[Agentic DX] tmuxp: low-to-high lift machine-output and command-contract roadmap

Context

Review focused on src/tmuxp/cli/* command modules, output helpers, and current JSON support scope.

Goal

Make tmuxp command behavior consistently machine-readable while keeping strong human UX.

Low-lift ideas

• Standardize --json/--ndjson support and semantics across all user-facing subcommands.
• Publish output schema examples (and schema version field) for machine-output commands.
• Document exit code contracts per command family.

Medium-lift ideas

• Ensure all commands route output through shared output abstractions for parity.
• Add --dry-run --json for side-effectful commands (load, import, convert, etc.).
• Add regression tests for output contract stability.

High-lift ideas

• Add plan/execution graph output for automation orchestrators.
• Expose machine-readable command metadata (args, side effects, output modes).

Done when

• Output contract is consistent across subcommands.
• Side-effectful operations have inspectable plan mode.
• Tooling integration requires less command-specific handling.

Start by reviewing the command modules under src/tmuxp/cli/*, the output helpers, and the current JSON support scope. This issue is a broad roadmap rather than a scoped change, so first identify one command family and define its output, schema, exit-code, and plan-mode contract. Done means the selected scope has consistent machine-readable behavior and regression coverage.