Keep tool calls in history, with placeholder results

History kept only what was said, so after a few factual answers the
model saw no tool behind them and invented the next one: asked for
pending updates it made up counts without calling the tool (1/10 on a
replayed session). Keeping each turn's tool calls brings it back to
10/10. Their results are replaced by a placeholder, which scores the
same and keeps the context close to what it was; a follow-up on an old
result calls the tool again. The window is now the last 10 whole turns.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/AGENTS.md b/AGENTS.md
index 6e66526..9966849 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -479,6 +479,28 @@ of 2000-character results ~4k), so the 20-message window and the
   `stop processing: n_tokens = N, truncated = 0` per request, but it is
   shared with every router client, so it cannot be attributed to the
   assistant. `truncated = 1` there would mean an overflow.
+- 2026-09-28: history now keeps tool calls with placeholder results (see
+  "Tool calls in history"), window 10 whole turns. Each past call adds
+  ~50 tokens, so the worst case goes from ~9k to ~10k (10 turns of 3
+  calls). Full results kept would
+  have been ~22k.
+
+### Tool calls in history (2026-09-28)
+
+"Ci sono aggiornamenti da installare?" after four exchanges (time, mail,
+calc, calendar) got "12 updates, 3 security fixes, a kernel bump" with
+no tool call: invented, the system was up to date. History kept only
+what was said, so the model saw factual answers with no tool behind them
+and copied that. Replayed against the live model, 10 runs each: that
+history 1/10 called `updates`, empty history 10/10; a system prompt
+line saying earlier answers came from hidden tool calls 0/10 (worse);
+the same history with its tool calls kept 10/10, whether results were
+kept whole, cut to 200 characters, or replaced by a placeholder "(shown
+to the user at the time)" (**chosen**, cheapest). With the placeholder, a
+follow-up on an old result ("chi ha mandato la terza email?") calls the
+tool again, 10/10, no invented answer; costs one extra tool call. The
+"never guess" rule alone does not hold once history shows tool-less
+answers.
 
 ### Barge-in (2026-09-26)