playground+repl: bend dispatch from WASM + 1.33 zoom + free-form runner

bend!-call from the WAT tier
  - New WAT import: (import "env" "bend_call"). The host loader supplies
    a sync XMLHttpRequest that POSTs the payload to a configured URL
    (workers only — sync XHR isn't allowed on main thread).
  - New primitive (bend!-call "<payload>") returns the response as a
    lumbda string. Works in playground and REPL once the bend URL is
    saved in the new top bar.
  - bendUrl persists in plain localStorage (not encrypted — it's a
    server address, not a secret).
  - Tests stub the import with a no-op so unit / integration / functional
    suites keep instantiating cleanly.

Playground + REPL zoom 133% by default
  - html { zoom: 1.33 } so the styleguide sizes read comfortably without
    requiring browser-level zoom.

Free-form default = cross-tier assertion runner in Lisp
  - The default editor content for "free form" is now a small assertion
    framework matching tests/functional.lsp's PASS/FAIL convention. A
    starter the user can extend, runs identically on the three tiers.

C tier + Python tier (bend) are wired through the runner stub; full
bend integration in those tiers comes next once their loaders learn
about setBendUrl.

wasm/app/app.js

@@ -12,7 +12,35 @@ import { oneDark } from "@codemirror/theme-one-dark";
 import { openVault } from "./crypto.js";
 
 const TIERS = { python: "python (pyodide)", c: "c (emcc)", asm: "asm (wat)" };
-const FREE_FORM_DEFAULT = "; free-form mode — unlock the vault below to persist this code\n; encrypted in localStorage with your password\n\n(+ 1 2)\n";
+const FREE_FORM_DEFAULT = `; free-form mode — write any lisp, race all three tiers.
+; unlock the vault below to persist this code (encrypted localStorage).
+;
+; below: a tiny version of the cross-tier functional.lsp runner.
+
+(define pass 0)
+(define fail 0)
+(define (check name got expected)
+  (cond ((equal? got expected)
+         (set! pass (+ pass 1))
+         (display "PASS: ") (display name) (newline))
+        (else
+         (set! fail (+ fail 1))
+         (display "FAIL: ") (display name)
+         (display " got=") (display got)
+         (display " expected=") (display expected) (newline))))
+
+(check "arithmetic"   (+ 1 2)                        3)
+(check "division"     (/ 42 6)                       7)
+(check "string"       (string-append "foo" "bar")    "foobar")
+(check "list reverse" (reverse (list 1 2 3))         (list 3 2 1))
+(check "vector len"   (vector-length (vector 1 2 3)) 3)
+(check "char"         (char->integer #\\A)            65)
+(check "let loop"     (let loop ((i 0) (n 0))
+                        (if (= i 10) n (loop (+ i 1) (+ n i)))) 45)
+
+(display pass) (display " pass, ") (display fail) (display " fail")
+(newline)
+`;
 
 const demoSources = {};
 // Vault state. When unlocked, free-form code auto-saves on every edit.
@@ -166,7 +194,9 @@ const workerState = {
 };
 
 function spawnWorker() {
-    return new Worker(new URL("./worker.mjs", import.meta.url), { type: "module" });
+    const w = new Worker(new URL("./worker.mjs", import.meta.url), { type: "module" });
+    if (bendState.url) w.postMessage({ kind: "config", bendUrl: bendState.url });
+    return w;
 }
 
 function ensureWorker(tier) {
@@ -174,6 +204,34 @@ function ensureWorker(tier) {
     return workerState.workers[tier];
 }
 
+// ─── Bend URL ──────────────────────────────────────────────────────
+const bendState = { url: localStorage.getItem("lumbda_bend_url") || "" };
+const bendUrlEl = document.getElementById("bend-url");
+const bendSaveBtn = document.getElementById("bend-save");
+const bendStateEl = document.getElementById("bend-state");
+if (bendState.url) {
+    bendUrlEl.value = bendState.url;
+    bendStateEl.textContent = "saved";
+}
+function saveBendUrl() {
+    bendState.url = bendUrlEl.value.trim();
+    if (bendState.url) {
+        localStorage.setItem("lumbda_bend_url", bendState.url);
+        bendStateEl.textContent = "saved";
+    } else {
+        localStorage.removeItem("lumbda_bend_url");
+        bendStateEl.textContent = "";
+    }
+    // Push config to any already-spawned workers.
+    for (const w of Object.values(workerState.workers)) {
+        if (w) w.postMessage({ kind: "config", bendUrl: bendState.url });
+    }
+}
+bendSaveBtn.addEventListener("click", saveBendUrl);
+bendUrlEl.addEventListener("keydown", (e) => {
+    if (e.key === "Enter") { e.preventDefault(); saveBendUrl(); }
+});
+
 function runOnTierInWorker(tier, src, onLoading) {
     return new Promise((resolve, reject) => {
         const w = ensureWorker(tier);

