fabric: codepoint -> glyph dispatch (DISPATCH-GLYPH, TOFU)

Punch list §25 item 4.3.6b complete.
capsules/fabric.4th blocks 4921-4924: DISPATCH-GLYPH routing via
WITHIN to six bucket words (DISPATCH-DIGIT/-UPPER/-LOWER/
-ASCII-PUNCT/-LATIN1/-GENPUNCT), TOFU fallback, DRAW-GLYPH. Buckets
carry one placeholder stroke word each (G-TEST-*), not the real
113-glyph set -- that's item 4.3.6c's scope, deliberately deferred.

Also: merged two lines in block 4920 (DECODE-UTF8) to fit mkcapsule's
real 64-char x 16-line block limit once a trailing blank separator
line is counted against it -- mechanical reformat, re-verified via a
DECODE-UTF8 regression check (65/176/8212, unchanged).

Verified live on amd64: one representative codepoint per bucket plus
one out-of-range codepoint, all seven DRAW-GLYPH results matched
expected exactly (400/600/450/250/550/700/500-TOFU). Three-arch
acceptance boot clean, Stadium conservation unaffected.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

FABRIC.md

@@ -4465,7 +4465,7 @@ document and committing that amendment as its own item.*
   > (`logs/20260809-185758`), aarch64 (`logs/20260809-185835`), riscv64
   > (`logs/20260809-185925`).
 
-- [ ] **4.3.6b — Codepoint → glyph dispatch.** Bucketed `CASE`/`OF`/`ENDOF` chain
+- [x] **4.3.6b — Codepoint → glyph dispatch.** Bucketed `CASE`/`OF`/`ENDOF` chain
   (`DISPATCH-DIGIT`/`-UPPER`/`-LOWER`/`-ASCII-PUNCT`/`-LATIN1`/`-GENPUNCT`) routed by
   `DISPATCH-GLYPH` via `WITHIN` range checks, per §27.6.3 — chosen over a flat xt-table
   despite the table composing more cleanly with override (§27.6.5's finding). Every glyph
@@ -4474,6 +4474,46 @@ document and committing that amendment as its own item.*
   least one codepoint from each of the six buckets, and falls through to `TOFU` (not a crash)
   for a codepoint outside all six ranges. *Refs:* §27.6.3.
 
+  > **Done, 2026-08-09.** Blocks 4921–4924 in `capsules/fabric.4th` (lint-clean).
+  > `DISPATCH-GLYPH` and the six bucket words exactly as §27.6.3 specifies, plus `TOFU`
+  > (empty box via four `G-LINE` calls, advance `500` per the section's own proposal) and
+  > `DRAW-GLYPH ( codepoint x y size color -- adv )`.
+  >
+  > **Deliberately minimal, not the real glyph set.** The 113-glyph repertoire is item
+  > 4.3.6c's scope, not this one's — building it now would be jumping ahead per §25.0 rule
+  > two. Each of the six buckets got exactly one placeholder stroke word
+  > (`G-TEST-DIGIT`/`-UPPER`/`-LOWER`/`-PUNCT`/`-LATIN1`/`-GENPUNCT`, obviously-temporary
+  > names, each drawing one `G-LINE` and returning a distinct advance) — enough to prove the
+  > routing mechanism without designing any real letterforms. 4.3.6c will need to add the
+  > full `CASE` coverage to these same six bucket words; these placeholder entries are
+  > expected to be superseded there, not treated as finished glyph art.
+  >
+  > **A real block-format limit found while landing this item, not previously hit:**
+  > `mkcapsule`'s actual rule is **64 chars × 16 content lines per block**, and — not
+  > previously noticed — a blank separator line between blocks is charged to the
+  > *preceding* block's line count, not free. Item 4.3.6a's `DECODE-UTF8` block (4920) was
+  > already at exactly 16 lines with zero slack, so appending this item's blocks after it
+  > pushed it to 17 via the following blank line. Fixed by merging two adjacent, unrelated
+  > lines in that block (`ULEN ! UADDR !` / `UADDR @ C@ ULEAD !` → one line) — a one-line
+  > mechanical reformat with identical semantics, not a scope change; re-verified via the
+  > `DECODE-UTF8` regression check below before relying on it.
+  >
+  > **Verified live on amd64**, same temporary-probe pattern as prior 4.3.6x items: a
+  > regression check of `DECODE-UTF8` (`65`/`176`/`8212`, matching item 4.3.6a's own values
+  > — confirms the block-4920 line merge changed nothing) followed by `DRAW-GLYPH` called
+  > with one representative codepoint per bucket plus one out-of-range codepoint (`1`, a
+  > control character outside all six `WITHIN` ranges). All seven results matched expected
+  > exactly: digit `48`→`400`, upper `65`→`600`, lower `97`→`450`, punct `33`→`250`, latin1
+  > `176`→`550`, genpunct `8212`→`700`, out-of-range `1`→`500` (`TOFU`). Extraction required
+  > care — injected commands raced ahead of the verbose per-word execution trace in the log,
+  > so printed results appeared shifted relative to naive line-proximity matching; resolved
+  > by anchoring on each command's own echo line as an ordered marker and taking the last
+  > printed value before the next marker, not by assuming adjacency.
+  >
+  > Three-architecture acceptance boot clean, Stadium conservation unchanged:
+  > amd64 (`logs/20260809-191200`), aarch64 (`logs/20260809-191237`), riscv64
+  > (`logs/20260809-191327`).
+
 - [ ] **4.3.6c — Default system font-set capsule.** The confirmed 113-glyph v1 repertoire
   (95 ASCII printable + 11 Latin-1 Supplement + 7 General Punctuation, itemized in §27.6.4),
   each glyph a stroke-drawing word in the 4.3.6 em-square convention returning its own