Compaction: the model's notes replace the middle of a long run (#158)

Before each driver call, over compact_at (0.6) of the prompt budget, the
same model is asked for notes over the very request it was about to get,
plus one message, so the server's cache covers all but the notes. The notes,
with code's list of the calls they replace, become a compaction event that
renders in place of its range, keeping word for word what started the work
and the last few turns. Rare, large steps keep the prompt's start unchanged
between them. A later compaction folds in the earlier; one from an earlier
run's view is hidden.

Failed notes are logged and fitting takes over. Fitting now applies
compactions before it measures, records what it cuts (Trim) and logs each
cut as context.trimmed. Wired into both agents' drivers and the benchmark;
nisse-dev's helper loop is a follow-up.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J5Utyfzw7gF7UhjRDEtjTk

nisse-core/src/nisse_core/loop/driver.py

@@ -2,7 +2,8 @@
 tool, runs out of turns, or is stopped.
 
 Everything the run does is written to the item's transcript as the driver
-(L7), and every model call sees the driver's view of it (L6). Execution tools
+(L7), and every model call sees the driver's view of it (L6), compacted
+when it grows long (``compact``). Execution tools
 go to the item's executor, on its tool VM (L13); control tools are answered
 here, and a waiting one ends the run, so the scheduler can put it to the
 operator. Which tools wait is the agent's: each run is told.
@@ -14,6 +15,7 @@ from typing import Any, Literal, Protocol
 
 from nisse_core.log.canonical import AssistantText, Fact, ToolCall, ToolResult
 from nisse_core.loop.tools import names
+from nisse_core.models.compact import Compactor
 from nisse_core.models.llm import LLMClient, LLMError
 from nisse_core.state.cancel import Cancel, skip_calls
 from nisse_core.state.store import Transcript
@@ -82,8 +84,10 @@ class Driver:
         max_turns: int = DEFAULT_MAX_TURNS,
         cancel: Cancel | None = None,
         failure_limit: int = 0,  # 0: no limit
+        compactor: Compactor | None = None,
     ) -> None:
         self._client = client
+        self._compactor = compactor
         self._model = model
         self._max_turns = max_turns
         self._failure_limit = failure_limit
@@ -123,6 +127,12 @@ class Driver:
             # L2: stop takes effect at the next tool boundary.
             if self._cancel.requested:
                 return RunOutcome("stopped", note=f"before turn {turn + 1}")
+            if self._compactor is not None:
+                # Not a turn: the model's notes replace the middle of a long
+                # run before it outgrows the window (L6).
+                self._compactor.compact(
+                    transcript, system=system, tools=tools, model=model
+                )
             try:
                 produced = self._client.complete(
                     transcript.view(), tools=tools, model=model, system=system