Stage S-1c: WORD's buffer is per VM; input buffers allotted at VM init, below all compiled code (FABRIC-3.9.0 §8.1)

- The static word_scratch_addr shared by every VM is gone: WORD builds in
  vm->word_buf (257 bytes: count + 255 + NUL). A token over 255 chars is
  refused whole (delimiter restored, >IN unconsumed, vm->error), logged at
  LOG_ERROR and counted -- no more silent cut to 62 chars.
- Pre-existing corruption found by the probe: TIB/>IN/SPAN (and WORD's
  scratch) were allotted lazily at HERE; POST's restore_dict_state(),
  FORGET and COLD rolled HERE below them and compiled the dictionary over
  them (Hera's TIB lay under ACL-RECHECK's body; QUERY/WORD wrote into
  code). Per Captain Bob, all four are now allotted first in both
  vm_init()s (offsets 0-1305); COLD's clamp never goes below them.

Probe (reverted), identical on amd64/aarch64/riscv64: 0 colon bodies inside
the buffers; per-VM isolation; 62/100/255-char tokens full length; 300
refused and counted; interpreter sane after full-width TIB writes.
3-ISA acceptance passes; M7.1a hash and dict_hash set unchanged (here
0xd8 -> 0x5f8).

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

FABRIC-3.9.8.md

@@ -1,6 +1,6 @@
 # FABRIC-3.9.8.md — Observers and participants: execution plan and log
 
-**Status: IN PROGRESS.** Done: O-A, the stack-convention fix, S-1a and S-1b (§2). The design and
+**Status: IN PROGRESS.** Done: O-A, the stack-convention fix, S-1a, S-1b and S-1c (§2). The design and
 its rulings (O-1 to O-4, the discard, and §7/§8's M- and S- rulings) are in `FABRIC-3.9.0.md`.
 
