diff --git a/daemon/daemon.cc b/daemon/daemon.cc
index 5326a8a51..14a6136c8 100644
--- a/daemon/daemon.cc
+++ b/daemon/daemon.cc
@@ -33,6 +33,7 @@
 #include <libtransmission/error.h>
 #include <libtransmission/file.h>
 #include <libtransmission/log.h>
+#include <libtransmission/quark.h>
 #include <libtransmission/timer-ev.h>
 #include <libtransmission/tr-getopt.h>
 #include <libtransmission/tr-strbuf.h>
diff --git a/libtransmission/announce-list.cc b/libtransmission/announce-list.cc
index 580f36a41..829125bff 100644
--- a/libtransmission/announce-list.cc
+++ b/libtransmission/announce-list.cc
@@ -6,6 +6,7 @@
 #include <algorithm>
 #include <string>
 #include <string_view>
+#include <utility>
 
 #include <fmt/core.h>
 
@@ -17,7 +18,6 @@
 #include "libtransmission/error.h"
 #include "libtransmission/quark.h"
 #include "libtransmission/tr-assert.h"
-#include "libtransmission/torrent-metainfo.h"
 #include "libtransmission/utils.h"
 #include "libtransmission/variant.h"
 #include "libtransmission/web-utils.h"
diff --git a/libtransmission/announce-list.h b/libtransmission/announce-list.h
index c51d80b1b..32fe33b36 100644
--- a/libtransmission/announce-list.h
+++ b/libtransmission/announce-list.h
@@ -13,7 +13,6 @@
 
 #include "libtransmission/transmission.h"
 
-#include "libtransmission/quark.h"
 #include "libtransmission/interned-string.h"
 #include "libtransmission/tr-macros.h"
 #include "libtransmission/variant.h"
diff --git a/libtransmission/announcer-http.cc b/libtransmission/announcer-http.cc
index 967611bfe..1d00a4c38 100644
--- a/libtransmission/announcer-http.cc
+++ b/libtransmission/announcer-http.cc
@@ -7,7 +7,6 @@
 #include <cctype>
 #include <cstddef> // std::byte, size_t
 #include <cstdint> // int64_t, uint8_t, uint...
-#include <cstdio> /* fprintf() */
 #include <iomanip>
 #include <iostream>
 #include <iterator>
@@ -34,7 +33,6 @@
 #include "libtransmission/net.h"
 #include "libtransmission/peer-mgr.h" /* pex */
 #include "libtransmission/session.h"
-#include "libtransmission/torrent.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-macros.h"
 #include "libtransmission/tr-strbuf.h" // tr_strbuf, tr_urlbuf
diff --git a/libtransmission/bandwidth.h b/libtransmission/bandwidth.h
index 56d67d808..c8527a317 100644
--- a/libtransmission/bandwidth.h
+++ b/libtransmission/bandwidth.h
@@ -16,9 +16,9 @@
 #include <utility> // for std::move()
 #include <vector>
 
-#include "transmission.h"
+#include "libtransmission/transmission.h"
 
-#include "tr-assert.h"
+#include "libtransmission/tr-assert.h"
 
 class tr_peerIo;
 
diff --git a/libtransmission/benc.h b/libtransmission/benc.h
index e02e37d27..39749c087 100644
--- a/libtransmission/benc.h
+++ b/libtransmission/benc.h
@@ -14,7 +14,7 @@
 #include <string_view>
 #include <utility> // make_pair
 
-#include "error.h"
+#include "libtransmission/error.h"
 
 namespace transmission::benc
 {
diff --git a/libtransmission/bitfield.h b/libtransmission/bitfield.h
index e88a8b1f7..bdb7e7d6a 100644
--- a/libtransmission/bitfield.h
+++ b/libtransmission/bitfield.h
@@ -13,7 +13,7 @@
 #include <cstdint> // uint8_t
 #include <vector> // std::vector
 
-#include "tr-macros.h" // TR_CONSTEXPR20
+#include "libtransmission/tr-macros.h" // TR_CONSTEXPR20
 
 /**
  * @brief Implementation of the BitTorrent spec's Bitfield array of bits.
diff --git a/libtransmission/block-info.h b/libtransmission/block-info.h
index 83228cc5e..9b2e3c9c6 100644
--- a/libtransmission/block-info.h
+++ b/libtransmission/block-info.h
@@ -7,7 +7,7 @@
 
 #include <cstdint> // uint32_t, uint64_t
 
-#include "transmission.h"
+#include "libtransmission/transmission.h"
 
 struct tr_block_info
 {
diff --git a/libtransmission/blocklist.h b/libtransmission/blocklist.h
index ea7df6282..70a3083a7 100644
--- a/libtransmission/blocklist.h
+++ b/libtransmission/blocklist.h
@@ -9,6 +9,8 @@
 #error only libtransmission should #include this header.
 #endif
 
+#include <algorithm> // std::any_of
+#include <cstddef> // size_t
 #include <numeric>
 #include <optional>
 #include <string>
diff --git a/libtransmission/cache.h b/libtransmission/cache.h
index b1d96e240..53b0467ef 100644
--- a/libtransmission/cache.h
+++ b/libtransmission/cache.h
@@ -17,9 +17,9 @@
 
 #include <small/vector.hpp>
 
-#include "transmission.h"
+#include "libtransmission/transmission.h"
 
-#include "block-info.h"
+#include "libtransmission/block-info.h"
 
 class tr_torrents;
 struct tr_torrent;
diff --git a/libtransmission/clients.cc b/libtransmission/clients.cc
index bf7609eb9..ce5348138 100644
--- a/libtransmission/clients.cc
+++ b/libtransmission/clients.cc
@@ -8,6 +8,7 @@
 #include <algorithm>
 #include <array>
 #include <cctype> /* isprint() */
+#include <cstdint> // uint8_t
 #include <optional>
 #include <string_view>
 #include <tuple>
@@ -17,6 +18,7 @@
 #include <fmt/core.h>
 
