Squashed 'src/ipc/libmultiprocess/' changes from b4120d34bad2..1b8d4a6f1e54

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2e751c5f..55bab53b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,18 +5,47 @@ on:
   pull_request:
 
 jobs:
+  build-openbsd:
+    runs-on: ubuntu-latest
+    name: build • openbsd
+    defaults:
+      run:
+        shell: openbsd {0}
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Start OpenBSD VM
+        uses: vmactions/openbsd-vm@v1
+        with:
+          prepare: |
+            pkg_add -v cmake ninja git python bash
+          run: |
+            git clone --depth=1 https://codeberg.org/OpenBSD/ports.git /usr/ports
+          sync: 'rsync'
+          copyback: false
+
+      - name: Install capnproto
+        run: |
+          cd /usr/ports/devel/capnproto/
+          make install
+
+      - name: Run CI script
+        run: |
+          cd ${{ github.workspace }}
+          CI_CONFIG="ci/configs/openbsd.bash" bash ci/scripts/ci.sh
+
   build:
     runs-on: ubuntu-latest
 
     strategy:
       fail-fast: false
       matrix:
-        config: [default, llvm, gnu32, sanitize]
+        config: [default, llvm, gnu32, sanitize, olddeps]
 
     name: build • ${{ matrix.config }}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - name: Install Nix
         uses: cachix/install-nix-action@v31       # 2025-05-27, from https://github.com/cachix/install-nix-action/tags
diff --git a/CMakeLists.txt b/CMakeLists.txt
index d29eb490..ef694412 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,8 +12,29 @@ endif()
 
 include("cmake/compat_find.cmake")
 
-find_package(CapnProto REQUIRED)
 find_package(Threads REQUIRED)
+find_package(CapnProto 0.7 REQUIRED)
+
+# Check for list-of-pointers memory access bug from Nov 2022
+# https://nvd.nist.gov/vuln/detail/CVE-2022-46149
+# https://github.com/advisories/GHSA-qqff-4vw4-f6hx
+# https://github.com/capnproto/capnproto/security/advisories/GHSA-qqff-4vw4-f6hx
+# https://github.com/capnproto/capnproto/blob/master/security-advisories/2022-11-30-0-pointer-list-bounds.md
+# https://capnproto.org/news/2022-11-30-CVE-2022-46149-security-advisory.html
+# https://dwrensha.github.io/capnproto-rust/2022/11/30/out_of_bounds_memory_access_bug.html
+if(CapnProto_VERSION STREQUAL "0.7.0"
+   OR CapnProto_VERSION STREQUAL "0.8.0"
+   OR CapnProto_VERSION STREQUAL "0.9.0"
+   OR CapnProto_VERSION STREQUAL "0.9.1"
+   OR CapnProto_VERSION STREQUAL "0.10.0"
+   OR CapnProto_VERSION STREQUAL "0.10.1"
+   OR CapnProto_VERSION STREQUAL "0.10.2")
+  message(FATAL_ERROR
+    "Cap'n Proto ${CapnProto_VERSION} is affected by CVE-2022-46149.\n"
+    "Please install an updated package.\n"
+    "Details: https://github.com/advisories/GHSA-qqff-4vw4-f6hx
+  ")
+endif()
 
 set(MPGEN_EXECUTABLE "" CACHE FILEPATH "If specified, should be full path to an external mpgen binary to use rather than the one built internally.")
 
