headroom/tests/test_netcost_gate.py

"""Net-cost mutation gate in ContentRouter (#856 P2, flag-gated).

``HEADROOM_NET_COST_POLICY=1`` routes every router mutation candidate
through ``CompressionPolicy.net_mutation_gain`` with the issue's v1
estimators (exact ΔT, S = token total after the slot, env-tunable R and
P_alive). Flag off (default) preserves exact current behavior.
"""

from __future__ import annotations

import json

import pytest

from headroom import OpenAIProvider, Tokenizer
from headroom.transforms.content_router import ContentRouter, ContentRouterConfig

_provider = OpenAIProvider()


@pytest.fixture
def tokenizer() -> Tokenizer:
    return Tokenizer(_provider.get_token_counter("gpt-4o"), "gpt-4o")


@pytest.fixture
def router() -> ContentRouter:
    return ContentRouter(ContentRouterConfig())


def _tool_json(rows: int) -> str:
    return json.dumps(
        [{"id": i, "name": f"item_{i}", "status": "ok", "score": i * 3.14} for i in range(rows)]
    )


def _messages(tool_content: str, suffix_filler_words: int) -> list[dict]:
    suffix = "analysis context word " * suffix_filler_words
    return [
        {"role": "user", "content": "fetch the records"},
        {"role": "tool", "content": tool_content},
        {"role": "user", "content": suffix},
        {"role": "user", "content": "summarize"},
    ]


def _tool_slot_compressed(result, messages) -> bool:
    return result.messages[1]["content"] != messages[1]["content"]


class TestNetCostGate:
    def test_flag_off_compresses_as_before(self, router, tokenizer, monkeypatch):
        monkeypatch.delenv("HEADROOM_NET_COST_POLICY", raising=False)
        messages = _messages(_tool_json(300), suffix_filler_words=4000)
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert _tool_slot_compressed(result, messages)
        assert not any(t.startswith("netcost:") for t in result.transforms_applied)

    def test_flag_on_blocks_when_suffix_dominates(self, router, tokenizer, monkeypatch):
        # Big suffix after a modest shave: corrected formula says the cache
        # invalidation outweighs the saving -> slot left untouched.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert not _tool_slot_compressed(result, messages)
        assert any(t.startswith("netcost:skip:") for t in result.transforms_applied)

    def test_flag_on_allows_when_shave_dominates(self, router, tokenizer, monkeypatch):
        # Tiny suffix after a huge shave -> gate allows, compression applies.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _messages(_tool_json(2000), suffix_filler_words=5)
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert _tool_slot_compressed(result, messages)
        assert not any(t.startswith("netcost:skip:") for t in result.transforms_applied)

    def test_one_hour_ttl_prices_write_tier(self, router, tokenizer, monkeypatch):
        # 5-minute pricing still admits this shave, while the larger 1h
        # cache-write multiplier must turn the same candidate into a skip.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _messages(_tool_json(300), suffix_filler_words=1000)

        monkeypatch.delenv("HEADROOM_NET_COST_CACHE_TTL_SECONDS", raising=False)
        five_minute = router.apply([dict(m) for m in messages], tokenizer)
        assert _tool_slot_compressed(five_minute, messages)

        monkeypatch.setenv("HEADROOM_NET_COST_CACHE_TTL_SECONDS", "3600")
        one_hour = router.apply([dict(m) for m in messages], tokenizer)
        assert not _tool_slot_compressed(one_hour, messages)
        assert any(t.startswith("netcost:skip:") for t in one_hour.transforms_applied)

    def test_request_one_hour_marker_overrides_env_fallback(self, router, tokenizer, monkeypatch):
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        monkeypatch.delenv("HEADROOM_NET_COST_CACHE_TTL_SECONDS", raising=False)
        for name in (
            "DISABLE_PROMPT_CACHING",
            "DISABLE_PROMPT_CACHING_SONNET",
            "ENABLE_PROMPT_CACHING_1H",
            "FORCE_PROMPT_CACHING_5M",
        ):
            monkeypatch.delenv(name, raising=False)