 #include "libtransmission/clients.h"
+#include "libtransmission/tr-macros.h" // tr_peer_id_t
 #include "libtransmission/utils.h"
 
 using namespace std::literals;
diff --git a/libtransmission/clients.h b/libtransmission/clients.h
index 573c63709..44db1165e 100644
--- a/libtransmission/clients.h
+++ b/libtransmission/clients.h
@@ -11,7 +11,7 @@
 
 #include <cstddef> // size_t
 
-#include "tr-macros.h" // tr_peer_id_t
+#include "libtransmission/tr-macros.h" // tr_peer_id_t
 
 /**
  * @brief parse a peer-id into a human-readable client name and version number
diff --git a/libtransmission/file-capacity.cc b/libtransmission/file-capacity.cc
index fa435e5c0..d0399a89f 100644
--- a/libtransmission/file-capacity.cc
+++ b/libtransmission/file-capacity.cc
@@ -5,6 +5,9 @@
 
 #include <algorithm>
 #include <cerrno>
+#include <cstdint> // int64_t
+#include <cstdio> // FILE
+#include <optional>
 #include <string>
 #include <string_view>
 
@@ -63,12 +66,10 @@
 #include <xfs/xqm.h>
 #endif
 
-#include "libtransmission/transmission.h"
-
 #include "libtransmission/error.h"
 #include "libtransmission/file.h"
 #include "libtransmission/tr-macros.h"
-#include "libtransmission/utils.h"
+#include "libtransmission/utils.h" // tr_win32_utf8_to_native
 
 namespace
 {
diff --git a/libtransmission/file-posix.cc b/libtransmission/file-posix.cc
index 3ac446717..19095e208 100644
--- a/libtransmission/file-posix.cc
+++ b/libtransmission/file-posix.cc
@@ -11,6 +11,7 @@
 #include <cerrno>
 #include <climits> /* PATH_MAX */
 #include <cstdint> /* SIZE_MAX */
+#include <cstdio> // remove, rename
 #include <cstdlib> // mkdtemp, mkstemp, realpath
 #include <optional>
 #include <string_view>
@@ -50,11 +51,8 @@
 
 #include <fmt/core.h>
 
-#include "libtransmission/transmission.h"
-
 #include "libtransmission/error.h"
 #include "libtransmission/file.h"
-#include "libtransmission/log.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-macros.h" // TR_UCLIBC_CHECK_VERSION
 #include "libtransmission/tr-strbuf.h"
diff --git a/libtransmission/global-ip-cache.cc b/libtransmission/global-ip-cache.cc
index 74ce99c98..f1fc3cd44 100644
--- a/libtransmission/global-ip-cache.cc
+++ b/libtransmission/global-ip-cache.cc
@@ -20,7 +20,6 @@
 #include "libtransmission/log.h"
 #include "libtransmission/global-ip-cache.h"
 #include "libtransmission/tr-assert.h"
-#include "libtransmission/tr-macros.h"
 #include "libtransmission/utils.h"
 
 namespace
diff --git a/libtransmission/handshake.h b/libtransmission/handshake.h
index 7c788854b..e8692756c 100644
--- a/libtransmission/handshake.h
+++ b/libtransmission/handshake.h
@@ -23,13 +23,19 @@
 
 #include "libtransmission/transmission.h"
 
-#include "libtransmission/net.h"
 #include "libtransmission/peer-mse.h" // tr_message_stream_encryption::DH
 #include "libtransmission/peer-io.h"
 #include "libtransmission/timer.h"
 #include "libtransmission/tr-macros.h" // tr_sha1_digest_t, tr_peer_id_t
 
 struct tr_error;
+struct tr_socket_address;
+
+namespace libtransmission
+{
+template<typename value_type>
+class BufferWriter;
+}
 
 // short-term class which manages the handshake phase of a tr_peerIo
 class tr_handshake
diff --git a/libtransmission/inout.cc b/libtransmission/inout.cc
index 56926b965..680b0e3d7 100644
--- a/libtransmission/inout.cc
+++ b/libtransmission/inout.cc
@@ -19,7 +19,6 @@
 #include "libtransmission/error.h"
 #include "libtransmission/file.h"
 #include "libtransmission/inout.h"
-#include "libtransmission/log.h"
 #include "libtransmission/session.h"
 #include "libtransmission/torrent.h"
 #include "libtransmission/torrent-files.h"
diff --git a/libtransmission/interned-string.h b/libtransmission/interned-string.h
index 5cc7efdf4..35cfd3620 100644
--- a/libtransmission/interned-string.h
+++ b/libtransmission/interned-string.h
@@ -9,7 +9,7 @@
 
 #include <fmt/core.h>
 
-#include "quark.h"
+#include "libtransmission/quark.h"
 
 /**
  * Helper functions wrapped around tr_quark
diff --git a/libtransmission/net.cc b/libtransmission/net.cc
index c6a236ece..a6938ba5e 100644
--- a/libtransmission/net.cc
+++ b/libtransmission/net.cc
@@ -12,8 +12,6 @@
 #include <string_view>
 #include <utility> // std::pair
 
-#include <sys/types.h>
-
 #ifdef _WIN32
 #include <ws2tcpip.h>
 #else
@@ -24,15 +22,13 @@
 
 #include <fmt/core.h>
 
-#include "libtransmission/transmission.h"
-
 #include "libtransmission/log.h"
 #include "libtransmission/net.h"
 #include "libtransmission/peer-socket.h"
 #include "libtransmission/session.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-macros.h"
-#include "libtransmission/tr-utp.h"
+#include "libtransmission/tr-strbuf.h"
 #include "libtransmission/utils.h"
 
 using namespace std::literals;
diff --git a/libtransmission/net.h b/libtransmission/net.h
index 5b1b1c2f0..7fb7c7a86 100644
--- a/libtransmission/net.h
+++ b/libtransmission/net.h
@@ -11,6 +11,7 @@
 #include <algorithm> // for std::copy_n
 #include <array>
 #include <cstddef> // size_t
+#include <cstdint> // uint16_t, uint32_t, uint8_t
 #include <functional>
 #include <optional>
 #include <string>
@@ -269,7 +270,7 @@ struct tr_address
 
