diff --git a/.drone.jsonnet b/.drone.jsonnet
index 0e878bbe..a97e0589 100644
--- a/.drone.jsonnet
+++ b/.drone.jsonnet
@@ -18,6 +18,30 @@ local default_deps_nocxx = [
 
 local default_deps = ['g++'] + default_deps_nocxx;
 
+// Everything we can link against rather than compiling our own copy of, for builds that are not
+// deliberately static (see `static_deps` in debian_build).  Two reasons: such a build is much
+// faster, and it is the only thing that tests us against the library versions distros actually
+// ship -- Debian 12's fmt 9, for instance, which our own code has to stay compatible with.
+//
+// liboxen-quic-dev pulls in liboxen-logging-dev, which is older than we accept
+// (OXEN_LOGGING_MIN_VERSION in external/CMakeLists.txt); the submodule is used for that one and
+// builds against the system fmt/spdlog, which is what puts fmt 9 in front of our code.
+//
+// A too-old system library is not an error: cmake falls back to building that one dependency.
+// libsodium is that case on Debian 12 and Ubuntu 22.04, which ship less than the 1.0.21 we need.
+local system_deps = [
+  'libevent-dev',
+  'libfmt-dev',
+  'liboxen-quic-dev',
+  'liboxenc-dev',
+  'libsodium-dev',
+  'libspdlog-dev',
+  'libsqlite3-dev',
+  'libutf8proc-dev',
+  'libzstd-dev',
+  'nettle-dev',
+];
+
 local default_test_deps = libngtcp2_deps;
 
 local docker_base = 'registry.oxen.rocks/';
@@ -102,6 +126,7 @@ local debian_build(name,
                    image,
                    arch='amd64',
                    deps=default_deps,
+                   static_deps=false/* build our own dependencies instead of using the distro's */,
                    test_deps=default_test_deps,
                    build_type='Release',
                    lto=false,
@@ -120,7 +145,7 @@ local debian_build(name,
   name,
   image,
   arch=arch,
-  deps=deps,
+  deps=deps + (if static_deps then [] else system_deps),
   stf_repo=stf_repo,
   kitware_repo=kitware_repo,
   allow_fail=allow_fail,
@@ -130,6 +155,7 @@ local debian_build(name,
     'cmake .. -DCMAKE_CXX_FLAGS=-fdiagnostics-color=always -DCMAKE_BUILD_TYPE=' + build_type + ' ' +
     (if werror then '-DWARNINGS_AS_ERRORS=ON ' else '') +
     (if shared_libs then '-DBUILD_SHARED_LIBS=ON ' else '') +
+    '-DBUILD_STATIC_DEPS=' + (if static_deps then 'ON ' else 'OFF ') +
     '-DUSE_LTO=' + (if lto then 'ON ' else 'OFF ') +
     '-DWITH_LTO=' + (if lto then 'ON ' else 'OFF ') +
     '-DWITH_TESTS=' + (if tests then 'ON ' else 'OFF ') +
@@ -444,6 +470,10 @@ local static_build(name,
   debian_build('Debian 12', docker_base + 'debian-bookworm'),
   debian_build('Ubuntu latest', docker_base + 'ubuntu-rolling'),
   debian_build('Ubuntu LTS', docker_base + 'ubuntu-lts'),
+  // The one build that compiles every dependency itself rather than taking the distro's, on the
+  // oldest distro we support: what the release artifacts do, and the only thing that notices when
+  // a dependency we vendor stops building.
+  debian_build('Ubuntu 22.04 (static deps)', docker_base + 'ubuntu-jammy', static_deps=true),
 
   // ARM builds (ARM64 and armhf)
   debian_build('Debian sid (ARM64)', docker_base + 'debian-sid', arch='arm64', jobs=4),
diff --git a/include/session/format.hpp b/include/session/format.hpp
index 24e73ccb..24fc32dc 100644
--- a/include/session/format.hpp
+++ b/include/session/format.hpp
@@ -10,7 +10,9 @@
 #include <concepts>
 #include <oxen/log/format.hpp>
 #include <ranges>
+#include <session/util.hpp>
 #include <span>
+#include <string>
 #include <type_traits>
 
 namespace session {
@@ -41,6 +43,18 @@ inline namespace literals {
 
 namespace fmt {
 
+/// Formats a byte count with an SI prefix: "12.3 kB".  See `session::human_size`.
+///
+/// A formatter specialization rather than fmt's `format_as` hook, as everywhere else here: the
+/// hook only reaches non-enum types from fmt 10, and a specialization is also what `std::format`
+/// takes, should we ever want it.
+template <>
+struct formatter<session::human_size, char> : formatter<std::string> {
+    auto format(session::human_size s, format_context& ctx) const {
+        return formatter<std::string>::format(s.str(), ctx);
+    }
+};
+
 // Disable fmt's generic range formatter for byte spans so that our byte_spannable formatter takes
 // precedence (avoids ambiguity when fmt/ranges.h is also included).
 template <session::byte_spannable T>
diff --git a/include/session/util.hpp b/include/session/util.hpp
index 7ebf5e38..44a363c6 100644
--- a/include/session/util.hpp
+++ b/include/session/util.hpp
@@ -388,12 +388,15 @@ std::vector<std::byte> zstd_compress(
 std::optional<std::vector<std::byte>> zstd_decompress(
         std::span<const std::byte> data, size_t max_size = 0);
 
