[auser]

Summary

Add opt-in, repeatable --config-file PATH to compose CLI options from explicit flags, ordered TOML/JSON files, and command-scoped environment variables. Scalars resolve explicit > last file > environment; repeatables append environment, files in order, then explicit values. Relative and absolute config paths are supported; files cannot select a command.

What changed

• Normalize TOML and JSON into one option model, then feed resolved arguments into the existing Clap parse and normal policy, signed-plan, and backend paths. Unknown keys, incompatible values, and conflicting options refuse before dispatch.
• Document [global] and [commands.machine.run] syntax and the behavior of booleans, counts, aliases, and empty lists. Add parser, CLI dry-run, and refusal regressions for precedence, multiple files, guest environment filtering, and host CPU ceilings.
• Re-measure the rebased tree and adjust the Rust-footprint ratchet to 967,269 SLOC / 1,232,680 physical lines without removing coverage.

Validation

• Passed: 13 focused resolver tests, 105 CLI integration tests, cargo test -p xtask, cargo clippy --workspace -- -D warnings, cargo check --workspace, formatting, and the new hermetic BDD scenario. The footprint check passes on this rebased branch.
• Passed: cargo run -p xtask -- check-all (84 gates) on the rebased branch. CI remains the final review gate.
• Full cargo test --workspace did not complete green locally: runs encountered a long macOS temporary socket path, intermittent unrelated agent timing/socket tests, and a workspace-only doctest failure (the doctest passed alone). Full just bdd::run timed out; the new scenario passed alone. No live backend witness was run.
• YAML is not supported.

Integration

This is independent of draft PR #5326; no changes were made to that branch. Review can proceed now; do not merge until its current work settles, then reconcile the footprint ratchet against the combined tree and validate before landing. A passing CI run or review alone is not authorization to merge.