SIP: PTB Dynamic Dispatch via Command Context & Scoped Execution

[92GC]

Add a new sui::ptb_context module with native functions for inspecting PTB execution context:

public native fun current_index(ctx: &TxContext): u16;
public native fun total_commands(ctx: &TxContext): u16;
public native fun command_at(ctx: &TxContext, index: u16): Option<CommandInfo>;
public native fun scope_depth(ctx: &TxContext): u8;
public native fun argument_source(ctx: &TxContext, arg_index: u8): Option<ArgumentSource>;
public native fun create_scope_witness(ctx: &mut TxContext): ScopeWitness;
public native fun in_same_scope(ctx: &TxContext, witness: &ScopeWitness): bool;

Plus a new Scope { commands, inherit_context } PTB command variant.

Problem

Composing Move protocols requires pre-built hot potato wrappers for every integration. A DAO executing "vault spend → DEX swap → vault deposit" needs a custom wrapper per DEX. New DEX = new code to write, audit, and deploy. There's no way for a contract to verify at runtime who produced a value or which commands are in the transaction.

Use Cases

• Dynamic dispatch — verify a coin came from an approved package at runtime, no wrapper needed. Adding a new DEX becomes an allowlist update, not new code.
• Scoped isolation — partition PTB commands so protocols can't see (or censor) each other. Prevents AMMs from refusing arbitrage by detecting competitors in the same transaction.