     [[nodiscard]] auto is_any() const noexcept
     {
-        return is_valid() ? *this == any(type) : false;
+        return is_valid() && *this == any(type);
     }
 };
 
diff --git a/libtransmission/observable.h b/libtransmission/observable.h
index 97c5c80fb..fcff8967e 100644
--- a/libtransmission/observable.h
+++ b/libtransmission/observable.h
@@ -9,13 +9,13 @@
 #error only libtransmission should #include this header.
 #endif
 
-#include <algorithm> // for std::move
 #include <cstddef> // for size_t
 #include <functional>
+#include <utility> // for std::move
 
 #include <small/map.hpp>
 
-#include "tr-assert.h"
+#include "libtransmission/tr-assert.h"
 
 namespace libtransmission
 {
@@ -30,13 +30,12 @@ public:
 
     ObserverTag() = default;
 
-    ObserverTag(ObserverTag&& that)
+    ObserverTag(ObserverTag&& that) noexcept
     {
-        on_destroy_ = std::move(that.on_destroy_);
-        that.on_destroy_ = nullptr;
+        *this = std::forward<ObserverTag>(that);
     }
 
-    ObserverTag& operator=(ObserverTag&& that)
+    ObserverTag& operator=(ObserverTag&& that) noexcept
     {
         on_destroy_ = std::move(that.on_destroy_);
         that.on_destroy_ = nullptr;
@@ -46,7 +45,7 @@ public:
     ObserverTag(ObserverTag const&) = delete;
     ObserverTag& operator=(ObserverTag const&) = delete;
 
-    ObserverTag(Callback on_destroy)
+    explicit ObserverTag(Callback on_destroy)
         : on_destroy_{ std::move(on_destroy) }
     {
     }
@@ -54,7 +53,9 @@ public:
     ~ObserverTag()
     {
         if (on_destroy_)
+        {
             on_destroy_();
+        }
     }
 
 private:
@@ -92,7 +93,7 @@ public:
     {
         for (auto& [tag, observer] : observers_)
         {
-            observer((args)...);
+            observer(args...);
         }
     }
 
diff --git a/libtransmission/open-files.h b/libtransmission/open-files.h
index f76d10aa1..852fbe0cb 100644
--- a/libtransmission/open-files.h
+++ b/libtransmission/open-files.h
@@ -15,10 +15,10 @@
 #include <string_view>
 #include <utility>
 
-#include "transmission.h"
+#include "libtransmission/transmission.h"
 
-#include "file.h" // tr_sys_file_t
-#include "lru-cache.h"
+#include "libtransmission/file.h" // tr_sys_file_t
+#include "libtransmission/lru-cache.h"
 
 // A pool of open files that are cached while reading / writing torrents' data
 class tr_open_files
diff --git a/libtransmission/peer-io.cc b/libtransmission/peer-io.cc
index 782f39f12..b63e90407 100644
--- a/libtransmission/peer-io.cc
+++ b/libtransmission/peer-io.cc
@@ -3,10 +3,10 @@
 // or any future license endorsed by Mnemosyne LLC.
 // License text can be found in the licenses/ folder.
 
-#include <array>
 #include <cerrno>
 #include <cstdint>
-#include <type_traits>
+#include <functional>
+#include <type_traits> // std::underlying_type_t
 
 #ifdef _WIN32
 #include <ws2tcpip.h>
diff --git a/libtransmission/peer-io.h b/libtransmission/peer-io.h
index d290a8856..068b558b4 100644
--- a/libtransmission/peer-io.h
+++ b/libtransmission/peer-io.h
@@ -22,7 +22,6 @@
 
 #include "libtransmission/bandwidth.h"
 #include "libtransmission/block-info.h"
-#include "libtransmission/net.h" // tr_address
 #include "libtransmission/peer-mse.h"
 #include "libtransmission/peer-socket.h"
 #include "libtransmission/tr-buffer.h"
@@ -32,6 +31,7 @@
 struct struct_utp_context;
 struct tr_error;
 struct tr_session;
+struct tr_socket_address;
 
 namespace libtransmission::test
 {
diff --git a/libtransmission/peer-mgr.cc b/libtransmission/peer-mgr.cc
index 168cabbc5..c8454bc00 100644
--- a/libtransmission/peer-mgr.cc
+++ b/libtransmission/peer-mgr.cc
@@ -46,6 +46,7 @@
 #include "libtransmission/timer.h"
 #include "libtransmission/torrent-magnet.h"
 #include "libtransmission/torrent.h"
+#include "libtransmission/torrents.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-macros.h"
 #include "libtransmission/utils.h"
diff --git a/libtransmission/peer-msgs.cc b/libtransmission/peer-msgs.cc
index a0477701b..56cc3f920 100644
--- a/libtransmission/peer-msgs.cc
+++ b/libtransmission/peer-msgs.cc
@@ -7,8 +7,8 @@
 #include <array>
 #include <bitset>
 #include <cerrno>
-#include <cstdint>
-#include <cstring>
+#include <cstddef>
+#include <cstdint> // uint8_t, uint32_t, int64_t
 #include <ctime>
 #include <iterator>
 #include <map>
@@ -17,6 +17,7 @@
 #include <queue>
 #include <string>
 #include <string_view>
+#include <tuple>
 #include <utility>
 #include <vector>
 
diff --git a/libtransmission/peer-socket.cc b/libtransmission/peer-socket.cc
index f726e9fa9..2bcdb0756 100644
--- a/libtransmission/peer-socket.cc
+++ b/libtransmission/peer-socket.cc
@@ -3,12 +3,15 @@
 // or any future license endorsed by Mnemosyne LLC.
 // License text can be found in the licenses/ folder.
 