        messages = _messages(_tool_json(300), suffix_filler_words=1000)
        messages[0] = {
            "role": "user",
            "content": [
                {
                    "type": "text",
                    "text": "fetch the records",
                    "cache_control": {"type": "ephemeral", "ttl": "1h"},
                }
            ],
        }

        from headroom.transforms.cold_prefix import anthropic_cache_ttl_seconds

        request_ttl = anthropic_cache_ttl_seconds("claude-sonnet-4-6", messages)
        assert request_ttl == 3600

        five_minute = router.apply([dict(m) for m in messages], tokenizer)
        assert _tool_slot_compressed(five_minute, messages)

        one_hour = router.apply(
            [dict(m) for m in messages],
            tokenizer,
            cache_ttl_seconds=request_ttl,
        )
        assert not _tool_slot_compressed(one_hour, messages)
        assert any(t.startswith("netcost:skip:") for t in one_hour.transforms_applied)

    def test_flag_on_gates_cached_results_too(self, router, tokenizer, monkeypatch):
        # First apply warms the result cache with the flag off; second apply
        # with the flag on must still gate the cache-hit path.
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        monkeypatch.delenv("HEADROOM_NET_COST_POLICY", raising=False)
        warm = router.apply([dict(m) for m in messages], tokenizer)
        assert _tool_slot_compressed(warm, messages)

        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        gated = router.apply([dict(m) for m in messages], tokenizer)
        assert not _tool_slot_compressed(gated, messages)
        assert any(t.startswith("netcost:skip:") for t in gated.transforms_applied)

    def test_malformed_env_falls_back_to_defaults(self, router, tokenizer, monkeypatch):
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        monkeypatch.setenv("HEADROOM_NET_COST_EXPECTED_READS", "lots")
        monkeypatch.setenv("HEADROOM_NET_COST_P_ALIVE", "warm")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        # Must not raise; defaults (R=10, P=1) still block this scenario.
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert not _tool_slot_compressed(result, messages)

    def test_p_alive_zero_disables_penalty(self, router, tokenizer, monkeypatch):
        # Cold cache (P_alive=0): no suffix penalty, mutation always wins.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        monkeypatch.setenv("HEADROOM_NET_COST_P_ALIVE", "0")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert _tool_slot_compressed(result, messages)

    def test_nonfinite_env_falls_back_to_defaults(self, router, tokenizer, monkeypatch):
        # ``float("inf")``/``float("nan")`` parse without ValueError; the gate
        # must reject them and fall back to defaults so telemetry isn't
        # poisoned. With R=10/P=1 defaults this scenario still skips.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        monkeypatch.setenv("HEADROOM_NET_COST_EXPECTED_READS", "inf")
        monkeypatch.setenv("HEADROOM_NET_COST_P_ALIVE", "nan")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert not _tool_slot_compressed(result, messages)
        # Marker must be a bounded band, never a raw float / "nan".
        skip_markers = [t for t in result.transforms_applied if t.startswith("netcost:skip:")]
        assert skip_markers
        assert all(m.split(":")[-1] in _GAIN_BANDS for m in skip_markers)


_GAIN_BANDS = {
    "0",
    "lt100",
    "lt1k",
    "lt10k",
    "gte10k",
    "neg_lt100",
    "neg_lt1k",
    "neg_lt10k",
    "neg_gte10k",
    "nan",
}


class TestNetCostHelpers:
    def test_gain_bucket_bands_and_sign(self):
        from headroom.transforms.content_router import _gain_bucket

        assert _gain_bucket(0) == "0"
        assert _gain_bucket(50) == "lt100"
        assert _gain_bucket(500) == "lt1k"
        assert _gain_bucket(5000) == "lt10k"
        assert _gain_bucket(50000) == "gte10k"
        assert _gain_bucket(-50) == "neg_lt100"
        assert _gain_bucket(-50000) == "neg_gte10k"
        assert _gain_bucket(float("nan")) == "nan"
        assert _gain_bucket(float("inf")) == "nan"

