chore: update meta files for multi-machine architecture session

docs/README.md

@@ -20,3 +20,4 @@ Project documentation lives here.
 | [phases.md](phases.md) | v2 implementation phases (1-7) with checklists |
 | [findings.md](findings.md) | Research findings (Agent SDK, Tauri, xterm.js, performance) |
 | [progress.md](progress.md) | Session-by-session progress log |
+| [multi-machine.md](multi-machine.md) | Multi-machine support architecture (WebSocket, relay binary) |

docs/phases.md

@@ -251,3 +251,15 @@ bterminal-v2/
 - Rust 1.77+ (for building from source)
 - WebKit2GTK 4.1+ (Tauri runtime)
 - Linux x86_64 (primary target)
+
+---
+
+## Future: Multi-Machine Support [status: designed]
+
+Architecture designed in [multi-machine.md](multi-machine.md). Extends BTerminal to manage agents and terminals on remote machines over WebSocket.
+
+### Implementation Phases (A-D)
+- [ ] **Phase A:** Extract `bterminal-core` crate (PtyManager + SidecarManager shared code)
+- [ ] **Phase B:** Build `bterminal-relay` binary (WebSocket server, token auth, CLI flags)
+- [ ] **Phase C:** Add `RemoteManager` to controller (remote.rs, WebSocket client connections)
+- [ ] **Phase D:** Frontend integration (bridge adapters with remoteMachineId routing, machine management UI)

docs/progress.md

@@ -252,8 +252,20 @@ Design: No separate sidecar process per subagent. Parent's sidecar handles all;
 #### TAURI_SIGNING_PRIVATE_KEY
 - [x] Set via `gh secret set` on DexterFromLab/BTerminal GitHub repo
 
+### Session: 2026-03-06 (continued) — Multi-Machine Architecture Design
+
+#### Multi-Machine Support Architecture
+- [x] Designed full multi-machine architecture in docs/multi-machine.md (303 lines)
+- [x] Three-layer model: BTerminal (controller) + bterminal-relay (remote binary) + unified frontend
+- [x] WebSocket NDJSON protocol: RelayCommand/RelayEvent envelope wrapping existing sidecar format
+- [x] Authentication: pre-shared token + TLS, rate limiting, lockout
+- [x] Autonomous relay model: agents keep running when controller disconnects
+- [x] Reconnection with exponential backoff (1s-30s), state_sync on reconnect
+- [x] 4-phase implementation plan: A (extract bterminal-core crate), B (relay binary), C (RemoteManager), D (frontend)
+- [x] Updated TODO.md and docs/task_plan.md to reference the design
+
 ### Next Steps
 - [ ] Deno sidecar: test with real claude CLI, benchmark startup time vs Node.js
 - [ ] E2E testing with Playwright/WebDriver (when display server available)
-- [ ] Multi-machine support (remote agents via WebSocket)
+- [ ] Multi-machine Phase A: extract bterminal-core crate
 - [ ] Test agent teams with CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1