MCPTool and DeferredMCPTool now declare approval = 'write' instead of
implicitly defaulting to 'exec'. Without this, the approval system
requires user confirmation for every MCP tool call in non-yolo modes,
but the confirmation prompt never renders in the TUI while streaming,
causing the agent to hang indefinitely.
Also propagate the approval property through customToolToDefinition()
in sdk.ts, which was silently dropping it during CustomTool ->
ToolDefinition conversion.
Guts
83c8105be6