test(compressor): tidy blank-line spacing + assert placeholder never overwrites text

Review follow-up on the batch salvage: normalize the inter-class spacing to two
blank lines (PEP8) between the three new test classes, and add an explicit
assertion in test_sanitizer_strips_orphaned_preserves_text_content that the
'(tool call removed)' placeholder does NOT overwrite existing assistant text.
No production change.

tests/agent/test_context_compressor.py

@@ -2921,8 +2921,6 @@ class TestTurnPairPreservation:
             )
 
 
-
-
 class TestSanitizerStripsOrphanedToolCalls:
     """PR #51218 (salvaged from #51225): orphaned tool_calls are stripped from
     assistant messages instead of having stub tool results inserted, avoiding
@@ -2997,6 +2995,8 @@ class TestSanitizerStripsOrphanedToolCalls:
         asst = next(m for m in sanitized if m.get("role") == "assistant")
         assert asst["content"] == "Let me search for that."
         assert not asst.get("tool_calls")
+        # The placeholder must NOT overwrite existing text content.
+        assert asst["content"] != "(tool call removed)"
 
     def test_sanitizer_strips_orphaned_with_call_id_mismatch(self, compressor):
         """Stubs with call_id != id used to be dropped by downstream
@@ -3025,8 +3025,6 @@ class TestSanitizerStripsOrphanedToolCalls:
         # No stub tool messages (which would have call_id != id mismatch)
 
 
-
-
 class TestCooldownReentryAbort:
     """Regression: a second compress() call during the failure cooldown must
     still abort when the original failure was a network/auth error.
@@ -3106,8 +3104,6 @@ class TestCooldownReentryAbort:
         assert c._last_summary_fallback_used is False
 
 
-
-
 class TestDoubleCompactionSummaryRole:
     """PR #52160 (salvaged from #52167): when only the system prompt is
     protected, the summary must lead with role=user (Anthropic/Bedrock send