Compression dropping required user turn bug fixes

Fixes on record

Merged to main. A stamp counts the issues a fix is linked to.

• #58974 fix(compressor): keep a user turn when compression would drop the only one (#58753)

  merged to main

  files: agent/context_compressor.py, tests/agent/test_compressor_zero_user_guard.py

  Show the diff

  • agent/context_compressor.py

    @@ -2910,6 +2910,33 @@ def compress(self, messages: List[Dict[str, Any]], current_tokens: int = None, f
             # is not role=user, so we must pin the summary to "user" and
             # prevent the flip logic below from reverting it (#52160).
             _force_user_leading = last_head_role == "system"
    +        # Zero-user-turn guard (#58753). The #52160 guard above only fires
    +        # when the system prompt sits *inside* ``messages`` (the gateway
    +        # ``/compress`` path). The main auto-compression path passes the
    +        # transcript WITHOUT the system prompt (it is prepended at
    +        # request-build time), so ``last_head_role`` defaults to "user" and
    +        # the summary is emitted as role="assistant". On a session whose only
    +        # genuine user turn falls into the compressed middle — e.g. a
    +        # ``hermes kanban`` worker seeded with a single short
    +        # ``"work kanban task <id>"`` prompt followed by nothing but
    +        # assistant/tool turns — that leaves the compressed transcript with
    +        # ZERO user-role messages. OpenAI-compatible backends (vLLM/Qwen)
    +        # reject such a request with a non-retryable
    +        # ``400 No user query found in messages``, crashing the worker with no
    +        # possible recovery (every resume replays the same poisoned history).
    +        # If no user-role message survives in either the protected head or the
    +        # preserved tail, the summary MUST carry role="user" so the request
    +        # always has at least one user turn.
    +        if not _force_user_leading:
    +            _user_survives = any(
    +                messages[i].get("role") == "user"
    +                for i in range(0, compress_start)
    +            ) or any(
    +                messages[i].get("role") == "user"
    +                for i in range(compress_end, n_messages)
    +            )
    +            if not _user_survives:
    +                _force_user_leading = True
             # Pick a role that avoids consecutive same-role with both neighbors.
             # Priority: avoid colliding with head (already committed), then tail.
             if last_head_role in {"assistant", "tool"} or _force_user_leading:

