Fix invisible text in composer code-block textarea

web/src/components/MessageInput.svelte

@@ -1267,6 +1267,7 @@
           {:else}{seg.text}{/if}{/each}{#if inputValue.endsWith('\n')}<span class="overlay-trailing-newline"> </span>{/if}</div>
       <textarea
         bind:this={inputEl}
+        class="inline-textarea"
         rows="1"
         placeholder="Message #{channelName}..."
         bind:value={inputValue}
@@ -1767,7 +1768,14 @@
     color: transparent;
   }
 
-  .input-wrap textarea {
+  /* Overlay-transparency rules are SCOPED to the inline textarea only
+     (.inline-textarea). The inline textarea is the "transparent-glyph +
+     .input-overlay" surface: its own glyphs MUST stay transparent so only
+     the overlay paints visible, syntax-highlighted text. Scoping by class
+     (instead of the broad `.input-wrap textarea`) keeps these rules from
+     bleeding onto the dedicated `.block-textarea`, which is a normal visible
+     textarea and was being forced transparent by the cascade. */
+  .input-wrap textarea.inline-textarea {
     width: 100%;
     background: none;
     border: none;
@@ -1807,17 +1815,17 @@
   }
 
   /* WebKit / Blink: remove the scrollbar entirely (see scrollbar-width above). */
-  .input-wrap textarea::-webkit-scrollbar {
+  .input-wrap textarea.inline-textarea::-webkit-scrollbar {
     width: 0;
     height: 0;
   }
 
-  .input-wrap textarea:focus-visible {
+  .input-wrap textarea.inline-textarea:focus-visible {
     outline: none !important;
     box-shadow: none !important;
   }
 
-  .input-wrap textarea::placeholder {
+  .input-wrap textarea.inline-textarea::placeholder {
     color: var(--text-faint);
   }
 
@@ -1830,7 +1838,7 @@
      reported when highlighting. Keeping it transparent means selecting only
      paints the semi-transparent ember background tint over the overlay's
      colored glyphs — no doubling, ever. */
-  .input-wrap textarea::selection {
+  .input-wrap textarea.inline-textarea::selection {
     background: rgba(245, 158, 11, 0.32);
     color: transparent;
   }
@@ -1909,6 +1917,15 @@
     box-shadow: none !important;
   }
 
+  /* The block textarea is a NORMAL visible textarea (not the overlay surface),
+     so its selection paints VISIBLE glyphs over the ember tint, the opposite
+     of the inline `.inline-textarea::selection` rule, which keeps selected
+     glyphs transparent to avoid doubling against the overlay. */
+  .block-textarea::selection {
+    background: rgba(245, 158, 11, 0.32);
+    color: var(--code-block-fg, var(--text-primary));
+  }
+
   .input-actions {
     display: flex;
     gap: 2px;

