Rust CLI: exit 2 for usage errors, matching the Node CLI

[poiley]

Summary

Follow-up to the Rust CLI port: align usage-error exit codes with the Node CLI.

The port exited 1 for every failure, while the Node CLI (oclif) exits 2 for usage errors and 1 for runtime failures. Scripts and agents that branch on that distinction would silently break when switching CLIs, and the parity fixtures had to encode the divergence in 11 expectByRunner waivers (all 11 were node: exitCode 2 vs rust: exitCode 1).

What changed

• New transparent UsageError marker + usage_err! macro in cli-rust/src/config.rs (lives there so the include-style integration tests resolve it), re-exported from lib.rs. main_entry picks the exit code by inspecting the error chain, so stderr output is byte-identical to before; only the exit code changes.
• Converted to exit 2: generated-command invocation parsing and parameter validation (execute_operation boundary), unknown command/subcommand/alias resolution across all command families, unknown-flag and missing-flag-value parsers, send body-source conflicts, and functions logs --follow/--cursor conflict.
• Deliberately left at exit 1 (the Node CLI also exits 1 there, per the existing fixtures): describe unknown operation, config mutation validation, doctor failures.
• Fixtures: the 11 waivers now assert exitCode: 2 on both runners. Where the node and rust expectations became identical the waiver is collapsed into the shared expect block (expectByRunner count 84 -> 77).
• Added unit tests: usage vs runtime exit-code selection, marker survival through context() wrapping, Display pass-through.

Validation

• make rust-cli-check (fmt, clippy -D warnings, doc, tests)
• make cli-parity green: 315/315 cases, command-surface parity, operation coverage, help sweep with --compare-flags
• make node-check cli-check go-check shared-check
• make rust-cli-full-check

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
cli-rust/src/auth_commands.rs	Auth command parsing now marks invalid argument forms with the usage-error path.
cli-rust/src/config.rs	Adds the usage-error marker, macro, and exit-code helper used by the Rust CLI.
cli-rust/src/lib.rs	Wires the Rust CLI entry path to choose the process exit code from the error chain.

_{Reviews (3): Last reviewed commit: "Mark post-parse invocation-shape errors ..." | Re-trigger Greptile}

[poiley]

Superseded by #332. The base branch was force-rebased (18e9f0c -> f1b5005) which made this PR unmergeable, and the rebased port already includes a CliError usage-error mechanism covering part of what this PR did. #332 rebuilds the remainder on the new base: ~100 uncovered parse/validation sites, auth post-parse checks, and chain-walking exit-code detection.