feat(v4.0.0): POST's cases as a table the kernel holds

mkpost.py writes v4/system/post_cases.c where it wrote the capsule: for
each case its name, its lines, and what it must do -- end in an error, or
leave v3's stack and print v3's output, which is now held in full where
the capsule held its length and a checksum.

The same 538 cases: checked against capsules/v4/post79.4th case by case --
names, lines, stacks, and the length and checksum of each output -- with
no difference.  The capsule is still what the boot runs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

v4/include/v4/post.h

@@ -0,0 +1,32 @@
+/* post.h -- POST, which is the kernel's.  docs/v4.0.0/NUCLEUS.md section 6.
+ *
+ * As in v3, the kernel holds the cases and runs them on the node: nothing
+ * of POST is in the node's dictionary.  A case is a name, its lines of
+ * FORTH, and what it must do.  The table is generated from v3's own cases
+ * (v4/tools/mkpost.py -> v4/system/post_cases.c).
+ */
+#ifndef V4_POST_H
+#define V4_POST_H
+
+#include "v4/node.h"
+
+#define V4_POST_STACK        0   /* its data stack and what it prints are compared */
+#define V4_POST_DEPTH        1   /* only how many values it leaves; what it prints is not compared */
+#define V4_POST_DEPTH_OUTPUT 2   /* how many values it leaves, and what it prints */
+#define V4_POST_ERROR        3   /* it must end in an error; nothing else is compared */
+
+typedef struct {
+    const char        *name;
+    const char *const *lines;        /* line_count of them, sent one at a time */
+    unsigned           line_count;
+    int                expect;       /* V4_POST_* */
+    const long long   *stack;        /* V4_POST_STACK: depth values, the deepest first; else 0 */
+    unsigned           depth;
+    const char        *output;       /* output_len characters */
+    unsigned           output_len;
+} v4_post_case;
+
+extern const v4_post_case v4_post_cases[];
+extern const unsigned     v4_post_case_count;
+
+#endif /* V4_POST_H */