The Bridge contract is the JSON data model

Values crossing the Bridge follow json.dumps / json.loads semantics exactly, and anything outside that set raises instead of converting. This replaces a best-effort scheme that guessed at the closest match and produced silent corruption: booleans arrived in JavaScript as numbers, dictionary keys of every type were silently coerced to strings, and bytes was documented as number[] while having no representation in the model at all.

The rule is chosen for the sentence it fits into rather than the table it generates — “whatever json accepts” is already in every Python developer’s head, and the default= hook they reach for is the same one json.dumps gives them.

Consequences

set and bytes leave the contract deliberately: neither has a JSON analogue, and both round-trip destructively. Integers outside ±2⁵³ raise rather than silently losing precision. Dictionary keys are coerced to strings exactly as json.dumps coerces them, so a round trip returns string keys. datetime, Decimal, Enum and dataclasses are the developer’s job, through the hook.