test(compression): drop moot digest-loop tests; match stamped backoff errors

PR #98628 removed _build_chunk_digests, so the two lean chunk-digest
cancellation tests reintroduced by the #97512 cherry-pick target a
deleted mechanism — removed. The #96775 stall-interrupt assertions now
match the stall_interrupted marker inside the strategy/kind-stamped
durable error instead of assuming it is the prefix.

tests/agent/test_compression_stall_interrupt_96775.py

@@ -171,7 +171,7 @@ class TestStallInterruptedBackoff:
         assert db.get_compression_lock_holder("STALL_AUX_CANCEL") is None
         state = db.get_compression_failure_cooldown("STALL_AUX_CANCEL")
         assert state is not None
-        assert str(state["error"]).startswith(STALL_INTERRUPTED_FAILURE_CLASS)
+        assert STALL_INTERRUPTED_FAILURE_CLASS in str(state["error"])
         assert "msgs=20" in str(state["error"])
         assert agent.context_compressor.should_compress(50_000) is False
 
@@ -222,7 +222,7 @@ class TestStallInterruptedBackoff:
         assert live == original
         state = db.get_compression_failure_cooldown("STALL_FENCE_CANCEL")
         assert state is not None
-        assert str(state["error"]).startswith(STALL_INTERRUPTED_FAILURE_CLASS)
+        assert STALL_INTERRUPTED_FAILURE_CLASS in str(state["error"])
         assert agent.context_compressor.should_compress(50_000) is False
         db.append_message("STALL_FENCE_CANCEL", "user", "next turn")
 
@@ -339,7 +339,7 @@ class TestStallInterruptedBackoff:
         after = db.get_compression_failure_cooldown("MERGE_MAX_STALL")
         assert after is not None
         assert float(after["cooldown_until"]) >= prior_until - 1.0
-        assert str(after["error"]).startswith(STALL_INTERRUPTED_FAILURE_CLASS)
+        assert STALL_INTERRUPTED_FAILURE_CLASS in str(after["error"])
 
 
 def test_session_db_cooldown_write_does_not_shorten_longer_deadline(

tests/agent/test_context_compressor.py

@@ -26,60 +26,6 @@ class StubProviderError(Exception):
         self.response = response
 
 
-def test_lean_chunk_digests_stop_after_host_cancellation(compressor, monkeypatch):
-    """A cancelled total-deadline candidate must not dispatch another digest."""
-    import agent.context_compressor as context_compressor_module
-
-    cancelled = False
-    calls = 0
-
-    def fake_call_llm(**_kwargs):
-        nonlocal cancelled, calls
-        calls += 1
-        cancelled = True
-        return SimpleNamespace(
-            choices=[SimpleNamespace(message=SimpleNamespace(content="digest"))]
-        )
-
-    monkeypatch.setattr(context_compressor_module, "_LEAN_DIGEST_CHUNK_CHARS", 20)
-    monkeypatch.setattr(context_compressor_module, "_LEAN_DIGEST_MAX_CHUNKS", 8)
-    monkeypatch.setattr("agent.auxiliary_client.call_llm", fake_call_llm)
-    compressor._compression_cancelled_check = lambda: cancelled
-
-    result = compressor._build_chunk_digests(
-        [{"role": "tool", "content": "x" * 200, "tool_call_id": "call-1"}]
-    )
-
-    assert calls == 1
-    assert "Segment 2/" not in result
-
-
-def test_lean_chunk_digests_do_not_start_after_deadline(compressor, monkeypatch):
-    """The shared compaction deadline is checked before the first digest."""
-    import agent.context_compressor as context_compressor_module
-    from agent.conversation_compression import CompressionCommitFence
-
-    calls = 0
-
-    def fake_call_llm(**_kwargs):
-        nonlocal calls
-        calls += 1
-        raise AssertionError("digest request started after total deadline")
-
-    fence = CompressionCommitFence(total_ceiling_seconds=1.0)
-    compressor._compression_cancelled_check = lambda: fence.is_cancelled
-    monkeypatch.setattr("agent.auxiliary_client.call_llm", fake_call_llm)
-
-    with patch(
-        "agent.conversation_compression.time.monotonic",
-        return_value=time.monotonic() + 2.0,
-    ):
-        assert compressor._build_chunk_digests(
-            [{"role": "user", "content": "late digest"}]
-        ) == ""
-    assert calls == 0
-
-
 @pytest.fixture()
 def compressor():
     """Create a ContextCompressor with mocked dependencies."""