The [Replying to: "..."] prefix is disambiguation, not deduplication. When
a user explicitly replies to a prior message, the agent needs a pointer to
which specific message they're referencing — even when the quoted text
already exists somewhere in history. History can contain the same or
similar text multiple times; without an explicit pointer the agent has to
guess (or answer for both subjects), and the reply signal is silently
dropped.
Example: in a conversation comparing Japan and Italy, replying to the
"Japan is great for culture..." message and asking "What's the best time
to go?" — previously the found_in_history check suppressed the prefix
because the quoted text was already in history, leaving the agent to
guess which destination the user meant. Now the pointer is always present.
Drops the found_in_history guard added in #1594. Token overhead is
minimal (snippet capped at 500 chars on the new user turn; cached prefix
unaffected). Behavior becomes deterministic: reply sent ⇒ pointer present.
Thanks to smartyi for flagging this.