+#include <algorithm> // std::min
+#include <cerrno>
+
 #include <fmt/core.h>
 
 #include <libutp/utp.h>
 
-#include "libtransmission/transmission.h"
-
+#include "libtransmission/error.h"
+#include "libtransmission/log.h"
 #include "libtransmission/peer-socket.h"
 #include "libtransmission/net.h"
 #include "libtransmission/session.h"
diff --git a/libtransmission/peer-socket.h b/libtransmission/peer-socket.h
index 11bc3d3d7..30c3add4d 100644
--- a/libtransmission/peer-socket.h
+++ b/libtransmission/peer-socket.h
@@ -12,15 +12,10 @@
 #include <atomic>
 #include <cstddef> // size_t
 #include <string>
-#include <string_view>
 #include <utility> // for std::make_pair()
 
-#include "transmission.h"
-
-#include "error.h"
-#include "net.h"
-#include "tr-assert.h"
-#include "tr-buffer.h"
+#include "libtransmission/net.h"
+#include "libtransmission/tr-buffer.h"
 
 struct UTPSocket;
 struct tr_session;
diff --git a/libtransmission/platform.cc b/libtransmission/platform.cc
index e85e2a964..a5f0a72f6 100644
--- a/libtransmission/platform.cc
+++ b/libtransmission/platform.cc
@@ -43,14 +43,11 @@
 #include "libtransmission/log.h"
 #include "libtransmission/platform.h"
 #include "libtransmission/session.h"
+#include "libtransmission/tr-strbuf.h"
 #include "libtransmission/utils.h"
 
 using namespace std::literals;
 
-// FIXME(ckerr) do not merge these three lines.
-// This comment is to make CI think libtransmission has
-// changed so that it will run the libtransmission CI tests
-
 namespace
 {
 #ifdef _WIN32
diff --git a/libtransmission/resume.cc b/libtransmission/resume.cc
index aa1e7b4a2..488a22351 100644
--- a/libtransmission/resume.cc
+++ b/libtransmission/resume.cc
@@ -3,6 +3,8 @@
 // or any future license endorsed by Mnemosyne LLC.
 // License text can be found in the licenses/ folder.
 
+#include <algorithm> // std::min
+#include <array>
 #include <cstring>
 #include <ctime>
 #include <string_view>
@@ -12,14 +14,17 @@
 
 #include "libtransmission/transmission.h"
 
+#include "libtransmission/bitfield.h"
 #include "libtransmission/error.h"
 #include "libtransmission/file.h"
 #include "libtransmission/log.h"
-#include "libtransmission/magnet-metainfo.h"
+#include "libtransmission/net.h"
 #include "libtransmission/peer-mgr.h" /* pex */
+#include "libtransmission/quark.h"
 #include "libtransmission/resume.h"
 #include "libtransmission/session.h"
 #include "libtransmission/torrent.h"
+#include "libtransmission/torrent-metainfo.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/utils.h"
 #include "libtransmission/variant.h"
diff --git a/libtransmission/session-alt-speeds.cc b/libtransmission/session-alt-speeds.cc
index e1855e657..d9ef603f8 100644
--- a/libtransmission/session-alt-speeds.cc
+++ b/libtransmission/session-alt-speeds.cc
@@ -5,6 +5,7 @@
 
 #include <chrono>
 #include <cstddef> // size_t
+#include <utility>
 
 #include <fmt/chrono.h>
 
diff --git a/libtransmission/session.h b/libtransmission/session.h
index d29e3157e..fc99204ea 100644
--- a/libtransmission/session.h
+++ b/libtransmission/session.h
@@ -49,11 +49,13 @@
 #include "libtransmission/open-files.h"
 #include "libtransmission/port-forwarding.h"
 #include "libtransmission/quark.h"
+#include "libtransmission/rpc-server.h"
 #include "libtransmission/session-alt-speeds.h"
 #include "libtransmission/session-id.h"
 #include "libtransmission/session-settings.h"
 #include "libtransmission/session-thread.h"
 #include "libtransmission/stats.h"
+#include "libtransmission/timer.h"
 #include "libtransmission/torrents.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-dht.h"
@@ -67,17 +69,10 @@ tr_peer_id_t tr_peerIdInit();
 
 class tr_peer_socket;
 struct tr_pex;
-class tr_rpc_server;
 struct tr_torrent;
 struct struct_utp_context;
 struct tr_variant;
 
-namespace libtransmission
-{
-class Timer;
-class TimerMaker;
-} // namespace libtransmission
-
 namespace libtransmission::test
 {
 
diff --git a/libtransmission/stats.cc b/libtransmission/stats.cc
index 39635e034..9c7a5666c 100644
--- a/libtransmission/stats.cc
+++ b/libtransmission/stats.cc
@@ -3,6 +3,10 @@
 // or any future license endorsed by Mnemosyne LLC.
 // License text can be found in the licenses/ folder.
 
+#include <array>
+#include <optional>
+#include <utility>
+
 #include "libtransmission/transmission.h"
 
 #include "libtransmission/file.h"
diff --git a/libtransmission/torrent-ctor.cc b/libtransmission/torrent-ctor.cc
index 3ff9275fb..adeeabd9b 100644
--- a/libtransmission/torrent-ctor.cc
+++ b/libtransmission/torrent-ctor.cc
@@ -3,9 +3,10 @@
 // or any future license endorsed by Mnemosyne LLC.
 // License text can be found in the licenses/ folder.
 
