diff --git a/backend/apps/agents/core/fault_injection.py b/backend/apps/agents/core/fault_injection.py
index ac060fdd..11f4fe26 100644
--- a/backend/apps/agents/core/fault_injection.py
+++ b/backend/apps/agents/core/fault_injection.py
@@ -28,6 +28,7 @@ KNOWN_FAULTS: Set[str] = {
     "dead_lane",         # the router has already given up on the credential (ENG-414 preflight)
     "cli_context_squeeze",  # a tiny context window, so autocompact thrash is drillable (ENG-418)
     "stale_tool_schema",  # the CLI's deferred-tool 400, byte-real incl. truncation (ENG-394 wall 2)
+    "unclassified_error",  # a raw runtime failure no classifier owns, so the snag card is drillable (self-heal audit)
 }
 
 # The window `cli_context_squeeze` pretends the model has, and the number is load-bearing.
diff --git a/backend/apps/agents/manager/run/TurnRunner.py b/backend/apps/agents/manager/run/TurnRunner.py
index 2d146182..c186656f 100644
--- a/backend/apps/agents/manager/run/TurnRunner.py
+++ b/backend/apps/agents/manager/run/TurnRunner.py
@@ -75,6 +75,10 @@ class TurnRunner(AgentManagerProtocol):
                 "'mcp__openswarm-core__ShowUI' cannot have both defer_loading=true and cache_ "
                 "(reset after 15s)\"}}"
             )
+        # One-shot, and deliberately a text NO classifier owns: it must fall through to the generic
+        # branch, whose raw "Error: ..." card used to render as nothing at all (self-heal audit, 2026-09-01).
+        if p_fault_once("unclassified_error"):
+            raise RuntimeError("Command failed with exit code 1 (exit code: 1)\nError output: Check stderr output for details")
 
         async def prompt_stream():
             yield {
diff --git a/backend/tests/test_fault_injection.py b/backend/tests/test_fault_injection.py
index c5caebf0..4e275177 100644
--- a/backend/tests/test_fault_injection.py
+++ b/backend/tests/test_fault_injection.py
@@ -63,6 +63,7 @@ WIRED_IN = {
     "dead_lane": "backend/apps/agents/manager/run/lane_preflight.py",
     "cli_context_squeeze": "backend/apps/agents/manager/configure_provider_env.py",
     "stale_tool_schema": TURN_RUNNER,
+    "unclassified_error": TURN_RUNNER,
 }
 
 
@@ -181,3 +182,19 @@ def test_the_harness_declares_what_it_cannot_reach():
     from backend.apps.agents.core.fault_injection import UNREACHABLE_WITH
     assert "empty_finish" in UNREACHABLE_WITH
     assert set(UNREACHABLE_WITH) <= KNOWN_FAULTS
+
+
+def test_the_unclassified_fault_is_owned_by_no_classifier():
+    """The drill exists to reach the generic branch; if any classifier ever claims this text the
+    drill silently measures a different door."""
+    from backend.apps.agents.core.error_classify import (
+        is_auth_error, is_connection_lost, is_context_overflow_error, is_external_kill_error,
+        is_stale_tool_schema_error, is_transient_capacity_error,
+    )
+    text = re.search(r'RuntimeError\("(.+?)"\)', p_block("unclassified_error")).group(1).encode().decode("unicode_escape")
+    exc = RuntimeError(text)
+    assert "exit code 1 " in text or "exit code 1\n" in text
+    for pred in (is_external_kill_error, is_stale_tool_schema_error, is_transient_capacity_error, is_context_overflow_error):
+        assert not pred(exc), pred.__name__
+    assert not is_auth_error(exc)
+    assert not is_connection_lost(exc)