tests/agent/test_context_compressor.py

"""Tests for agent/context_compressor.py — compression logic, thresholds, truncation fallback."""

import pytest
from unittest.mock import patch, MagicMock

from agent.context_compressor import ContextCompressor, SUMMARY_PREFIX


@pytest.fixture()
def compressor():
    """Create a ContextCompressor with mocked dependencies."""
    with patch("agent.context_compressor.get_model_context_length", return_value=100000):
        c = ContextCompressor(
            model="test/model",
            threshold_percent=0.85,
            protect_first_n=2,
            protect_last_n=2,
            quiet_mode=True,
        )
        return c


class TestShouldCompress:
    def test_below_threshold(self, compressor):
        compressor.last_prompt_tokens = 50000
        assert compressor.should_compress() is False

    def test_above_threshold(self, compressor):
        compressor.last_prompt_tokens = 90000
        assert compressor.should_compress() is True

    def test_exact_threshold(self, compressor):
        compressor.last_prompt_tokens = 85000
        assert compressor.should_compress() is True

    def test_explicit_tokens(self, compressor):
        assert compressor.should_compress(prompt_tokens=90000) is True
        assert compressor.should_compress(prompt_tokens=50000) is False



class TestUpdateFromResponse:
    def test_updates_fields(self, compressor):
        compressor.update_from_response({
            "prompt_tokens": 5000,
            "completion_tokens": 1000,
            "total_tokens": 6000,
        })
        assert compressor.last_prompt_tokens == 5000
        assert compressor.last_completion_tokens == 1000

    def test_missing_fields_default_zero(self, compressor):
        compressor.update_from_response({})
        assert compressor.last_prompt_tokens == 0



class TestCompress:
    def _make_messages(self, n):
        return [{"role": "user" if i % 2 == 0 else "assistant", "content": f"msg {i}"} for i in range(n)]

    def test_too_few_messages_returns_unchanged(self, compressor):
        msgs = self._make_messages(4)  # protect_first=2 + protect_last=2 + 1 = 5 needed
        result = compressor.compress(msgs)
        assert result == msgs

    def test_truncation_fallback_no_client(self, compressor):
        # compressor has client=None, so should use truncation fallback
        msgs = [{"role": "system", "content": "System prompt"}] + self._make_messages(10)
        result = compressor.compress(msgs)
        assert len(result) < len(msgs)
        # Should keep system message and last N
        assert result[0]["role"] == "system"
        assert compressor.compression_count == 1

    def test_compression_increments_count(self, compressor):
        msgs = self._make_messages(10)
        compressor.compress(msgs)
        assert compressor.compression_count == 1
        compressor.compress(msgs)
        assert compressor.compression_count == 2

    def test_protects_first_and_last(self, compressor):
        msgs = self._make_messages(10)
        result = compressor.compress(msgs)
        # First 2 messages should be preserved (protect_first_n=2)
        # Last 2 messages should be preserved (protect_last_n=2)
        assert result[-1]["content"] == msgs[-1]["content"]
        # The second-to-last tail message may have the summary merged
        # into it when a double-collision prevents a standalone summary
        # (head=assistant, tail=user in this fixture).  Verify the
        # original content is present in either case.
        assert msgs[-2]["content"] in result[-2]["content"]


class TestGenerateSummaryNoneContent:
    """Regression: content=None (from tool-call-only assistant messages) must not crash."""

    def test_none_content_does_not_crash(self):
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "[CONTEXT SUMMARY]: tool calls happened"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True)

        messages = [
            {"role": "user", "content": "do something"},
            {"role": "assistant", "content": None, "tool_calls": [
                {"function": {"name": "search"}}
            ]},
            {"role": "tool", "content": "result"},
            {"role": "assistant", "content": None},
            {"role": "user", "content": "thanks"},
        ]

