Add capsules/sdk.4th: SDK v1.9.0 vocabulary + FENCE over the cookbook capsules

Loads turtle.4th and doe.4th, defines SDK-VERSION/SDK-HELP into an SDK
vocabulary, then calls FENCE once everything is loaded -- protecting the
base wordset and both cookbook capsules from FORGET. Kernel-only (EXEC
doesn't exist hosted), REPL-invoked via S" sdk.4th" EXEC, not part of
init.4th's boot sequence.

Verified before writing the capsule, not assumed: VOCABULARY/DEFINITIONS
does not actually scope word visibility in this interpreter -- vm_find_word
is a flat dictionary scan that never consults CONTEXT/CURRENT. Documented
plainly in the HOWTO so this isn't mistaken for namespace isolation later.

Block range 5109-5115 -- discovered along the way that user-block space is
capped at [2048, 5120) by mkcapsule, tighter than expected.

Verified: mkcapsule --lint clean, hosted-build trace runs SDK-HELP with
zero attributable VM errors, zero build warnings and identical 1012/0/0
POST results with matching dict_hash on all three kernel architectures.

HOWTO: docs/working/architecture/SDK-HOWTO-20260819.md

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

FABRIC-2.md

@@ -1802,3 +1802,36 @@ matching the new test count exactly), 0 failed, 0 errors; three-arch kernel boot
 (1012/0/0 on amd64/aarch64/riscv64), `dict_hash` matches exactly across all three (changed from
 the pre-`FENCE` baseline as expected — a new C word legitimately changes the dictionary hash;
 cross-arch agreement is what's being checked, not stability against the prior baseline).
+
+**`capsules/sdk.4th` written — the SDK capsule itself, done.** Block range `5109`–`5115` (clear
+of `turtle.4th`'s `5100`–`5108`; discovered along the way that user-block space is actually
+capped at `[2048, 5120)` by `mkcapsule`, tighter than the `4000+`/"5000s in practice" impression
+from earlier sessions — `turtle.4th` at `5100`–`5108` and `sdk.4th` at `5109`–`5115` together
+leave only 4 blocks of headroom before the hard ceiling). Loads `turtle.4th` and `doe.4th` via
+`EXEC` (confirming the kernel-only decision was necessary, not just cautious), defines `SDK-
+VERSION`/`SDK-HELP` into an `SDK` vocabulary, restores `FORTH DEFINITIONS`, then calls the new
+`FENCE` — protecting the base wordset, both cookbook capsules, and its own two words in one
+call. Verified before writing a line of the capsule, not assumed: whether `VOCABULARY`/
+`DEFINITIONS` actually scope word visibility in this interpreter. It does not — `vm_find_word`
+(the interpreter's primary dispatch) is a flat, first-character-bucketed scan that never
+consults `CONTEXT`/`CURRENT`; a word defined under a custom vocabulary remained globally
+callable immediately after switching back to `FORTH DEFINITIONS`, confirmed by direct hosted
+test before committing to the capsule's design. Documented plainly in the HOWTO so nobody
+later assumes `SDK DEFINITIONS` provides isolation it doesn't.
+
+Verified: `mkcapsule --lint` clean; hosted-build trace (`fabric.4th` core + `turtle.4th` +
+`doe.4th` + `sdk.4th`'s own blocks, its two `EXEC` lines stripped and the target capsules
+concatenated directly instead, since `EXEC` doesn't exist hosted) runs `SDK-HELP` correctly
+with zero VM errors attributable to any of this content; zero build warnings and identical
+`1012 passed / 0 failed / 0 errors` boot on all three kernel architectures, `dict_hash`
+unchanged from the pre-`sdk.4th` baseline on all three (expected — not autoloaded, so it cannot
+affect boot-time dictionary content). HOWTO: `docs/working/architecture/SDK-HOWTO-20260819.md`.
+Not yet driven interactively through a live REPL, same DoE-before-REPL practical limit as
+`turtle.4th`'s own still-open item.
+
+This closes the mechanism + capsule work for SDK v1.9.0 scoping. Still open, not decided here:
+the `1.5.4`→`1.9.0` version-string bump itself, and whether to verify `turtle.4th`'s actual
+rendering before treating either it or this SDK as release-ready — both are release-process
+decisions, not implementation work, and belong to the user's call per the same pattern used
+throughout this scoping (`AskUserQuestion` for the calls that are genuinely the user's, not
+inferred).