web/tests/message-input-block-textarea-visible.spec.js

@@ -0,0 +1,164 @@
+// Regression test for the "invisible code-block text" bug.
+//
+// The inline composer textarea uses a "transparent-glyph + overlay" technique:
+// its own glyphs are `color: transparent` and the separate `.input-overlay`
+// paints the visible, syntax-highlighted text. That transparency rule used to
+// be written as the broad descendant selector `.input-wrap textarea`
+// (specificity 0,1,1). The dedicated block-mode textarea (`.block-textarea`,
+// specificity 0,1,0) lives INSIDE `.input-wrap`, so the broad rule beat its
+// own `color` and forced its glyphs transparent, so typed code was invisible.
+//
+// The fix scopes the transparency rules to the inline textarea via a dedicated
+// `.inline-textarea` class. This test proves the CASCADE OUTCOME (not merely
+// that a class exists): it parses the component's real <style> rules and uses
+// `element.matches()` against the live rendered DOM. The rendered elements keep
+// their authored classes (plus Svelte's scope class) and are attached to the
+// document, so descendant combinators like `.input-wrap textarea.inline-textarea`
+// resolve exactly as the browser cascade would when deciding applicability.
+
+import { describe, it, expect, afterEach } from 'vitest';
+import { render, cleanup, fireEvent } from '@testing-library/svelte';
+import { tick } from 'svelte';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, resolve } from 'node:path';
+
+import MessageInput from '../src/components/MessageInput.svelte';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const COMPONENT_PATH = resolve(__dirname, '../src/components/MessageInput.svelte');
+
+const PARTICIPANTS = {
+  'phil-key': { key: 'phil-key', name: 'phil', type: 'human', connections: { 'web-1': {} } },
+};
+
+function makeStore() {
+  return {
+    participants: PARTICIPANTS,
+    userProfile: { key: 'phil-key', name: 'phil', type: 'human' },
+    sendMessage: () => {},
+    notifyTyping: () => {},
+  };
+}
+
+/**
+ * Parse the component's <style> block into a flat list of
+ * { selector, declarations } records. Comments are stripped first; the CSS in
+ * this component is flat (no nested rules) so a single brace pass is exact.
+ */
+function parseStyleRules() {
+  const src = readFileSync(COMPONENT_PATH, 'utf-8');
+  const styleMatch = src.match(/<style[^>]*>([\s\S]*?)<\/style>/);
+  if (!styleMatch) throw new Error('no <style> block found in MessageInput.svelte');
+  const css = styleMatch[1].replace(/\/\*[\s\S]*?\*\//g, '');
+  const rules = [];
+  const re = /([^{}]+)\{([^{}]*)\}/g;
+  let m;
+  while ((m = re.exec(css)) !== null) {
+    const selector = m[1].trim();
+    const declarations = m[2].trim();
+    if (selector) rules.push({ selector, declarations });
+  }
+  return rules;
+}
+
+/** Pull the `color:` value out of a declaration block, or null if absent. */
+function colorOf(declarations) {
+  const m = declarations.match(/(?:^|;)\s*color\s*:\s*([^;]+?)\s*(?:;|$)/);
+  return m ? m[1].trim() : null;
+}
+
+/** matches() that swallows pseudo-element selectors jsdom can't evaluate. */
+function matchesSafe(el, selector) {
+  try {
+    return el.matches(selector);
+  } catch {
+    return false;
+  }
+}
+
+async function enterBlockMode() {
+  const store = makeStore();
+  const { container } = render(MessageInput, {
+    props: { store, channelName: 'general', typingUsers: [], onOpenEmoji: () => {} },
+  });
+  const inline = container.querySelector('textarea[data-testid="message-input"]');
+  // Trigger B: ``` on its own line + Shift+Enter opens the dedicated block textarea.
+  inline.value = '```';
+  inline.setSelectionRange(3, 3);
+  await fireEvent.input(inline, { target: inline });
+  await tick();
+  await fireEvent.keyDown(inline, { key: 'Enter', shiftKey: true });
+  await tick();
+  await Promise.resolve();
+  await tick();
+  const block = container.querySelector('[data-testid="block-textarea"]');
+  return { container, inline, block };
+}
+
+afterEach(() => cleanup());
+
+describe('MessageInput block textarea visibility (regression: invisible code-block text)', () => {
+  it('block textarea glyph color is NOT forced transparent by the inline overlay rules', async () => {
+    const { inline, block } = await enterBlockMode();
+    expect(block).toBeTruthy();
+
+    const rules = parseStyleRules();
+    // Base color rules only (drop pseudo-element selectors like ::selection).
+    const colorRules = rules
+      .map((r) => ({ selector: r.selector, color: colorOf(r.declarations) }))
+      .filter((r) => r.color !== null && !r.selector.includes('::'));
+
+    const transparentRules = colorRules.filter((r) => r.color === 'transparent');
+    const visibleRules = colorRules.filter((r) => r.color !== 'transparent');
+
+    // Sanity: the transparent-glyph overlay technique is still present.
+    expect(transparentRules.length).toBeGreaterThan(0);
+
+    // CASCADE OUTCOME 1, the bug: NO transparent-color rule may apply to the
+    // block textarea. If none match, it cannot be transparent at any specificity.
+    for (const r of transparentRules) {
+      expect(
+        matchesSafe(block, r.selector),
+        `block textarea must not match transparent-color rule "${r.selector}"`,
+      ).toBe(false);
+    }
+
+    // CASCADE OUTCOME 2: the block textarea is targeted by a VISIBLE color rule
+    // (its own `.block-textarea` rule), so its glyphs render.
+    expect(visibleRules.some((r) => matchesSafe(block, r.selector))).toBe(true);
+
+    // CASCADE OUTCOME 3: the inline overlay technique is unchanged: the inline
+    // textarea IS still targeted by a transparent-glyph rule.
+    expect(transparentRules.some((r) => matchesSafe(inline, r.selector))).toBe(true);
+    // ...and is NOT targeted by any visible-color textarea rule that would
+    // defeat the overlay (only the overlay paints inline text).
+    const inlineTextareaVisible = visibleRules.filter(
+      (r) => matchesSafe(inline, r.selector) && /textarea/.test(r.selector),
+    );
+    expect(inlineTextareaVisible).toHaveLength(0);
+  });
+
+  it('focused DOM check: block has block-textarea (not inline-textarea); inline has inline-textarea', async () => {
+    const { inline, block } = await enterBlockMode();
+    expect(block).toBeTruthy();
+    expect(block.classList.contains('block-textarea')).toBe(true);
+    expect(block.classList.contains('inline-textarea')).toBe(false);
+    expect(inline.classList.contains('inline-textarea')).toBe(true);
+  });
+
+  it('block selection paints VISIBLE glyphs while the inline selection stays transparent', async () => {
+    await enterBlockMode();
+    const rules = parseStyleRules();
+
+    const blockSelection = rules.find((r) => /\.block-textarea[^,{]*::selection/.test(r.selector));
+    expect(blockSelection, '.block-textarea::selection rule must exist').toBeTruthy();
+    expect(colorOf(blockSelection.declarations)).not.toBe('transparent');
+
+    const inlineSelection = rules.find((r) => /\.inline-textarea[^,{]*::selection/.test(r.selector));
+    expect(inlineSelection, '.inline-textarea::selection rule must exist').toBeTruthy();
+    // Load-bearing: keeping the inline selected glyphs transparent prevents the
+    // "doubled text" regression (overlay + textarea both painting).
+    expect(colorOf(inlineSelection.declarations)).toBe('transparent');
+  });
+});