        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            summary = c._generate_summary(messages)
        assert isinstance(summary, str)
        assert summary.startswith(SUMMARY_PREFIX)

    def test_none_content_in_system_message_compress(self):
        """System message with content=None should not crash during compress."""
        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=2, protect_last_n=2)

        msgs = [{"role": "system", "content": None}] + [
            {"role": "user" if i % 2 == 0 else "assistant", "content": f"msg {i}"}
            for i in range(10)
        ]
        result = c.compress(msgs)
        assert len(result) < len(msgs)


class TestNonStringContent:
    """Regression: content as dict (e.g., llama.cpp tool calls) must not crash."""

    def test_dict_content_coerced_to_string(self):
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = {"text": "some summary"}

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True)

        messages = [
            {"role": "user", "content": "do something"},
            {"role": "assistant", "content": "ok"},
        ]

        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            summary = c._generate_summary(messages)
        assert isinstance(summary, str)
        assert summary.startswith(SUMMARY_PREFIX)

    def test_none_content_coerced_to_empty(self):
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = None

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True)

        messages = [
            {"role": "user", "content": "do something"},
            {"role": "assistant", "content": "ok"},
        ]

        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            summary = c._generate_summary(messages)
        # None content → empty string → standardized compaction handoff prefix added
        assert summary is not None
        assert summary == SUMMARY_PREFIX

    def test_summary_call_does_not_force_temperature(self):
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "ok"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True)

        messages = [
            {"role": "user", "content": "do something"},
            {"role": "assistant", "content": "ok"},
        ]

        with patch("agent.context_compressor.call_llm", return_value=mock_response) as mock_call:
            c._generate_summary(messages)

        kwargs = mock_call.call_args.kwargs
        assert "temperature" not in kwargs

    def test_summary_call_passes_live_main_runtime(self):
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "ok"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(
                model="gpt-5.4",
                provider="openai-codex",
                base_url="https://chatgpt.com/backend-api/codex",
                api_key="codex-token",
                api_mode="codex_responses",
                quiet_mode=True,
            )

        messages = [
            {"role": "user", "content": "do something"},
            {"role": "assistant", "content": "ok"},
        ]

        with patch("agent.context_compressor.call_llm", return_value=mock_response) as mock_call:
            c._generate_summary(messages)

        assert mock_call.call_args.kwargs["main_runtime"] == {
            "model": "gpt-5.4",
            "provider": "openai-codex",
            "base_url": "https://chatgpt.com/backend-api/codex",
            "api_key": "codex-token",
            "api_mode": "codex_responses",
        }


class TestSummaryFailureCooldown:
    def test_summary_failure_enters_cooldown_and_skips_retry(self):
        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True)

        messages = [
            {"role": "user", "content": "do something"},
            {"role": "assistant", "content": "ok"},
        ]

        with patch("agent.context_compressor.call_llm", side_effect=Exception("boom")) as mock_call:
            first = c._generate_summary(messages)
            second = c._generate_summary(messages)

        assert first is None
        assert second is None
        assert mock_call.call_count == 1


class TestSummaryPrefixNormalization:
    def test_legacy_prefix_is_replaced(self):
        summary = ContextCompressor._with_summary_prefix("[CONTEXT SUMMARY]: did work")
        assert summary == f"{SUMMARY_PREFIX}\ndid work"

    def test_existing_new_prefix_is_not_duplicated(self):
        summary = ContextCompressor._with_summary_prefix(f"{SUMMARY_PREFIX}\ndid work")
        assert summary == f"{SUMMARY_PREFIX}\ndid work"


class TestCompressWithClient:
    def test_summarization_path(self):
        mock_client = MagicMock()
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "[CONTEXT SUMMARY]: stuff happened"
        mock_client.chat.completions.create.return_value = mock_response

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=2, protect_last_n=2)

        msgs = [{"role": "user" if i % 2 == 0 else "assistant", "content": f"msg {i}"} for i in range(10)]
        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)

        # Should have summary message in the middle
        contents = [m.get("content", "") for m in result]
        assert any(c.startswith(SUMMARY_PREFIX) for c in contents)
        assert len(result) < len(msgs)

    def test_summarization_does_not_split_tool_call_pairs(self):
        mock_client = MagicMock()
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "[CONTEXT SUMMARY]: compressed middle"
        mock_client.chat.completions.create.return_value = mock_response