wasm/app/index.html

@@ -59,6 +59,15 @@
   <span id="status" class="status"></span>
 </section>
 
+<section class="bend-bar">
+  <span class="bend-icon" title="gpu-worker bend URL">⚡</span>
+  <label>bend URL
+    <input id="bend-url" type="url" placeholder="https://your-gpu-worker.example/bend  (sets (bend!-call ...) destination)">
+  </label>
+  <button id="bend-save" class="secondary">save</button>
+  <span id="bend-state" class="bend-state"></span>
+</section>
+
 <section class="vault-bar" id="vault-bar" hidden>
   <span class="vault-icon" title="local vault">🔒</span>
   <span id="vault-state" class="vault-state">locked</span>

wasm/app/runner.js

@@ -8,6 +8,15 @@ import { createCTier } from "./c/lumbda-c.loader.js";
 import { createAsmTier } from "./asm/lumbda-asm.loader.js";
 
 const cache = {};
+const config = { bendUrl: null };
+
+export function setBendUrl(url) {
+    config.bendUrl = url || null;
+    // Propagate to already-loaded tiers.
+    for (const t of Object.values(cache)) {
+        if (t && t.setBendUrl) t.setBendUrl(config.bendUrl);
+    }
+}
 
 export async function getTier(name, onLoad) {
     if (cache[name]) return cache[name];
@@ -16,6 +25,7 @@ export async function getTier(name, onLoad) {
     else if (name === "c") cache[name] = await createCTier();
     else if (name === "asm") cache[name] = await createAsmTier();
     else throw new Error(`unknown tier: ${name}`);
+    if (cache[name].setBendUrl) cache[name].setBendUrl(config.bendUrl);
     return cache[name];
 }
 

wasm/app/style.css

@@ -42,6 +42,12 @@
 
 * { box-sizing: border-box; }
 
+html {
+  /* Default zoom so text is comfortably readable. Native CSS zoom
+   * preserves layout proportions across the whole document. */
+  zoom: 1.33;
+}
+
 html, body {
   margin: 0; padding: 0;
   background: var(--bg);
@@ -189,6 +195,46 @@ header code {
 .controls .status.err  { color: var(--err); }
 .controls .status.ok   { color: var(--green); }
 
+.bend-bar {
+  padding: 0.4rem 1.5rem;
+  border-bottom: 1px solid var(--rule);
+  display: flex; align-items: center; gap: 0.6rem;
+  background: var(--bg);
+  font-size: 0.85em;
+}
+.bend-bar .bend-icon { font-size: 1em; }
+.bend-bar label {
+  flex: 1;
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  color: var(--muted);
+}
+.bend-bar input[type=url] {
+  flex: 1;
+  background: var(--code-bg);
+  border: 1px solid var(--rule);
+  color: var(--fg);
+  padding: 0.3rem 0.5rem;
+  font-family: var(--mono);
+  font-size: 0.9em;
+  border-radius: 3px;
+}
+.bend-bar input[type=url]:focus { outline: none; border-color: var(--green); }
+.bend-bar button {
+  background: transparent;
+  color: var(--green);
+  border: 1px solid var(--green);
+  font-family: var(--mono);
+  font-size: 0.85em;
+  font-weight: 600;
+  padding: 0.3rem 0.8rem;
+  border-radius: 3px;
+  cursor: pointer;
+}
+.bend-bar button:hover { background: var(--code-bg); }
+.bend-bar .bend-state { color: var(--green); font-size: 0.8em; min-width: 4em; }
+
 .vault-bar {
   padding: 0.5rem 1.5rem;
   border-bottom: 1px solid var(--rule);

wasm/app/worker.mjs

@@ -3,11 +3,16 @@
 // live ms counter actually ticks AND so cancel works (main thread
 // terminates this worker via worker.terminate()).
 
-import { evalOnTier } from "./runner.js";
+import { evalOnTier, setBendUrl } from "./runner.js";
 
 self.onmessage = async (e) => {
-    const { kind, runId, tier, src } = e.data;
+    const { kind } = e.data;
+    if (kind === "config") {
+        setBendUrl(e.data.bendUrl);
+        return;
+    }
     if (kind !== "eval") return;
+    const { runId, tier, src } = e.data;
     try {
         const output = await evalOnTier(tier, src, (loadingTier) => {
             self.postMessage({ kind: "loading", runId, tier: loadingTier });

wasm/asm/lumbda-asm.loader.js

@@ -4,18 +4,57 @@
 // Memory layout (mirrors lumbda.wat):
 //   0x10000  output buffer (read after each call)
 //   0x20000  source buffer (write before each call)
+//   0x40000  bend response scratch (host writes here when JS dispatches)
 
 async function _bootstrap() {
     const wasmURL = new URL("./lumbda-asm.wasm", import.meta.url).href;
     const resp = await fetch(wasmURL);
     const bytes = await resp.arrayBuffer();
-    const { instance } = await WebAssembly.instantiate(bytes);
-    const exp = instance.exports;
 
