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/calc.c

@@ -0,0 +1,58 @@
+/* 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;
+}