fix(tui): render MEDIA: as a clickable file chip, drop audio directive

The agent emits `MEDIA:<path>` to signal file delivery to the gateway,
and `[[audio_as_voice]]` as a voice-delivery hint. The gateway strips
both before sending to Telegram/Discord/Slack, but the TUI was rendering
them raw through markdown — which is also how the intraword underscore
bug originally surfaced (`browser_screenshot_ecc…`).

At the `Md` layer, detect both sentinels on their own line:
- `MEDIA:<path>` → `▸ <path>` with the path rendered literal and wrapped
  in a `Link` for OSC 8 hyperlink support (absolute paths get a
  `file://` URL, so modern terminals make them click-to-open).
- `[[audio_as_voice]]` → dropped silently; it has no meaning in TUI.

Covers tests for quoted/backticked MEDIA variants, Windows drive paths,
whitespace, and the inline-in-prose case (left untouched — still
protected by the intraword-underscore guard).

ui-tui/src/__tests__/markdown.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
-import { INLINE_RE, stripInlineMarkup } from '../components/markdown.js'
+import { AUDIO_DIRECTIVE_RE, INLINE_RE, MEDIA_LINE_RE, stripInlineMarkup } from '../components/markdown.js'
 
 const matches = (text: string) => [...text.matchAll(INLINE_RE)].map(m => m[0])
 
@@ -32,3 +32,25 @@ describe('stripInlineMarkup', () => {
     expect(stripInlineMarkup('__bold__ and foo__bar__')).toBe('bold and foo__bar__')
   })
 })
+
+describe('protocol sentinels', () => {
+  it('captures MEDIA: paths with surrounding quotes or backticks', () => {
+    expect('MEDIA:/tmp/a.png'.match(MEDIA_LINE_RE)?.[1]).toBe('/tmp/a.png')
+    expect('  MEDIA: /home/me/.hermes/cache/screenshots/browser_screenshot_ecc.png  '.match(MEDIA_LINE_RE)?.[1]).toBe(
+      '/home/me/.hermes/cache/screenshots/browser_screenshot_ecc.png'
+    )
+    expect('`MEDIA:/tmp/a.png`'.match(MEDIA_LINE_RE)?.[1]).toBe('/tmp/a.png')
+    expect('"MEDIA:C:\\files\\a.png"'.match(MEDIA_LINE_RE)?.[1]).toBe('C:\\files\\a.png')
+  })
+
+  it('ignores MEDIA: tokens embedded in prose', () => {
+    expect('here is MEDIA:/tmp/a.png for you'.match(MEDIA_LINE_RE)).toBeNull()
+    expect('the media: section is empty'.match(MEDIA_LINE_RE)).toBeNull()
+  })
+
+  it('matches the [[audio_as_voice]] directive', () => {
+    expect(AUDIO_DIRECTIVE_RE.test('[[audio_as_voice]]')).toBe(true)
+    expect(AUDIO_DIRECTIVE_RE.test('  [[audio_as_voice]]  ')).toBe(true)
+    expect(AUDIO_DIRECTIVE_RE.test('audio_as_voice')).toBe(false)
+  })
+})