fix(background-review): freeze review fork tool snapshot generation against compaction refresh

Freezes review_agent._tool_snapshot_generation to _FROZEN_TOOL_SNAPSHOT_GENERATION
(2_147_483_647) when inheriting the parent tool surface for same-model cache parity.

When in-place compaction boundaries trigger refresh_agent_mcp_tools(content_aware=True),
the staleness guard in _publish_tool_snapshot refuses the rebuild (snapshot_generation < published_gen),
preventing agent.tools from being reconstructed from the raw registry and preserving
inherited memory-provider and late tools across compaction boundaries (#103579).

Adds unit regression test verifying tool preservation across content_aware refresh.

Co-authored-by: joaomarcos <joaomarcosdias444@gmail.com>

agent/background_review.py

@@ -842,6 +842,13 @@ def _fork_init_kwargs(agent: Any, rt: Dict[str, Any], routed: bool, max_iteratio
     return kwargs
 
 
+# Sentinel generation above any live registry generation. Mid-review compaction
+# boundaries re-run refresh_agent_mcp_tools(content_aware=True); freezing the
+# snapshot generation prevents compaction from rebuilding agent.tools and dropping
+# inherited provider tools (#103579).
+_FROZEN_TOOL_SNAPSHOT_GENERATION: int = 2_147_483_647
+
+
 def _inherit_parent_tool_surface(review_agent: Any, agent: Any) -> None:
     """Copy the parent's advertised tools for a same-model cache-parity fork.
 
@@ -851,6 +858,10 @@ def _inherit_parent_tool_surface(review_agent: Any, agent: Any) -> None:
     restricted by the thread whitelist. Copying the whole surface covers every
     dynamically injected tool (memory-provider, late MCP, and plugin-registered),
     not just memory tools.
+
+    Freezes ``_tool_snapshot_generation`` so mid-review compaction boundaries
+    (which invoke ``refresh_agent_mcp_tools(content_aware=True)``) refuse the
+    rebuild and do not clobber the inherited tools (#103579).
     """
     parent_tools = getattr(agent, "tools", None)
     if not isinstance(parent_tools, (list, tuple)) or not parent_tools:
@@ -863,6 +874,7 @@ def _inherit_parent_tool_surface(review_agent: Any, agent: Any) -> None:
         and isinstance(entry.get("function"), dict)
         and isinstance(entry["function"].get("name"), str)
     }
+    review_agent._tool_snapshot_generation = _FROZEN_TOOL_SNAPSHOT_GENERATION
 
 
 def build_cache_parity_fork(

tests/run_agent/test_background_review_cache_parity.py

@@ -103,6 +103,7 @@ def _make_recorder_class(captured=None, record_on_run=()):
             self.session_id = None
             self.tools = None
             self.valid_tool_names = set()
+            self._tool_snapshot_generation = 0
             self.ephemeral_system_prompt = kwargs.get("ephemeral_system_prompt")
 
         def run_conversation(self, *args, **kwargs):
@@ -407,3 +408,48 @@ def test_routed_review_fork_does_not_inherit_tool_surface():
         assert routed
         assert fork.tools is None
 
+
+def test_review_fork_inherited_tools_survive_compaction_refresh():
+    """Inherited tools survive mid-review compaction refresh (#103579).
+
+    Acceptance criterion 1 requires the fork to advertise the same tools[] as
+    the parent when targeting the same cache scope. Mid-review compaction
+    boundaries invoke refresh_agent_mcp_tools(content_aware=True), which re-reads
+    the live registry and drops memory provider tools unless the snapshot
+    generation staleness check refuses the rebuild.
+    """
+    import run_agent
+    from agent.background_review import build_cache_parity_fork
+    from tools.mcp_tool_agent import refresh_agent_mcp_tools
+
+    agent = _make_agent_stub(run_agent.AIAgent)
+    parent_tools = [
+        {"type": "function", "function": {"name": "terminal_command"}},
+        {"type": "function", "function": {"name": "read_file"}},
+        {"type": "function", "function": {"name": "memory"}},
+        {"type": "function", "function": {"name": "fact_store"}},
+        {"type": "function", "function": {"name": "fact_feedback"}},
+    ]
+    agent.tools = parent_tools
+
+    _Recorder = _make_recorder_class()
+
+    with patch.object(run_agent, "AIAgent", _Recorder):
+        fork, _rt, routed = build_cache_parity_fork(agent, max_iterations=5)
+        assert not routed
+        assert fork._tool_snapshot_generation == 2_147_483_647
+        assert [t["function"]["name"] for t in fork.tools] == [
+            "terminal_command", "read_file", "memory", "fact_store", "fact_feedback"
+        ]
+
+        # Simulate mid-review compaction boundary tool refresh
+        added = refresh_agent_mcp_tools(fork, content_aware=True)
+        assert added == set()
+        assert [t["function"]["name"] for t in fork.tools] == [
+            "terminal_command", "read_file", "memory", "fact_store", "fact_feedback"
+        ]
+        assert fork.valid_tool_names == {
+            "terminal_command", "read_file", "memory", "fact_store", "fact_feedback"
+        }
+
+