  • tests/agent/test_compressor_zero_user_guard.py

    @@ -0,0 +1,180 @@
    +"""Regression coverage for #58753 — compression could drop the only
    +user-role message, leaving a transcript with ZERO user turns.
    +
    +The compressor already pins the handoff summary to ``role="user"`` when
    +the only protected head message is the system prompt (#52160). But that
    +guard keys off ``last_head_role == "system"``, which is only true when
    +the system prompt actually sits inside ``messages`` — the gateway
    +``/compress`` path. The main auto-compression path passes the transcript
    +WITHOUT the system prompt (it is prepended at request-build time, see
    +``conversation_loop`` — ``api_messages = [{"role": "system", ...}] +
    +api_messages``). There ``last_head_role`` defaults to ``"user"`` and the
    +summary is emitted as ``role="assistant"``.
    +
    +On a session whose only genuine user turn falls into the compressed
    +middle — the canonical shape being a ``hermes kanban`` worker seeded with
    +a single short ``"work kanban task <id>"`` prompt followed by nothing but
    +assistant/tool turns — the compressed output then contains no user-role
    +message at all. OpenAI-compatible backends (vLLM/Qwen) reject such a
    +request with a non-retryable ``400 No user query found in messages``,
    +crashing the worker with no possible recovery (every resume replays the
    +same poisoned history).
    +
    +The fix generalises the #52160 guard: when NO user-role message survives
    +in the protected head or preserved tail, the summary MUST carry
    +``role="user"``.
    +"""
    +
    +from __future__ import annotations
    +
    +from unittest.mock import patch
    +
    +import pytest
    +
    +
    [redacted:email]()
    +def compressor():
    +    from agent.context_compressor import ContextCompressor
    +
    +    with patch(
    +        "agent.context_compressor.get_model_context_length",
    +        return_value=100_000,
    +    ):
    +        c = ContextCompressor(
    +            model="test/model",
    +            threshold_percent=0.50,
    +            protect_first_n=3,
    +            protect_last_n=20,
    +            quiet_mode=True,
    +        )
    +        c.tail_token_budget = 40
    +        return c
    +
    +
    +def _tool_turns(start: int, n: int) -> list[dict]:
    +    out: list[dict] = []
    +    for i in range(start, start + n):
    +        out.append(
    +            {
    +                "role": "assistant",
    +                "content": None,
    +                "tool_calls": [
    +                    {
    +                        "id": f"c{i}",
    +                        "function": {"name": "read_task", "arguments": "{}"},
    +                    }
    +                ],
    +            }
    +        )
    +        out.append({"role": "tool", "content": "x" * 300, "tool_call_id": f"c{i}"})
    +    return out
    +
    +
    +def _role_hist(messages: list[dict]) -> dict[str, int]:
    +    hist: dict[str, int] = {}
    +    for m in messages:
    +        hist[m.get("role")] = hist.get(m.get("role"), 0) + 1
    +    return hist
    +
    +
    +class TestCompressAlwaysKeepsAUserTurn:
    +    def test_kanban_worker_recompaction_keeps_user_turn(self, compressor):
    +        """The exact #58753 shape: no system prompt in the list, a
    +        re-compaction (``protect_first_n`` decayed to 0), and the only
    +        user turn old enough to fall into the compressed middle. Before
    +        the fix, the summary was emitted as ``assistant`` and the output
    +        had zero user-role messages."""
    +        from agent.context_compressor import SUMMARY_PREFIX
    +
    +        c = compressor
    +        # A prior compaction has already happened → protect_first_n decays
    +        # to 0 so compress_start lands at 0 (no protected head).
    +        c.compression_count = 1
    +        # No system message: the main loop prepends it separately.
    +        messages = [{"role": "user", "content": "work kanban task 42"}]
    +        messages += _tool_turns(0, 12)
    +
    +        mocked = f"{SUMMARY_PREFIX}\nrolled-up summary of the tool work"
    +        with patch.object(c, "_generate_summary", return_value=mocked):
    +            out = c.compress(messages, current_tokens=[redacted:secret-assignment]
    +
    +        hist = _role_hist(out)
    +        assert hist.get("user", 0) >= 1, (
    +            "REGRESSION (#58753): compression produced a transcript with "
    +            f"zero user-role messages, which vLLM/Qwen reject with a "
    +            f"non-retryable 400. Role histogram: {hist}"
    +        )
    +
    +    def test_summary_pinned_to_user_when_no_user_survives(self, compressor):
    +        """When the whole compressible region is assistant/tool and no
    +        user message survives in head or tail, the inserted summary
    +        itself must be the user turn."""
    +        from agent.context_compressor import (
    +            SUMMARY_PREFIX,
    +            COMPRESSED_SUMMARY_METADATA_KEY,
    +        )
    +
    +        c = compressor
    +        c.compression_count = 1
    +        messages = [{"role": "user", "content": "work kanban task 7"}]
    +        messages += _tool_turns(0, 12)
    +
    +        mocked = f"{SUMMARY_PREFIX}\nsummary body"
    +        with patch.object(c, "_generate_summary", return_value=mocked):
    +            out = c.compress(messages, current_tokens=[redacted:secret-assignment]
    +
    +        summary_rows = [m for m in out if m.get(COMPRESSED_SUMMARY_METADATA_KEY)]
    +        assert len(summary_rows) == 1
    +        assert summary_rows[0].get("role") == "user", (
    +            "The handoff summary must carry role=user when it is the only "
    +            "possible user turn in the compressed transcript (#58753)."
    +        )
    +
    +    def test_no_consecutive_user_roles_introduced(self, compressor):
    +        """Forcing the summary to role=user must not create two
    +        consecutive user-role messages (strict alternation invariant).
    +        When a user survives in the tail we do NOT force, so the pinned
    +        summary can never collide with a user-role neighbour."""
    +        from agent.context_compressor import SUMMARY_PREFIX
    +
    +        c = compressor
    +        c.compression_count = 1
    +        messages = [{"role": "user", "content": "work kanban task 9"}]
    +        messages += _tool_turns(0, 12)
    +
    +        mocked = f"{SUMMARY_PREFIX}\nsummary body"
    +        with patch.object(c, "_generate_summary", return_value=mocked):
    +            out = c.compress(messages, current_tokens=[redacted:secret-assignment]
    +
    +        for prev, cur in zip(out, out[1:]):
    +            assert not (
    +                prev.get("role") == "user" and cur.get("role") == "user"
    +            ), "compression introduced consecutive user-role messages"
    +
    +    def test_preserved_tail_user_is_not_overridden(self, compressor):
    +        """When a genuine user message survives in the tail, the guard
    +        must NOT fire (the summary keeps its alternation-driven role) —
    +        the request already has a user turn."""
    +        from agent.context_compressor import SUMMARY_PREFIX
    +
    +        c = compressor
    +        c.compression_count = 1
    +        c.tail_token_budget = 10  # tight tail so most turns compress
    +        messages = [{"role": "user", "content": "old task"}]
    +        messages += _tool_turns(0, 10)
    +        # A recent, genuine user turn that will be preserved in the tail.
    +        messages += [
    +            {"role": "user", "content": "the latest live user question"},
    +            {"role": "assistant", "content": "on it"},
    +        ]
    +
    +        mocked = f"{SUMMARY_PREFIX}\nsummary body"
    +        with patch.object(c, "_generate_summary", return_value=mocked):
    +            out = c.compress(messages, current_tokens=[redacted:secret-assignment]
    +
    +        hist = _role_hist(out)
    +        assert hist.get("user", 0) >= 1
    +        joined = "\n".join(
    +            m.get("content") for m in out if isinstance(m.get("content"), str)
    +        )
    +        assert "the latest live user question" in joined