{"version":"2.1.301","anchor":"bash-tool-gains-run-in-background-keep-path-and-leanrewrite","canonical_anchor":"bash-tool-gains-run-in-background-keep-path-and-leanrewrite","heading":"Bash gains a keep-in-background path, and MCP results not meant for the model skip size handling","tier":"notice","area":"Background Shells","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.301\/e\/bash-tool-gains-run-in-background-keep-path-and-leanrewrite","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.301","markdown":"### Bash gains a keep-in-background path, and MCP results not meant for the model skip size handling\n\nBash can force commands into the background with a `keptBackgroundShells` starter, and MCP results flagged not for the model bypass output limits\n\n**What**\n\nThe Bash tool, which runs shell commands for Claude, gains a new way to run commands in the background.\n\n- When this path is used, `run_in_background` is forced to true, and Bash gets a `keptBackgroundShells` starter to work with. One finding reports that `run_in_background` is removed from the tool's options on this path. The other reports that it is kept in the input.\n\n- The tool setup now passes a `leanRewrite` option into tool descriptions, and the Bash description accepts it. Descriptions can now differ depending on that option.\n\n- The stock Bash description captured under this release is 9,857 characters in its longest of 3 versions, unchanged from the previous release.\n\n- `tengu_structured_output_strict` is unchanged in this build and still defaults to false.\n\nSeparately, MCP tool calls gain a `resultNotForModel` option, false by default. MCP tools come from add-on servers. When the option is set, the result's content is returned as is, and the usual image and size checks are skipped, along with saving large output to a file.\n\n**Why**\n\nMCP results that are not meant for the model should no longer be shortened or moved into files. The Bash changes lay the groundwork for keeping shells running in the background and for a different Bash description, without visible effect described yet.\n\n- Flag `tengu_structured_output_strict`: Off in both readings (read for one account on one subscription tier against v2.1.301; this account: off, anonymous baseline: off, compiled default: off) These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.\n- Area: Background Shells\n- Tier: You'll notice\n- Useful: 2\/5\n- Signal: 4\/5\n- Scope: individual\n- Heads-up: no"}