Rust rewrite scaffold: clap command tree, core modules, endpoint/company list ported with Python parity

[igor-ctrl]

Summary

This is an exploratory Rust scaffold for a possible rewrite of bcli. It lives in a new rust/ Cargo workspace next to the Python code, and the Python implementation is untouched. The full 58-command clap tree mirrors the Typer CLI. A few commands are ported end to end, and their output matches Python byte for byte.

Changes

• rust/crates/bcli-core (library):
  • config loading: ~/.config/bcli, the .bcli.toml merge and sanitising, env overrides
  • error/exit-code taxonomy (0–8)
  • URL building, with the bearer token sent only to BC hosts
  • registry: shares src/bcli/registry/standard_v2.json via include_str!
  • tokens.json cache, format-compatible with Python
  • client_credentials auth with keyring/env secret resolution
  • reqwest transport with Python's retry/backoff/correlation-id behaviour
  • a Python-json.dumps-compatible serializer
• rust/crates/bcli-cli (binary bcli):
  • clap tree with all commands and flags; unported commands exit 1 with not yet ported
  • output formats table/markdown/json/csv/ndjson/raw, plus the automatic records view
  • ported: --version, endpoint list, endpoint search, endpoint info, company list
• Tests:
  • unit tests
  • wiremock tests for token, retry and company list HTTP flows
  • golden parity: 18 cases recorded from the Python CLI, identical stdout, stderr and exit code
  • surface parity: the clap tree must match a JSON dump of the Typer tree
• rust/scripts/parity.sh and dump_python_surface.py regenerate the goldens and the surface fixture from the Python CLI.
• .github/workflows/rust.yml runs fmt, build, clippy -D warnings and tests on Linux and macOS, triggered only by rust/** changes.

Test plan

• cargo build --workspace --locked
• cargo clippy --workspace --all-targets -- -D warnings, with default features and with --no-default-features
• cargo test --workspace: 45 passed
• PY_BCLI=/path/to/python/bcli rust/scripts/parity.sh reports all goldens identical to Python
• Python suite unaffected (no Python files changed)

Breaking changes

None. This is additive, and the Rust binary isn't distributed yet.

Notes and open questions

• Python save_config drops [telemetry]/[audit], allowed_* and disable_writes when it rewrites config. The Rust port plans surgical toml_edit saves. Should we also fix this in Python separately?
• AGENTS.md says non-TTY output defaults to markdown, but the code defaults to json. The port follows the code.
• company list prints errors to stdout and exits 1, bypassing the exit-code taxonomy. The port reproduces this for parity.
• Windows CI is deferred until the goldens are path-normalised.