capsules/BLOCK_MAP.md

@@ -1,5 +1,5 @@
 # Capsule Block Manifest — Auto-generated
-<!-- Generated by mkcapsule --manifest  2026-08-19T09:54:15Z -->
+<!-- Generated by mkcapsule --manifest  2026-08-19T10:07:24Z -->
 <!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh.  -->
 <!-- Hand-written justifications and immutability notes live  -->
 <!-- in MANIFEST.md alongside this auto-generated index.      -->
@@ -35,6 +35,7 @@
 | `init.4th` | 2049, 2050, 2057 | `0x214d424abd382707` |
 | `lib.4th` | 4050 | `0x20625ebf1276c239` |
 | `process.4th` | 4300, 4301 | `0x781afc1dbd0294f7` |
+| `sdk.4th` | 5109, 5110, 5111, 5112, 5113, 5114, 5115 | `0x008fdbbb62c94a3a` |
 | `turtle.4th` | 5100, 5101, 5102, 5103, 5104, 5105, 5106, 5107, 5108 | `0x4d470418ca543365` |
 | `user-font-demo.4th` | 4200, 4201, 4202 | `0xce1fd7d1b581a56d` |
 | `zuse.4th` | 4016, 4017, 4018 | `0x12f38ec782434a77` |
@@ -335,10 +336,17 @@
 | 5106 | `turtle.4th` | `0x4d470418ca543365` | ok |
 | 5107 | `turtle.4th` | `0x4d470418ca543365` | ok |
 | 5108 | `turtle.4th` | `0x4d470418ca543365` | ok |
+| 5109 | `sdk.4th` | `0x008fdbbb62c94a3a` | ok |
+| 5110 | `sdk.4th` | `0x008fdbbb62c94a3a` | ok |
+| 5111 | `sdk.4th` | `0x008fdbbb62c94a3a` | ok |
+| 5112 | `sdk.4th` | `0x008fdbbb62c94a3a` | ok |
+| 5113 | `sdk.4th` | `0x008fdbbb62c94a3a` | ok |
+| 5114 | `sdk.4th` | `0x008fdbbb62c94a3a` | ok |
+| 5115 | `sdk.4th` | `0x008fdbbb62c94a3a` | ok |
 
 ## Conflicts
 
 None.
 
 ---
-*30 capsule(s) scanned.  Re-run `mkcapsule --manifest <dir>` to refresh.*
+*31 capsule(s) scanned.  Re-run `mkcapsule --manifest <dir>` to refresh.*

