc
index a0598ca13..0c9f778f0 100644
--- a/src/nix/log.cc
+++ b/src/nix/log.cc
@@ -53,7 +53,7 @@ struct CmdLog : InstallableCommand
             if (!log) continue;
             stopProgressBar();
             printInfo("got build log for '%s' from '%s'", installable->what(), logSub.getUri());
-            std::cout << *log;
+            writeFull(STDOUT_FILENO, *log);
             return;
         }
 
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index e964b01b3..c990a303c 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -93,7 +93,7 @@ struct MixLs : virtual Args, MixJSON
         if (json) {
             if (showDirectory)
                 throw UsageError("'--directory' is useless with '--json'");
-            std::cout << listNar(accessor, path, recursive);
+            logger->cout("%s", listNar(accessor, path, recursive));
         } else
             listText(accessor);
     }
diff --git a/src/nix/main.cc b/src/nix/main.cc
index d3d2f5b16..53bf649d4 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -292,7 +292,7 @@ void mainWrapped(int argc, char * * argv)
     NixArgs args;
 
     if (argc == 2 && std::string(argv[1]) == "__dump-args") {
-        std::cout << args.toJSON().dump() << "\n";
+        logger->cout("%s", args.toJSON());
         return;
     }
 
@@ -312,7 +312,7 @@ void mainWrapped(int argc, char * * argv)
             b["doc"] = trim(stripIndentation(primOp->doc));
             res[state.symbols[builtin.name]] = std::move(b);
         }
-        std::cout << res.dump() << "\n";
+        logger->cout("%s", res);
         return;
     }
 
@@ -321,14 +321,14 @@ void mainWrapped(int argc, char * * argv)
         if (completions) {
             switch (completionType) {
             case ctNormal:
-                std::cout << "normal\n"; break;
+                logger->cout("normal"); break;
             case ctFilenames:
-                std::cout << "filenames\n"; break;
+                logger->cout("filenames"); break;
             case ctAttrs:
-                std::cout << "attrs\n"; break;
+                logger->cout("attrs"); break;
             }
             for (auto & s : *completions)
-                std::cout << s.completion << "\t" << trim(s.description) << "\n";
+                logger->cout(s.completion + "\t" + trim(s.description));
         }
     });
 
diff --git a/src/nix/make-content-addressed.cc b/src/nix/make-content-addressed.cc
index d86b90fc7..6693c55ac 100644
--- a/src/nix/make-content-addressed.cc
+++ b/src/nix/make-content-addressed.cc
@@ -45,7 +45,7 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
             }
             auto json = json::object();
             json["rewrites"] = jsonRewrites;
-            std::cout << json.dump();
+            logger->cout("%s", json);
         } else {
             for (auto & path : storePaths) {
                 auto i = remappings.find(path);
diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index fc3823406..51c8a3319 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -234,9 +234,9 @@ static int main_nix_prefetch_url(int argc, char * * argv)
         if (!printPath)
             printInfo("path is '%s'", store->printStorePath(storePath));
 
-        std::cout << printHash16or32(hash) << std::endl;
+        logger->cout(printHash16or32(hash));
         if (printPath)
-            std::cout << store->printStorePath(storePath) << std::endl;
+            logger->cout(store->printStorePath(storePath));
 
         return 0;
     }
diff --git a/src/nix/profile.cc b/src/nix/profile.cc
index 208542a5c..eef33b3d9 100644
--- a/src/nix/profile.cc
+++ b/src/nix/profile.cc
@@ -228,12 +228,12 @@ struct ProfileManifest
 