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(
                model="test",
                quiet_mode=True,
                protect_first_n=3,
                protect_last_n=4,
            )

        msgs = [
            {"role": "user", "content": "Could you address the reviewer comments in PR#71"},
            {
                "role": "assistant",
                "content": "",
                "tool_calls": [
                    {"id": "call_a", "type": "function", "function": {"name": "skill_view", "arguments": "{}"}},
                    {"id": "call_b", "type": "function", "function": {"name": "skill_view", "arguments": "{}"}},
                ],
            },
            {"role": "tool", "tool_call_id": "call_a", "content": "output a"},
            {"role": "tool", "tool_call_id": "call_b", "content": "output b"},
            {"role": "user", "content": "later 1"},
            {"role": "assistant", "content": "later 2"},
            {"role": "tool", "tool_call_id": "call_x", "content": "later output"},
            {"role": "assistant", "content": "later 3"},
            {"role": "user", "content": "later 4"},
        ]

        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)

        answered_ids = {
            msg.get("tool_call_id")
            for msg in result
            if msg.get("role") == "tool" and msg.get("tool_call_id")
        }
        for msg in result:
            if msg.get("role") == "assistant" and msg.get("tool_calls"):
                for tc in msg["tool_calls"]:
                    assert tc["id"] in answered_ids

    def test_summary_role_avoids_consecutive_user_messages(self):
        """Summary role should alternate with the last head message to avoid consecutive same-role messages."""
        mock_client = MagicMock()
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "[CONTEXT SUMMARY]: stuff happened"
        mock_client.chat.completions.create.return_value = mock_response

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=2, protect_last_n=2)

        # Last head message (index 1) is "assistant" → summary should be "user".
        # With min_tail=3, tail = last 3 messages (indices 5-7).
        # head_last=assistant, tail_first=assistant → summary_role="user", no collision.
        # Need 8 messages: min_for_compress = 2+3+1 = 6, must have > 6.
        msgs = [
            {"role": "user", "content": "msg 0"},
            {"role": "assistant", "content": "msg 1"},
            {"role": "user", "content": "msg 2"},
            {"role": "assistant", "content": "msg 3"},
            {"role": "user", "content": "msg 4"},
            {"role": "assistant", "content": "msg 5"},
            {"role": "user", "content": "msg 6"},
            {"role": "assistant", "content": "msg 7"},
        ]
        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)
        summary_msg = [
            m for m in result if (m.get("content") or "").startswith(SUMMARY_PREFIX)
        ]
        assert len(summary_msg) == 1
        assert summary_msg[0]["role"] == "user"

    def test_summary_role_avoids_consecutive_user_when_head_ends_with_user(self):
        """When last head message is 'user', summary must be 'assistant' to avoid two consecutive user messages."""
        mock_client = MagicMock()
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "[CONTEXT SUMMARY]: stuff happened"
        mock_client.chat.completions.create.return_value = mock_response

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=3, protect_last_n=2)

        # Last head message (index 2) is "user" → summary should be "assistant"
        msgs = [
            {"role": "system", "content": "system prompt"},
            {"role": "user", "content": "msg 1"},
            {"role": "user", "content": "msg 2"},  # last head — user
            {"role": "assistant", "content": "msg 3"},
            {"role": "user", "content": "msg 4"},
            {"role": "assistant", "content": "msg 5"},
            {"role": "user", "content": "msg 6"},
            {"role": "assistant", "content": "msg 7"},
        ]
        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)
        summary_msg = [
            m for m in result if (m.get("content") or "").startswith(SUMMARY_PREFIX)
        ]
        assert len(summary_msg) == 1
        assert summary_msg[0]["role"] == "assistant"

    def test_summary_role_flips_to_avoid_tail_collision(self):
        """When summary role collides with the first tail message but flipping
        doesn't collide with head, the role should be flipped."""
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "summary text"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=2, protect_last_n=2)

