test: push event system coverage to ≥80% on all three modules

Add 3 targeted tests for infrastructure/error_capture.py:
- test_stale_entries_pruned: exercises dedup cache pruning (line 61)
- test_git_context_fallback_on_failure: exercises exception path (lines 90-91)
- test_returns_none_when_feedback_disabled: exercises early return (line 112)

Coverage results (63 tests, all passing):
- error_capture.py: 75.6% → 80.0%
- broadcaster.py: 93.9% (unchanged)
- bus.py: 92.9% (unchanged)
- Total: 88.1% → 89.4%

Closes #45

tests/infrastructure/test_error_capture.py

@@ -1,6 +1,8 @@
 """Tests for infrastructure.error_capture module."""
 
 import sqlite3
+from datetime import UTC, datetime, timedelta
+from unittest.mock import patch
 
 from infrastructure.error_capture import (
     _dedup_cache,
@@ -67,6 +69,21 @@ class TestIsDuplicate:
         _is_duplicate("hash_1")
         assert _is_duplicate("hash_2") is False
 
+    def test_stale_entries_pruned(self):
+        """Old entries beyond 2x the dedup window should be pruned."""
+        from config import settings
+
+        window = settings.error_dedup_window_seconds
+        # Seed a stale entry far in the past
+        stale_time = datetime.now(UTC) - timedelta(seconds=window * 3)
+        _dedup_cache["stale_hash"] = stale_time
+
+        # Calling _is_duplicate on a new hash triggers pruning
+        _is_duplicate("fresh_hash")
+
+        assert "stale_hash" not in _dedup_cache
+        assert "fresh_hash" in _dedup_cache
+
     def teardown_method(self):
         _dedup_cache.clear()
 
@@ -82,6 +99,12 @@ class TestGetGitContext:
         assert isinstance(ctx["branch"], str)
         assert isinstance(ctx["commit"], str)
 
+    def test_git_context_fallback_on_failure(self):
+        """When subprocess.run fails, returns 'unknown' for both fields."""
+        with patch("subprocess.run", side_effect=OSError("git not found")):
+            ctx = _get_git_context()
+        assert ctx == {"branch": "unknown", "commit": "unknown"}
+
 
 class TestCaptureError:
     """Test the main capture_error function."""
@@ -100,6 +123,23 @@ class TestCaptureError:
             result = capture_error(e, source="test")
             assert result is None
 
+    def test_returns_none_when_feedback_disabled(self):
+        """capture_error returns None immediately when error_feedback_enabled is False."""
+        _dedup_cache.clear()
+
+        import config
+
+        original = config.settings.error_feedback_enabled
+        try:
+            config.settings.error_feedback_enabled = False
+            try:
+                raise RuntimeError("disabled test")
+            except RuntimeError as e:
+                result = capture_error(e, source="test")
+            assert result is None
+        finally:
+            config.settings.error_feedback_enabled = original
+
     def test_capture_does_not_crash_on_missing_deps(self):
         """capture_error should never crash even if optional deps are missing."""
         _dedup_cache.clear()