[plainprogrammer]

Closes #268.

Cause

Two things, both about the environment Orca's setup shell (bash -lc 'eval "${ORCA_SEQUENCED_SETUP_SCRIPT}"') has, which #226's check (from an interactive shell with mise active) never saw:

1. No mise on the PATH. The Orca app's PATH is /usr/bin:/bin:/usr/sbin:/sbin; a login bash doesn't activate mise. mise exec gives command not found (127), and the post-checkout hook's "no mise, run as is" fallback ran bin/setup on macOS's Ruby 2.6 (the error in Orca worktree setup still runs bin/setup on the system Ruby #268).
2. mise found, system Ruby still first. In a worker's setup terminal (zsh with mise active, then bash -lc), mise's installs/ruby/4.0.7/bin is in the PATH but behind /usr/bin (macOS path_helper), and mise exec doesn't move a directory already in the PATH. mise exec -- ruby -v said 4.0.7, but mise exec -- sh -c 'command -v ruby' said /usr/bin/ruby, so bin/setup's #!/usr/bin/env ruby and bundle ran on 2.6. Unsetting the __MISE_* variables changed nothing; only the PATH order matters.

Fix

script/worktree/with_mise [--optional] COMMAND… finds mise (PATH, then ~/.local/bin, /opt/homebrew/bin, /usr/local/bin, Linuxbrew, ~/.cargo/bin; COLLECTOR_MISE_SEARCH overrides), drops mise's own installs/* and shims directories from the PATH, and runs mise exec -- COMMAND. No mise is exit 127 with a message; --optional (the hook, for CI runners) runs the command as is. orca.yaml and .githooks/post-checkout use it. Cause recorded in the orca.yaml comment, the script's header, CLAUDE.md's Worktrees fact and docs/lessons/2026-11-09-orca-setup-shell-has-no-mise.md.

Evidence

Before (main, real worker-start worktree; the setup terminal): Could not find 'bundler' (4.0.20) … Ruby.framework/Versions/2.6 … bin/setup:10:in 'system', agent skipped (failedStage=agent_readiness). The first version of the fix (finding mise only) failed identically in that terminal, which is how cause 2 was found.

After (this branch, orca orchestration worker-start --worktree new-top-level --base-branch 268-orca-setup-system-ruby): state ready, setup terminal:

bash -lc 'eval "${ORCA_SEQUENCED_SETUP_SCRIPT:?missing}"'
== Installing dependencies ==
The Gemfile's dependencies are satisfied
== Installing the OCR engine == … == Preparing database == … == Dev server URL: http://localhost:3925 ==

Specs: spec/script/worktree/with_mise_spec.rb (9), spec/githooks/post_checkout_spec.rb, spec/project_config_spec.rb; bin/ci passes at the pushed SHA (pre-push hook).

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