diff --git a/tests/agents/test_token_estimation_consistency.py b/tests/agents/test_token_estimation_consistency.py
new file mode 100644
index 000000000..51ea68f7e
--- /dev/null
+++ b/tests/agents/test_token_estimation_consistency.py
@@ -0,0 +1,52 @@
+"""Tests for token estimation consistency across modules.
+
+Ensures file_operations._read_file and BaseAgent.estimate_token_count
+use the same chars-per-token heuristic to prevent unexpected early
+compaction triggered by estimation mismatch.
+"""
+
+import math
+
+from code_puppy.agents.agent_code_puppy import CodePuppyAgent
+
+
+class TestTokenEstimationConsistency:
+    """Token estimation should be consistent between file_operations and BaseAgent."""
+
+    def test_estimate_token_count_matches_file_operations_heuristic(self):
+        """
+        BaseAgent.estimate_token_count and file_operations._read_file
+        must use the same 2.5 chars/token heuristic.
+        """
+        agent = CodePuppyAgent()
+        content = "x" * 1000
+
+        base_agent_estimate = agent.estimate_token_count(content)
+        file_ops_estimate = math.floor(len(content) / 2.5)
+
+        assert base_agent_estimate == file_ops_estimate
+
+    def test_estimation_consistent_across_content_sizes(self):
+        """
+        Consistency holds across small, medium, and large content sizes.
+        """
+        agent = CodePuppyAgent()
+
+        for size in [100, 1000, 10000, 25000]:
+            content = "x" * size
+            base_agent_estimate = agent.estimate_token_count(content)
+            file_ops_estimate = math.floor(len(content) / 2.5)
+            assert base_agent_estimate == file_ops_estimate, (
+                f"Mismatch at size {size}: "
+                f"base_agent={base_agent_estimate}, "
+                f"file_ops={file_ops_estimate}"
+            )
+
+    def test_minimum_token_count_is_one(self):
+        """
+        Both estimators enforce a minimum of 1 token even for empty content.
+        """
+        agent = CodePuppyAgent()
+
+        result = agent.estimate_token_count("")
+        assert result >= 1
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