        # Head ends with tool (index 1), tail starts with user (index 6).
        # Default: tool → summary_role="user" → collides with tail.
        # Flip to "assistant" → tool→assistant is fine.
        msgs = [
            {"role": "user", "content": "msg 0"},
            {"role": "assistant", "content": "", "tool_calls": [
                {"id": "call_1", "type": "function", "function": {"name": "t", "arguments": "{}"}},
            ]},
            {"role": "tool", "tool_call_id": "call_1", "content": "result 1"},
            {"role": "assistant", "content": "msg 3"},
            {"role": "user", "content": "msg 4"},
            {"role": "assistant", "content": "msg 5"},
            {"role": "user", "content": "msg 6"},
            {"role": "assistant", "content": "msg 7"},
        ]
        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)
        # Verify no consecutive user or assistant messages
        for i in range(1, len(result)):
            r1 = result[i - 1].get("role")
            r2 = result[i].get("role")
            if r1 in ("user", "assistant") and r2 in ("user", "assistant"):
                assert r1 != r2, f"consecutive {r1} at indices {i-1},{i}"

    def test_double_collision_merges_summary_into_tail(self):
        """When neither role avoids collision with both neighbors, the summary
        should be merged into the first tail message rather than creating a
        standalone message that breaks role alternation.

        Common scenario: head ends with 'assistant', tail starts with 'user'.
        summary='user' collides with tail, summary='assistant' collides with head.
        """
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "summary text"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=3, protect_last_n=3)

        # Head: [system, user, assistant]  →  last head = assistant
        # Tail: [user, assistant, user]    →  first tail = user
        # summary_role="user" collides with tail, "assistant" collides with head → merge
        msgs = [
            {"role": "system", "content": "system prompt"},
            {"role": "user", "content": "msg 1"},
            {"role": "assistant", "content": "msg 2"},
            {"role": "user", "content": "msg 3"},      # compressed
            {"role": "assistant", "content": "msg 4"},  # compressed
            {"role": "user", "content": "msg 5"},       # compressed
            {"role": "user", "content": "msg 6"},       # tail start
            {"role": "assistant", "content": "msg 7"},
            {"role": "user", "content": "msg 8"},
        ]
        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)

        # Verify no consecutive user or assistant messages
        for i in range(1, len(result)):
            r1 = result[i - 1].get("role")
            r2 = result[i].get("role")
            if r1 in ("user", "assistant") and r2 in ("user", "assistant"):
                assert r1 != r2, f"consecutive {r1} at indices {i-1},{i}"

        # The summary text should be merged into the first tail message
        first_tail = [m for m in result if "msg 6" in (m.get("content") or "")]
        assert len(first_tail) == 1
        assert "summary text" in first_tail[0]["content"]

    def test_double_collision_user_head_assistant_tail(self):
        """Reverse double collision: head ends with 'user', tail starts with 'assistant'.
        summary='assistant' collides with tail, 'user' collides with head → merge."""
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "summary text"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=2, protect_last_n=2)

        # Head: [system, user]        → last head = user
        # Tail: [assistant, user, assistant] → first tail = assistant
        # summary_role="assistant" collides with tail, "user" collides with head → merge
        # With min_tail=3, tail = last 3 messages (indices 5-7).
        # Need 8 messages: min_for_compress = 2+3+1 = 6, must have > 6.
        msgs = [
            {"role": "system", "content": "system prompt"},
            {"role": "user", "content": "msg 1"},
            {"role": "assistant", "content": "msg 2"},   # compressed
            {"role": "user", "content": "msg 3"},        # compressed
            {"role": "assistant", "content": "msg 4"},   # compressed
            {"role": "assistant", "content": "msg 5"},   # tail start
            {"role": "user", "content": "msg 6"},
            {"role": "assistant", "content": "msg 7"},
        ]
        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)

        # Verify no consecutive user or assistant messages
        for i in range(1, len(result)):
            r1 = result[i - 1].get("role")
            r2 = result[i].get("role")
            if r1 in ("user", "assistant") and r2 in ("user", "assistant"):
                assert r1 != r2, f"consecutive {r1} at indices {i-1},{i}"

