Map Python ProtocolError responses to BridgeProtocolError

[bbopen]

Summary

When the Python bridge returns an error payload with type: "ProtocolError", NodeBridge/OptimizedNodeBridge wraps it as BridgeExecutionError. This misclassifies protocol violations as execution errors and makes it harder to differentiate user-code failures from protocol issues.

Failure mode

• Python bridge returns { error: { type: "ProtocolError", message: "..." } }.
• JS side throws BridgeExecutionError instead of BridgeProtocolError.

Evidence

• src/runtime/node.ts errorFrom always returns BridgeExecutionError.
• src/runtime/optimized-node.ts errorFrom same pattern.

Proposed fix

• If err.type === 'ProtocolError', return BridgeProtocolError (and include message/traceback).
• Otherwise keep BridgeExecutionError.

Acceptance criteria

• ProtocolError from Python surfaces as BridgeProtocolError on the JS side.
• Tests cover a custom bridge returning ProtocolError.

[bbopen]

Resolved by PR #150. BoundedContext.classifyError() maps protocol error patterns to BridgeProtocolError.