diff --git a/ci/README.md b/ci/README.md
index 85eb467c..2ddaa9e1 100644
--- a/ci/README.md
+++ b/ci/README.md
@@ -20,6 +20,7 @@ CI_CONFIG=ci/configs/default.bash  ci/scripts/run.sh
 CI_CONFIG=ci/configs/llvm.bash     ci/scripts/run.sh
 CI_CONFIG=ci/configs/gnu32.bash    ci/scripts/run.sh
 CI_CONFIG=ci/configs/sanitize.bash ci/scripts/run.sh
+CI_CONFIG=ci/configs/olddeps.bash  ci/scripts/run.sh
 ```
 
 By default CI jobs will reuse their build directories. `CI_CLEAN=1` can be specified to delete them before running instead.
diff --git a/ci/configs/olddeps.bash b/ci/configs/olddeps.bash
new file mode 100644
index 00000000..4684bd58
--- /dev/null
+++ b/ci/configs/olddeps.bash
@@ -0,0 +1,5 @@
+CI_DESC="CI job using old Cap'n Proto version"
+CI_DIR=build-olddeps
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wno-error=array-bounds"
+NIX_ARGS=(--argstr capnprotoVersion "0.7.1")
+BUILD_ARGS=(-k)
diff --git a/ci/configs/openbsd.bash b/ci/configs/openbsd.bash
new file mode 100644
index 00000000..a404e2bc
--- /dev/null
+++ b/ci/configs/openbsd.bash
@@ -0,0 +1,5 @@
+CI_DESC="CI config for OpenBSD"
+CI_DIR=build-openbsd
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter"
+CMAKE_ARGS=(-G Ninja)
+BUILD_ARGS=(-k 0)
diff --git a/ci/patches/spaceship.patch b/ci/patches/spaceship.patch
new file mode 100644
index 00000000..08a885dd
--- /dev/null
+++ b/ci/patches/spaceship.patch
@@ -0,0 +1,29 @@
+commit e3da7da967b94f373c29a198ce45f30fb9f0e517
+Author: Ed Catmur <ed@catmur.uk>
+Date:   Tue Jan 31 16:27:04 2023 +0000
+
+    Remove operator!= synthesized by spaceship
+    
+    An operator!= suppresses the reversed equality comparison candidate generation.
+    
+    This is visible in clang 16 (rc0 just released) and in gcc trunk (so probably gcc 13).
+
+diff --git a/c++/src/kj/string.h b/c++/src/kj/string.h
+index 193442aa..17835892 100644
+--- a/c++/src/kj/string.h
++++ b/c++/src/kj/string.h
+@@ -122,10 +122,14 @@ public:
+   inline constexpr const char* end() const { return content.end() - 1; }
+ 
+   inline constexpr bool operator==(decltype(nullptr)) const { return content.size() <= 1; }
++#if !__cpp_impl_three_way_comparison
+   inline constexpr bool operator!=(decltype(nullptr)) const { return content.size() > 1; }
++#endif
+ 
+   inline bool operator==(const StringPtr& other) const;
++#if !__cpp_impl_three_way_comparison
+   inline bool operator!=(const StringPtr& other) const { return !(*this == other); }
++#endif
+   inline bool operator< (const StringPtr& other) const;
+   inline bool operator> (const StringPtr& other) const { return other < *this; }
+   inline bool operator<=(const StringPtr& other) const { return !(other < *this); }
diff --git a/doc/install.md b/doc/install.md
index 3fe7c7b2..ac2f7f6a 100644
--- a/doc/install.md
+++ b/doc/install.md
@@ -1,6 +1,6 @@
 # libmultiprocess Installation
 
-Installation currently requires Cap'n Proto:
+Installation currently requires Cap'n Proto 0.7 or higher:
 
 ```sh
 apt install libcapnp-dev capnproto
diff --git a/example/CMakeLists.txt b/example/CMakeLists.txt
index 0e758d57..7da049c3 100644
--- a/example/CMakeLists.txt
+++ b/example/CMakeLists.txt
@@ -24,6 +24,5 @@ add_executable(mpexample
 target_capnp_sources(mpexample ${CMAKE_CURRENT_SOURCE_DIR} init.capnp calculator.capnp printer.capnp)
 target_include_directories(mpexample PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
 target_link_libraries(mpexample PRIVATE Threads::Threads)
-target_link_libraries(mpexample PRIVATE stdc++fs)
 
 add_custom_target(mpexamples DEPENDS mpexample mpcalculator mpprinter)
diff --git a/shell.nix b/shell.nix
index eacfdc2a..0b7dce89 100644
--- a/shell.nix
+++ b/shell.nix
@@ -2,12 +2,39 @@
 , crossPkgs ? import <nixpkgs> {}
 , enableLibcxx ? false # Whether to use libc++ toolchain and libraries instead of libstdc++
 , minimal ? false # Whether to create minimal shell without extra tools (faster when cross compiling)
+, capnprotoVersion ? null
 }:
 
