fix(hooks,mobile): the merge-time items from the #367 and #368 reviews

#367 (UserPromptSubmit hook): `hook:prompt_submitted` went on the wire
unregistered; it is now in both SSE registries (158 = 158), and the hook only
lands in the run summary when the conversation actually moved, since one row
per prompt would evict useful rows from the 1000-event FIFO and clutter the
Summary timeline and /api/search.

#368 (Add Case header submit): the pending-state dimming targeted the footer
button, which the <=860px layout hides, so on a phone the only visible submit
control stayed at full brightness while a clone ran. The header button now
dims too, and a static test pins the header-submit contract so it cannot
silently disappear again.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

test/create-case-modal-structure.test.ts

@@ -0,0 +1,59 @@
+/**
+ * @fileoverview Static guard for the Add Case modal's submit controls (#368).
+ *
+ * Below 860px the shared set-* surface hides the modal footer, and for eight
+ * releases that footer held the only Create/Clone/Link button, so no case could
+ * be added from a phone and nothing failed. This pins the contract that fixed it:
+ * a header submit button exists after the close button, and the two JS paths
+ * that toggle submit state drive BOTH buttons.
+ */
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+
+const publicDir = resolve(import.meta.dirname, '../src/web/public');
+const html = readFileSync(resolve(publicDir, 'index.html'), 'utf8');
+const sessionUi = readFileSync(resolve(publicDir, 'session-ui.js'), 'utf8');
+const mobileCss = readFileSync(resolve(publicDir, 'mobile.css'), 'utf8');
+
+function caseModal(): string {
+  const start = html.indexOf('<div class="modal" id="createCaseModal">');
+  expect(start).toBeGreaterThan(-1);
+  const next = html.indexOf('<div class="modal"', start + 1);
+  return html.slice(start, next === -1 ? html.length : next);
+}
+
+function methodBody(signature: string): string {
+  const start = sessionUi.indexOf(`\n  ${signature} {`);
+  expect(start, `${signature} not found in session-ui.js`).toBeGreaterThan(-1);
+  return sessionUi.slice(start, sessionUi.indexOf('\n  },', start));
+}
+
+describe('Add Case modal submit controls', () => {
+  it('hides the footer on phones, so the header must carry a submit button', () => {
+    expect(mobileCss).toMatch(
+      /:is\(#appSettingsModal, #sessionOptionsModal, #createCaseModal\) \.set-foot \{\s*display: none;/
+    );
+    const modal = caseModal();
+    const head = modal.slice(0, modal.indexOf('<div class="set-body">'));
+    const closeIdx = head.indexOf('class="modal-close"');
+    const saveIdx = head.indexOf('class="set-head-save" id="caseModalSubmitMobile" onclick="app.submitCaseModal()"');
+    expect(closeIdx).toBeGreaterThan(-1);
+    expect(saveIdx).toBeGreaterThan(-1);
+    // Close stays first in the DOM; row-reverse paints Save to its left.
+    expect(closeIdx).toBeLessThan(saveIdx);
+    expect(modal).toContain('id="caseModalSubmit" onclick="app.submitCaseModal()"');
+  });
+
+  it('drives the footer and header submit buttons together', () => {
+    for (const sig of ['switchCaseModalTab(tabName)', 'async submitCaseModal()']) {
+      const body = methodBody(sig);
+      expect(body, sig).toContain("'caseModalSubmit'");
+      expect(body, sig).toContain("'caseModalSubmitMobile'");
+    }
+  });
+
+  it('dims the header button while a submit is pending, where it is the only one visible', () => {
+    expect(mobileCss).toMatch(/#createCaseModal \.set-head-save\.loading \{\s*opacity: 0\.6;\s*pointer-events: none;/);
+  });
+});