fix(agent): don't abort legitimate tool batches as runaway loops (#3183)

The loop-breaker's runaway backstop counted per-tool-type call totals and
tripped whenever any tool was used >=15 times — treating 15+ DISTINCT calls
to one tool as a stuck loop. A real batch (e.g. "add these 18 birthdays to my
calendar" emits 18 distinct manage_calendar create_event calls in one round)
got flagged "calling manage_calendar over and over", the calls were discarded
(next round tools_sent=0), and 0 events were created.

Count IDENTICAL repeated call signatures instead (same tool AND args), via a
small, unit-testable _detect_runaway_call() helper. Genuine batches pass; a
model truly stuck repeating one call still trips the backstop. Adds a
regression test.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_loop_breaker_runaway.py

@@ -0,0 +1,61 @@
+"""Regression test for the agent loop-breaker's runaway backstop.
+
+A legitimate batch of DISTINCT tool calls (e.g. creating 18 calendar events at
+once) must not be flagged as a runaway loop. Only the SAME exact call repeated
+an absurd number of times is a real runaway. Previously the backstop counted
+per-tool-type totals, so any batch of >=15 distinct calls to one tool was
+aborted and the calls were silently discarded.
+"""
+import sys
+import collections
+from unittest.mock import MagicMock
+
+# Mock heavy deps so importing src.agent_loop doesn't load the full app stack.
+_MOCKED = [
+    'sqlalchemy', 'sqlalchemy.orm', 'sqlalchemy.ext', 'sqlalchemy.ext.declarative',
+    'sqlalchemy.ext.hybrid', 'sqlalchemy.sql', 'sqlalchemy.sql.expression',
+    'src.database', 'src.agent_tools', 'core.models', 'core.database',
+]
+for _m in _MOCKED:
+    sys.modules.setdefault(_m, MagicMock())
+
+from src.agent_loop import _detect_runaway_call
+
+
+def _freq(sigs):
+    c = collections.Counter()
+    for s in sigs:
+        c[s] += 1
+    return c
+
+
+def test_distinct_batch_is_not_runaway():
+    # 18 distinct manage_calendar create_event calls (the "add 18 birthdays" case)
+    sigs = [f'manage_calendar:{{"action":"create_event","summary":"Birthday {n}"}}'
+            for n in range(18)]
+    assert _detect_runaway_call(_freq(sigs)) is None
+
+
+def test_many_distinct_same_tool_is_not_runaway():
+    sigs = [f'bash:echo {i}' for i in range(30)]
+    assert _detect_runaway_call(_freq(sigs)) is None
+
+
+def test_identical_call_repeated_is_runaway():
+    sigs = ['manage_calendar:{"action":"list_events"}'] * 15
+    assert _detect_runaway_call(_freq(sigs)) == 'manage_calendar'
+
+
+def test_below_threshold_is_not_runaway():
+    sigs = ['bash:ls'] * 14
+    assert _detect_runaway_call(_freq(sigs)) is None
+
+
+def test_threshold_is_configurable():
+    sigs = ['web_search:python'] * 5
+    assert _detect_runaway_call(_freq(sigs), threshold=5) == 'web_search'
+    assert _detect_runaway_call(_freq(sigs), threshold=6) is None
+
+
+def test_empty_is_not_runaway():
+    assert _detect_runaway_call(collections.Counter()) is None