send_slash_confirm cut the RAW message to 3800 chars and only then ran format_message,
whose MarkdownV2 escaping expands text (3800 dots -> 7600 chars), so the button card could
still exceed the 4096 cap and fail exactly like the approval card this branch fixed. It now
fits the message with the shared _ea_fit bisection measured after format_message (the
suffix's own rendering is reserved from the budget).
_ea_fit takes an optional `escape` renderer (default _ea_escape) and measures in the
adapter's message_len_fn units, and the Telegram command budget sums the framing with
utf16_len, so astral chars (emoji) are budgeted the way the adapter's 4096 chunker counts
them (len() undercounted them by half).
Tests: slash-confirm preview for a 3800-char message and the approval card for an
emoji-dense command both stay <= 4096 UTF-16 units (red before, green after).
edd9fd66a4