        # The summary should be merged into the first tail message (assistant at index 5)
        first_tail = [m for m in result if "msg 5" in (m.get("content") or "")]
        assert len(first_tail) == 1
        assert "summary text" in first_tail[0]["content"]

    def test_no_collision_scenarios_still_work(self):
        """Verify that the common no-collision cases (head=assistant/tail=assistant,
        head=user/tail=user) still produce a standalone summary message."""
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "summary text"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(model="test", quiet_mode=True, protect_first_n=2, protect_last_n=2)

        # Head=assistant, Tail=assistant → summary_role="user", no collision.
        # With min_tail=3, tail = last 3 messages (indices 5-7).
        # Need 8 messages: min_for_compress = 2+3+1 = 6, must have > 6.
        msgs = [
            {"role": "user", "content": "msg 0"},
            {"role": "assistant", "content": "msg 1"},
            {"role": "user", "content": "msg 2"},
            {"role": "assistant", "content": "msg 3"},
            {"role": "user", "content": "msg 4"},
            {"role": "assistant", "content": "msg 5"},
            {"role": "user", "content": "msg 6"},
            {"role": "assistant", "content": "msg 7"},
        ]
        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)
        summary_msgs = [m for m in result if (m.get("content") or "").startswith(SUMMARY_PREFIX)]
        assert len(summary_msgs) == 1, "should have a standalone summary message"
        assert summary_msgs[0]["role"] == "user"

    def test_summarization_does_not_start_tail_with_tool_outputs(self):
        mock_response = MagicMock()
        mock_response.choices = [MagicMock()]
        mock_response.choices[0].message.content = "[CONTEXT SUMMARY]: compressed middle"

        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
            c = ContextCompressor(
                model="test",
                quiet_mode=True,
                protect_first_n=2,
                protect_last_n=3,
            )

        msgs = [
            {"role": "user", "content": "earlier 1"},
            {"role": "assistant", "content": "earlier 2"},
            {"role": "user", "content": "earlier 3"},
            {
                "role": "assistant",
                "content": "",
                "tool_calls": [
                    {"id": "call_c", "type": "function", "function": {"name": "search_files", "arguments": "{}"}},
                ],
            },
            {"role": "tool", "tool_call_id": "call_c", "content": "output c"},
            {"role": "user", "content": "latest user"},
        ]

        with patch("agent.context_compressor.call_llm", return_value=mock_response):
            result = c.compress(msgs)

        called_ids = {
            tc["id"]
            for msg in result
            if msg.get("role") == "assistant" and msg.get("tool_calls")
            for tc in msg["tool_calls"]
        }
        for msg in result:
            if msg.get("role") == "tool" and msg.get("tool_call_id"):
                assert msg["tool_call_id"] in called_ids


class TestSummaryTargetRatio:
    """Verify that summary_target_ratio properly scales budgets with context window."""

    def test_tail_budget_scales_with_context(self):
        """Tail token budget should be threshold_tokens * summary_target_ratio."""
        with patch("agent.context_compressor.get_model_context_length", return_value=200_000):
            c = ContextCompressor(model="test", quiet_mode=True, summary_target_ratio=0.40)
        # 200K * 0.50 threshold * 0.40 ratio = 40K
        assert c.tail_token_budget == 40_000

        with patch("agent.context_compressor.get_model_context_length", return_value=1_000_000):
            c = ContextCompressor(model="test", quiet_mode=True, summary_target_ratio=0.40)
        # 1M * 0.50 threshold * 0.40 ratio = 200K
        assert c.tail_token_budget == 200_000

    def test_summary_cap_scales_with_context(self):
        """Max summary tokens should be 5% of context, capped at 12K."""
        with patch("agent.context_compressor.get_model_context_length", return_value=200_000):
            c = ContextCompressor(model="test", quiet_mode=True)
        assert c.max_summary_tokens == 10_000  # 200K * 0.05

        with patch("agent.context_compressor.get_model_context_length", return_value=1_000_000):
            c = ContextCompressor(model="test", quiet_mode=True)
        assert c.max_summary_tokens == 12_000  # capped at 12K ceiling