-    exp.lumbda_init();
+    // Closure-captured holder so the imported function can see the
+    // instance's memory after instantiation completes.
+    const refs = { instance: null, bendUrl: null };
+
+    const importObj = {
+        env: {
+            // bend_call(src_ptr, src_len, resp_ptr) -> resp_len.
+            // Synchronous XHR is the only sync HTTP available in workers;
+            // perfect for the WAT tier's blocking eval model.
+            bend_call(srcPtr, srcLen, respPtr) {
+                if (!refs.bendUrl) {
+                    const msg = "no bend URL configured";
+                    const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                    mem.set(new TextEncoder().encode(msg), respPtr);
+                    return msg.length;
+                }
+                const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                const payload = new TextDecoder().decode(mem.slice(srcPtr, srcPtr + srcLen));
+                try {
+                    const xhr = new XMLHttpRequest();
+                    xhr.open("POST", refs.bendUrl, false);  // sync
+                    xhr.setRequestHeader("Content-Type", "text/plain; charset=utf-8");
+                    xhr.send(payload);
+                    const respText = xhr.responseText || "";
+                    const respBytes = new TextEncoder().encode(respText);
+                    new Uint8Array(refs.instance.exports.memory.buffer).set(respBytes, respPtr);
+                    return respBytes.length;
+                } catch (e) {
+                    const err = "bend error: " + (e.message || String(e));
+                    new Uint8Array(refs.instance.exports.memory.buffer)
+                        .set(new TextEncoder().encode(err), respPtr);
+                    return err.length;
+                }
+            },
+        },
+    };
+
+    const { instance } = await WebAssembly.instantiate(bytes, importObj);
+    refs.instance = instance;
+    instance.exports.lumbda_init();
 
     const enc = new TextEncoder();
     const dec = new TextDecoder();
+    const exp = instance.exports;
 
     return {
         async evalLisp(src) {
@@ -32,6 +71,7 @@ async function _bootstrap() {
             const outLen = exp.lumbda_output_len();
             return dec.decode(new Uint8Array(exp.memory.buffer, outPtr, outLen));
         },
+        setBendUrl(url) { refs.bendUrl = url || null; },
     };
 }
 

wasm/asm/lumbda.wat

@@ -38,6 +38,14 @@
 ;; Built-in symbols (interned at init) live early on the heap.
 
 (module
+  ;; ─── Imports from host JS ──────────────────────────────────────
+  ;; bend_call(src_ptr, src_len, resp_ptr) -> resp_len.
+  ;; JS does a synchronous XHR to the configured gpu-worker URL,
+  ;; writes the response bytes at resp_ptr, returns the byte length.
+  ;; Worker context only — sync XHR isn't allowed on the main thread.
+  (import "env" "bend_call"
+    (func $js_bend_call (param i32 i32 i32) (result i32)))
+
   ;; ─── Memory & exports ──────────────────────────────────────────
   (memory (export "memory") 32 4096)  ;; 32 pages = 2 MB initial, grow to 256 MB
 
@@ -1943,6 +1951,35 @@
         (br $l)))
     (local.get $head))
 
+  ;; ─── Bend dispatch ─────────────────────────────────────────────
+  ;; Send a payload string to the configured gpu-worker via host XHR.
+  ;; Response is written into the scratch area at 0x40000 (64 KB), then
+  ;; copied into a freshly-allocated lumbda string.
+  (func $bend_call_op (param $payload i32) (result i32)
+    (local $resp_buf i32)
+    (local $resp_len i32)
+    (local $payload_ptr i32)
+    (local $payload_len i32)
+    (local $out i32)
+    (local $i i32)
+    (if (i32.eqz (call $is_string (local.get $payload)))
+      (then (return (global.get $FALSE))))
+    (local.set $resp_buf (i32.const 0x40000))
+    (local.set $payload_ptr (i32.add (local.get $payload) (i32.const 8)))
+    (local.set $payload_len (call $string_len (local.get $payload)))
+    (local.set $resp_len
+      (call $js_bend_call (local.get $payload_ptr) (local.get $payload_len) (local.get $resp_buf)))
+    (local.set $out (call $make_string_raw (local.get $resp_len)))
+    (local.set $i (i32.const 0))
+    (block $done
+      (loop $l
+        (br_if $done (i32.ge_u (local.get $i) (local.get $resp_len)))
+        (call $string_set_byte (local.get $out) (local.get $i)
+              (i32.load8_u (i32.add (local.get $resp_buf) (local.get $i))))
+        (local.set $i (i32.add (local.get $i) (i32.const 1)))
+        (br $l)))
+    (local.get $out))
+
   ;; ─── Primitives ────────────────────────────────────────────────
   (func $apply_primitive (param $id i32) (param $args i32) (result i32)
     (local $a i32)
@@ -2668,6 +2705,11 @@
                   (call $string_len (local.get $a)))))
         (return (global.get $VOID))))
 
+    ;; bend!-call (109) — dispatch a payload string to the configured
+    ;; gpu-worker URL via host JS sync XHR. Returns the response as a string.
+    (if (i32.eq (local.get $id) (i32.const 109))
+      (then (return (call $bend_call_op (local.get $a)))))
+
     (global.get $VOID))
 
   ;; ─── Init ──────────────────────────────────────────────────────
@@ -2821,6 +2863,7 @@
   (data (i32.const 0xE5A4) "hash-table->alist")
   (data (i32.const 0xE5B8) "write")
   (data (i32.const 0xE5C0) "write-string")
+  (data (i32.const 0xE5D0) "bend!-call")
 