         while (i != prevElems.end() || j != curElems.end()) {
             if (j != curElems.end() && (i == prevElems.end() || i->describe() > j->describe())) {
-                std::cout << fmt("%s%s: ∅ -> %s\n", indent, j->describe(), j->versions());
+                logger->cout("%s%s: ∅ -> %s", indent, j->describe(), j->versions());
                 changes = true;
                 ++j;
             }
             else if (i != prevElems.end() && (j == curElems.end() || i->describe() < j->describe())) {
-                std::cout << fmt("%s%s: %s -> ∅\n", indent, i->describe(), i->versions());
+                logger->cout("%s%s: %s -> ∅", indent, i->describe(), i->versions());
                 changes = true;
                 ++i;
             }
@@ -241,7 +241,7 @@ struct ProfileManifest
                 auto v1 = i->versions();
                 auto v2 = j->versions();
                 if (v1 != v2) {
-                    std::cout << fmt("%s%s: %s -> %s\n", indent, i->describe(), v1, v2);
+                    logger->cout("%s%s: %s -> %s", indent, i->describe(), v1, v2);
                     changes = true;
                 }
                 ++i;
@@ -250,7 +250,7 @@ struct ProfileManifest
         }
 
         if (!changes)
-            std::cout << fmt("%sNo changes.\n", indent);
+            logger->cout("%sNo changes.", indent);
     }
 };
 
@@ -330,7 +330,63 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
             manifest.elements.push_back(std::move(element));
         }
 
-        updateProfile(manifest.build(store));
+        try {
+            updateProfile(manifest.build(store));
+        } catch (BuildEnvFileConflictError & conflictError) {
+            // FIXME use C++20 std::ranges once macOS has it
+            //       See https://github.com/NixOS/nix/compare/3efa476c5439f8f6c1968a6ba20a31d1239c2f04..1fe5d172ece51a619e879c4b86f603d9495cc102
+            auto findRefByFilePath = [&]<typename Iterator>(Iterator begin, Iterator end) {
+                for (auto it = begin; it != end; it++) {
+                    auto profileElement = *it;
+                    for (auto & storePath : profileElement.storePaths) {
+                        if (conflictError.fileA.starts_with(store->printStorePath(storePath))) {
+                            return std::pair(conflictError.fileA, profileElement.source->originalRef);
+                        }
+                        if (conflictError.fileB.starts_with(store->printStorePath(storePath))) {
+                            return std::pair(conflictError.fileB, profileElement.source->originalRef);
+                        }
+                    }
+                }
+                throw conflictError;
+            };
+            // There are 2 conflicting files. We need to find out which one is from the already installed package and
+            // which one is the package that is the new package that is being installed.
+            // The first matching package is the one that was already installed (original).
+            auto [originalConflictingFilePath, originalConflictingRef] = findRefByFilePath(manifest.elements.begin(), manifest.elements.end());
+            // The last matching package is the one that was going to be installed (new).
+            auto [newConflictingFilePath, newConflictingRef] = findRefByFilePath(manifest.elements.rbegin(), manifest.elements.rend());
+
+            throw Error(
+                "An existing package already provides the following file:\n"
+                "\n"
+                "  %1%\n"
+                "\n"
+                "This is the conflicting file from the new package:\n"
+                "\n"
+                "  %2%\n"
+                "\n"
+                "To remove the existing package:\n"
+                "\n"
+                "  nix profile remove %3%\n"
+                "\n"
+                "The new package can also be installed next to the existing one by assigning a different priority.\n"
+                "The conflicting packages have a priority of %5%.\n"
+                "To prioritise the new package:\n"
+                "\n"
+                "  nix profile install %4% --priority %6%\n"
+                "\n"
+                "To prioritise the existing package:\n"
+                "\n"
+                "  nix profile install %4% --priority %7%\n",
+                originalConflictingFilePath,
+                newConflictingFilePath,
+                originalConflictingRef.to_string(),
+                newConflictingRef.to_string(),
+                conflictError.priority,
+                conflictError.priority - 1,
+                conflictError.priority + 1
+            );
+        }
     }
 };
 
