When internal tools (e.g. TTS) emit MEDIA:/tmp/... with absolute paths,
isValidMedia() correctly rejects them for security. However, the rejected
MEDIA: line was kept as visible text in the output, leaking the path to
the user.
Now strip MEDIA: lines that look like local paths even when the path
is invalid, so they never appear as user-visible text.
Closes#14365
Co-authored-by: Echo Ito <echoito@MacBook-Air.local>