RC2_STATE_DICT_KEY

Dict keys must be string literals.

What it means

A class-body dict literal used a non-string key. Persistent-state dict keys are always strings — the slot is stored and restored by key, and a string key is the one form that survives that round trip unambiguously.

Why it happens

class Bad(Strategy):
    trade = Symbol()
    sizing = FixedCapital()

    by_index = {1: "long", 2: "short"}   # ❌ int keys

    def execute(self):
        if self.trade.is_flat:
            self.buy(self.trade)

How to fix it

Use string keys. If integer indexing was the real intent, a list is the better shape.

class Good(Strategy):
    trade = Symbol()
    sizing = FixedCapital()

    # String-keyed dict
    labels = {"1": "long", "2": "short"}

    # …or a list, when the position IS the identity
    states = ["long", "short", "flat"]

    def execute(self):
        if self.trade.is_flat:
            self.buy(self.trade, reason=self.states[0])

Persistent State
RC2_STATE_MIXED — the values in a dict must share one type.
RC2_STATE_NESTED — a dict value may not itself be a collection.