@@ -584,9 +640,9 @@ struct CmdProfileDiffClosures : virtual StoreCommand, MixDefaultProfile
 
         for (auto & gen : gens) {
             if (prevGen) {
-                if (!first) std::cout << "\n";
+                if (!first) logger->cout("");
                 first = false;
-                std::cout << fmt("Version %d -> %d:\n", prevGen->number, gen.number);
+                logger->cout("Version %d -> %d:", prevGen->number, gen.number);
                 printClosureDiff(store,
                     store->followLinksToStorePath(prevGen->path),
                     store->followLinksToStorePath(gen.path),
@@ -622,10 +678,10 @@ struct CmdProfileHistory : virtual StoreCommand, EvalCommand, MixDefaultProfile
         for (auto & gen : gens) {
             ProfileManifest manifest(*getEvalState(), gen.path);
 
-            if (!first) std::cout << "\n";
+            if (!first) logger->cout("");
             first = false;
 
-            std::cout << fmt("Version %s%d" ANSI_NORMAL " (%s)%s:\n",
+            logger->cout("Version %s%d" ANSI_NORMAL " (%s)%s:",
                 gen.number == curGen ? ANSI_GREEN : ANSI_BOLD,
                 gen.number,
                 std::put_time(std::gmtime(&gen.creationTime), "%Y-%m-%d"),
diff --git a/src/nix/realisation.cc b/src/nix/realisation.cc
index c9a7157cd..0d3466515 100644
--- a/src/nix/realisation.cc
+++ b/src/nix/realisation.cc
@@ -65,18 +65,16 @@ struct CmdRealisationInfo : BuiltPathsCommand, MixJSON
 
                 res.push_back(currentPath);
             }
-            std::cout << res.dump();
+            logger->cout("%s", res);
         }
         else {
             for (auto & path : realisations) {
                 if (auto realisation = std::get_if<Realisation>(&path.raw)) {
-                    std::cout <<
-                        realisation->id.to_string() << " " <<
-                        store->printStorePath(realisation->outPath);
+                    logger->cout("%s %s",
+                        realisation->id.to_string(),
+                        store->printStorePath(realisation->outPath));
                 } else
-                    std::cout << store->printStorePath(path.path());
-
-                std::cout << std::endl;
+                    logger->cout("%s", store->printStorePath(path.path()));
             }
         }
     }
diff --git a/src/nix/search.cc b/src/nix/search.cc
index 4fa1e7837..2e38f7e4b 100644
--- a/src/nix/search.cc
+++ b/src/nix/search.cc
@@ -196,9 +196,8 @@ struct CmdSearch : InstallableCommand, MixJSON
         for (auto & cursor : installable->getCursors(*state))
             visit(*cursor, cursor->getAttrPath(), true);
 
-        if (json) {
-            std::cout << jsonOut->dump() << std::endl;
-        }
+        if (json)
+            logger->cout("%s", *jsonOut);
 
         if (!json && !results)
             throw Error("no results for the given search term(s)!");
diff --git a/src/nix/show-derivation.cc b/src/nix/show-derivation.cc
index d1a516cad..520e8b1ce 100644
--- a/src/nix/show-derivation.cc
+++ b/src/nix/show-derivation.cc
@@ -57,7 +57,7 @@ struct CmdShowDerivation : InstallablesCommand
             jsonRoot[store->printStorePath(drvPath)] =
                 store->readDerivation(drvPath).toJSON(*store);
         }
-        std::cout << jsonRoot.dump(2) << std::endl;
+        logger->cout(jsonRoot.dump(2));
     }
 };
 
diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index 3d659d6d2..ee27e3725 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -173,7 +173,7 @@ struct CmdKeyGenerateSecret : Command
         if (!keyName)
             throw UsageError("required argument '--key-name' is missing");
 
-        std::cout << SecretKey::generate(*keyName).to_string();
+        writeFull(STDOUT_FILENO, SecretKey::generate(*keyName).to_string());
     }
 };
 
@@ -194,7 +194,7 @@ struct CmdKeyConvertSecretToPublic : Command
     void run() override
     {
         SecretKey secretKey(drainFD(STDIN_FILENO));
-        std::cout << secretKey.toPublicKey().to_string();
+        writeFull(STDOUT_FILENO, secretKey.toPublicKey().to_string());
     }
 };
 
diff --git a/tests/binary-cache.sh b/tests/binary-cache.sh
index 0361ac6a8..b38db8a15 100644
--- a/tests/binary-cache.sh
+++ b/tests/binary-cache.sh
@@ -23,7 +23,7 @@ nix log $outPath 2>&1 | grep 'is not available'
 nix log --substituters file://$cacheDir $outPath | grep FOO
 
