docs: TODO markers for deferred macos work (default-static flip, floor 11, stdmod boundary)

Author: Sunrisepeak

src/build/flags.cppm

@@ -378,9 +378,19 @@ CompileFlags compute_flags(const BuildPlan& plan) {
         // env var or [build] macos_deployment_target, the static LLVM
         // libc++ is what makes that floor real (the system libc++ caps it
         // at the build host's OS). With no declared floor, keep the
-        // 0.0.49 behavior — dynamic system libc++, host-coupled — which
-        // also sidesteps a still-open SIGSEGV in mixed C/C++ static
-        // binaries (e2e 36; tracked in the design doc).
+        // 0.0.49 behavior — dynamic system libc++, host-coupled.
+        //
+        // TODO(macos-static-default): flip static to the unconditional
+        // default (rust-style "portable by default") once two tracked
+        // issues are fixed — (1) mixed C/C++ static binaries SIGSEGV at
+        // runtime (e2e 36_llvm_toolchain: answer.c + std::cout main.cpp,
+        // exit 139; root cause not yet isolated), (2) the std-module
+        // staging/fingerprint boundary (see canonical_compile_flags).
+        // TODO(macos-floor-11): the official LLVM archives are built for
+        // macOS 14; supporting 11-13 needs a custom libc++ build shipped
+        // via xlings-res (data-only change — swap the archive source).
+        // Both tracked in xlings
+        // .agents/docs/2026-06-05-macos-min-version-support.md §5.
         if (f.staticStdlib && !macosDeploymentTarget.empty()
             && !llvmRootForStdlib.empty()) {
             auto libDir     = llvmRootForStdlib / "lib";

src/cli.cppm

@@ -593,6 +593,14 @@ std::string canonical_compile_flags(const mcpp::manifest::Manifest& m) {
     // (env override > [build] macos_deployment_target manifest default)
     // into the fingerprint so switching targets rebuilds the BMI cache
     // instead of dying with a module config mismatch.
+    //
+    // TODO(macos-default-floor): a built-in default floor (rustc-style,
+    // see the 0.0.50 revert) cannot land until the std-module prebuild /
+    // staging pipeline consumes the SAME resolved value as this rule and
+    // flags.cppm — injecting a default here alone left the test build's
+    // std.pcm unstaged (import std failed wholesale on macos CI).
+    // Centralize the resolution in one helper, then re-land.
+    // See xlings .agents/docs/2026-06-05-macos-min-version-support.md §5.
     if constexpr (mcpp::platform::is_macos) {
         std::string dtv;
         if (const char* dt = std::getenv("MACOSX_DEPLOYMENT_TARGET"); dt && *dt) {