diff --git a/headroom/learn/_shared.py b/headroom/learn/_shared.py
index cb3a926f6..ba6f9944e 100644
--- a/headroom/learn/_shared.py
+++ b/headroom/learn/_shared.py
@@ -85,6 +85,14 @@ def classify_error(content: str) -> ErrorCategory:
     return ErrorCategory.UNKNOWN
 
 
+# "exit code" only signals an error for a NONZERO code. Agent harnesses (Codex,
+# Grok, opencode, ...) append "exit code 0" to every SUCCESSFUL shell command,
+# so a bare "exit code" substring wrongly flagged those as errors and inflated
+# the learned failure rate. Match a nonzero code (case-insensitive, so
+# "Exit code: 1" counts too), never "exit code 0".
+_NONZERO_EXIT_RE = re.compile(r"exit code:?\s*(?!0\b)\d", re.IGNORECASE)
+
+
 def is_error_content(content: str) -> bool:
     """Heuristic: does this tool result look like an error?"""
     if not content or len(content) < 10:
@@ -105,10 +113,11 @@ def is_error_content(content: str) -> bool:
         "auto-denied",
         "Sibling tool call errored",
         "timed out",
-        "exit code",
         "FileNotFoundError",
     ]
-    return any(ind in snippet for ind in indicators)
+    if any(ind in snippet for ind in indicators):
+        return True
+    return bool(_NONZERO_EXIT_RE.search(snippet))
 
 
 # =============================================================================
diff --git a/tests/test_learn/test_integration.py b/tests/test_learn/test_integration.py
index c1b21215c..3ed01d189 100644
--- a/tests/test_learn/test_integration.py
+++ b/tests/test_learn/test_integration.py
@@ -114,6 +114,20 @@ class TestFalsePositiveFiltering:
         )
         assert is_error_content("bash: unknown_cmd: command not found")
 
+    def test_exit_code_zero_is_not_an_error(self):
+        """Agent harnesses append 'exit code 0' to every successful command;
+        that must not be classified as an error."""
+        from headroom.learn.scanner import is_error_content
+
+        assert not is_error_content("Ran the tests.\nProcess finished with exit code 0")
+
+    def test_nonzero_exit_code_is_an_error(self):
+        """A nonzero exit code (any casing / with a colon) is still an error."""
+        from headroom.learn.scanner import is_error_content
+
+        assert is_error_content("build failed\ncommand exited with exit code 1")
+        assert is_error_content("npm run build\nExit code: 127")
+
 
 # =============================================================================
 # Real-World Integration Tests (skipped if data not present)