   ;; ── Embedded Lisp prelude. Evaluated at end of init. ─────────────
   (data (i32.const 0x50000)
@@ -3009,6 +3052,7 @@
     (call $bind_prim (i32.const 0xE5A4) (i32.const 17) (i32.const 106))  ;; hash-table->alist
     (call $bind_prim (i32.const 0xE5B8) (i32.const 5)  (i32.const 107))  ;; write
     (call $bind_prim (i32.const 0xE5C0) (i32.const 12) (i32.const 108))  ;; write-string
+    (call $bind_prim (i32.const 0xE5D0) (i32.const 10) (i32.const 109))  ;; bend!-call
     (call $eval_prelude))
 
   ;; ─── Public eval entry ─────────────────────────────────────────

wasm/dist-repl/asm/lumbda-asm.loader.js

@@ -4,18 +4,57 @@
 // Memory layout (mirrors lumbda.wat):
 //   0x10000  output buffer (read after each call)
 //   0x20000  source buffer (write before each call)
+//   0x40000  bend response scratch (host writes here when JS dispatches)
 
 async function _bootstrap() {
     const wasmURL = new URL("./lumbda-asm.wasm", import.meta.url).href;
     const resp = await fetch(wasmURL);
     const bytes = await resp.arrayBuffer();
-    const { instance } = await WebAssembly.instantiate(bytes);
-    const exp = instance.exports;
 
-    exp.lumbda_init();
+    // Closure-captured holder so the imported function can see the
+    // instance's memory after instantiation completes.
+    const refs = { instance: null, bendUrl: null };
+
+    const importObj = {
+        env: {
+            // bend_call(src_ptr, src_len, resp_ptr) -> resp_len.
+            // Synchronous XHR is the only sync HTTP available in workers;
+            // perfect for the WAT tier's blocking eval model.
+            bend_call(srcPtr, srcLen, respPtr) {
+                if (!refs.bendUrl) {
+                    const msg = "no bend URL configured";
+                    const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                    mem.set(new TextEncoder().encode(msg), respPtr);
+                    return msg.length;
+                }
+                const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                const payload = new TextDecoder().decode(mem.slice(srcPtr, srcPtr + srcLen));
+                try {
+                    const xhr = new XMLHttpRequest();
+                    xhr.open("POST", refs.bendUrl, false);  // sync
+                    xhr.setRequestHeader("Content-Type", "text/plain; charset=utf-8");
+                    xhr.send(payload);
+                    const respText = xhr.responseText || "";
+                    const respBytes = new TextEncoder().encode(respText);
+                    new Uint8Array(refs.instance.exports.memory.buffer).set(respBytes, respPtr);
+                    return respBytes.length;
+                } catch (e) {
+                    const err = "bend error: " + (e.message || String(e));
+                    new Uint8Array(refs.instance.exports.memory.buffer)
+                        .set(new TextEncoder().encode(err), respPtr);
+                    return err.length;
+                }
+            },
+        },
+    };
+
+    const { instance } = await WebAssembly.instantiate(bytes, importObj);
+    refs.instance = instance;
+    instance.exports.lumbda_init();
 
     const enc = new TextEncoder();
     const dec = new TextDecoder();
+    const exp = instance.exports;
 
     return {
         async evalLisp(src) {
@@ -32,6 +71,7 @@ async function _bootstrap() {
             const outLen = exp.lumbda_output_len();
             return dec.decode(new Uint8Array(exp.memory.buffer, outPtr, outLen));
         },
+        setBendUrl(url) { refs.bendUrl = url || null; },
     };
 }
 

wasm/dist-repl/runner.js

@@ -8,6 +8,15 @@ import { createCTier } from "./c/lumbda-c.loader.js";
 import { createAsmTier } from "./asm/lumbda-asm.loader.js";
 
 const cache = {};
+const config = { bendUrl: null };
+
+export function setBendUrl(url) {
+    config.bendUrl = url || null;
+    // Propagate to already-loaded tiers.
+    for (const t of Object.values(cache)) {
+        if (t && t.setBendUrl) t.setBendUrl(config.bendUrl);
+    }
+}
 
 export async function getTier(name, onLoad) {
     if (cache[name]) return cache[name];
@@ -16,6 +25,7 @@ export async function getTier(name, onLoad) {
     else if (name === "c") cache[name] = await createCTier();
     else if (name === "asm") cache[name] = await createAsmTier();
     else throw new Error(`unknown tier: ${name}`);
+    if (cache[name].setBendUrl) cache[name].setBendUrl(config.bendUrl);
     return cache[name];
 }
 

wasm/dist-repl/style.css

@@ -42,6 +42,12 @@
 
 * { box-sizing: border-box; }
 
+html {
+  /* Default zoom so text is comfortably readable. Native CSS zoom
+   * preserves layout proportions across the whole document. */
+  zoom: 1.33;
+}
+
 html, body {
   margin: 0; padding: 0;
   background: var(--bg);
@@ -189,6 +195,46 @@ header code {
 .controls .status.err  { color: var(--err); }
 .controls .status.ok   { color: var(--green); }
 
