Initial CST-Agent: portable Linux/Termux/Windows coding agent.

Vendored sashidown, OpenAI-compatible env (OPENAI_*), and bootstrap scripts.

Co-authored-by: Cursor <cursoragent@cursor.com>

fixtures/mini_calc/Makefile

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+CC ?= gcc
+CFLAGS ?= -std=c11 -Wall -Wextra -O2
+
+.PHONY: all clean test
+
+all: calc
+
+calc: calc.c
+	$(CC) $(CFLAGS) -o $@ $<
+
+test: calc
+	./tests/smoke.sh
+
+clean:
+	rm -f calc

fixtures/mini_calc/README.md

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+# mini_calc
+
+Tiny integer calculator CLI for CST-Agent e2e demos.
+
+## Ops
+
+`add` `sub` `mul` `div` — all four work (see `make test`).
+
+```bash
+./calc add 2 3   # → 5
+./calc div 8 2   # → 4
+```
+
+## Build
+
+```bash
+make
+make test
+```

fixtures/mini_calc/TASK.md

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+# 任务：修好 mini_calc
+
+你在一个很小的 C 项目里。请完成下列事项后结束（不要无关重构）：
+
+1. 阅读 `README.md`、`calc.c`、`tests/smoke.sh`。
+2. 修复 `add` 的 off-by-one bug（应为 `a+b`，不是 `a+b+1`）。
+3. 实现真正的整数除法 `div_ints`（`a/b`，调用方已保证 `b!=0`）。
+4. 运行 `make test`，确保全部用例通过。
+5. 用简短中文说明你改了什么。
+
+可用工具：`read_file`、`run_shell`、`write_file` / `apply_patch`。工作区根目录就是本项目。

fixtures/mini_calc/calc.c

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+/* mini_calc — intentionally broken fixture for CST-Agent e2e / paper case study.
+ *
+ * Bugs (for the agent to fix):
+ * 1) add(): off-by-one — returns a+b+1
+ * 2) div(): missing — only stub returns 0
+ * README claims all four ops work (false until fixed).
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int add(int a, int b) {
+  /* BUG: off-by-one */
+  return a + b + 1;
+}
+
+int sub(int a, int b) { return a - b; }
+
+int mul(int a, int b) { return a * b; }
+
+int div_ints(int a, int b) {
+  /* BUG: not implemented */
+  (void)a;
+  (void)b;
+  return 0;
+}
+
+static void usage(const char *argv0) {
+  fprintf(stderr, "Usage: %s <add|sub|mul|div> <a> <b>\n", argv0);
+}
+
+int main(int argc, char **argv) {
+  if (argc != 4) {
+    usage(argv[0]);
+    return 2;
+  }
+  int a = atoi(argv[2]);
+  int b = atoi(argv[3]);
+  int r = 0;
+  if (strcmp(argv[1], "add") == 0)
+    r = add(a, b);
+  else if (strcmp(argv[1], "sub") == 0)
+    r = sub(a, b);
+  else if (strcmp(argv[1], "mul") == 0)
+    r = mul(a, b);
+  else if (strcmp(argv[1], "div") == 0) {
+    if (b == 0) {
+      fprintf(stderr, "div by zero\n");
+      return 3;
+    }
+    r = div_ints(a, b);
+  } else {
+    usage(argv[0]);
+    return 2;
+  }
+  printf("%d\n", r);
+  return 0;
+}

fixtures/mini_calc/tests/smoke.sh

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+#!/usr/bin/env bash
+# Smoke tests for mini_calc. Exit 0 only when add/sub/mul/div are correct.
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+CALC="$ROOT/calc"
+fail=0
+
+expect() {
+  local op=$1 a=$2 b=$3 want=$4
+  local got
+  got="$("$CALC" "$op" "$a" "$b")"
+  if [[ "$got" != "$want" ]]; then
+    echo "FAIL: $op $a $b → got '$got' want '$want'"
+    fail=1
+  else
+    echo "ok: $op $a $b → $got"
+  fi
+}
+
+expect add 2 3 5
+expect sub 9 4 5
+expect mul 3 4 12
+expect div 8 2 4
+
+if [[ "$fail" -ne 0 ]]; then
+  echo "smoke: FAILED"
+  exit 1
+fi
+echo "smoke: PASSED"
+exit 0