feat(config): auto_evict_tool_use_blocks — strip tool_use blocks after every turn

New Config field auto_evict_tool_use_blocks (default False). When True,
the agent strips tool_use blocks from the just-persisted assistant row at
the end of every turn, scoped to that row only (same pattern as
auto_evict_after_write). Pinned rows skipped. ~870 bytes freed per block
on average; safe because the model has already consumed the results by the
time eviction fires.

Enabled on all five persistent panel configs: substrate, theseus,
majordomo, cognition-researcher, herald.

3 new tests; 373 passed, 5 skipped.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Workspace User

src/mnemara/agent.py

@@ -345,6 +345,25 @@ async def _stamping_on_tool_result(
                 # Eviction failures must never crash a turn; audit-trail
                 # eviction is opportunistic.
                 log("auto_evict_pairs_error", error=str(exc))
+        # Auto-evict tool_use blocks: if the toggle is on, strip all tool_use
+        # blocks from the just-persisted assistant row after every turn.
+        # ~870 bytes per block on average; safe since the model has already
+        # consumed the results. Pinned rows skipped.
+        if getattr(self.cfg, "auto_evict_tool_use_blocks", False):
+            try:
+                tu_result = self.store.evict_tool_use_blocks(
+                    ids=[assistant_row_id],
+                    skip_pinned=True,
+                )
+                if tu_result.get("blocks_evicted", 0) > 0:
+                    log(
+                        "auto_evict_tool_use",
+                        blocks=tu_result["blocks_evicted"],
+                        rows=tu_result["rows_modified"],
+                        bytes_freed=tu_result["bytes_freed"],
+                    )
+            except Exception as exc:
+                log("auto_evict_tool_use_error", error=str(exc))
         # Compress repeated Read results after every turn when the flag is on.
         # Outside the auto_evict_after_write guard so it fires on read-heavy
         # turns too, not just write turns. compress_repeated_reads is

src/mnemara/config.py

@@ -146,6 +146,14 @@ class Config:
     # wherever the tool wrote; only the in-context audit body goes.
     # Off by default; opt-in per instance.
     auto_evict_after_write: bool = False
+    # v0.3.2b — auto-evict tool_use blocks after every turn.
+    # When True, after each turn the tool_use blocks from the just-persisted
+    # assistant row are stripped entirely (audit-trail loss; see
+    # evict_tool_use_blocks for the trade-off note). High byte savings
+    # (~870 bytes per call on average) with zero effect on the turn that just
+    # completed — the model has already processed the results. Pinned rows
+    # are always skipped. Off by default; opt-in per instance.
+    auto_evict_tool_use_blocks: bool = False
     # v0.3.3 — token-aware row-cap slack
     # When > 0, the cap-FIFO eviction loop allows n_turns to exceed
     # max_window_turns by up to this many rows, BUT only when current
@@ -323,6 +331,7 @@ def from_dict(cls, d: dict[str, Any]) -> "Config":
             rag_auto_index_memory=bool(d.get("rag_auto_index_memory", True)),
             rag_auto_index_wiki=bool(d.get("rag_auto_index_wiki", True)),
             auto_evict_after_write=bool(d.get("auto_evict_after_write", False)),
+            auto_evict_tool_use_blocks=bool(d.get("auto_evict_tool_use_blocks", False)),
             row_cap_slack_when_token_headroom=int(
                 d.get("row_cap_slack_when_token_headroom", 0)
             ),

tests/test_smoke.py

@@ -4671,6 +4671,34 @@ def test_config_auto_evict_after_write_missing_field_defaults_false():
     assert cfg.auto_evict_after_write is False
 
 
+def test_config_auto_evict_tool_use_blocks_default_false():
+    from mnemara.config import Config
+
+    cfg = Config()
+    assert cfg.auto_evict_tool_use_blocks is False
+
+
+def test_config_auto_evict_tool_use_blocks_round_trips_through_dict():
+    from mnemara.config import Config
+
+    cfg = Config()
+    cfg.auto_evict_tool_use_blocks = True
+    d = cfg.to_dict()
+    assert d["auto_evict_tool_use_blocks"] is True
+
+    cfg2 = Config.from_dict(d)
+    assert cfg2.auto_evict_tool_use_blocks is True
+
+
+def test_config_auto_evict_tool_use_blocks_missing_field_defaults_false():
+    """Pre-existing config.json files without the field load as False."""
+    from mnemara.config import Config
+
+    minimal = {"role_doc_path": "", "model": "claude-opus-4-7"}
+    cfg = Config.from_dict(minimal)
+    assert cfg.auto_evict_tool_use_blocks is False
+
+
 def test_config_default_includes_evict_write_pairs_policy():
     """Fresh instances get EvictWritePairs allowlisted by default."""
     from mnemara.config import Config