Post-#48648, oversized mid-stream edits truncate to a 4096-char preview
instead of splitting. But when rich messages raise the consumer's overflow
budget to 32k, the consumer keeps accumulating past 4096 and keeps issuing
progressive edits every edit_interval — each one truncating to the SAME
preview text. Telegram counts every one of those no-op requests against the
flood budget: a long streamed reply fires ~1 identical edit per 0.8s for
the rest of the stream, trips flood control (200s+ penalties), and the
final delivery hangs behind inline flood sleeps. Users see the bot stuck
'streaming' and the chat unresponsive.
Fix at the chokepoint: track the last truncated preview per
(chat_id, message_id) and skip the API call when the new truncation is
identical. Previews still update when the visible prefix actually changes
(e.g. chunk-count marker 1/2 → 1/3). State clears on finalize and when
content shrinks back under the cap, so dedup can never mask a real edit.
Live repro: 19,956-char streamed reply, transport=edit, rich available —
4x flood-control hits within ~700ms, 250s penalties, hung final delivery.
E2E harness on the same stream: 14 edit calls on main vs 7 with the fix
(the delta is pure no-op duplicates; scales with stream length).
a0a3c716fc