    def test_message_tokens_block_list_beats_repr(self, tokenizer):
        # str(content) over a block list embeds the whole base64 payload; the
        # block-aware helper prices the image at its pixel cost instead.
        #
        # This used to use a 500-char stub image, which is *smaller* than a
        # single image's real token cost -- so repr looked cheap and the
        # payload-scaling bug stayed invisible. Use a realistically sized
        # payload, which is what actually occurs (screenshots).
        from headroom.transforms.content_router import _netcost_message_tokens

        text = "word " * 200
        block_msg = {
            "role": "user",
            "content": [
                {"type": "text", "text": text},
                {"type": "image", "source": {"data": "x" * 200_000}},
            ],
        }
        helper = _netcost_message_tokens(block_msg, tokenizer)
        text_only = tokenizer.count_text(text)
        # The text payload is still counted in full, and the image adds a
        # bounded pixel-based cost rather than a payload-scaled one.
        assert helper >= text_only
        assert helper - text_only <= 2000
        # ...which is dramatically less than stringifying the whole list.
        assert helper < tokenizer.count_text(str(block_msg["content"])) / 10

    def test_message_tokens_tool_result_blocks(self, tokenizer):
        from headroom.transforms.content_router import _netcost_message_tokens

        payload = "log line " * 100
        msg = {
            "role": "user",
            "content": [
                {
                    "type": "tool_result",
                    "tool_use_id": "t1",
                    "content": [{"type": "text", "text": payload}],
                }
            ],
        }
        assert _netcost_message_tokens(msg, tokenizer) >= tokenizer.count_text(payload) * 0.8

    def test_message_tokens_string_content(self, tokenizer):
        from headroom.transforms.content_router import _netcost_message_tokens

        s = "plain string content " * 50
        assert _netcost_message_tokens({"role": "user", "content": s}, tokenizer) == (
            tokenizer.count_text(s)
        )


def _frozen_messages(tool_content: str, suffix_filler_words: int) -> list[dict]:
    """A short conversation whose compressible tool dump sits *inside* the
    frozen prefix (index 1, with frozen_message_count=2)."""
    suffix = "analysis context word " * suffix_filler_words
    return [
        {"role": "user", "content": "fetch the records"},
        {"role": "tool", "content": tool_content},
        {"role": "user", "content": suffix},
        {"role": "user", "content": "summarize"},
    ]


class TestNetCostFrozenUnlock:
    """#856 P2b: let formula-positive deep edits through the frozen floor."""

    def test_flag_off_frozen_stays_frozen(self, router, tokenizer, monkeypatch):
        # Default (flag off): a message in the prefix cache is never mutated,
        # however compressible it is — the binary floor wins.
        monkeypatch.delenv("HEADROOM_NET_COST_POLICY", raising=False)
        messages = _frozen_messages(_tool_json(2000), suffix_filler_words=5)
        result = router.apply([dict(m) for m in messages], tokenizer, frozen_message_count=2)
        assert not _tool_slot_compressed(result, messages)
        assert "router:netcost_frozen_unlock" not in result.transforms_applied

    def test_flag_on_unlocks_when_shave_dominates(self, router, tokenizer, monkeypatch):
        # Huge shave deep in the frozen zone, tiny suffix after -> the
        # break-even gate clears the deep edit and it proceeds (the "50K
        # stale dump, 10K suffix" user story).
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _frozen_messages(_tool_json(2000), suffix_filler_words=5)
        result = router.apply([dict(m) for m in messages], tokenizer, frozen_message_count=2)
        assert _tool_slot_compressed(result, messages)
        assert "router:netcost_frozen_unlock" in result.transforms_applied

    def test_flag_on_keeps_frozen_when_suffix_dominates(self, router, tokenizer, monkeypatch):
        # Modest shave, big cached suffix -> gate runs on the unlocked slot
        # but rejects it. The frozen message is left byte-identical and no
        # unlock marker is emitted, proving the floor opened yet the formula
        # still protected the cache.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _frozen_messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer, frozen_message_count=2)
        assert not _tool_slot_compressed(result, messages)
        assert "router:netcost_frozen_unlock" not in result.transforms_applied
        assert any(t.startswith("netcost:skip:") for t in result.transforms_applied)

