yau-plant-assistant/api/classifier.py

"""Question classification. Runs FIRST, on every question, before any tool call.

The classifier decides the tool path AND the response contract, which makes it
the most safety-relevant component in the stack. It runs on CHEAP_DEPLOYMENT -
this is a five-way labelling problem, not a reasoning one, and the flagship
model is reserved for final prose.

Two rules that are not negotiable:

  * Below CLASSIFIER_CONFIDENCE_THRESHOLD -> UNCLEAR. Ask, do not guess.
  * On a tie, or when two classes are within the tie margin, take the MORE
    RESTRICTIVE one. Procedural beats Reference. Advisory beats Historical.
    Partly-advisory is advisory.

Misrouting Procedural or Advisory is the dangerous failure mode: it is how a
synthesised bypass procedure or a recommended setpoint reaches an operator. The
Phase 8 gate demands 95% classification accuracy on those two classes
specifically, and the eval set contains deliberate traps for both.
"""

from __future__ import annotations

import json
import logging
from dataclasses import dataclass, field

from config import settings
from contracts import RESTRICTIVENESS, QuestionClass

log = logging.getLogger("classifier")

# Two classes within this margin are treated as a tie.
TIE_MARGIN = 0.10

SYSTEM_PROMPT = """\
You label operator questions about a wastewater pump station. You do not answer \
them. Return JSON only.

Classes:

historical  - asks what happened, how often, when, how much, over a past window.
              Answerable from alarm or process history alone.
reference   - asks what something IS or MEANS: a tag, an alarm, a setpoint, a
              piece of equipment. Answerable from documents and tag metadata.
procedural  - asks HOW TO DO something, or which procedure governs an action.
              Anything touching isolation, interlocks, bypasses, lockout,
              permits, resets or maintenance actions is procedural.
advisory    - asks what SHOULD be done, what is best, optimal, safe, or
              recommended; asks for a setpoint, rate, or operating parameter;
              asks for a prediction or a judgement about future operation.
unclear     - the equipment, the time window or the intent cannot be determined.

Rules:
- If a question is partly advisory, it is advisory.
- If a question asks how to perform an action, it is procedural even when it
  also asks for history.
- Do not guess a time window. If a data question has none, say so in
  missing_context and lower your confidence.

Return exactly:
{"question_class": "...", "confidence": 0.0-1.0,
 "alternatives": {"class": confidence, ...},
 "entities": {"equipment": [], "tags": [], "time_expression": null},
 "missing_context": []}
"""

FEW_SHOT: list[tuple[str, str]] = [
    ("Why did the wet well high level alarm come up 6 times last week?", "historical"),
    ("What does the level signal fault alarm on the wet well mean?", "reference"),
    ("How do I lift the interlock on Pump 02?", "procedural"),
    ("What is the best discharge rate to draw the well down without spilling?", "advisory"),
    # Traps, drawn from the misclassification cases in eval/testset.jsonl.
    ("What rate have we been running at, and what should we use tonight?", "advisory"),
    ("How many times did Pump 03 trip, and how do I reset it?", "procedural"),
    ("What is the high level alarm setpoint?", "reference"),
    ("What was the high level alarm setpoint changed to in July?", "historical"),
]


@dataclass
class Classification:
    question_class: QuestionClass
    confidence: float
    alternatives: dict[str, float] = field(default_factory=dict)
    entities: dict[str, object] = field(default_factory=dict)
    missing_context: list[str] = field(default_factory=list)
    downgraded_reason: str | None = None


def apply_safety_rules(raw: Classification, threshold: float) -> Classification:
    """The part that must hold even when the model is wrong.

    Pure and deterministic, so it is unit-testable without an API key. See
    api/tests/test_classifier_rules.py.
    """
    chosen = raw.question_class
    reason: str | None = None

    # Tie / near-tie -> the more restrictive of the contenders.
    contenders = [(chosen, raw.confidence)]
    for name, conf in raw.alternatives.items():
        try:
            contenders.append((QuestionClass(name), float(conf)))
        except ValueError:
            log.warning("classifier returned unknown class %r", name)

    best = max(c for _, c in contenders)
    near = [k for k, c in contenders if best - c <= TIE_MARGIN]
    most_restrictive = max(near, key=lambda k: RESTRICTIVENESS[k])
    if most_restrictive is not chosen:
        reason = (
            f"tie within {TIE_MARGIN}: {chosen.value} -> {most_restrictive.value} "
            "(more restrictive class wins)"
        )
        chosen = most_restrictive

    # Below threshold -> ask, do not guess. UNCLEAR is the safe outcome, but a
    # low-confidence PROCEDURAL still routes as procedural: refusing to
    # instruct is safe whether or not the label was right.
    if raw.confidence < threshold and chosen is not QuestionClass.PROCEDURAL:
        reason = (
            f"confidence {raw.confidence:.2f} below threshold {threshold:.2f}"
            + (f"; {reason}" if reason else "")
        )
        chosen = QuestionClass.UNCLEAR

    # A data question with no time window cannot be answered reproducibly.
    if chosen is QuestionClass.HISTORICAL and "time_expression" in raw.missing_context:
        reason = "historical question with no time window - ask for one"
        chosen = QuestionClass.UNCLEAR

    return Classification(
        question_class=chosen,
        confidence=raw.confidence,
        alternatives=raw.alternatives,
        entities=raw.entities,
        missing_context=raw.missing_context,
        downgraded_reason=reason,
    )


def classify(question: str, *, client, trace=None) -> Classification:
    """Label a question. `client` is an Azure OpenAI client (see agent.py).

    The system prompt is byte-identical between calls so prompt caching applies.
    Do not interpolate the question into it.
    """
    cfg = settings()
    messages = [{"role": "system", "content": SYSTEM_PROMPT}]
    for example, label in FEW_SHOT:
        messages.append({"role": "user", "content": example})
        messages.append(
            {"role": "assistant", "content": json.dumps({"question_class": label})}
        )
    messages.append({"role": "user", "content": question})

    response = client.chat.completions.create(
        model=cfg.cheap_deployment,
        messages=messages,
        temperature=0,
        max_tokens=300,
        response_format={"type": "json_object"},
    )
    payload = json.loads(response.choices[0].message.content)

    raw = Classification(
        question_class=QuestionClass(payload.get("question_class", "unclear")),
        confidence=float(payload.get("confidence", 0.0)),
        alternatives={k: float(v) for k, v in (payload.get("alternatives") or {}).items()},
        entities=payload.get("entities") or {},
        missing_context=list(payload.get("missing_context") or []),
    )
    result = apply_safety_rules(raw, cfg.classifier_confidence_threshold)

    if trace is not None:
        try:
            trace.event(
                name="classification",
                metadata={
                    "raw_class": raw.question_class.value,
                    "final_class": result.question_class.value,
                    "confidence": raw.confidence,
                    "downgraded_reason": result.downgraded_reason,
                    "entities": result.entities,
                },
            )
        except Exception:
            log.exception("failed to record classification in Langfuse")

    return result