+.bend-bar {
+  padding: 0.4rem 1.5rem;
+  border-bottom: 1px solid var(--rule);
+  display: flex; align-items: center; gap: 0.6rem;
+  background: var(--bg);
+  font-size: 0.85em;
+}
+.bend-bar .bend-icon { font-size: 1em; }
+.bend-bar label {
+  flex: 1;
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  color: var(--muted);
+}
+.bend-bar input[type=url] {
+  flex: 1;
+  background: var(--code-bg);
+  border: 1px solid var(--rule);
+  color: var(--fg);
+  padding: 0.3rem 0.5rem;
+  font-family: var(--mono);
+  font-size: 0.9em;
+  border-radius: 3px;
+}
+.bend-bar input[type=url]:focus { outline: none; border-color: var(--green); }
+.bend-bar button {
+  background: transparent;
+  color: var(--green);
+  border: 1px solid var(--green);
+  font-family: var(--mono);
+  font-size: 0.85em;
+  font-weight: 600;
+  padding: 0.3rem 0.8rem;
+  border-radius: 3px;
+  cursor: pointer;
+}
+.bend-bar button:hover { background: var(--code-bg); }
+.bend-bar .bend-state { color: var(--green); font-size: 0.8em; min-width: 4em; }
+
 .vault-bar {
   padding: 0.5rem 1.5rem;
   border-bottom: 1px solid var(--rule);

wasm/dist-repl/worker.mjs

@@ -3,11 +3,16 @@
 // live ms counter actually ticks AND so cancel works (main thread
 // terminates this worker via worker.terminate()).
 
-import { evalOnTier } from "./runner.js";
+import { evalOnTier, setBendUrl } from "./runner.js";
 
 self.onmessage = async (e) => {
-    const { kind, runId, tier, src } = e.data;
+    const { kind } = e.data;
+    if (kind === "config") {
+        setBendUrl(e.data.bendUrl);
+        return;
+    }
     if (kind !== "eval") return;
+    const { runId, tier, src } = e.data;
     try {
         const output = await evalOnTier(tier, src, (loadingTier) => {
             self.postMessage({ kind: "loading", runId, tier: loadingTier });

wasm/tests/functional-cross.mjs

@@ -19,7 +19,8 @@ function countPassFail(out) {
 
 async function runAsm() {
     const wasmBytes = fs.readFileSync(path.join(dist, "asm", "lumbda-asm.wasm"));
-    const { instance } = await WebAssembly.instantiate(wasmBytes);
+    const importObj = { env: { bend_call(_p, _l, _r) { return 0; } } };
+    const { instance } = await WebAssembly.instantiate(wasmBytes, importObj);
     const exp = instance.exports;
     exp.lumbda_init();
     const bytes = new TextEncoder().encode(functionalLsp);

wasm/tests/integration.mjs

@@ -31,7 +31,8 @@ function nativePython(demoPath) {
 
 async function runAsm(src) {
     const wasmBytes = fs.readFileSync(path.join(dist, "asm", "lumbda-asm.wasm"));
-    const { instance } = await WebAssembly.instantiate(wasmBytes);
+    const importObj = { env: { bend_call(_p, _l, _r) { return 0; } } };
+    const { instance } = await WebAssembly.instantiate(wasmBytes, importObj);
     const exp = instance.exports;
     exp.lumbda_init();
     const bytes = new TextEncoder().encode(src);

wasm/tests/unit.mjs

@@ -23,7 +23,8 @@ function check(name, cond, detail) {
 async function testAsm() {
     console.log("── asm tier ──");
     const wasmBytes = fs.readFileSync(path.join(dist, "asm", "lumbda-asm.wasm"));
-    const { instance } = await WebAssembly.instantiate(wasmBytes);
+    const importObj = { env: { bend_call(_p, _l, _r) { return 0; } } };
+    const { instance } = await WebAssembly.instantiate(wasmBytes, importObj);
     const exp = instance.exports;
     exp.lumbda_init();
 

www/playground/app.js

@@ -12,7 +12,35 @@ import { oneDark } from "@codemirror/theme-one-dark";
 import { openVault } from "./crypto.js";
 
 const TIERS = { python: "python (pyodide)", c: "c (emcc)", asm: "asm (wat)" };
-const FREE_FORM_DEFAULT = "; free-form mode — unlock the vault below to persist this code\n; encrypted in localStorage with your password\n\n(+ 1 2)\n";
+const FREE_FORM_DEFAULT = `; free-form mode — write any lisp, race all three tiers.
+; unlock the vault below to persist this code (encrypted localStorage).
+;
+; below: a tiny version of the cross-tier functional.lsp runner.
+
+(define pass 0)
+(define fail 0)
+(define (check name got expected)
+  (cond ((equal? got expected)
+         (set! pass (+ pass 1))
+         (display "PASS: ") (display name) (newline))
+        (else
+         (set! fail (+ fail 1))
+         (display "FAIL: ") (display name)
+         (display " got=") (display got)
+         (display " expected=") (display expected) (newline))))
+
+(check "arithmetic"   (+ 1 2)                        3)
+(check "division"     (/ 42 6)                       7)
+(check "string"       (string-append "foo" "bar")    "foobar")
+(check "list reverse" (reverse (list 1 2 3))         (list 3 2 1))
+(check "vector len"   (vector-length (vector 1 2 3)) 3)
+(check "char"         (char->integer #\\A)            65)
+(check "let loop"     (let loop ((i 0) (n 0))
+                        (if (= i 10) n (loop (+ i 1) (+ n i)))) 45)
+
+(display pass) (display " pass, ") (display fail) (display " fail")
+(newline)
+`;
 
 const demoSources = {};
 // Vault state. When unlocked, free-form code auto-saves on every edit.
@@ -166,7 +194,9 @@ const workerState = {
 };
 
 function spawnWorker() {
-    return new Worker(new URL("./worker.mjs", import.meta.url), { type: "module" });
+    const w = new Worker(new URL("./worker.mjs", import.meta.url), { type: "module" });
+    if (bendState.url) w.postMessage({ kind: "config", bendUrl: bendState.url });
+    return w;
 }
 
 function ensureWorker(tier) {
@@ -174,6 +204,34 @@ function ensureWorker(tier) {
     return workerState.workers[tier];
 }
 