 # Test copying build logs from the binary cache.
-nix store copy-log --from file://$cacheDir $(nix-store -qd $outPath)
+nix store copy-log --from file://$cacheDir $(nix-store -qd $outPath)^'*'
 nix log $outPath | grep FOO
 
 basicDownloadTests() {
diff --git a/tests/ca/build.sh b/tests/ca/build.sh
index cc225c6c8..8783525e7 100644
--- a/tests/ca/build.sh
+++ b/tests/ca/build.sh
@@ -2,14 +2,14 @@
 
 source common.sh
 
-drv=$(nix-instantiate --experimental-features ca-derivations ./content-addressed.nix -A rootCA --arg seed 1)
-nix --experimental-features 'nix-command ca-derivations' show-derivation "$drv" --arg seed 1
+drv=$(nix-instantiate ./content-addressed.nix -A rootCA --arg seed 1)
+nix show-derivation "$drv" --arg seed 1
 
 buildAttr () {
     local derivationPath=$1
     local seedValue=$2
     shift; shift
-    local args=("--experimental-features" "ca-derivations" "./content-addressed.nix" "-A" "$derivationPath" --arg seed "$seedValue" "--no-out-link")
+    local args=("./content-addressed.nix" "-A" "$derivationPath" --arg seed "$seedValue" "--no-out-link")
     args+=("$@")
     nix-build "${args[@]}"
 }
@@ -46,17 +46,17 @@ testCutoff () {
 }
 
 testGC () {
-    nix-instantiate --experimental-features ca-derivations ./content-addressed.nix -A rootCA --arg seed 5
-    nix-collect-garbage --experimental-features ca-derivations --option keep-derivations true
+    nix-instantiate ./content-addressed.nix -A rootCA --arg seed 5
+    nix-collect-garbage --option keep-derivations true
     clearStore
     buildAttr rootCA 1 --out-link $TEST_ROOT/rootCA
-    nix-collect-garbage --experimental-features ca-derivations
+    nix-collect-garbage
     buildAttr rootCA 1 -j0
 }
 
 testNixCommand () {
     clearStore
-    nix build --experimental-features 'nix-command ca-derivations' --file ./content-addressed.nix --no-link
+    nix build --file ./content-addressed.nix --no-link
 }
 
 # Regression test for https://github.com/NixOS/nix/issues/4775
diff --git a/tests/ca/substitute.sh b/tests/ca/substitute.sh
index 819f3fd85..ea981adc4 100644
--- a/tests/ca/substitute.sh
+++ b/tests/ca/substitute.sh
@@ -28,6 +28,12 @@ nix realisation info --file ./content-addressed.nix transitivelyDependentCA
 nix realisation info --file ./content-addressed.nix dependentCA
 # nix realisation info --file ./content-addressed.nix rootCA --outputs out
 
+if isDaemonNewer "2.13"; then
+    pushToStore="../push-to-store.sh"
+else
+    pushToStore="../push-to-store-old.sh"
+fi
+
 # Same thing, but
 # 1. With non-ca derivations
 # 2. Erasing the realisations on the remote store
@@ -37,7 +43,7 @@ nix realisation info --file ./content-addressed.nix dependentCA
 #
 # Regression test for #4725
 clearStore
-nix build --file ../simple.nix -L --no-link --post-build-hook ../push-to-store.sh
+nix build --file ../simple.nix -L --no-link --post-build-hook "$pushToStore"
 clearStore
 rm -r "$REMOTE_STORE_DIR/realisations"
 nix build --file ../simple.nix -L --no-link --substitute --substituters "$REMOTE_STORE" --no-require-sigs -j0
@@ -52,7 +58,7 @@ if [[ -z "$(ls "$REMOTE_STORE_DIR/realisations")" ]]; then
 fi
 
