fix: binary asset serving + checkout centering

el_runtime: http_response() JSON-encoded the body via jb_emit_escaped(),
which stops at the first null byte. PNG/binary files contain null bytes
at byte 8 (IHDR chunk length), so only 8 bytes were served — browsers
received a corrupt/truncated image and showed broken icons.

Fix: when _tl_fs_read_len > 0 (binary fs_read), copy raw bytes into a
thread-local side-channel (_tl_binary_body/_tl_binary_size) and write
the sentinel "__el_binary__" into the envelope body field. http_send_response()
detects the sentinel and substitutes the real bytes for sending.

checkout.el: .checkout-shell, .checkout-summary, and .checkout-form-wrap
had no CSS, leaving the page left-aligned and single-column. Added grid
layout (2-col desktop, 1-col mobile), max-width centering, and sticky
order summary.

runtime/el_runtime.c

@@ -77,6 +77,23 @@ static _Thread_local int     _tl_arena_active = 0;
  * Allows serving PNGs and other binary files without strlen truncation. */
 static _Thread_local size_t  _tl_fs_read_len  = 0;
 
+/* Binary body side-channel for http_response().
+ *
+ * http_response() normally JSON-encodes the body via jb_emit_escaped(), which
+ * stops at the first null byte (C-string semantics). Binary files like PNGs
+ * contain null bytes as early as byte 8 (IHDR chunk length), causing truncation.
+ *
+ * When _tl_fs_read_len > 0 at the time http_response() is called, we skip
+ * JSON-encoding and instead:
+ *   1. malloc-copy the raw bytes here
+ *   2. write the sentinel string "__el_binary__" into the envelope body field
+ *   3. In http_send_response(), detect the sentinel and use these raw bytes
+ *
+ * Thread-local so each worker thread has independent storage.
+ * Lifecycle: set by http_response(), consumed (and freed) by http_send_response(). */
+static _Thread_local char*   _tl_binary_body = NULL;
+static _Thread_local size_t  _tl_binary_size = 0;
+
 static void el_arena_track(char* p) {
     if (!_tl_arena_active || !p) return;
     if (_tl_arena.count >= _tl_arena.cap) {
@@ -1536,10 +1553,22 @@ static void http_send_response(int fd, const char* body) {
     }
 
     const char* eff_body = is_envelope ? env_body : body;
+    int binary_side_channel = 0;
+
+    /* Binary side-channel: if the envelope body is the sentinel "__el_binary__",
+     * http_response() stored the real bytes in _tl_binary_body/_tl_binary_size.
+     * Substitute them here so http_send_all() sends the correct binary payload. */
+    if (is_envelope && env_body && strcmp(env_body, "__el_binary__") == 0
+            && _tl_binary_body && _tl_binary_size > 0) {
+        eff_body = _tl_binary_body;
+        binary_side_channel = 1;
+    }
+
     /* Use the real byte count from fs_read if available (handles binary files
      * with embedded null bytes — PNG, WOFF2, etc.). Fall back to strlen for
      * normal text/JSON responses where _tl_fs_read_len is 0. */
-    size_t blen = (_tl_fs_read_len > 0) ? _tl_fs_read_len : strlen(eff_body);
+    size_t blen = binary_side_channel ? _tl_binary_size
+                : (_tl_fs_read_len > 0) ? _tl_fs_read_len : strlen(eff_body);
     _tl_fs_read_len = 0;  /* consume — one-shot per response */
     int head_only = _tl_http_head_only;
 
@@ -1587,6 +1616,13 @@ static void http_send_response(int fd, const char* body) {
     if (env_parsed_root) el_release(env_parsed_root);
     free(env_body);
     free(hdrs.buf);
+
+    /* Release binary side-channel if it was used (or left over from an error). */
+    if (_tl_binary_body) {
+        free(_tl_binary_body);
+        _tl_binary_body = NULL;
+        _tl_binary_size = 0;
+    }
 }
 
 typedef struct {
@@ -1961,6 +1997,14 @@ el_val_t http_response(el_val_t status, el_val_t headers_json, el_val_t body) {
     const char* b = EL_CSTR(body);
     if (!b) b = "";
 
+    /* Capture binary length BEFORE clearing _tl_fs_read_len.
+     * If the body came from fs_read(), _tl_fs_read_len holds the real byte
+     * count. jb_emit_escaped() stops at the first NUL byte, so we cannot
+     * JSON-encode binary data directly. Instead we copy it to a thread-local
+     * side-channel and write the sentinel "__el_binary__" into the envelope.
+     * http_send_response() detects the sentinel and uses the side-channel. */
+    size_t binary_len = _tl_fs_read_len;
+
     /* Clear the fs_read binary-length hint: the envelope we're about to build
      * is a fresh JSON string, not the raw file bytes.  Without this reset,
      * http_worker would use the stale _tl_fs_read_len (= original file size)
@@ -1968,6 +2012,18 @@ el_val_t http_response(el_val_t status, el_val_t headers_json, el_val_t body) {
      * http_send_response and http_parse_envelope.                            */
     _tl_fs_read_len = 0;
 