+#include <array>
 #include <cerrno> // EINVAL
 #include <cstddef> // size_t
-#include <cstdint> //uint16_t
+#include <cstdint> // uint16_t
 #include <optional>
 #include <string>
 #include <string_view>
@@ -15,7 +16,6 @@
 #include "libtransmission/transmission.h"
 
 #include "libtransmission/error.h"
-#include "libtransmission/quark.h"
 #include "libtransmission/session.h"
 #include "libtransmission/torrent-metainfo.h"
 #include "libtransmission/torrent.h"
diff --git a/libtransmission/torrent-magnet.cc b/libtransmission/torrent-magnet.cc
index 68bb24771..7f9ee786d 100644
--- a/libtransmission/torrent-magnet.cc
+++ b/libtransmission/torrent-magnet.cc
@@ -9,7 +9,9 @@
 #include <ctime>
 #include <deque>
 #include <fstream>
+#include <memory>
 #include <string>
+#include <utility> // std::move
 #include <vector>
 
 #include <fmt/core.h>
diff --git a/libtransmission/torrent-metainfo.h b/libtransmission/torrent-metainfo.h
index db688570d..d8340298c 100644
--- a/libtransmission/torrent-metainfo.h
+++ b/libtransmission/torrent-metainfo.h
@@ -11,11 +11,12 @@
 #include <string_view>
 #include <vector>
 
-#include "transmission.h"
+#include "libtransmission/transmission.h"
 
-#include "block-info.h"
-#include "magnet-metainfo.h"
-#include "torrent-files.h"
+#include "libtransmission/block-info.h"
+#include "libtransmission/magnet-metainfo.h"
+#include "libtransmission/torrent-files.h"
+#include "libtransmission/tr-macros.h"
 
 struct tr_error;
 
diff --git a/libtransmission/torrent.cc b/libtransmission/torrent.cc
index ed29a6b95..1936b947a 100644
--- a/libtransmission/torrent.cc
+++ b/libtransmission/torrent.cc
@@ -7,6 +7,7 @@
 #include <array>
 #include <cerrno> // EINVAL
 #include <climits> /* INT_MAX */
+#include <cstddef> // size_t
 #include <ctime>
 #include <map>
 #include <sstream>
@@ -15,13 +16,6 @@
 #include <utility>
 #include <vector>
 
-#ifndef _WIN32
-#include <sys/wait.h> /* wait() */
-#include <unistd.h> /* fork(), execvp(), _exit() */
-#else
-#include <windows.h> /* CreateProcess(), GetLastError() */
-#endif
-
 #include <fmt/chrono.h>
 #include <fmt/core.h>
 
@@ -47,10 +41,13 @@
 #include "libtransmission/torrent-metainfo.h"
 #include "libtransmission/torrent.h"
 #include "libtransmission/tr-assert.h"
+#include "libtransmission/tr-strbuf.h"
 #include "libtransmission/utils.h"
 #include "libtransmission/version.h"
 #include "libtransmission/web-utils.h"
 
+struct tr_ctor;
+
 using namespace std::literals;
 
 // ---
diff --git a/libtransmission/torrent.h b/libtransmission/torrent.h
index 82c05ea30..000ed674f 100644
--- a/libtransmission/torrent.h
+++ b/libtransmission/torrent.h
@@ -10,6 +10,7 @@
 #endif
 
 #include <cstddef> // size_t
+#include <cstdint> // uint64_t, uint16_t
 #include <ctime>
 #include <functional>
 #include <memory>
@@ -32,17 +33,16 @@
 #include "libtransmission/log.h"
 #include "libtransmission/observable.h"
 #include "libtransmission/session.h"
+#include "libtransmission/torrent-files.h"
 #include "libtransmission/torrent-magnet.h"
 #include "libtransmission/torrent-metainfo.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-macros.h"
 #include "libtransmission/verify.h"
 
+struct tr_ctor;
 class tr_swarm;
 struct tr_error;
-struct tr_magnet_info;
-struct tr_metainfo_parsed;
-struct tr_session;
 struct tr_torrent;
 struct tr_torrent_announcer;
 
diff --git a/libtransmission/torrents.h b/libtransmission/torrents.h
index da643acb0..9874fec0b 100644
--- a/libtransmission/torrents.h
+++ b/libtransmission/torrents.h
@@ -24,7 +24,6 @@
 #include "libtransmission/tr-macros.h"
 
 struct tr_torrent;
-struct tr_torrent_metainfo;
 
 // A helper class to manage tracking sets of tr_torrent objects.
 class tr_torrents
diff --git a/libtransmission/tr-assert.mm b/libtransmission/tr-assert.mm
index ada037cd8..d85c855dc 100644
--- a/libtransmission/tr-assert.mm
+++ b/libtransmission/tr-assert.mm
@@ -9,7 +9,7 @@
 
 #include <fmt/core.h>
 
-#include "tr-assert.h"
+#include "libtransmission/tr-assert.h"
 
 #if !defined(NDEBUG) || defined(TR_FORCE_ASSERTIONS)
 
diff --git a/libtransmission/tr-buffer.h b/libtransmission/tr-buffer.h
index fc1067d65..7382d4dc5 100644
--- a/libtransmission/tr-buffer.h
+++ b/libtransmission/tr-buffer.h
@@ -14,9 +14,9 @@
 
 #include <small/vector.hpp>
 
-#include "error.h"
-#include "net.h" // tr_socket_t
-#include "utils.h" // for tr_htonll(), tr_ntohll()
+#include "libtransmission/error.h"
+#include "libtransmission/net.h" // tr_socket_t
+#include "libtransmission/utils.h" // for tr_htonll(), tr_ntohll()
 
 namespace libtransmission
 {
diff --git a/libtransmission/tr-lpd.cc b/libtransmission/tr-lpd.cc
index c66f84c98..bfc89ea46 100644
--- a/libtransmission/tr-lpd.cc
+++ b/libtransmission/tr-lpd.cc
@@ -5,8 +5,10 @@
 #include <algorithm>
 #include <array>
 #include <chrono>
-#include <cstdint>
+#include <cstddef> // std::byte
+#include <cstdint> // uint16_t
 #include <cstring>
+#include <ctime> // time_t
 #include <functional>
 #include <memory>
 #include <optional>
@@ -15,7 +17,6 @@
 #ifdef _WIN32
 #include <ws2tcpip.h>
 #else
-#include <ctime>
 #include <sys/socket.h> /* socket(), bind() */
 #include <netinet/in.h> /* sockaddr_in */
 #endif
diff --git a/libtransmission/tr-utp.cc b/libtransmission/tr-utp.cc
index f9210a34e..191955b49 100644
--- a/libtransmission/tr-utp.cc
+++ b/libtransmission/tr-utp.cc
@@ -9,16 +9,12 @@
 