 # Test the local realisation disk cache
-buildDrvs --post-build-hook ../push-to-store.sh
+buildDrvs --post-build-hook "$pushToStore"
 clearStore
 # Add the realisations of rootCA to the cachecache
 clearCacheCache
diff --git a/tests/nix-profile.sh b/tests/nix-profile.sh
index 266dc9e49..652e8a8f2 100644
--- a/tests/nix-profile.sh
+++ b/tests/nix-profile.sh
@@ -140,6 +140,36 @@ printf World2 > $flake2Dir/who
 
 nix profile install $flake1Dir
 [[ $($TEST_HOME/.nix-profile/bin/hello) = "Hello World" ]]
+expect 1 nix profile install $flake2Dir
+diff -u <(
+    nix --offline profile install $flake2Dir 2>&1 1> /dev/null \
+        | grep -vE "^warning: " \
+        || true
+) <(cat << EOF
+error: An existing package already provides the following file:
+
+         $(nix build --no-link --print-out-paths ${flake1Dir}"#default.out")/bin/hello
+
+       This is the conflicting file from the new package:
+
+         $(nix build --no-link --print-out-paths ${flake2Dir}"#default.out")/bin/hello
+
+       To remove the existing package:
+
+         nix profile remove path:${flake1Dir}
+
+       The new package can also be installed next to the existing one by assigning a different priority.
+       The conflicting packages have a priority of 5.
+       To prioritise the new package:
+
+         nix profile install path:${flake2Dir} --priority 4
+
+       To prioritise the existing package:
+
+         nix profile install path:${flake2Dir} --priority 6
+EOF
+)
+[[ $($TEST_HOME/.nix-profile/bin/hello) = "Hello World" ]]
 nix profile install $flake2Dir --priority 100
 [[ $($TEST_HOME/.nix-profile/bin/hello) = "Hello World" ]]
 nix profile install $flake2Dir --priority 0
diff --git a/tests/post-hook.sh b/tests/post-hook.sh
index 4eff5f511..0266eb15d 100644
--- a/tests/post-hook.sh
+++ b/tests/post-hook.sh
@@ -9,8 +9,14 @@ echo 'require-sigs = false' >> $NIX_CONF_DIR/nix.conf
 
 restartDaemon
 
+if isDaemonNewer "2.13"; then
+    pushToStore="$PWD/push-to-store.sh"
+else
+    pushToStore="$PWD/push-to-store-old.sh"
+fi
+
 # Build the dependencies and push them to the remote store.
-nix-build -o $TEST_ROOT/result dependencies.nix --post-build-hook $PWD/push-to-store.sh
+nix-build -o $TEST_ROOT/result dependencies.nix --post-build-hook "$pushToStore"
 
 clearStore
 
diff --git a/tests/push-to-store-old.sh b/tests/push-to-store-old.sh
new file mode 100755
index 000000000..b1495c9e2
--- /dev/null
+++ b/tests/push-to-store-old.sh
@@ -0,0 +1,10 @@
+#!/bin/sh
+
+set -x
+set -e
+
+[ -n "$OUT_PATHS" ]
+[ -n "$DRV_PATH" ]
+
+echo Pushing "$OUT_PATHS" to "$REMOTE_STORE"
+printf "%s" "$DRV_PATH" | xargs nix copy --to "$REMOTE_STORE" --no-require-sigs
diff --git a/tests/push-to-store.sh b/tests/push-to-store.sh
index b1495c9e2..0b090e1b3 100755
--- a/tests/push-to-store.sh
+++ b/tests/push-to-store.sh
@@ -7,4 +7,4 @@ set -e
 [ -n "$DRV_PATH" ]
 
 echo Pushing "$OUT_PATHS" to "$REMOTE_STORE"
-printf "%s" "$DRV_PATH" | xargs nix copy --to "$REMOTE_STORE" --no-require-sigs
+printf "%s" "$DRV_PATH"^'*' | xargs nix copy --to "$REMOTE_STORE" --no-require-sigs