File and shell tools fail clearly in diskless sessions that run them only in the cloud

What

A diskless session is one launched with an option saying the process running Claude has no local disk to work on, so file and shell tools only run in a separate cloud environment.

• A new guard covers a fixed set of built-in file and shell tools. In a diskless session, when a call cannot be sent to the cloud environment, it throws NeverRunsInThisProcessError with a message telling Claude the tool "is unavailable: this session runs file and shell tools only in its cloud environment, and this call could not be sent there. Retrying will not help."
• Tool results that come back from another process and cannot be read now say whether it is safe to run the tool again, based on whether the tool only reads.
• The check for whether a file is tracked by git now answers "tracked" straight away in a diskless session instead of running git ls-files. Starting programs is refused in diskless sessions, with the note "a program start was refused in a diskless session".
• New diagnostic entries were added around cloud-container tool routing.

Why

This only affects hosted or remote setups where tools run in the cloud. Claude gets a clear answer instead of retrying a call that can never run locally.