 #include <libutp/utp.h>
 
-#include "libtransmission/transmission.h"
-
 #include "libtransmission/crypto-utils.h" // tr_rand_int()
 #include "libtransmission/log.h"
 #include "libtransmission/net.h"
 #include "libtransmission/peer-io.h"
-#include "libtransmission/peer-mgr.h"
 #include "libtransmission/peer-socket.h"
 #include "libtransmission/session.h"
-#include "libtransmission/timer.h"
 #include "libtransmission/tr-utp.h"
 #include "libtransmission/utils.h"
 
diff --git a/libtransmission/tr-utp.h b/libtransmission/tr-utp.h
index 35b0d2976..2cb658536 100644
--- a/libtransmission/tr-utp.h
+++ b/libtransmission/tr-utp.h
@@ -10,6 +10,12 @@
 
 #include <cstddef> // size_t
 
+#ifndef _WIN32
+#include <sys/socket.h>
+#else
+#include <ws2tcpip.h>
+#endif
+
 struct tr_session;
 
 void tr_utpInit(tr_session* session);
diff --git a/libtransmission/transmission.h b/libtransmission/transmission.h
index d4397c2ea..1b5ed6263 100644
--- a/libtransmission/transmission.h
+++ b/libtransmission/transmission.h
@@ -21,7 +21,7 @@
 #include <stdbool.h> // bool
 #endif
 
-#include "tr-macros.h"
+#include "libtransmission/tr-macros.h"
 
 using tr_file_index_t = size_t;
 using tr_piece_index_t = uint32_t;
diff --git a/libtransmission/utils.cc b/libtransmission/utils.cc
index c71f473f4..065efc1de 100644
--- a/libtransmission/utils.cc
+++ b/libtransmission/utils.cc
@@ -17,9 +17,11 @@
 #include <locale>
 #include <optional>
 #include <set>
+#include <stdexcept> // std::runtime_error
 #include <string>
 #include <string_view>
 #include <system_error>
+#include <utility>
 #include <vector>
 
 #ifdef _WIN32
diff --git a/libtransmission/utils.h b/libtransmission/utils.h
index 3a55a7347..4c5351445 100644
--- a/libtransmission/utils.h
+++ b/libtransmission/utils.h
@@ -5,7 +5,6 @@
 
 #pragma once
 
-#include <algorithm>
 #include <cctype>
 #include <cstdint> // uint8_t, uint32_t, uint64_t
 #include <cstddef> // size_t
@@ -19,6 +18,7 @@
 #include <vector>
 
 #include "libtransmission/tr-macros.h"
+#include "libtransmission/variant.h"
 
 struct tr_error;
 
diff --git a/libtransmission/utils.mm b/libtransmission/utils.mm
index 669ca50b7..89acec815 100644
--- a/libtransmission/utils.mm
+++ b/libtransmission/utils.mm
@@ -8,7 +8,7 @@
 #include <string>
 #include <string_view>
 
-#include "utils.h"
+#include "libtransmission/utils.h"
 
 // macOS implementation of tr_strv_convert_utf8() that autodetects the encoding.
 // This replaces the generic implementation of the function in utils.cc.
diff --git a/libtransmission/variant-benc.cc b/libtransmission/variant-benc.cc
index 547bdbda2..7cae56af1 100644
--- a/libtransmission/variant-benc.cc
+++ b/libtransmission/variant-benc.cc
@@ -9,9 +9,10 @@
 #include <cstddef> // size_t, std::byte
 #include <cstdint> // int64_t
 #include <deque>
+#include <optional>
 #include <string>
 #include <string_view>
-#include <optional>
+#include <utility>
 
 #include <fmt/core.h>
 #include <fmt/compile.h>
@@ -24,8 +25,6 @@
 #include "libtransmission/utils.h"
 #include "libtransmission/variant.h"
 
-struct tr_error;
-
 using namespace std::literals;
 
 auto constexpr MaxBencStrLength = size_t{ 128 * 1024 * 1024 }; // arbitrary
diff --git a/libtransmission/variant.h b/libtransmission/variant.h
index 96faacb3b..aa9cbbfc9 100644
--- a/libtransmission/variant.h
+++ b/libtransmission/variant.h
@@ -9,7 +9,6 @@
 #include <cstddef> // size_t
 #include <cstdint> // int64_t
 #include <optional>
-#include <numeric>
 #include <string>
 #include <string_view>
 #include <type_traits> // std::is_same_v
diff --git a/libtransmission/verify.cc b/libtransmission/verify.cc
index 0d82b5f81..13f006c02 100644
--- a/libtransmission/verify.cc
+++ b/libtransmission/verify.cc
@@ -5,17 +5,15 @@
 
 #include <algorithm>
 #include <chrono>
-#include <ctime>
+#include <cstddef> // std::byte
+#include <cstdint> // uint64_t, uint32_t
 #include <mutex>
 #include <optional>
 #include <thread>
 #include <vector>
 
-#include <fmt/core.h>
-
 #include "libtransmission/transmission.h"
 
-#include "libtransmission/completion.h"
 #include "libtransmission/crypto-utils.h"
 #include "libtransmission/file.h"
 #include "libtransmission/verify.h"
diff --git a/libtransmission/verify.h b/libtransmission/verify.h
index 8dbb5b107..1790a6c5f 100644
--- a/libtransmission/verify.h
+++ b/libtransmission/verify.h
@@ -11,16 +11,18 @@
 
 #include <atomic>
 #include <condition_variable>
-#include <cstdint>
-#include <functional>
-#include <list>
 #include <memory>
 #include <mutex>
 #include <optional>
 #include <set>
+#include <string>
 #include <thread>
+#include <utility> // std::move
+
+#include "libtransmission/transmission.h"
 
