From c696a5fd9cf7ffaf32efec10a4a2a48255217f54 Mon Sep 17 00:00:00 2001
From: kshitijk4poor <82637225+kshitijk4poor@users.noreply.github.com>
Date: Fri, 31 Jul 2026 16:10:12 +0530
Subject: [PATCH] fix(agent): harden the finalize-turn micro-compaction gate
 against duck-typed compressors
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tests/run_agent/test_proactive_prune_loop_wiring.py builds agents with a
MagicMock compressor; getattr(mock, '_micro_compact_enabled', False)
returns a truthy auto-attribute, so the hook called _micro_compact on the
mock and spliced its (empty-iterating) return over the transcript —
wiping all messages before persist (CI slice 7/8 failure).

Gate now requires _micro_compact_enabled is True, a callable
_micro_compact, and a non-empty list result before touching messages.
Same hardening protects production plugin context engines that don't
subclass ContextCompressor.
---
 agent/turn_finalizer.py | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/agent/turn_finalizer.py b/agent/turn_finalizer.py
index 110a104c46c..5078eed9d3e 100644
--- a/agent/turn_finalizer.py
+++ b/agent/turn_finalizer.py
@@ -358,13 +358,21 @@ def finalize_turn(
         if not interrupted and not failed:
             try:
                 _compressor = getattr(agent, "context_compressor", None)
+                # Strict `is True` + isinstance gates: plugin context engines
+                # (and MagicMock compressors in tests) satisfy getattr/duck
+                # checks with truthy auto-attributes — a bare truthiness check
+                # here called _micro_compact on a mock and spliced its (empty-
+                # iterating) return value over the transcript, wiping it.
                 if (
                     _compressor
-                    and getattr(_compressor, '_micro_compact_enabled', False)
+                    and getattr(_compressor, '_micro_compact_enabled', False) is True
+                    and callable(getattr(_compressor, '_micro_compact', None))
                     and final_response
                 ):
                     _before = len(messages)
-                    messages[:] = _compressor._micro_compact(messages) or messages
+                    _compacted = _compressor._micro_compact(messages)
+                    if isinstance(_compacted, list) and _compacted:
+                        messages[:] = _compacted
                     _after = len(messages)
                     if _before != _after:
                         logger.info(