+// ─── Bend URL ──────────────────────────────────────────────────────
+const bendState = { url: localStorage.getItem("lumbda_bend_url") || "" };
+const bendUrlEl = document.getElementById("bend-url");
+const bendSaveBtn = document.getElementById("bend-save");
+const bendStateEl = document.getElementById("bend-state");
+if (bendState.url) {
+    bendUrlEl.value = bendState.url;
+    bendStateEl.textContent = "saved";
+}
+function saveBendUrl() {
+    bendState.url = bendUrlEl.value.trim();
+    if (bendState.url) {
+        localStorage.setItem("lumbda_bend_url", bendState.url);
+        bendStateEl.textContent = "saved";
+    } else {
+        localStorage.removeItem("lumbda_bend_url");
+        bendStateEl.textContent = "";
+    }
+    // Push config to any already-spawned workers.
+    for (const w of Object.values(workerState.workers)) {
+        if (w) w.postMessage({ kind: "config", bendUrl: bendState.url });
+    }
+}
+bendSaveBtn.addEventListener("click", saveBendUrl);
+bendUrlEl.addEventListener("keydown", (e) => {
+    if (e.key === "Enter") { e.preventDefault(); saveBendUrl(); }
+});
+
 function runOnTierInWorker(tier, src, onLoading) {
     return new Promise((resolve, reject) => {
         const w = ensureWorker(tier);

www/playground/asm/lumbda-asm.loader.js

@@ -4,18 +4,57 @@
 // Memory layout (mirrors lumbda.wat):
 //   0x10000  output buffer (read after each call)
 //   0x20000  source buffer (write before each call)
+//   0x40000  bend response scratch (host writes here when JS dispatches)
 
 async function _bootstrap() {
     const wasmURL = new URL("./lumbda-asm.wasm", import.meta.url).href;
     const resp = await fetch(wasmURL);
     const bytes = await resp.arrayBuffer();
-    const { instance } = await WebAssembly.instantiate(bytes);
-    const exp = instance.exports;
 
-    exp.lumbda_init();
+    // Closure-captured holder so the imported function can see the
+    // instance's memory after instantiation completes.
+    const refs = { instance: null, bendUrl: null };
+
+    const importObj = {
+        env: {
+            // bend_call(src_ptr, src_len, resp_ptr) -> resp_len.
+            // Synchronous XHR is the only sync HTTP available in workers;
+            // perfect for the WAT tier's blocking eval model.
+            bend_call(srcPtr, srcLen, respPtr) {
+                if (!refs.bendUrl) {
+                    const msg = "no bend URL configured";
+                    const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                    mem.set(new TextEncoder().encode(msg), respPtr);
+                    return msg.length;
+                }
+                const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                const payload = new TextDecoder().decode(mem.slice(srcPtr, srcPtr + srcLen));
+                try {
+                    const xhr = new XMLHttpRequest();
+                    xhr.open("POST", refs.bendUrl, false);  // sync
+                    xhr.setRequestHeader("Content-Type", "text/plain; charset=utf-8");
+                    xhr.send(payload);
+                    const respText = xhr.responseText || "";
+                    const respBytes = new TextEncoder().encode(respText);
+                    new Uint8Array(refs.instance.exports.memory.buffer).set(respBytes, respPtr);
+                    return respBytes.length;
+                } catch (e) {
+                    const err = "bend error: " + (e.message || String(e));
+                    new Uint8Array(refs.instance.exports.memory.buffer)
+                        .set(new TextEncoder().encode(err), respPtr);
+                    return err.length;
+                }
+            },
+        },
+    };
+
+    const { instance } = await WebAssembly.instantiate(bytes, importObj);
+    refs.instance = instance;
+    instance.exports.lumbda_init();
 
     const enc = new TextEncoder();
     const dec = new TextDecoder();
+    const exp = instance.exports;
 
     return {
         async evalLisp(src) {
@@ -32,6 +71,7 @@ async function _bootstrap() {
             const outLen = exp.lumbda_output_len();
             return dec.decode(new Uint8Array(exp.memory.buffer, outPtr, outLen));
         },
+        setBendUrl(url) { refs.bendUrl = url || null; },
     };
 }
 

www/playground/index.html

@@ -59,6 +59,15 @@
   <span id="status" class="status"></span>
 </section>
 
+<section class="bend-bar">
+  <span class="bend-icon" title="gpu-worker bend URL">⚡</span>
+  <label>bend URL
+    <input id="bend-url" type="url" placeholder="https://your-gpu-worker.example/bend  (sets (bend!-call ...) destination)">
+  </label>
+  <button id="bend-save" class="secondary">save</button>
+  <span id="bend-state" class="bend-state"></span>
+</section>
+
 <section class="vault-bar" id="vault-bar" hidden>
   <span class="vault-icon" title="local vault">🔒</span>
   <span id="vault-state" class="vault-state">locked</span>

