"""Supervisor with explicit dispatch policy. Author: Sandeep Belgavi."""
from dataclasses import dataclass

@dataclass(frozen=True)
class Ticket:
    incident: str
    service: str
    symptom: str

def dispatch(ticket, router, specialists, allowed_services):
    if not isinstance(ticket, Ticket) or not ticket.incident:
        raise ValueError("invalid ticket")
    if ticket.service not in allowed_services:
        return {"status": "denied", "route": "none"}
    try:
        route = router(ticket.symptom)
    except Exception:
        return {"status": "route_error", "route": "none"}
    if not isinstance(route, str) or route not in {"latency", "availability"}:
        return {"status": "escalate", "route": "none"}
    if route not in specialists:
        return {"status": "unavailable", "route": route}
    # Only this typed envelope crosses into a specialist, never raw credentials.
    envelope = {"incident": ticket.incident, "service": ticket.service}
    try:
        result = specialists[route](envelope)
    except Exception:
        return {"status": "worker_error", "route": route}
    if not isinstance(result, str) or not result.startswith("fixture:"):
        return {"status": "invalid_result", "route": route}
    return {"status": "review", "route": route, "evidence": result}

if __name__ == "__main__":
    result = dispatch(Ticket("INC-42", "checkout", "slow"), lambda _: "latency",
                      {"latency": lambda _: "fixture:L1"}, {"checkout"})
    print(f"status={result['status']} route={result['route']} evidence={result['evidence']}")