    def test_ratio_clamped(self):
        """Ratio should be clamped to [0.10, 0.80]."""
        with patch("agent.context_compressor.get_model_context_length", return_value=100_000):
            c = ContextCompressor(model="test", quiet_mode=True, summary_target_ratio=0.05)
        assert c.summary_target_ratio == 0.10

        with patch("agent.context_compressor.get_model_context_length", return_value=100_000):
            c = ContextCompressor(model="test", quiet_mode=True, summary_target_ratio=0.95)
        assert c.summary_target_ratio == 0.80

    def test_default_threshold_is_50_percent(self):
        """Default compression threshold should be 50%, with a 64K floor."""
        with patch("agent.context_compressor.get_model_context_length", return_value=100_000):
            c = ContextCompressor(model="test", quiet_mode=True)
        assert c.threshold_percent == 0.50
        # 50% of 100K = 50K, but the floor is 64K
        assert c.threshold_tokens == 64_000

    def test_threshold_floor_does_not_apply_above_128k(self):
        """On large-context models the 50% percentage is used directly."""
        with patch("agent.context_compressor.get_model_context_length", return_value=200_000):
            c = ContextCompressor(model="test", quiet_mode=True)
        # 50% of 200K = 100K, which is above the 64K floor
        assert c.threshold_tokens == 100_000

    def test_default_protect_last_n_is_20(self):
        """Default protect_last_n should be 20."""
        with patch("agent.context_compressor.get_model_context_length", return_value=100_000):
            c = ContextCompressor(model="test", quiet_mode=True)
        assert c.protect_last_n == 20


class TestTokenBudgetTailProtection:
    """Tests for token-budget-based tail protection (PR #6240).

    The core change: tail protection is now based on a token budget rather
    than a fixed message count.  This prevents large tool outputs from
    blocking compaction.
    """

    @pytest.fixture()
    def budget_compressor(self):
        """Compressor with known token budget for tail protection tests."""
        with patch("agent.context_compressor.get_model_context_length", return_value=200_000):
            c = ContextCompressor(
                model="test/model",
                threshold_percent=0.50,  # 100K threshold
                protect_first_n=2,
                protect_last_n=20,
                quiet_mode=True,
            )
            return c

    def test_large_tool_outputs_no_longer_block_compaction(self, budget_compressor):
        """The motivating scenario: 20 messages with large tool outputs should
        NOT prevent compaction.  With message-count tail protection they would
        all be protected, leaving nothing to summarize."""
        c = budget_compressor
        messages = [
            {"role": "user", "content": "Start task"},
            {"role": "assistant", "content": "On it"},
        ]
        # Add 20 messages with large tool outputs (~5K chars each ≈ 1250 tokens)
        for i in range(10):
            messages.append({
                "role": "assistant", "content": None,
                "tool_calls": [{"function": {"name": f"tool_{i}", "arguments": "{}"}}],
            })
            messages.append({
                "role": "tool", "content": "x" * 5000,
                "tool_call_id": f"call_{i}",
            })
        # Add 3 recent small messages
        messages.append({"role": "user", "content": "What's the status?"})
        messages.append({"role": "assistant", "content": "Here's what I found..."})
        messages.append({"role": "user", "content": "Continue"})

        # The tail cut should NOT protect all 20 tool messages
        head_end = c.protect_first_n
        cut = c._find_tail_cut_by_tokens(messages, head_end)
        tail_size = len(messages) - cut
        # With token budget, the tail should be much smaller than 20+
        assert tail_size < 20, f"Tail {tail_size} messages — large tool outputs are blocking compaction"
        # But at least 3 (hard minimum)
        assert tail_size >= 3

    def test_min_tail_always_3_messages(self, budget_compressor):
        """Even with a tiny token budget, at least 3 messages are protected."""
        c = budget_compressor
        # Override to a tiny budget
        c.tail_token_budget = 10
        messages = [
            {"role": "user", "content": "hello"},
            {"role": "assistant", "content": "hi"},
            {"role": "user", "content": "do something"},
            {"role": "assistant", "content": "working on it"},
            {"role": "user", "content": "more work"},
            {"role": "assistant", "content": "done"},
            {"role": "user", "content": "thanks"},
        ]
        head_end = 2
        cut = c._find_tail_cut_by_tokens(messages, head_end)
        tail_size = len(messages) - cut
        assert tail_size >= 3, f"Tail is only {tail_size} messages, min should be 3"

