feat(neo): RPC bridge protocol + stdio transport (neo-go-tui task 3)

[code-yeongyu]

Summary

Plan task 3 of .omo/plans/neo-go-tui.md: the Go mirror of senpi's JSONL RPC protocol — the wire layer every neo TUI feature drives the TS agent through. Additive only, packages/neo internal.

Changes

• internal/bridge/types.go: structs for all RpcCommand variants, RpcResponse union, session state, slash commands, 9 extension-UI methods, every AgentSessionEvent variant + extension_error.
• codec.go/demux.go: JSONL codec; four-way stdout demux (response / extension_ui_request / extension_error / event).
• transport.go/client.go: Transport interface + StdioTransport spawning node <cli> --mode rpc with rpc-client.ts parity (100ms init wait, req_N correlation, 30s timeout, stderr capture, typed exit errors).
• testdata/: fixtures generated by gen-fixtures.mjs against the mock-loop (regeneration reproducible, never hand-edited); extract-ts-union.mjs extracts the TS unions at test time.

QA / Evidence

Evidence: .omo/evidence/task-3-neo-go-tui.txt (+ task-3-artifacts/) in the work worktree.

• Exhaustiveness gate: a Go variant must exist for every TS union member, extracted live from rpc-types.ts + agent-session.ts — 31 commands / 9 ext-UI methods / 22 events today; the test, not a hand count, is the gate.
• Decode→encode round-trip byte-equal on all fixtures; demux covers all four shapes (incl. a labeled post-hoc mutation proof for the demux gate).
• Real-CLI QA in tmux (non-blank transcript archived): Go client against senpi --mode rpc + mock-loop — get_state, prompt→agent_end, get_commands; kill-child-mid-request yields a typed exit error carrying stderr (nil ExitError now fails the test explicitly); malformed JSONL line ignored. Real ~/.senpi hash unchanged (receipt).
• Gates: go build/vet/gofmt/test green; GOOS=windows and GOOS=linux cross-compile OK; npm run check exit 0. An adversarial audit round fixed evidence-wording/artifact gaps; re-audit verdict: real.

Risks

• TS protocol drift would silently outdate the mirror — mitigated by the extraction test failing on any union change, which is exactly the plan's intent.

Secret safety

No secrets; sandboxed QA; auth hash receipts before/after.

---

Summary by cubic

Implements the Go RPC bridge for the neo TUI: a JSONL codec/demux, StdioTransport that spawns the TS CLI, and a Client that mirrors rpc-client.ts semantics. This unlocks driving the TS agent from Go and gates drift with TS via exhaustive tests.

• New Features
  • Strict JSONL codec with LF framing and byte-equal round-trip; four-way demux: response, extension_ui_request, extension_error, event.
  • Transport interface and StdioTransport that runs node <cli> --mode rpc, captures stderr, and surfaces typed exit errors; graceful SIGTERM with SIGKILL fallback.
  • Client with req_N correlation, per-request timeout (30s default, overridable), malformed-line tolerance, and event/message listeners.
  • Go mirror of all RpcCommand/RpcResponse variants, 9 extension-UI methods, session state, and every AgentSessionEvent plus extension_error.
  • Golden fixtures generated from the real CLI; exhaustiveness test parses TS unions at test time and fails on any protocol drift.
  • Integration tests against the real CLI and a fake model server; asserts sandbox isolation (no ~/.senpi changes).

^{Written for commit 7b3a7f1. Summary will update on new commits.}