v2: clean-sheet rewrite — Go client + multiplexed protocol

[bradgessler]

Clean-sheet v2 of Terminalwire. No backwards compatibility with v1 (install base is small).

North stars

• Go thin client (Tebako is no longer maintained; Go gives static cross-compiled binaries + easy distribution + goroutines that fit a multiplexed protocol).
• Ruby/Rails server stays Ruby, but behind a framework-agnostic adapter.
• Conformance-harness-first: the protocol test harness is the keystone, built before the client or any server. Protocol-level TDD.

Settled design decisions

• One WebSocket connection, multiplexed with stream_id + type per frame (SSH-channel model). Not separate sockets.
• stdout/stderr are one-way streamed frames (no per-write ack) — kills the per-line round trip that's the real stdio bottleneck. stdin stays request/response. Large transfers chunked.
• Versioned + capability-negotiated handshake from the first commit (clean-sheet on v1 ≠ skip forward-compat for v2).
• Consent-based entitlements: server declares what it wants, client prompts the user once, client enforces.
• Structured errors that don't tear down the connection; heartbeats for liveness.
• Sans-IO protocol core (pure state machine, no sockets/clock) so one corpus validates client + multiple servers, and tests are fast and precise (deterministic).

Licensing

• v2 is proprietary/closed-source (reverted from AGPL).
• Test harness follows the SQLite/TH3 model, two-tier: spec open + a "starter" corpus open; the exhaustive adversarial/fuzz/security harness closed. Built internal + fast now, kept accurate/precise.

Workstreams tracked as sub-issues below, in priority order.

[bradgessler]

Autonomous build progress — branch v2

Harness-first, per the plan. All committed to v2 and verified green.

Done & tested

• Protocol spec v2 (sans-IO, multiplexed, negotiated) #12 Protocol spec — v2/PROTOCOL.md: multiplexed framing (sid per frame), negotiated handshake, one-way stdout/stderr, request/response, structured errors. Sans-IO.
• Conformance test harness (RSpec) — KEYSTONE #13 / Sans-IO protocol core + golden vector corpus format #19 Conformance harness — v2/conformance/: language-neutral corpus (negotiate, roundtrip, golden msgpack bytes, malformed validation). Driven natively by both Ruby (RSpec) and Go. This is the cross-impl contract and it passes on both sides.
• Ruby/Rails server v2 (framework-agnostic adapter) #15 Ruby server — terminalwire2 gem: sans-IO core (codec/negotiator/frames/mux), Server::Connection/Runtime/Context/Handler/Session, Thor integration. 89 examples, 0 failures, 99.5% line / 88% branch.
• Go thin client #14 Go client — protocol (92.9%), entitlement with doublestar ** globbing (100%), client connection+resources (85.6%); WebSocket transport + cmd/terminalwire build a ~7 MB static binary.

Coverage is ≥80% on both the Go client and the Ruby server, line and branch.

Remaining (unchanged scope): #16 consent entitlements (client uses a conservative default policy for now), #21 interop matrix CI, #17 distribution, #20/#22 closed exhaustive harness.

See v2/README.md for how to run the tests, build the client, and wire a Rails server.