 let
   lib  = pkgs.lib;
   llvm = crossPkgs.llvmPackages_20;
-  capnproto = crossPkgs.capnproto.override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
+  capnprotoHashes = {
+    "0.7.0" = "sha256-Y/7dUOQPDHjniuKNRw3j8dG1NI9f/aRWpf8V0WzV9k8=";
+    "0.7.1" = "sha256-3cBpVmpvCXyqPUXDp12vCFCk32ZXWpkdOliNH37UwWE=";
+    "0.8.0" = "sha256-rfiqN83begjJ9eYjtr21/tk1GJBjmeVfa3C3dZBJ93w=";
+    "0.8.1" = "sha256-OZqNVYdyszro5rIe+w6YN00g6y8U/1b8dKYc214q/2o=";
+    "0.9.0" = "sha256-yhbDcWUe6jp5PbIXzn5EoKabXiWN8lnS08hyfxUgEQ0=";
+    "0.9.2" = "sha256-BspWOPZcP5nCTvmsDE62Zutox+aY5pw42d6hpH3v4cM=";
+    "0.10.0" = "sha256-++F4l54OMTDnJ+FO3kV/Y/VLobKVRk461dopanuU3IQ=";
+    "0.10.4" = "sha256-45sxnVyyYIw9i3sbFZ1naBMoUzkpP21WarzR5crg4X8=";
+    "1.0.0" = "sha256-NLTFJdeOzqhk4ATvkc17Sh6g/junzqYBBEoXYGH/czo=";
+    "1.0.2" = "sha256-LVdkqVBTeh8JZ1McdVNtRcnFVwEJRNjt0JV2l7RkuO8=";
+    "1.1.0" = "sha256-gxkko7LFyJNlxpTS+CWOd/p9x/778/kNIXfpDGiKM2A=";
+    "1.2.0" = "sha256-aDcn4bLZGq8915/NPPQsN5Jv8FRWd8cAspkG3078psc=";
+  };
+  capnprotoBase = if capnprotoVersion == null then crossPkgs.capnproto else crossPkgs.capnproto.overrideAttrs (old: {
+    version = capnprotoVersion;
+    src = crossPkgs.fetchFromGitHub {
+      owner = "capnproto";
+      repo  = "capnproto";
+      rev   = "v${capnprotoVersion}";
+      hash  = lib.attrByPath [capnprotoVersion] "" capnprotoHashes;
+    };
+    patches = lib.optionals (lib.versionAtLeast capnprotoVersion "0.9.0" && lib.versionOlder capnprotoVersion "0.10.4") [ ./ci/patches/spaceship.patch ];
+  } // (lib.optionalAttrs (lib.versionOlder capnprotoVersion "0.10") {
+    env = { }; # Drop -std=c++20 flag forced by nixpkgs
+  }));
+  capnproto = capnprotoBase.override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
   clang = if enableLibcxx then llvm.libcxxClang else llvm.clang;
   clang-tools = llvm.clang-tools.override { inherit enableLibcxx; };
 in crossPkgs.mkShell {
diff --git a/src/mp/gen.cpp b/src/mp/gen.cpp
index 21a4d931..18400710 100644
--- a/src/mp/gen.cpp
+++ b/src/mp/gen.cpp
@@ -146,7 +146,7 @@ static void Generate(kj::StringPtr src_prefix,
     const std::vector<kj::Own<const kj::ReadableDirectory>>& import_dirs)
 {
     std::string output_path;
-    if (src_prefix == ".") {
+    if (src_prefix == kj::StringPtr{"."}) {
         output_path = src_file;
     } else if (!src_file.startsWith(src_prefix) || src_file.size() <= src_prefix.size() ||
                src_file[src_prefix.size()] != '/') {
@@ -156,7 +156,7 @@ static void Generate(kj::StringPtr src_prefix,
     }
 
     std::string include_path;
-    if (include_prefix == ".") {
+    if (include_prefix == kj::StringPtr{"."}) {
         include_path = src_file;
     } else if (!src_file.startsWith(include_prefix) || src_file.size() <= include_prefix.size() ||
                src_file[include_prefix.size()] != '/') {
@@ -425,8 +425,8 @@ static void Generate(kj::StringPtr src_prefix,
 
                 const std::string method_prefix = Format() << message_namespace << "::" << method_interface.getShortDisplayName()
                                                            << "::" << Cap(method_name);
-                const bool is_construct = method_name == "construct";
-                const bool is_destroy = method_name == "destroy";
+                const bool is_construct = method_name == kj::StringPtr{"construct"};
+                const bool is_destroy = method_name == kj::StringPtr{"destroy"};
 
                 struct Field
                 {
@@ -465,7 +465,7 @@ static void Generate(kj::StringPtr src_prefix,
                         field.result_is_set = true;
                     }
 
-                    if (!param && field_name == "result") {
+                    if (!param && field_name == kj::StringPtr{"result"}) {
                         field.retval = true;
                         has_result = true;
                     }
diff --git a/src/mp/util.cpp b/src/mp/util.cpp
index a9485399..da7c3b0b 100644
--- a/src/mp/util.cpp
+++ b/src/mp/util.cpp
@@ -16,6 +16,7 @@
 #include <sys/socket.h>
 #include <sys/wait.h>
 #include <system_error>
+#include <thread> // NOLINT(misc-include-cleaner) // IWYU pragma: keep
 #include <unistd.h>
 #include <utility>
 #include <vector>