    def test_flag_on_block_content_frozen_stays_frozen(self, router, tokenizer, monkeypatch):
        # The gate is wired into the string and parallel-merge paths only;
        # block-list frozen content (whose per-block cache_control contract
        # is not net-cost aware) stays frozen even with a tiny suffix.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        big = "log line of output " * 400
        messages = [
            {"role": "user", "content": "fetch"},
            {
                "role": "user",
                "content": [
                    {
                        "type": "tool_result",
                        "tool_use_id": "t1",
                        "content": [{"type": "text", "text": big}],
                    }
                ],
            },
            {"role": "user", "content": "summarize"},
        ]
        original = [dict(m) for m in messages]
        result = router.apply([dict(m) for m in messages], tokenizer, frozen_message_count=2)
        assert result.messages[1]["content"] == original[1]["content"]
        assert "router:netcost_frozen_unlock" not in result.transforms_applied


class TestNetCostBatchReclaim:
    """#856 P3a: batch deep edits -- once one net-positive edit is admitted at
    slot K, deeper candidates ride that cache-bust for free (S charged as 0).

    Tests are cache-cold (fresh router per fixture) so every candidate flows
    through the parallel-merge pass in ascending slot order, which is where the
    shared batch_state floor is set and then reclaimed.
    """

    @staticmethod
    def _convo(slot1: str, slot2: str, filler_words: int) -> list[dict]:
        # Two consecutive tool dumps (slots 1 and 2) followed by a filler
        # suffix. Slot 1 is the shallower candidate; slot 2 the deeper one.
        suffix = "analysis context word " * filler_words
        return [
            {"role": "user", "content": "fetch the records"},
            {"role": "tool", "content": slot1},
            {"role": "tool", "content": slot2},
            {"role": "user", "content": suffix},
            {"role": "user", "content": "summarize"},
        ]

    @staticmethod
    def _compressed(result, original, idx: int) -> bool:
        return result.messages[idx]["content"] != original[idx]["content"]

    def test_flag_off_no_batch_marker(self, router, tokenizer, monkeypatch):
        # Without the flag the batch path is inert -- no marker, no counter.
        monkeypatch.delenv("HEADROOM_NET_COST_POLICY", raising=False)
        messages = self._convo(_tool_json(2000), _tool_json(800), filler_words=5)
        original = [dict(m) for m in messages]
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert "router:netcost_batch_admit" not in result.transforms_applied
        # Both deep edits still compress (no gate at all when flag off).
        assert self._compressed(result, original, 1)
        assert self._compressed(result, original, 2)

    def test_deeper_edit_rides_free(self, router, tokenizer, monkeypatch):
        # Slot 1 (huge shave) admits on its own merit and opens the floor;
        # slot 2 then admits via the batch reclaim path and emits the marker.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = self._convo(_tool_json(2000), _tool_json(800), filler_words=5)
        original = [dict(m) for m in messages]
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert self._compressed(result, original, 1)
        assert self._compressed(result, original, 2)
        markers = [t for t in result.transforms_applied if t == "router:netcost_batch_admit"]
        # Exactly one deeper slot rode the floor for free.
        assert len(markers) == 1

    def test_batch_admits_otherwise_blocked_edit(self, router, tokenizer, monkeypatch):
        # Slot 2 (modest shave, large suffix after it) would be blocked on its
        # own S, but slot 1's admit already busted the suffix -- so slot 2 rides
        # free. Pairs with test_no_prior_admit_keeps_block, which shows the same
        # slot-2 config stays blocked when no shallower edit opens the floor.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = self._convo(_tool_json(2000), _tool_json(300), filler_words=4000)
        original = [dict(m) for m in messages]
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert self._compressed(result, original, 1)  # floor-setting admit
        assert self._compressed(result, original, 2)  # rode free
        assert "router:netcost_batch_admit" in result.transforms_applied

