When echoTranscript is enabled in tools.media.audio config, the
transcription text is sent back to the originating chat immediately
after successful audio transcription — before the agent processes it.
This lets users verify what was heard from their voice note.
Changes:
- config/types.tools.ts: add echoTranscript (bool) and echoFormat
(string template) to MediaUnderstandingConfig
- media-understanding/apply.ts: sendTranscriptEcho() helper that
resolves channel/to from ctx, guards on isDeliverableMessageChannel,
and calls deliverOutboundPayloads best-effort
- config/schema.help.ts: help text for both new fields
- config/schema.labels.ts: labels for both new fields
- media-understanding/apply.echo-transcript.test.ts: 10 vitest cases
covering disabled/enabled/custom-format/no-audio/failed-transcription/
non-deliverable-channel/missing-from/OriginatingTo/delivery-failure
Default echoFormat: '📝 "{transcript}"'
Closes#32102
