Code mode gets a setup opt-in, warning banners and changes to MCP and file-read tools

What

Several pieces of a feature called code mode appear in this release. Some of them concern MCP tools, which are extra tools that outside services provide to Claude. Others concern the REPL, an environment where Claude runs code:

• Setup opt-in: the series of dialogs shown at startup has a new step. If a check passes, it shows CodeModeOptIn (reviewCodeModeOptInInSetup). Before, that step was an empty placeholder that showed nothing.
• Warning banners: a new list has two warnings, code-mode-opt-in and code-mode-remote-control. The first appears when code mode reports a reason it refused, or a notice when code mode is "on". The second appears under a condition related to Remote Control.
• Model notice: a new warning keyed code-mode-model shows notices about the model in code mode. It is high priority, lasts 15 seconds, and is cleared when there is no notice. It only runs when a build-time check, ae(), is true.
• MCP tools in the REPL: when the REPL routes MCP tools, the message shown after waiting for servers now says their tools are "callable inside the REPL environment" and not as top-level tools. Before, it always said they were available to call directly. MCP servers are also skipped in REPL mode, with a warning.
• Tool information: MCP tool information gains a codeModeRouted marker when ae() is true and the tools are routed this way. Before, nothing was added there.
• File reads: the file-read tool now refuses, with reason not_available and detail code_mode, when a recipient check is present and code mode tools are in use.

Why

If code mode reaches you, you may see an opt-in step at startup and new warnings. MCP tools may stop showing up as ordinary tools and instead be reached inside the REPL. Some file reads that worked before may be refused while code mode tools are in use.