    def test_no_prior_admit_keeps_block(self, router, tokenizer, monkeypatch):
        # Neither candidate beats its own S (both modest shaves under a huge
        # suffix), so the floor is never opened and no slot rides free. Guards
        # against a floor-init / off-by-one bug that would grant a free ride
        # with no genuine shallower mutation behind it.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = self._convo(_tool_json(300), _tool_json(300), filler_words=40000)
        original = [dict(m) for m in messages]
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert not self._compressed(result, original, 1)
        assert not self._compressed(result, original, 2)
        assert "router:netcost_batch_admit" not in result.transforms_applied

    def test_frozen_unlock_and_batch_combine(self, router, tokenizer, monkeypatch):
        # Two frozen string slots inside the prefix (frozen_message_count=3).
        # Slot 1 unlocks and sets the floor; slot 2 unlocks AND rides free.
        # Slot 2 carries both markers; the batch counter must not double-count.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = self._convo(_tool_json(2000), _tool_json(800), filler_words=5)
        original = [dict(m) for m in messages]
        result = router.apply([dict(m) for m in messages], tokenizer, frozen_message_count=3)
        assert self._compressed(result, original, 1)
        assert self._compressed(result, original, 2)
        unlocks = [t for t in result.transforms_applied if t == "router:netcost_frozen_unlock"]
        batch = [t for t in result.transforms_applied if t == "router:netcost_batch_admit"]
        assert len(unlocks) == 2  # both frozen slots opened
        assert len(batch) == 1  # only the deeper one rode free -- no double-count


class TestNetCostIdleCompaction:
    """#856 P3b: derive P_alive from idle time. As the session goes idle the
    cached suffix nears TTL lapse, P_alive -> 0, the net-cost penalty term
    vanishes, and edits that lose to a warm suffix become free.

    Baseline shape (mirrors TestNetCostGate.test_flag_on_blocks...): a modest
    tool-dump shave under a huge cached suffix is BLOCKED at the default
    P_alive=1.0. These tests vary only the idle signal.
    """

    def test_idle_near_ttl_unlocks_blocked_edit(self, router, tokenizer, monkeypatch):
        # idle ~= cache TTL (default 300s) -> P_alive ~= 0 -> penalty ~= 0 ->
        # the otherwise-blocked deep edit is admitted and marked.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer, idle_seconds=295.0)
        assert _tool_slot_compressed(result, messages)
        assert "router:netcost_idle_compaction" in result.transforms_applied
        assert not any(t.startswith("netcost:skip:") for t in result.transforms_applied)

    def test_idle_zero_matches_constant_baseline(self, router, tokenizer, monkeypatch):
        # idle=0 -> P_alive=1.0, identical to the env-constant default: the
        # edit stays blocked and no idle marker is emitted.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer, idle_seconds=0.0)
        assert not _tool_slot_compressed(result, messages)
        assert "router:netcost_idle_compaction" not in result.transforms_applied
        assert any(t.startswith("netcost:skip:") for t in result.transforms_applied)

    def test_idle_absent_uses_env_constant(self, router, tokenizer, monkeypatch):
        # No idle_seconds kwarg -> override is None -> P2 env-constant path.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer)
        assert not _tool_slot_compressed(result, messages)
        assert "router:netcost_idle_compaction" not in result.transforms_applied

    def test_malformed_idle_falls_back_to_constant(self, router, tokenizer, monkeypatch):
        # Non-numeric idle_seconds is ignored (override stays None), so the
        # gate keeps the constant behaviour rather than crashing the request.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer, idle_seconds="soon")
        assert not _tool_slot_compressed(result, messages)
        assert "router:netcost_idle_compaction" not in result.transforms_applied

    def test_custom_ttl_env_controls_decay(self, router, tokenizer, monkeypatch):
        # A shorter TTL makes the same idle fully decay P_alive -> unlock.
        monkeypatch.setenv("HEADROOM_NET_COST_POLICY", "1")
        monkeypatch.setenv("HEADROOM_NET_COST_CACHE_TTL_SECONDS", "60")
        messages = _messages(_tool_json(300), suffix_filler_words=40000)
        result = router.apply([dict(m) for m in messages], tokenizer, idle_seconds=59.0)
        assert _tool_slot_compressed(result, messages)
        assert "router:netcost_idle_compaction" in result.transforms_applied