 Each stage:
@@ -338,3 +338,78 @@ Evidence is named **before** each stage runs.
           callers.
         - No word-id field narrower than 32 bits.
         - Nothing else found.
+- [x] **Stage S-1c — `WORD`'s buffer is per VM, and the input buffers sit below all compiled
+      code (`FABRIC-3.9.0.md` §8.1, class C).** 2026-09-24. Captain Bob: *"go ahead with S-1c"*,
+      then, on the defect below, *"Allot at VM init"*.
+
+      **The defect as scoped.** `WORD` built its counted string in one `static vaddr_t
+      word_scratch_addr` shared by every VM:
+      - It was `vm_allot`'d once, in whichever VM called first, at wherever that VM's `HERE` stood.
+      - A second VM got an address meant for someone else's space.
+      - Tokens were silently cut to 62 characters (a 64-byte buffer).
+
+      **The deeper defect, found by the first probe.** The input buffers were allotted lazily by
+      `vm_input_ensure()` at the current `HERE`: the TIB (`INPUT_BUFFER_SIZE`), `>IN`, `SPAN`, and
+      `WORD`'s scratch.
+      - Three things later roll `HERE` back below them and compile the dictionary over them: POST's
+        test harness (`restore_dict_state()`), `FORGET`, and `COLD` (which clamps `HERE` to 1024).
+      - On Hera, POST allotted the TIB at offset 120 and then restored `HERE`. **`ACL-RECHECK`'s
+        colon body lived at offset 824, inside the TIB.**
+      - The first S-1c probe wrote the TIB, as `QUERY` does, which zeroed that body. Hera hit
+        `execute_colon_word: NULL cell in 'ACL-RECHECK'` and never reached her prompt
+        (`logs/20260924-151033/amd64/`; layout diagnostic `-152047/amd64/`).
+      - So before this stage, `QUERY` wrote into Hera's compiled code, and so did `WORD` through
+        the old static scratch. Nothing in a normal boot calls either afterwards, which is why
+        acceptance never saw it. The first draft of the per-VM buffer, allotted the same lazy way,
+        inherited the defect.
+
+      **The change:**
+      - **`vm.h`:**
+        - `VM.word_buf`, one per VM.
+        - `WORD_BUFFER_SIZE 257`: a count byte, 255 characters (the most a counted string can
+          hold, a format limit, not a chosen bound), and a NUL.
+      - **`vm_api.c`:** `vm_input_ensure()` also allots `word_buf`, after `SPAN`, so TIB/`>IN`/
+        `SPAN` keep their relative layout.
+      - **Both `vm_init()`s** (`src/vm_bootstrap.c`, `src/starkernel/vm/vm_bootstrap.c`) call
+        `vm_input_ensure()` first, before POST, capsules or any definition.
+        - The buffers take offsets 0–1305 in every VM.
+        - Every later `HERE` rollback (test restore, `FORGET`) lands above them.
+        - If the allotment fails, `vm_init` fails with an error.
+      - **`COLD`** (`system_words.c`) still clamps `HERE` to 1024, but never below the end of the
+        input buffers.
+      - **`string_words.c`:** the static is gone. `WORD` builds into `vm->word_buf`.
+        - A token over 255 characters is **refused whole**: the delimiter goes back on the stack,
+          `>IN` is not consumed, and `vm->error` is set.
+        - The refusal is logged at `LOG_ERROR` ("WORD: token over 255 chars refused") and counted
+          (`string_word_word_refusals()`).
+
+      **Evidence** (probe, reverted; byte-identical on all three ISAs, 37 lines;
+      `logs/20260924-152935/amd64/`, `-153409/aarch64/`, `-153842/riscv64/`):
+
+      | Check | Result |
+      |---|---|
+      | Layout, Hera and Hestia | TIB offset 0, `>IN` 1032, `SPAN` 1040, `word_buf` 1048, end 1305. Colon bodies inside the buffers: **0** (Hera 26 checked, Hestia 179). |
+      | Isolation | Hera's `WORD` returns her own `word_buf`, in her own memory. Hestia's returns hers, in hers, and the two are distinct. Hera's `HERAWORD` is intact after Hestia parses `HESTIAWORD`. |
+      | Length | 62, 100 and 255 characters come back at full length with the correct last character. It used to be 62 at most. |
+      | 300-char token | Refused, `vm->error=1`, refusals 1, the ERROR line logged, the delimiter restored, `>IN` 0. |
+      | After the probe | The probe wrote the TIB full-width, and `1 2 + .` still prints `3`. Hera reaches `[zuse@Hera] ok>`. |
+
+      **Acceptance** on the clean tree (`logs/20260924-154256/amd64/`, `-155542/aarch64/`,
+      `-160845/riscv64/`):
+      - Boot M7.1a `word_count=531`, hash `0x572daac83b797332`, unchanged. Only its `here` moves,
+        from `0xd8` to `0x5f8`, the 1,305 buffer bytes now allotted first.
+      - The `dict_hash` set is unchanged (Hera `0xda9742ce9c3376a2`, Hestia `0x413e7d086f342d8b`,
+        Artemis `0xdfd68316d5f5ba85`). The canonical hash walks word ids and body cells, and no
+        colon body carries an absolute address that the shift would change.
+      - The O-A checks pass: G interleave 40/40/48, `HHH` precedence, and a typed `1 2 + .` gives
+        `3` mid-stream.
+      - Mint → WIREBIND → `USE` → `3`. Idle log growth 0. No faults. QEMU exits cleanly.
+      - Clean kernel builds on all three ISAs, plus the hosted build.
+
+      **Found, reported, not fixed:**
+      1. **`COLD` rewinds `HERE` to 1024 without rewinding `latest`.** Every word defined past 1024
+         stays linked while new definitions are compiled over its body. S-1c only keeps the clamp
+         off the input buffers.
+      2. **`PAD` overlaps the block I/O window.** It returns `VM_MEMORY_SIZE - 512`, which is inside
+         the top block slot (`BLK_VM_WINDOW_BASE` = `VM_MEMORY_SIZE - 4096`), so `PAD` and the
+         4th `BLOCK` buffer share bytes.