www/playground/runner.js

@@ -8,6 +8,15 @@ import { createCTier } from "./c/lumbda-c.loader.js";
 import { createAsmTier } from "./asm/lumbda-asm.loader.js";
 
 const cache = {};
+const config = { bendUrl: null };
+
+export function setBendUrl(url) {
+    config.bendUrl = url || null;
+    // Propagate to already-loaded tiers.
+    for (const t of Object.values(cache)) {
+        if (t && t.setBendUrl) t.setBendUrl(config.bendUrl);
+    }
+}
 
 export async function getTier(name, onLoad) {
     if (cache[name]) return cache[name];
@@ -16,6 +25,7 @@ export async function getTier(name, onLoad) {
     else if (name === "c") cache[name] = await createCTier();
     else if (name === "asm") cache[name] = await createAsmTier();
     else throw new Error(`unknown tier: ${name}`);
+    if (cache[name].setBendUrl) cache[name].setBendUrl(config.bendUrl);
     return cache[name];
 }
 

www/playground/style.css

@@ -42,6 +42,12 @@
 
 * { box-sizing: border-box; }
 
+html {
+  /* Default zoom so text is comfortably readable. Native CSS zoom
+   * preserves layout proportions across the whole document. */
+  zoom: 1.33;
+}
+
 html, body {
   margin: 0; padding: 0;
   background: var(--bg);
@@ -189,6 +195,46 @@ header code {
 .controls .status.err  { color: var(--err); }
 .controls .status.ok   { color: var(--green); }
 
+.bend-bar {
+  padding: 0.4rem 1.5rem;
+  border-bottom: 1px solid var(--rule);
+  display: flex; align-items: center; gap: 0.6rem;
+  background: var(--bg);
+  font-size: 0.85em;
+}
+.bend-bar .bend-icon { font-size: 1em; }
+.bend-bar label {
+  flex: 1;
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  color: var(--muted);
+}
+.bend-bar input[type=url] {
+  flex: 1;
+  background: var(--code-bg);
+  border: 1px solid var(--rule);
+  color: var(--fg);
+  padding: 0.3rem 0.5rem;
+  font-family: var(--mono);
+  font-size: 0.9em;
+  border-radius: 3px;
+}
+.bend-bar input[type=url]:focus { outline: none; border-color: var(--green); }
+.bend-bar button {
+  background: transparent;
+  color: var(--green);
+  border: 1px solid var(--green);
+  font-family: var(--mono);
+  font-size: 0.85em;
+  font-weight: 600;
+  padding: 0.3rem 0.8rem;
+  border-radius: 3px;
+  cursor: pointer;
+}
+.bend-bar button:hover { background: var(--code-bg); }
+.bend-bar .bend-state { color: var(--green); font-size: 0.8em; min-width: 4em; }
+
 .vault-bar {
   padding: 0.5rem 1.5rem;
   border-bottom: 1px solid var(--rule);

www/playground/worker.mjs

@@ -3,11 +3,16 @@
 // live ms counter actually ticks AND so cancel works (main thread
 // terminates this worker via worker.terminate()).
 
-import { evalOnTier } from "./runner.js";
+import { evalOnTier, setBendUrl } from "./runner.js";
 
 self.onmessage = async (e) => {
-    const { kind, runId, tier, src } = e.data;
+    const { kind } = e.data;
+    if (kind === "config") {
+        setBendUrl(e.data.bendUrl);
+        return;
+    }
     if (kind !== "eval") return;
+    const { runId, tier, src } = e.data;
     try {
         const output = await evalOnTier(tier, src, (loadingTier) => {
             self.postMessage({ kind: "loading", runId, tier: loadingTier });

www/repl/asm/lumbda-asm.loader.js

@@ -4,18 +4,57 @@
 // Memory layout (mirrors lumbda.wat):
 //   0x10000  output buffer (read after each call)
 //   0x20000  source buffer (write before each call)
+//   0x40000  bend response scratch (host writes here when JS dispatches)
 
 async function _bootstrap() {
     const wasmURL = new URL("./lumbda-asm.wasm", import.meta.url).href;
     const resp = await fetch(wasmURL);
     const bytes = await resp.arrayBuffer();
-    const { instance } = await WebAssembly.instantiate(bytes);
-    const exp = instance.exports;
 
