Support Astation device authentication v2

[guohai]

What changed

• answer Astation v2 challenges with matching HMAC-SHA256 proofs for loopback, LAN, and identity-relay connections
• require a well-formed v2 challenge and refuse bearer-session downgrade
• bind pairing and reconnect requests to the stable atem_id, with invalid sessions falling back to pairing on the same socket
• complete first-time remote pairing with a reusable identity-relay device session before reporting success
• honor the local --save choice even when an older Astation always reports session-only credentials
• bound authentication handshakes and cancel owned WebSocket tasks on failure or client drop
• keep automatic TUI reconnects proof-only; interactive approval runs only through atem pair
• fail pairing when the reusable device session cannot be persisted securely
• persist session files as 0600 under a 0700 config directory and refuse symlink-backed secret files
• automatically learn and reload the authenticated Astation identity for live relay fallback
• replace stale session, connection-priority, universal-session, and relay documents with the v2 contract and current security status

Practical coverage

• shared Swift/Rust HMAC protocol vector
• local bootstrap acceptance at 0600 and rejection at 0644
• private session write, permission migration, ownership, and symlink refusal
• real loopback WebSocket pairing/denial path
• downgrade rejection without sending credentials
• bounded authentication when a challenged peer becomes silent
• proof-only background reconnect with no pairing message or terminal output
• pairing failure propagation when secure session persistence is unavailable
• existing identity, session, serialization, and connection coverage

Verification

• cargo test -- --test-threads=1 --format terse (699 passed)
• git diff --check

The suite is run serially because four existing agent_visualize tests share ~/.agent/diagrams and can race under the default parallel runner. Repository-wide cargo fmt --check also has pre-existing formatting drift outside this change.

Coordinated rollout

Requires Agora-Build/Astation#13. Merge both repositories before releasing either client; Astation v2 intentionally rejects legacy session-ID-only authentication.

Remote first-time pairing now has two explicit approvals: the short relay-room code connects the peers, then the 8-digit device code authorizes and stores the durable identity-relay session.

Security status

Direct LAN remains plaintext ws://. Proofs improve device authentication but do not encrypt initial pairing or application traffic. WSS certificate pinning is still required before treating direct LAN as production-ready.

Generated with SMT smt@agora.build

[guohai]

Manual review completed at exact head d45e972651784cdf19c78bf4255c5c279bc232a2.

Resolved during review:

• bounded all post-challenge authentication waits and completed reusable remote session pairing;
• refreshed learned relay identity in the running TUI;
• aborted failed authentication transports and kept background reconnects proof-only;
• made first-time credential persistence fatal while keeping existing authenticated reconnects alive when only activity metadata cannot be refreshed;
• isolated session and relay-code test state from the developer config, while preserving direct-to-relay identity learning.

Validation:

• cargo test -- --test-threads=1 --format terse: 700 passed, 0 failed;
• all 6 practical WebSocket authentication tests passed;
• git diff --check passed;
• final exact-commit Codex review: no actionable regressions.

No critical or high-severity findings remain. Repository-wide formatting drift and the documented LAN-WSS / relay-owner-auth production blockers predate this final follow-up and remain explicitly documented. GitHub Claude/Codex jobs are currently skipped by their workflow conditions; local Claude review was unavailable because that CLI is not logged in.