    def test_soft_ceiling_allows_oversized_message(self, budget_compressor):
        """The 1.5x soft ceiling allows an oversized message to be included
        rather than splitting it."""
        c = budget_compressor
        # Set a small budget — 500 tokens
        c.tail_token_budget = 500
        messages = [
            {"role": "user", "content": "hello"},
            {"role": "assistant", "content": "hi"},
            {"role": "user", "content": "read the file"},
            # This message is ~600 tokens (> budget of 500, but < 1.5x = 750)
            {"role": "assistant", "content": "a" * 2400},
            {"role": "user", "content": "short"},
            {"role": "assistant", "content": "short reply"},
            {"role": "user", "content": "continue"},
        ]
        head_end = 2
        cut = c._find_tail_cut_by_tokens(messages, head_end)
        # The oversized message at index 3 should NOT be the cut point
        # because 1.5x ceiling = 750 tokens and accumulated would be ~610
        # (short msgs + oversized msg) which is < 750
        tail_size = len(messages) - cut
        assert tail_size >= 3

    def test_small_conversation_still_compresses(self, budget_compressor):
        """With the new min of 8 messages (head=2 + 3 + 1 guard + 2 middle),
        a small but compressible conversation should still compress."""
        c = budget_compressor
        # 9 messages: head(2) + 4 middle + 3 tail = compressible
        messages = []
        for i in range(9):
            role = "user" if i % 2 == 0 else "assistant"
            messages.append({"role": role, "content": f"Message {i}"})

        # Should not early-return (needs > protect_first_n + 3 + 1 = 6)
        # Mock the summary generation to avoid real API call
        with patch.object(c, "_generate_summary", return_value="Summary of conversation"):
            result = c.compress(messages, current_tokens=90_000)
        # Should have compressed (fewer messages than original)
        assert len(result) < len(messages)

    def test_prune_with_token_budget(self, budget_compressor):
        """_prune_old_tool_results with protect_tail_tokens respects the budget."""
        c = budget_compressor
        messages = [
            {"role": "user", "content": "start"},
            {"role": "assistant", "content": None,
             "tool_calls": [{"function": {"name": "read_file", "arguments": '{"path": "big.txt"}'}}]},
            {"role": "tool", "content": "x" * 10000, "tool_call_id": "c1"},  # ~2500 tokens
            {"role": "assistant", "content": None,
             "tool_calls": [{"function": {"name": "read_file", "arguments": '{"path": "small.txt"}'}}]},
            {"role": "tool", "content": "y" * 10000, "tool_call_id": "c2"},  # ~2500 tokens
            {"role": "user", "content": "short recent message"},
            {"role": "assistant", "content": "short reply"},
        ]
        # With a 1000-token budget, only the last couple messages should be protected
        result, pruned = c._prune_old_tool_results(
            messages, protect_tail_count=2, protect_tail_tokens=1000,
        )
        # At least one old tool result should have been pruned
        assert pruned >= 1

    def test_prune_without_token_budget_uses_message_count(self, budget_compressor):
        """Without protect_tail_tokens, falls back to message-count behavior."""
        c = budget_compressor
        messages = [
            {"role": "user", "content": "start"},
            {"role": "assistant", "content": None,
             "tool_calls": [{"function": {"name": "tool", "arguments": "{}"}}]},
            {"role": "tool", "content": "x" * 5000, "tool_call_id": "c1"},
            {"role": "user", "content": "recent"},
            {"role": "assistant", "content": "reply"},
        ]
        # protect_tail_count=3 means last 3 messages protected
        result, pruned = c._prune_old_tool_results(
            messages, protect_tail_count=3,
        )
        # Tool at index 2 is outside the protected tail (last 3 = indices 2,3,4)
        # so it might or might not be pruned depending on boundary
        assert isinstance(pruned, int)