SDK gets a verbatimPrompts option to skip client_composed processing

What

• The SDK session class now accepts a verbatimPrompts constructor option. By default (verbatimPrompts: false), outgoing messages are tagged client_composed: true; when verbatimPrompts is set, that tag is no longer added.
• The client_composed schema field's documentation was expanded to explain exactly what that marker does: turns marked this way (composed by the client rather than typed by the user) skip @-path file-mention expansion, slash-command dispatch, @server:resource MCP mention expansion, and the whole turn-start attachment pass (nested CLAUDE.md/rules files, skill/tool listings, reminders). The separate between-tool-calls attachment pass is unaffected.

Why

This gives SDK integrators control over whether their outgoing messages get Claude Code's normal client-side preprocessing (mention/slash-command expansion, context attachment) or are sent through verbatim, which matters when a client wants precise control over exactly what content reaches the model.