test(pairing-cli): add unit coverage for buzz-pairing-cli

[SeanGearin]

Problem

crates/buzz-pairing-cli (623 LOC) had zero tests. All of its relay-protocol
parsing, CLI argument handling, and error paths were unverified — regressions
in QR/offer/abort handling or NIP-42 auth framing would only surface during a
live interop run against a real relay.

Fix

Adds a #[cfg(test)] unit suite (42 tests) inside src/main.rs, mirroring the
inline-test idiom used in buzz-auth (crates/buzz-auth/src/nip42.rs). No
live relay is used anywhere: WebSocket I/O is stubbed with in-memory
futures_util::stream sources and a small CaptureSink that records outgoing
frames, and time-dependent paths run under #[tokio::test(start_paused = true)]
so timeout tests complete instantly.

Coverage by area:

• CLI arg parsing (8): clap debug_assert, source default relay +
  --relay/--nsec, target defaults + --relay/--show-secret,
  test-vectors, missing-subcommand and unknown-flag rejection.
• parse_auth_challenge (6): valid AUTH frame, non-AUTH types, malformed
  JSON, short array, non-string challenge, non-array JSON.
• parse_relay_event (6): valid EVENT for the right sub id, wrong sub id,
  OK/EOSE frames, short array, invalid event payload, non-array JSON.
• resolve_payload (3): valid nsec passthrough, invalid nsec ->
  CliError::InvalidNsec, generated test key parses as an nsec.
• hex_to_32 (3): round trip, non-hex input, wrong length.
• parse_yes_no (2): affirmative and negative variants. (Tiny seam
  extraction: the matches! in read_yes_no moved to a pure
  parse_yes_no(&str) so the logic is testable without stdin — behavior
  unchanged.)
• cmd_test_vectors (1): spec vectors derive without error.
• check_for_abort (2): non-abort events pass through; a real peer abort
  (full offline source->target handshake via PairingSession::new_source /
  new_target / handle_offer) is surfaced with its reason.
• publish_event (1): emits a ["EVENT", ...] frame that round-trips to
  the same event id.
• wait_for_event (4): skips junk/OK/EOSE/binary/wrong-sub frames then
  returns the matching event; timeout -> CliError::Timeout; closed stream ->
  CliError::Other; websocket error propagates as CliError::WebSocket.
• wait_for_eose (2): matches only its sub id; timeout path.
• handle_nip42_auth (4): no-challenge relays are skipped cleanly (nothing
  sent); a challenge is answered with a kind-22242 event signed by the
  session's ephemeral key (signature verified, challenge tag present);
  missing OK after AUTH is tolerated; invalid relay URL is rejected.

Only non-test changes: the 4-line parse_yes_no extraction and a
[dev-dependencies] entry adding tokio's test-util feature (same pattern as
buzz-pair-relay, buzz-media, buzz-relay-mesh, buzz-acp).

Test evidence

cargo fmt -p buzz-pairing-cli          # clean
cargo clippy -p buzz-pairing-cli --all-targets   # no warnings
cargo nextest run -p buzz-pairing-cli  # 42/42 passed

Links

• Crate: crates/buzz-pairing-cli/src/main.rs
• Test idiom mirrored from: crates/buzz-auth/src/nip42.rs

🤖 Generated with Claude Code