hermes - 💡(How to fix) Fix Hindsight plugin: sync_turn resends full session transcript on every retain, duplicating content with update_mode=append

sync_turn() accumulates every turn in self._session_turns and never clears the list after a retain call. On the update_mode='append' path (Hindsight >= 0.5.0), this means each retain appends the full growing transcript to the document, not just the new turns since last retain.

In a 30-turn session with retain_every_n_turns=3, retain #1 sends turns 1-3, retain #2 sends turns 1-6, retain #3 sends turns 1-9, etc. The server appends each payload, so turns 1-3 end up in the document 10 times.

Introduced in 3082fa0 (probe API for update_mode='append' support). Before that commit, each retain replaced the document (idempotent). The switch to append semantics didn't adjust _session_turns to only send deltas.

Observed impact

Querying document chunks for a live session (20260511_144205_620bda, 6 chunks) shows identical user turns appearing in multiple chunks:

chunk 0: "Let's reframe from home lab..."
chunk 2: "Let's reframe from home lab..."   # same content

chunk 1: "Rename Bob to..."
chunk 3: "Rename Bob to..."                 # same content

Each duplicated chunk gets independently extracted, producing 3-4x duplicate facts per session. The delta-retain chunk dedup mentioned in vectorize-io/hindsight#932 doesn't prevent this (presumably because chunk boundaries shift as the document grows with each append).

Practical cost: ~80% more extraction LLM tokens than necessary, and a bank full of duplicate memories that the consolidation layer then has to clean up.

Fix

One line after building content in sync_turn():

content = "[" + ",".join(self._session_turns) + "]"
self._session_turns = []  # only send new turns next time; append preserves earlier content server-side

update_mode='append' on the server already preserves prior document content. The client doesn't need to resend it.

The session-switch path (on_session_switch / c38dac74) already flushes _session_turns before clearing, so it handles the edge case of buffered turns at switch time. This fix covers the normal within-session retain path.

Environment

• Hermes: latest main as of 2026-05-11 (a63a2b7)
• Hindsight API: 0.6.1 (self-hosted)
• retain_every_n_turns: 3
• retain_async: true