fix(v4.0.0): POST leaves nothing, as v3 really does; and what the review of step 6b found

Captain Bob was told that v3 leaves the words POST's cases define in the
dictionary, and ruled that v4 should.  That was false: v3's run_test_suite
puts the dictionary back after each word's cases (test_common.c:333,
:365).  Shown that, he ruled that POST leaves nothing.  The boot now
seals the system, runs POST, and has the node do COLD, whose printing is
not shown; PARITY:V4_SYSTEM is the system as sealed.

A case the node does not come back from ends POST there, named, with how
many were not run: it would have stalled the boot for hours, where the
capsule had ended it.  The runner's test of it now uses a word that
really never ends.

hosted-check also requires that RS1 and T{ are unknown after boot, and
boots a program whose POST has failing cases (tests/post_cases_fail.c):
PARITY:FAIL, POST: FAILED, no prompt, none of a case's printing shown.

Comments and documents that still named the POST capsule or its two
hooks are brought up to date; NUCLEUS.md 6.3 says what v3 does, with the
lines, and how the wrong ruling came about.

make -C v4 test, sanitize and hosted-check pass; amd64, aarch64 and
riscv64 boot, POST 538 of 538, word_count=314, dict_hash
0x220ab283a504a3b3 on all six: logs/20261007-112638, -112901, -113220.

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

docs/v4.0.0/ENGINE.md

@@ -194,7 +194,7 @@ program with the node as its interpreter. That is withdrawn. From here:
 
 **What the two share (confirmed by Captain Bob the same day, "yes,
 exactly"):** the engine in `v4/src`; the FORTH-79 capsule,
-`capsules/v4/forth79.4th`; and its POST, `capsules/v4/post79.4th`. **The
+`capsules/v4/forth79.4th`; and its POST (then `capsules/v4/post79.4th`; since `MESH.md` step 6b, 2026-10-07, the kernel's cases, `v4/system/post_cases.c`). **The
 nuclei are separate.** The bare-metal nucleus needs word IDs in its
 headers and words that are called where the hosted one compiles them in
 line; the hosted nucleus need not have either. The hosted product may
@@ -346,7 +346,7 @@ not written yet. Nothing of it is built.
 | `v4/system/boot.c`: its own capsule loader and `PARITY:V4_*` lines | Stays for the hosted product. On bare metal v3's birth protocol loads the capsules and prints v3's parity lines (step 4). |
 | The node's prompt loop, and the code that strips ` ok` from its output | Goes at step 1. |
 | `capsules/v4/forth79.4th`, `post79.4th`, `mkpost.py`, the rules | Stay. POST is the gate for every word moved out of the nucleus. |
-| `(CATCH)`, `(EMIT-HOOK)`, `NODE-ERROR` by name | Stay; POST uses them. |
+| `(CATCH)`, `(EMIT-HOOK)`, `NODE-ERROR` by name | `NODE-ERROR` stays. `(CATCH)` and `(EMIT-HOOK)` went with the POST capsule, `MESH.md` step 6b, 2026-10-07: POST is the kernel's and needs neither. |
 | The per-call-target count (`v4/src/heat.c`, `call[]`) | Goes at step 3, when the node does at `call` what v3 does. |
 | The hosted Linux product (`v4/tools/hosted.c`, `v4/system/boot.c`) | Stays, as its own product (3c). |