 #include "libtransmission/torrent-metainfo.h"
+#include "libtransmission/tr-macros.h"
 
 class tr_verify_worker
 {
diff --git a/libtransmission/watchdir-base.h b/libtransmission/watchdir-base.h
index e9db7f8b8..6dcf74936 100644
--- a/libtransmission/watchdir-base.h
+++ b/libtransmission/watchdir-base.h
@@ -20,8 +20,8 @@
 #include <string_view>
 #include <utility>
 
-#include "timer.h"
-#include "watchdir.h"
+#include "libtransmission/timer.h"
+#include "libtransmission/watchdir.h"
 
 namespace libtransmission::impl
 {
diff --git a/libtransmission/watchdir-inotify.cc b/libtransmission/watchdir-inotify.cc
index 35b5d7951..b820afe8a 100644
--- a/libtransmission/watchdir-inotify.cc
+++ b/libtransmission/watchdir-inotify.cc
@@ -25,8 +25,11 @@
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-strbuf.h"
 #include "libtransmission/utils.h"
+#include "libtransmission/watchdir.h"
 #include "libtransmission/watchdir-base.h"
 
+struct event_base;
+
 namespace libtransmission
 {
 
diff --git a/libtransmission/watchdir.h b/libtransmission/watchdir.h
index 7e4467fe7..d9718c6b2 100644
--- a/libtransmission/watchdir.h
+++ b/libtransmission/watchdir.h
@@ -10,10 +10,7 @@
 #include <memory>
 #include <string_view>
 
-extern "C"
-{
-    struct event_base;
-}
+struct event_base;
 
 namespace libtransmission
 {
diff --git a/libtransmission/webseed.cc b/libtransmission/webseed.cc
index 730bd969e..b2979b095 100644
--- a/libtransmission/webseed.cc
+++ b/libtransmission/webseed.cc
@@ -13,7 +13,6 @@
 #include <string>
 #include <string_view>
 #include <utility>
-#include <vector>
 
 #include <event2/buffer.h>
 
@@ -32,17 +31,19 @@
 #include "libtransmission/torrent.h"
 #include "libtransmission/tr-assert.h"
 #include "libtransmission/tr-macros.h"
+#include "libtransmission/tr-strbuf.h"
 #include "libtransmission/utils-ev.h"
 #include "libtransmission/utils.h"
 #include "libtransmission/web-utils.h"
 #include "libtransmission/web.h"
 #include "libtransmission/webseed.h"
 
+struct evbuffer;
+
 using namespace std::literals;
 
 namespace
 {
-
 class tr_webseed;
 
 void on_idle(tr_webseed* w);
diff --git a/tests/libtransmission/announce-list-test.cc b/tests/libtransmission/announce-list-test.cc
index b92e8fda5..2b9263088 100644
--- a/tests/libtransmission/announce-list-test.cc
+++ b/tests/libtransmission/announce-list-test.cc
@@ -17,7 +17,6 @@
 
 #include <libtransmission/announce-list.h>
 #include <libtransmission/error.h>
-#include <libtransmission/quark.h>
 #include <libtransmission/torrent-metainfo.h>
 #include <libtransmission/tr-strbuf.h>
 #include <libtransmission/utils.h>
diff --git a/tests/libtransmission/announcer-test.cc b/tests/libtransmission/announcer-test.cc
index 6c280a855..b0b7efb40 100644
--- a/tests/libtransmission/announcer-test.cc
+++ b/tests/libtransmission/announcer-test.cc
@@ -11,13 +11,10 @@
 
 #define LIBTRANSMISSION_ANNOUNCER_MODULE
 
-#include <libtransmission/transmission.h>
-
 #include <libtransmission/announcer-common.h>
 #include <libtransmission/net.h>
 
 #include "gtest/gtest.h"
-#include "test-fixtures.h"
 
 using AnnouncerTest = ::testing::Test;
 
diff --git a/tests/libtransmission/benc-test.cc b/tests/libtransmission/benc-test.cc
index c28fee9b5..7f66bba82 100644
--- a/tests/libtransmission/benc-test.cc
+++ b/tests/libtransmission/benc-test.cc
@@ -8,8 +8,6 @@
 
 #include <fmt/core.h>
 
-#include <libtransmission/transmission.h>
-
 #include <libtransmission/benc.h>
 #include <libtransmission/error.h>
 
diff --git a/tests/libtransmission/buffer-test.cc b/tests/libtransmission/buffer-test.cc
index 316d16415..715177fad 100644
--- a/tests/libtransmission/buffer-test.cc
+++ b/tests/libtransmission/buffer-test.cc
@@ -8,13 +8,10 @@
 #include <memory>
 #include <string_view>
 
-#include <libtransmission/transmission.h>
-
 #include <libtransmission/crypto-utils.h>
 #include <libtransmission/tr-buffer.h>
 
 #include "gtest/gtest.h"
-#include "test-fixtures.h"
 
 using BufferTest = ::testing::Test;
 using namespace std::literals;
diff --git a/tests/libtransmission/dht-test.cc b/tests/libtransmission/dht-test.cc
index 048f83645..6c6fc0b2d 100644
--- a/tests/libtransmission/dht-test.cc
+++ b/tests/libtransmission/dht-test.cc
@@ -10,6 +10,7 @@
 #include <cstddef> // size_t, std::byte
 #include <ctime> // time(), time_t
 #include <fstream>
+#include <functional>
 #include <iterator> // std::back_inserter
 #include <map>
 #include <memory>
@@ -35,6 +36,7 @@
 
 #include <libtransmission/crypto-utils.h> // tr_rand_obj
 #include <libtransmission/file.h>
+#include <libtransmission/log.h>
 #include <libtransmission/net.h>
 #include <libtransmission/quark.h>
 #include <libtransmission/session-thread.h> // for tr_evthread_init();
diff --git a/tests/libtransmission/file-test.cc b/tests/libtransmission/file-test.cc
index 109aad6d2..1a4c7936d 100644
--- a/tests/libtransmission/file-test.cc
+++ b/tests/libtransmission/file-test.cc
@@ -14,6 +14,7 @@
 #include <string>
 #include <string_view>
 #include <utility>
+#include <vector>
 