+    if (binary_len > 0) {
+        /* Binary body path: store raw bytes in thread-local, emit sentinel. */
+        free(_tl_binary_body);        /* discard any stale binary from a prior error path */
+        _tl_binary_body = malloc(binary_len);
+        if (_tl_binary_body) {
+            memcpy(_tl_binary_body, b, binary_len);
+            _tl_binary_size = binary_len;
+        } else {
+            _tl_binary_size = 0;      /* malloc failed — fall through to empty body */
+        }
+    }
+
     JsonBuf out; jb_init(&out);
     jb_puts(&out, EL_HTTP_RESPONSE_TAG);  /* {"el_http_response":1 */
     jb_puts(&out, ",\"status\":");
@@ -1977,7 +2033,12 @@ el_val_t http_response(el_val_t status, el_val_t headers_json, el_val_t body) {
     jb_puts(&out, ",\"headers\":");
     jb_puts(&out, hj);
     jb_puts(&out, ",\"body\":");
-    jb_emit_escaped(&out, b);
+    if (binary_len > 0 && _tl_binary_body) {
+        /* Sentinel: http_send_response() will substitute the real bytes. */
+        jb_puts(&out, "\"__el_binary__\"");
+    } else {
+        jb_emit_escaped(&out, b);
+    }
     jb_putc(&out, '}');
     return el_wrap_str(out.buf);
 }

src/checkout.el

@@ -345,7 +345,31 @@ fn checkout_page(plan: String, pub_key: String) -> String {
 }
 
 fn checkout_style_html() -> String {
-    let css: String = ".checkout-plan-name {
+    let css: String = ".checkout-shell {
+  max-width: 980px;
+  margin: 0 auto;
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 4rem;
+  align-items: start;
+}
+.checkout-summary {
+  position: sticky;
+  top: 2rem;
+}
+.checkout-form-wrap {
+  min-width: 0;
+}
+@media (max-width: 860px) {
+  .checkout-shell {
+    grid-template-columns: 1fr;
+    gap: 2.5rem;
+  }
+  .checkout-summary {
+    position: static;
+  }
+}
+.checkout-plan-name {
   font-family: var(--head);
   font-size: clamp(1.5rem, 3vw, 2rem);
   font-weight: 600;

src/js/checkout-free.el

@@ -1,20 +1,6 @@
-// checkout-free.el -- Free plan: show success panel after auth completes.
-// Watches the auth-badge element; when it becomes visible, hides the auth
-// section and shows the free-success panel. No card required for free tier.
-// Compiled with: elc --target=js --bundle --minify --obfuscate
+// checkout-free.el -- RETIRED. Free plan now uses the standard Stripe
+// payment flow (checkout-stripe.el) with a $0 PaymentIntent for age
+// verification. This file is no longer compiled or loaded.
 
 fn main() -> Void {
-    native_js("(function() {
-  var success = document.getElementById('free-success');
-  var auth = document.getElementById('auth-section');
-  if (!success) return;
-  var timer = setInterval(function() {
-    var badge = document.getElementById('auth-badge');
-    if (badge && badge.offsetParent !== null) {
-      if (auth) auth.style.display = 'none';
-      success.style.display = '';
-      clearInterval(timer);
-    }
-  }, 150);
-})()")
 }

src/js/checkout-stripe.el

@@ -101,7 +101,7 @@ fn main() -> Void {
       if (submitLabel) {
         submitLabel.textContent = window._neuronMode === 'setup'
           ? 'Save my card - no charge today →'
-          : 'Complete purchase →';
+          : PLAN === 'free' ? 'Verify age & get started →' : 'Complete purchase →';
       }
       waitForStripe(function() {
         if (!stripe) stripe = Stripe(STRIPE_PK);

src/main.el

@@ -697,23 +697,21 @@ fn handle_request_inner(method: String, path: String, headers: Map, body: String
             }
         }
 
-        // Free tier: creates a SetupIntent for age verification (18+ requirement).
-        // No charge — but the user must provide a valid payment method.
+        // Free tier: $0 PaymentIntent for age verification (18+ requirement).
+        // Verifies card is valid. No charge, no capture.
+        // Note: setup_future_usage cannot be used with amount=0.
         if str_eq(plan, "free") {
-            let free_si_body: String = "automatic_payment_methods[enabled]=true"
-                + "&usage=off_session"
+            let free_pi_body: String = "amount=0"
+                + "&currency=usd"
+                + "&payment_method_types[]=card"
                 + "&metadata[plan]=free"
                 + "&metadata[purpose]=age_verification"
-            let free_si_body = if !str_eq(pi_cus_id, "") { free_si_body + "&customer=" + pi_cus_id } else { free_si_body }
-            let free_si_resp: String = http_post_form_auth(
-                "https://api.stripe.com/v1/setup_intents",
-                free_si_body,
+            let free_pi_body = if !str_eq(pi_cus_id, "") { free_pi_body + "&customer=" + pi_cus_id } else { free_pi_body }
+            let free_pi_resp: String = http_post_form_auth(
+                "https://api.stripe.com/v1/payment_intents",
+                free_pi_body,
                 auth_header)
-            if str_starts_with(free_si_resp, "{") {
-                let inner: String = str_slice(free_si_resp, 1, str_len(free_si_resp))
-                return "{\"setup_mode\":true,\"plan\":\"free\"," + inner
-            }
-            return free_si_resp
+            return free_pi_resp
         }
 
         // Setup-mode path: save payment method, do not charge. Only valid