fix: dispatch compiler argv before global option scans

Author: Sunrisepeak

.agents/docs/2026-11-06-bmi-publication-and-compiler-cap-closeout.md

@@ -56,7 +56,8 @@ permit, so waiting joins cannot form a permit dependency cycle.
 
 The internal executor introduces no user mode and no argument serialization.
 It receives the compiler's actual argv, inherits the existing streams and
-returns its status. Existing response files retain their original owner and
+returns its status. It dispatches before global option scans so child flags
+cannot configure mcpp. Existing response files retain their original owner and
 encoding. Ordinary completion and interrupt cleanup release a permit once;
 release cannot remove a permit already acquired by another compiler.
 Failure to create or acquire the semaphore is reported rather than followed

src/cli.cppm

@@ -274,6 +274,32 @@ int cmd_toolchain_any(const mcpplibs::cmdline::ParsedArgs& p) {
 
 int run(int argc, char** argv) {
     namespace cl = mcpplibs::cmdline;
+
+    // Internal split-schedule executor. Everything after `--` is the
+    // compiler's argv, including flags with the same names as these options.
+    // Dispatch before global option scans: child words never configure mcpp.
+    if (argc > 1 && std::string_view(argv[1]) == "__compiler-cap") {
+        std::filesystem::path semaphore;
+        int cap = 0, i = 2;
+        for (; i < argc && std::string_view(argv[i]) != "--"; ++i) {
+            const std::string_view option = argv[i];
+            if ((option != "--sem" && option != "--cap") || i + 1 >= argc) {
+                std::println(stderr, "error: __compiler-cap: expected --sem <dir> --cap <N> -- <compiler>...");
+                return 2;
+            }
+            const std::string_view value = argv[++i];
+            if (option == "--sem") semaphore = value;
+            else {
+                const auto [end, ec] = std::from_chars(value.data(), value.data() + value.size(), cap);
+                if (ec != std::errc{} || end != value.data() + value.size()) return 2;
+            }
+        }
+        if (semaphore.empty() || cap <= 0 || i + 1 >= argc) return 2;
+        std::vector<std::string> command;
+        for (++i; i < argc; ++i) command.emplace_back(argv[i]);
+        return mcpp::build::schedule::detach::run_capped(command, semaphore, cap);
+    }
+
     ReportUnnarrowablePaths reportUnnarrowable_;
 
     // What a build that waits for this one is told it waits for (mcpp#839):
@@ -1493,30 +1519,6 @@ int run(int argc, char** argv) {
     // check and no `prepare`. On the MSVC ABI the first build after upgrading
     // to 2026.9.28.2 re-runs each action once, because its command line gained
     // the directory.
-    // Internal split-schedule executor. Everything after `--` is the
-    // compiler's argv, including flags with the same names as these options.
-    if (std::string_view(argv[1]) == "__compiler-cap") {
-        std::filesystem::path semaphore;
-        int cap = 0, i = 2;
-        for (; i < argc && std::string_view(argv[i]) != "--"; ++i) {
-            const std::string_view option = argv[i];
-            if ((option != "--sem" && option != "--cap") || i + 1 >= argc) {
-                std::println(stderr, "error: __compiler-cap: expected --sem <dir> --cap <N> -- <compiler>...");
-                return 2;
-            }
-            const std::string_view value = argv[++i];
-            if (option == "--sem") semaphore = value;
-            else {
-                const auto [end, ec] = std::from_chars(value.data(), value.data() + value.size(), cap);
-                if (ec != std::errc{} || end != value.data() + value.size()) return 2;
-            }
-        }
-        if (semaphore.empty() || cap <= 0 || i + 1 >= argc) return 2;
-        std::vector<std::string> command;
-        for (++i; i < argc; ++i) command.emplace_back(argv[i]);
-        return mcpp::build::schedule::detach::run_capped(command, semaphore, cap);
-    }
-
     // `mcpp depfile-filter --raw <file> --out <file> -- <compiler argv>...`
     // (internal: written into build.ninja for GCC on a Windows host, WS2 of
     // the 2026-09-28 design). Runs the compile with inherited stdio and no

tests/e2e/helpers/check_shared_compiler_cap.py

@@ -147,7 +147,8 @@ def check_cancellation(mcpp, root):
         assert not list(semaphore.iterdir()), "cancellation retained its compiler permit"
         result = subprocess.run([*command, sys.executable, "-c", "raise SystemExit(7)"], cwd=root)
         assert result.returncode == 7 and not list(semaphore.iterdir()), "failure lost its status or leaked a permit"
-        words = ["space value", 'literal "quote"', "back\\slash", "$literal", "", "Ω"]
+        words = ["space value", 'literal "quote"', "back\\slash", "$literal", "", "Ω",
+                 "--system", "--home", "--deny", "--toolchain", "-j200", "--sem", "--cap"]
         result = subprocess.run([*command, sys.executable, "-c", "import json,sys;print(json.dumps(sys.argv[1:]))", *words],
                                 cwd=root, capture_output=True, text=True)
         assert result.returncode == 0 and json.loads(result.stdout) == words, "compiler argument words changed"