-/// Wrapper for formatting byte sizes with SI prefixes via fmt/oxen-logging.  Provides a
-/// `format_as` friend function discoverable via ADL, so no fmt headers are needed here.
+/// Wrapper for formatting byte sizes with SI prefixes via fmt/oxen-logging.  The fmt formatter
+/// lives in session/format.hpp, alongside the others, so that no fmt headers are needed here;
+/// formatting one of these means including that header.
 /// Usage: `log::info(cat, "Size: {}", human_size{12345});` => "Size: 12.3 kB"
 struct human_size {
     int64_t bytes;
-    friend std::string format_as(human_size s);
+
+    /// "12.3 kB", which is what the formatter prints.
+    std::string str() const;
 };
 
 /// NTTP helper struct for the `_bytes` user-defined literal.
diff --git a/src/core/devices.cpp b/src/core/devices.cpp
index 493d80db..3c54b398 100644
--- a/src/core/devices.cpp
+++ b/src/core/devices.cpp
@@ -30,6 +30,22 @@
 
 #include "../internal-util.hpp"
 
+/// Logs a key pair as "X25519[abcd…wxyz], MLKEM768[abcd…wxyz]".
+///
+/// Out here, rather than beside the type, because a formatter specialization belongs to namespace
+/// fmt and `session::core` does not enclose it.  A specialization rather than fmt's ADL `format_as`
+/// hook because that hook only reaches non-enum types from fmt 10 onwards, and because this is also
+/// the form `std::format` takes.
+/// (`fmt::format_context` spelled out: an out-of-line partial specialization like this one does
+/// not get namespace fmt into its unqualified lookup on gcc 12 / fmt 9.)
+template <std::derived_from<session::core::Devices::XWingKeys> Keys>
+struct fmt::formatter<Keys, char> : fmt::formatter<std::string> {
+    auto format(const Keys& k, fmt::format_context& ctx) const {
+        return formatter<std::string>::format(
+                fmt::format("X25519[{:9.4}], MLKEM768[{:9.4}]", k.x25519_pub, k.mlkem768_pub), ctx);
+    }
+};
+
 namespace session::core {
 
 using namespace fmt::literals;
@@ -149,13 +165,6 @@ namespace {
 
 }  // namespace
 
-// format_as for XWingKeys-derived types (DeviceKeys, AccountKeys), defined in session::core so
-// that fmtlib's ADL-based lookup can find it when logging these types.
-template <std::derived_from<Devices::XWingKeys> Keys>
-std::string format_as(const Keys& k) {
-    return "X25519[{:9.4}], MLKEM768[{:9.4}]"_format(k.x25519_pub, k.mlkem768_pub);
-}
-
 Devices::DeviceKeys Devices::rotate_device_keys() {
     // We store just one single seed value, then use SHAKE256 to expand it into separate X25519
     // (32B) and MLKEM-768 (64B) seeds.
@@ -771,7 +780,7 @@ namespace {
         Removed = 3,      // device newly transitioned to Unregistered
     };
 
-    constexpr std::string_view format_as(Processing p) {
+    constexpr std::string_view to_string(Processing p) {
         switch (p) {
             case Processing::LinkRequest: return "link-request";
             case Processing::Registered: return "registered";
@@ -816,6 +825,20 @@ namespace {
 
 }  // namespace
 
+}  // namespace session::core
+
+/// Logs a `Processing` as the word `to_string` gives for it.  Out here for the reason given at the
+/// top of this file; `session::core::Processing` names the type because the unnamed namespace it
+/// lives in is reachable from its enclosing namespace.
+template <>
+struct fmt::formatter<session::core::Processing, char> : fmt::formatter<std::string_view> {
+    auto format(session::core::Processing p, fmt::format_context& ctx) const {
+        return formatter<std::string_view>::format(to_string(p), ctx);
+    }
+};
+
+namespace session::core {
+
 std::vector<std::byte> Devices::encrypt_device_data(const device::map& devices) {
     cleared_b32 a;
     random::fill(a);
diff --git a/src/util.cpp b/src/util.cpp
index 9cd33f2e..81948c46 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -41,11 +41,11 @@ std::vector<std::string_view> split(std::string_view str, const std::string_view
     return results;
 }
 
-std::string format_as(human_size s) {
-    if (s.bytes < 1000)
-        return fmt::format("{} B", s.bytes);
+std::string human_size::str() const {
+    if (bytes < 1000)
+        return fmt::format("{} B", bytes);
     constexpr std::array prefixes = {'k', 'M', 'G', 'T'};
-    double b = s.bytes;
+    double b = bytes;
     for (auto prefix : prefixes) {
         b /= 1000.;
         if (b < 1000.)
diff --git a/tests/quic-files.cpp b/tests/quic-files.cpp
index d48a4580..991c3a4a 100644
--- a/tests/quic-files.cpp
+++ b/tests/quic-files.cpp
@@ -15,6 +15,7 @@
 #include <session/network/backends/session_file_server.hpp>
 #include <session/network/network_opt.hpp>
 #include <session/network/session_network.hpp>
+#include <session/format.hpp>
 #include <session/util.hpp>
 
 #include "dns_utils.hpp"