capsules/sdk.4th

@@ -0,0 +1,60 @@
+Block 5109
+( sdk.4th -- SDK v1.9.0 scoping. Loads the cookbook       )
+( capsules (turtle.4th, doe.4th), a discoverable SDK      )
+( vocabulary entry point, and raises FENCE once           )
+( everything is loaded, so a developer at the REPL can    )
+( FORGET their own scratch work afterward without         )
+( disturbing any of this. Kernel-only (EXEC is kernel-    )
+( only); REPL-invoked -- S" sdk.4th" EXEC -- not part of  )
+( init.4th's boot sequence, matching turtle.4th's own     )
+( choice. NOTE: VOCABULARY/DEFINITIONS here is            )
+( organizational, not isolating -- this VM's word lookup  )
+( is a flat dictionary scan, so SDK words remain           )
+( globally callable like any other word, both before and  )
+( after this capsule loads. Verified directly on the       )
+( hosted build before writing this file.                   )
+VOCABULARY SDK
+
+Block 5110
+( Load the cookbook capsules this SDK re-exports. )
+S" turtle.4th" EXEC
+S" doe.4th" EXEC
+
+Block 5111
+( SDK's own words, defined into the SDK vocabulary for   )
+( introspection -- see the note above, they are just as  )
+( callable from FORTH context as anywhere else.          )
+SDK DEFINITIONS
+
+: SDK-VERSION ( -- )
+  ." SDK v1.9.0 (scoping)" CR ;
+
+Block 5112
+: SDK-HELP ( -- )
+  ." SDK vocabulary: turtle.4th + doe.4th + FENCE." CR
+  ." Turtle graphics (docs/working/architecture/" CR
+  ."   TURTLE-GRAPHICS-HOWTO-20260819.md):" CR
+  ."   HOME CS FORWARD BACK LEFT RIGHT PENUP PENDOWN" CR
+  ."   SETCOLOR SETXY SETHEADING POLYGON STAR TURTLE-DEMO" CR
+
+Block 5113
+  ." DoE library (docs/working/architecture/" CR
+  ."   DOE-LIBRARY-HOWTO-20260819.md):" CR
+  ."   DOE ( -- )  or  seed n-reps EXEC-DOE" CR
+  ." SDK-VERSION prints the release tag." CR ;
+
+Block 5114
+( Back to FORTH context -- CURRENT no longer targets  )
+( SDK, so anything typed at the REPL after this loads  )
+( defines normally.                                    )
+FORTH DEFINITIONS
+
+Block 5115
+( Raise FENCE now that the base wordset, turtle.4th,  )
+( doe.4th, and this file's own words are all loaded -- )
+( a developer can FORGET their own later scratch       )
+( definitions without being able to reach back          )
+( through any of this.                                  )
+FENCE
+SDK-VERSION
+." Loaded. Run SDK-HELP for the word list." CR