 #ifndef _WIN32
 #include <sys/stat.h>
diff --git a/tests/libtransmission/global-ip-cache-test.cc b/tests/libtransmission/global-ip-cache-test.cc
index 73bba1b6b..ea6078cd1 100644
--- a/tests/libtransmission/global-ip-cache-test.cc
+++ b/tests/libtransmission/global-ip-cache-test.cc
@@ -6,6 +6,7 @@
 #include <array>
 #include <chrono>
 #include <cstddef> // size_t
+#include <functional>
 #include <memory>
 #include <optional>
 #include <string>
diff --git a/tests/libtransmission/json-test.cc b/tests/libtransmission/json-test.cc
index 5f614d33c..b8a2be052 100644
--- a/tests/libtransmission/json-test.cc
+++ b/tests/libtransmission/json-test.cc
@@ -8,7 +8,6 @@
 #include <cstdint> // int64_t
 #include <locale>
 #include <optional>
-#include <stdexcept> // std::runtime_error
 #include <string>
 #include <string_view>
 
diff --git a/tests/libtransmission/lpd-test.cc b/tests/libtransmission/lpd-test.cc
index c035a0f24..77b01201d 100644
--- a/tests/libtransmission/lpd-test.cc
+++ b/tests/libtransmission/lpd-test.cc
@@ -16,6 +16,7 @@
 #include <libtransmission/crypto-utils.h> // tr_rand_obj()
 #include <libtransmission/net.h>
 #include <libtransmission/session.h>
+#include <libtransmission/timer.h>
 #include <libtransmission/tr-lpd.h>
 #include <libtransmission/utils.h>
 
diff --git a/tests/libtransmission/magnet-metainfo-test.cc b/tests/libtransmission/magnet-metainfo-test.cc
index 7c9403135..8e59b5efc 100644
--- a/tests/libtransmission/magnet-metainfo-test.cc
+++ b/tests/libtransmission/magnet-metainfo-test.cc
@@ -9,8 +9,6 @@
 
 #include "gtest/gtest.h"
 
-#include <libtransmission/transmission.h>
-
 #include <libtransmission/crypto-utils.h> // tr_rand_buffer()
 #include <libtransmission/magnet-metainfo.h>
 #include <libtransmission/tr-macros.h>
diff --git a/tests/libtransmission/peer-msgs-test.cc b/tests/libtransmission/peer-msgs-test.cc
index 86f0b8869..4c45e55e9 100644
--- a/tests/libtransmission/peer-msgs-test.cc
+++ b/tests/libtransmission/peer-msgs-test.cc
@@ -3,11 +3,6 @@
 // or any future license endorsed by Mnemosyne LLC.
 // License text can be found in the licenses/ folder.
 
-#include <cstring>
-
-#include <libtransmission/transmission.h>
-#include <libtransmission/peer-msgs.h>
-
 #include "gtest/gtest.h"
 
 TEST(PeerMsgs, placeholder)
diff --git a/tests/libtransmission/remove-test.cc b/tests/libtransmission/remove-test.cc
index 600be61fa..6e5c02744 100644
--- a/tests/libtransmission/remove-test.cc
+++ b/tests/libtransmission/remove-test.cc
@@ -6,6 +6,7 @@
 #include <array>
 #include <cstdint> // uint64_t
 #include <set>
+#include <string>
 #include <string_view>
 #include <utility>
 
diff --git a/tests/libtransmission/session-alt-speeds-test.cc b/tests/libtransmission/session-alt-speeds-test.cc
index 4944978ba..1b39decb9 100644
--- a/tests/libtransmission/session-alt-speeds-test.cc
+++ b/tests/libtransmission/session-alt-speeds-test.cc
@@ -8,7 +8,6 @@
 #include <vector>
 
 #include <libtransmission/transmission.h>
-#include <libtransmission/session.h>
 #include <libtransmission/session-alt-speeds.h>
 
 #include "gtest/gtest.h"
diff --git a/tests/libtransmission/settings-test.cc b/tests/libtransmission/settings-test.cc
index a61d530d3..b5282edee 100644
--- a/tests/libtransmission/settings-test.cc
+++ b/tests/libtransmission/settings-test.cc
@@ -12,6 +12,7 @@
 
 #include <libtransmission/log.h>
 #include <libtransmission/net.h>
+#include <libtransmission/peer-io.h>
 #include <libtransmission/quark.h>
 #include <libtransmission/session-settings.h>
 #include <libtransmission/variant.h>
diff --git a/tests/libtransmission/tr-peer-info-test.cc b/tests/libtransmission/tr-peer-info-test.cc
index 31313e80d..8041c9a55 100644
--- a/tests/libtransmission/tr-peer-info-test.cc
+++ b/tests/libtransmission/tr-peer-info-test.cc
@@ -4,10 +4,13 @@
 // License text can be found in the licenses/ folder.
 
 #include <array>
+#include <ctime>
 #include <optional>
 #include <tuple>
 #include <utility>
 
+#include <libtransmission/transmission.h>
+
 #include <libtransmission/net.h>
 #include <libtransmission/peer-mgr.h>
 
diff --git a/tests/libtransmission/variant-test.cc b/tests/libtransmission/variant-test.cc
index 225f8b5b1..49ac58b37 100644
--- a/tests/libtransmission/variant-test.cc
+++ b/tests/libtransmission/variant-test.cc
@@ -8,11 +8,11 @@
 #include <cassert>
 #include <cerrno>
 #include <cmath> // lrint()
-#include <cctype> // isspace()
 #include <cstddef> // size_t
 #include <cstdint> // int64_t
 #include <string>
 #include <string_view>
+#include <vector>
 
 #define LIBTRANSMISSION_VARIANT_MODULE