Split a single-argument tmux command string in __tmux-compat

[teamleaderleo]

Summary

Claude Code 2.1.272 runs tmux "display-message -p #{pane_id}" with the whole command in one argument. splitTmuxCommand treated that string as the command name, lowercased all of it (so -F became -f), and the shim failed with Unsupported tmux compatibility command: display-message -p #{pane_id}. Named teammate spawns then failed with "Could not determine current tmux pane/window".

tmux parses a lone argument as a command string. The shim now does the same: when the first non-flag argument contains whitespace, it splits it with the existing tmuxShellWords tokenizer, lowercases only the command name, and prepends the remaining words to the rest of argv. Ordinary multi-argument calls are unchanged.

Fixes #12682 (reopen context: #13608 added display-message/list-panes, but the single-argument form still missed the switch).

Testing

• New CLITmuxCompatRemoteSplitTests.singleArgumentCommandStringIsSplitShellStyle runs the bundled CLI with __tmux-compat "show-options -v extended-keys" and with -L cmux "SHOW-OPTIONS -v 'extended-keys'", and expects on. Both fail on main with the unsupported-command error.
• python3 scripts/verify-local.py --affected upstream/main --swift-changed upstream/main: swift-syntax, test-wiring, feature-flags passed. Native compile and tests run in CI.

🤖 Generated with Claude Code

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Summary by cubic

Fixes __tmux-compat failing when Claude Code passes a whole tmux command as one argument.

• The shim previously treated the string as a command name and lowercased all of it, so flags like -F became -f and the command was rejected with "Unsupported tmux compatibility command".
• It now splits a lone argument shell-style, lowercasing only the command name.

Fixes #12682.

^{Written for commit 89e6c93. Summary will update on new commits.}

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📥 Commits

Reviewing files that changed from the base of the PR and between e142cac and 89e6c93.

📒 Files selected for processing (2)

• CLI/cmux.swift
• cmuxTests/CLITmuxCompatRemoteSplitTests.swift

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[github-actions]

Merge receipt for 89e6c93cb1, merged 2026-09-25 18:52:29 UTC

• Not verified at merge: CLA policy guard (failure)
• Verified: app-host unit tests, ci-status, macOS compile admission, Web complexity, web-validation, CLI product tests, Fast static checks, GhosttyKit release check, guards (17), linux-preflight, macOS admission gate, macOS status, and 2 more
• Skipped by policy: browser, Claude wrapper regressions, late-placement, release-admission, release-build, remote-daemon, suite-coverage, swift-package-tests, tests-build-and-lag, web, web-build, web-database-tests, and 1 more
• Full suite: runs on main after merge.