-    exp.lumbda_init();
+    // Closure-captured holder so the imported function can see the
+    // instance's memory after instantiation completes.
+    const refs = { instance: null, bendUrl: null };
+
+    const importObj = {
+        env: {
+            // bend_call(src_ptr, src_len, resp_ptr) -> resp_len.
+            // Synchronous XHR is the only sync HTTP available in workers;
+            // perfect for the WAT tier's blocking eval model.
+            bend_call(srcPtr, srcLen, respPtr) {
+                if (!refs.bendUrl) {
+                    const msg = "no bend URL configured";
+                    const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                    mem.set(new TextEncoder().encode(msg), respPtr);
+                    return msg.length;
+                }
+                const mem = new Uint8Array(refs.instance.exports.memory.buffer);
+                const payload = new TextDecoder().decode(mem.slice(srcPtr, srcPtr + srcLen));
+                try {
+                    const xhr = new XMLHttpRequest();
+                    xhr.open("POST", refs.bendUrl, false);  // sync
+                    xhr.setRequestHeader("Content-Type", "text/plain; charset=utf-8");
+                    xhr.send(payload);
+                    const respText = xhr.responseText || "";
+                    const respBytes = new TextEncoder().encode(respText);
+                    new Uint8Array(refs.instance.exports.memory.buffer).set(respBytes, respPtr);
+                    return respBytes.length;
+                } catch (e) {
+                    const err = "bend error: " + (e.message || String(e));
+                    new Uint8Array(refs.instance.exports.memory.buffer)
+                        .set(new TextEncoder().encode(err), respPtr);
+                    return err.length;
+                }
+            },
+        },
+    };
+
+    const { instance } = await WebAssembly.instantiate(bytes, importObj);
+    refs.instance = instance;
+    instance.exports.lumbda_init();
 
     const enc = new TextEncoder();
     const dec = new TextDecoder();
+    const exp = instance.exports;
 
     return {
         async evalLisp(src) {
@@ -32,6 +71,7 @@ async function _bootstrap() {
             const outLen = exp.lumbda_output_len();
             return dec.decode(new Uint8Array(exp.memory.buffer, outPtr, outLen));
         },
+        setBendUrl(url) { refs.bendUrl = url || null; },
     };
 }
 

www/repl/runner.js

@@ -8,6 +8,15 @@ import { createCTier } from "./c/lumbda-c.loader.js";
 import { createAsmTier } from "./asm/lumbda-asm.loader.js";
 
 const cache = {};
+const config = { bendUrl: null };
+
+export function setBendUrl(url) {
+    config.bendUrl = url || null;
+    // Propagate to already-loaded tiers.
+    for (const t of Object.values(cache)) {
+        if (t && t.setBendUrl) t.setBendUrl(config.bendUrl);
+    }
+}
 
 export async function getTier(name, onLoad) {
     if (cache[name]) return cache[name];
@@ -16,6 +25,7 @@ export async function getTier(name, onLoad) {
     else if (name === "c") cache[name] = await createCTier();
     else if (name === "asm") cache[name] = await createAsmTier();
     else throw new Error(`unknown tier: ${name}`);
+    if (cache[name].setBendUrl) cache[name].setBendUrl(config.bendUrl);
     return cache[name];
 }
 

www/repl/style.css

@@ -42,6 +42,12 @@
 
 * { box-sizing: border-box; }
 
+html {
+  /* Default zoom so text is comfortably readable. Native CSS zoom
+   * preserves layout proportions across the whole document. */
+  zoom: 1.33;
+}
+
 html, body {
   margin: 0; padding: 0;
   background: var(--bg);
@@ -189,6 +195,46 @@ header code {
 .controls .status.err  { color: var(--err); }
 .controls .status.ok   { color: var(--green); }
 
+.bend-bar {
+  padding: 0.4rem 1.5rem;
+  border-bottom: 1px solid var(--rule);
+  display: flex; align-items: center; gap: 0.6rem;
+  background: var(--bg);
+  font-size: 0.85em;
+}
+.bend-bar .bend-icon { font-size: 1em; }
+.bend-bar label {
+  flex: 1;
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  color: var(--muted);
+}
+.bend-bar input[type=url] {
+  flex: 1;
+  background: var(--code-bg);
+  border: 1px solid var(--rule);
+  color: var(--fg);
+  padding: 0.3rem 0.5rem;
+  font-family: var(--mono);
+  font-size: 0.9em;
+  border-radius: 3px;
+}
+.bend-bar input[type=url]:focus { outline: none; border-color: var(--green); }
+.bend-bar button {
+  background: transparent;
+  color: var(--green);
+  border: 1px solid var(--green);
+  font-family: var(--mono);
+  font-size: 0.85em;
+  font-weight: 600;
+  padding: 0.3rem 0.8rem;
+  border-radius: 3px;
+  cursor: pointer;
+}
+.bend-bar button:hover { background: var(--code-bg); }
+.bend-bar .bend-state { color: var(--green); font-size: 0.8em; min-width: 4em; }
+
 .vault-bar {
   padding: 0.5rem 1.5rem;
   border-bottom: 1px solid var(--rule);

www/repl/worker.mjs

@@ -3,11 +3,16 @@
 // live ms counter actually ticks AND so cancel works (main thread
 // terminates this worker via worker.terminate()).
 
-import { evalOnTier } from "./runner.js";
+import { evalOnTier, setBendUrl } from "./runner.js";
 
 self.onmessage = async (e) => {
-    const { kind, runId, tier, src } = e.data;
+    const { kind } = e.data;
+    if (kind === "config") {
+        setBendUrl(e.data.bendUrl);
+        return;
+    }
     if (kind !== "eval") return;
+    const { runId, tier, src } = e.data;
     try {
         const output = await evalOnTier(tier, src, (loadingTier) => {
             self.postMessage({ kind: "loading", runId, tier: loadingTier });