Providers stream commentary as cumulative snapshots, and the draft line id was derived from the commentary text, so each snapshot minted a new id and stacked another line instead of replacing the open one. Id-less commentary now remembers its open line and reuses that id when the next snapshot continues it; a snapshot sanitized to nothing no longer clears the line, since only an explicit item id retracts.
Also fixes activation: the commentary gate guessed "partial" when streaming.mode was unset, which made progress.commentary a silent no-op on channels whose own default is progress (Telegram, Discord). It now takes the caller's resolved mode, matching resolveChannelStreamingPreviewToolProgress. Proven live on Telegram: three overlapping commentary lines collapse to one.
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