fix: 问「这是不是终端」的那个请求,不是端口层认得的那一个

musl 的 `isatty` 用 **TIOCGWINSZ** 问,而端口层只答 **TCGETS** ——
TCGETS 是**读**终端设置用的请求,不是**问它是不是终端**用的那个:

    int isatty(int fd) {
        struct winsize wsz;
        unsigned long r = syscall(SYS_ioctl, fd, TIOCGWINSZ, &wsz);
        if (r == 0) return 1;
        ...
    }

⇒ 这个端口之上的每一次 `isatty` 都返回 0 —— 对一个真终端和对一个管道一样。

## ⚠️ 什么都没有失败,这正是它的形状

`std::print` 只是从不走终端那一支;任何靠「问一下」来决定用不用颜色、
用什么缓冲策略的程序,都在无声地决定错。

## 判据(实测,2026-08-27,同一套 harness 下带原生对照)

                  管道   伪终端
    原生 glibc      0        1
    本端口(修前)    0        0
    本端口(修后)    0        1     ← 与原生逐字一致

⭐ **判据是一个关系,不是一个值。** 只断言「管道下为 0」在整个缺陷期间都会通过;
必须断言管道与伪终端**不同**,且与系统自己的 C 库**同样地**不同。CI 里带了原生
对照:若 `script` 分配不出伪终端,这条检查会说自己什么也证明不了,而不是把端口
判成坏的。

## ⭐ 尺寸报「不知道」,不编一个出来

openkal 没有回答窗口尺寸的操作,而 `winsize` 已被调用方清零。
编一个 80x24 出来会是这份文件唯一明令禁止的形状 ——「报成功而什么也没做」。
一个要尺寸的调用方读到零,而一条串口线报的也是零。

Author: speak-agent

.github/workflows/ci.yml

@@ -190,6 +190,61 @@ jobs:
                  grep kal_random syms.txt; exit 1; }
           echo "  ok  kal_random_fill is weak, kal_time_sleep is strong"
 
+      # ⭐⭐ ASKING WHETHER A STREAM IS A TERMINAL GETS THE RIGHT ANSWER.
+      #
+      # musl's `isatty' asks with TIOCGWINSZ; this port answered only TCGETS,
+      # so every `isatty' returned 0 — for a real terminal as readily as for a
+      # pipe. Nothing failed: `std::print' simply never took its terminal path,
+      # and a program deciding on colour or on line buffering decided wrongly
+      # and in silence.
+      #
+      # ⭐ THE CRITERION IS A RELATION, NOT A VALUE. `isatty` under a pipe and
+      # under a pseudo-terminal must DIFFER, and must differ the same way the
+      # system's own C library does. A test asserting "0 in a pipe" alone would
+      # have passed throughout the defect.
+      - name: Asking whether a stream is a terminal is answered, not refused
+        if: runner.os == 'Linux' && matrix.target == ''
+        run: |
+          d="$(mktemp -d)"; mkdir -p "$d/src"
+          cat > "$d/mcpp.toml" <<TOML
+          [package]
+          name    = "isattyprobe"
+          version = "0.1.0"
+
+          [dependencies]
+          openkal-musl = { path = "$PWD" }
+
+          [targets.isattyprobe]
+          kind = "bin"
+          main = "src/main.c"
+
+          [build]
+          cxx_runtime = "host-coupled"
+          TOML
+          sed -i 's/^          //' "$d/mcpp.toml"
+          printf '#include <unistd.h>\n#include <stdio.h>\nint main(void){ printf("%%d\\n", isatty(1)); return 0; }\n' > "$d/src/main.c"
+          ( cd "$d" && "$MCPP" build --toolchain '${{ matrix.toolchain }}' )
+          bin="$(find "$d/target" -name isattyprobe -type f | head -1)"
+          test -n "$bin" || { echo "::error::the probe did not build"; exit 1; }
+
+          # The control: the system's own C library, through the same harness.
+          # Without it a `script` that fails to allocate a pty would make the
+          # port look broken.
+          printf '#include <unistd.h>\n#include <stdio.h>\nint main(void){ printf("%%d\\n", isatty(1)); return 0; }\n' > "$d/ctrl.c"
+          cc "$d/ctrl.c" -o "$d/ctrl"
+          ctrl_pipe="$("$d/ctrl" | cat | tr -d '\r')"
+          ctrl_tty="$(script -qec "$d/ctrl" /dev/null | tr -d '\r' | head -1)"
+          [ "$ctrl_pipe" = 0 ] && [ "$ctrl_tty" = 1 ] \
+            || { echo "::error::the harness cannot tell a pty from a pipe (control gave $ctrl_pipe/$ctrl_tty) — this check would prove nothing"
+                 exit 1; }
+
+          port_pipe="$("$bin" | cat | tr -d '\r')"
+          port_tty="$(script -qec "$bin" /dev/null | tr -d '\r' | head -1)"
+          echo "  control: pipe=$ctrl_pipe tty=$ctrl_tty    port: pipe=$port_pipe tty=$port_tty"
+          [ "$port_pipe" = "$ctrl_pipe" ] && [ "$port_tty" = "$ctrl_tty" ] \
+            || { echo "::error::isatty over this port disagrees with the system's own C library"; exit 1; }
+          echo "  ok  isatty answers the same as the system's own C library"
+
       # ⭐⭐ THE INTERNAL OVERLAY STOPS AT THIS PACKAGE'S BOUNDARY.
       #
       # musl reaches its own declarations through `src/include`, whose headers

port/src/okm_syscall.c

@@ -749,9 +749,38 @@ syscall_arg_t __okm_syscall(syscall_arg_t n, syscall_arg_t a1, syscall_arg_t a2,
 			/* The only question a C library asks through this call is whether
 			 * the stream is a terminal, and openkal answers it. Everything a
 			 * terminal can be asked to do beyond that is not an operation
-			 * openkal has. */
+			 * openkal has.
+			 *
+			 * ⚠️⚠️ AND THE REQUEST IT ASKS IT WITH IS NOT THE ONE THIS BRANCH
+			 * FIRST RECOGNISED. `TCGETS' is the request a C library uses to
+			 * READ a terminal's settings; the one it uses to ASK WHETHER
+			 * something is a terminal is musl's own `isatty':
+			 *
+			 *     struct winsize wsz;
+			 *     r = syscall(SYS_ioctl, fd, TIOCGWINSZ, &wsz);
+			 *     if (r == 0) return 1;
+			 *
+			 * So every `isatty' over this port answered 0 --- for a real
+			 * terminal as readily as for a pipe. Measured 2026-08-27 against a
+			 * native control under one harness:
+			 *
+			 *                       pipe   pseudo-terminal
+			 *     native glibc        0            1
+			 *     this port           0            0
+			 *
+			 * ⇒ `std::print' never took its terminal path, and any program
+			 * that decides on colour or on line buffering by asking decided
+			 * wrongly and in silence.
+			 *
+			 * ⭐ THE SIZE IS REPORTED AS UNKNOWN RATHER THAN GUESSED. openkal
+			 * has no operation that answers it, and `winsize' is already
+			 * zeroed by the caller; a fabricated 80x24 would be this file's one
+			 * forbidden shape --- reporting success having done nothing.
+			 * A caller that wants the size reads zero, which is what a serial
+			 * line reports too. */
 			if (!interactive) return -ENOTTY;
-			if ((unsigned long)a2 == TCGETS) return 0;
+			if ((unsigned long)a2 == TCGETS)     return 0;
+			if ((unsigned long)a2 == TIOCGWINSZ) return 0;
 			return -ENOTTY;
 		}
 		return -ENOTTY;