docs/working/architecture/SDK-HOWTO-20260819.md

@@ -0,0 +1,95 @@
+<!-- Living draft (docs/working/ tier). Source for a future docs/formal/cookbook
+     scrap once reviewed -- see docs/formal/CLAUDE.md's Scraps System. Not yet
+     promoted; do not cite. -->
+
+# SDK HOWTO — `capsules/sdk.4th`
+
+**Status:** WORKING. Part of the v1.9.0 scoping work (FABRIC-2.md section K).
+Loads the two cookbook capsules (turtle graphics, DoE library) and adds an
+`SDK` vocabulary entry point plus `FENCE` protection on top of them.
+
+## Loading it
+
+Kernel-only (it loads other capsules via `EXEC`, which does not exist in
+the hosted build), REPL-invoked — not part of `init.4th`'s boot sequence,
+matching `turtle.4th`'s own choice:
+
+```forth
+S" sdk.4th" EXEC
+```
+
+This loads `turtle.4th` and `doe.4th`, defines an `SDK` vocabulary with two
+introspection words (`SDK-VERSION`, `SDK-HELP`), then calls `FENCE` to
+protect everything loaded so far — the base wordset, both cookbook
+capsules, and `sdk.4th`'s own words — from `FORGET`. Prints a one-line
+confirmation and hint on load; run `SDK-HELP` for the full word list.
+
+## What `VOCABULARY` actually does here — read before assuming isolation
+
+`sdk.4th` defines its own words (`SDK-VERSION`, `SDK-HELP`) into a named
+`SDK` vocabulary via `SDK DEFINITIONS`. This is **organizational, not
+isolating**: this VM's primary word lookup (`vm_find_word`, used by the
+ordinary interpreter loop) is a flat, first-character-bucketed scan of the
+whole dictionary — it does not consult `CONTEXT`/`CURRENT` at all. Verified
+directly before writing this file: a word defined while `CURRENT` targeted
+a custom vocabulary remained globally callable immediately after switching
+back to `FORTH DEFINITIONS`, exactly as if no vocabulary had been involved.
+The `VOCABULARY`/`DEFINITIONS`/`CONTEXT`/`ORDER`/`(FIND)` machinery is real,
+standard FORTH-79, and useful for anything that explicitly walks vocabulary
+chains (`(FIND)`, `ORDER`) — it just isn't what makes SDK words reachable
+day to day. Don't build anything on the assumption that loading a second
+vocabulary hides or scopes its words from the rest of the system.
+
+## FENCE — and the bug it surfaced
+
+`FENCE ( -- )` is new (this scoping pass) — it raises the dictionary's
+`FORGET` boundary to whatever is currently the newest word, so anything
+defined afterward can be safely `FORGET`ten without reaching back into
+protected territory. `sdk.4th` calls it once, at the very end of loading.
+
+Building a direct test for `FENCE` surfaced a real, severe, pre-existing
+bug in `FORGET` itself — completely independent of `FENCE`, reproducible
+with the *original* boot-time fence alone. Forgetting the single newest
+word wrongly destroyed every other word back to the fence too; forgetting
+an older word (which correctly cascades to remove newer words, per
+FORTH-79 semantics) crashed with a SIGSEGV — a use-after-free in the
+dictionary relink logic. Found and fixed as part of this work; full
+root-cause writeup in FABRIC-2.md section K. Three POST cases were added to
+`dictionary_manipulation_words_test.c` (Module 14) alongside `FORGET`'s
+own, including the exact regression scenario, so it can't silently return.
+
+## Vocabulary
+
+| Word | Effect |
+|------|--------|
+| `SDK-VERSION` | Prints the release tag (`SDK v1.9.0 (scoping)`). |
+| `SDK-HELP` | Prints the full word list for both cookbook capsules, with HOWTO pointers. |
+| `FENCE` | (Not SDK-specific — a base word, used by this capsule.) Raises the `FORGET` boundary to the current dictionary top. |
+
+Everything from `turtle.4th` and `doe.4th` is also available after loading
+— see their own HOWTOs (`TURTLE-GRAPHICS-HOWTO-20260819.md`,
+`DOE-LIBRARY-HOWTO-20260819.md`) for their vocabularies.
+
+## Verification performed
+
+- `mkcapsule --lint capsules/` clean (block range `5109`–`5115`, clear of
+  `turtle.4th`'s `5100`–`5108`).
+- Hosted-build logic trace: `fabric.4th`'s core blocks + `turtle.4th` +
+  `doe.4th` + `sdk.4th`'s own blocks (with its two `EXEC` lines stripped,
+  since `EXEC` doesn't exist hosted — the capsules they'd load were
+  concatenated directly instead) piped into the hosted binary. `SDK-HELP`
+  runs and prints correctly; zero VM errors from any of this content
+  (all errors present in the log are the built-in POST suite's own
+  deliberate error-injection cases, confirmed by cross-checking against
+  the same baseline used for the cookbook capsules' own verification).
+- Built cleanly (zero warnings) and baked into the capsule set on all
+  three kernel architectures (amd64/aarch64/riscv64); boot verified clean
+  through POST on all three, `1012 passed / 0 failed / 0 errors`
+  identically, `dict_hash` unchanged from the pre-`sdk.4th` baseline on
+  all three (expected — `sdk.4th` isn't autoloaded, so it cannot affect
+  boot-time dictionary content).
+- Not yet driven interactively through a live REPL — same practical
+  limitation as `turtle.4th`'s own HOWTO documents (the DoE campaign that
+  auto-runs on every kernel boot blocks the REPL for ~25–30 minutes before
+  serial commands can reach it). The FORTH logic is verified; the
+  interactive load-and-run experience is not.