docs: update docs for relay hardening, reconnection, and session wrap

Update multi-machine docs with reconnection implementation details,
command response propagation, and pty_created confirmation flow.
Mark reconnection as complete in phases.md, progress.md, TODO.md.
Update CLAUDE.md files with reconnection and relay response info.
Add CHANGELOG entries for new features.

TODO.md

@@ -4,26 +4,19 @@
 
 - [ ] **Deno sidecar real-world testing** -- Integrated into sidecar.rs (Deno-first + Node.js fallback). Needs testing with real claude CLI and startup time benchmark vs Node.js.
 - [ ] **E2E testing (Playwright/WebDriver)** -- Scaffold at v2/tests/e2e/README.md. Needs display server to run. Test: open terminal, run command, open agent, verify output.
-- [ ] **Multi-machine reconnection** -- Implement exponential backoff reconnection logic (1s-30s cap) in RemoteManager for dropped WebSocket connections.
 - [ ] **Multi-machine real-world testing** -- Test bterminal-relay with 2 machines (local + 1 remote). Verify PTY + agent operations over WebSocket.
 - [ ] **Multi-machine TLS/certificate pinning** -- Add TLS support to bterminal-relay and certificate pinning in RemoteManager for production security.
 - [ ] **Agent Teams real-world testing** -- Frontend routing implemented (Phase 7). Needs testing with CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1 and real subagent spawning.
 
 ## Completed
 
+- [x] **Multi-machine reconnection** -- Exponential backoff reconnection (1s-30s cap) in RemoteManager, attempt_ws_connect() probe, reconnection events. | Done: 2026-03-06
+- [x] **Relay command response propagation** -- Structured responses (pty_created, pong, error) with commandId correlation, send_error() helper. | Done: 2026-03-06
 - [x] **Multi-machine support (Phases A-D)** -- bterminal-core crate extraction, bterminal-relay WebSocket binary, RemoteManager, frontend integration. | Done: 2026-03-06
-
-- [x] **Set TAURI_SIGNING_PRIVATE_KEY secret** -- Set via `gh secret set` on DexterFromLab/BTerminal. | Done: 2026-03-06
-- [x] **Dispatcher tests for subagent routing** -- 10 new tests covering spawn, dedup, child message routing, init/cost forwarding, fallbacks. Total: 28 dispatcher tests. | Done: 2026-03-06
-- [x] **Subagent cost aggregation** -- `getTotalCost()` recursive helper in agents store, total cost shown in parent pane done-bar when children present. | Done: 2026-03-06
 - [x] **Agent Teams frontend support** -- Subagent pane spawning, parent/child navigation, message routing by parentId, SUBAGENT_TOOL_NAMES detection in dispatcher. | Done: 2026-03-06
+- [x] **Subagent cost aggregation** -- `getTotalCost()` recursive helper in agents store, total cost shown in parent pane done-bar when children present. | Done: 2026-03-06
+- [x] **Dispatcher tests for subagent routing** -- 10 new tests covering spawn, dedup, child message routing, init/cost forwarding, fallbacks. Total: 28 dispatcher tests. | Done: 2026-03-06
 - [x] **Session groups/folders** -- group_name column in sessions table, setPaneGroup in layout store, collapsible group headers in sidebar, right-click to set group. | Done: 2026-03-06
-- [x] **Auto-update signing key** -- Generated minisign keypair, pubkey set in tauri.conf.json. | Done: 2026-03-06
 - [x] **Deno sidecar integration** -- SidecarCommand struct, resolve_sidecar_command() with Deno-first + Node.js fallback, both runners bundled in tauri.conf.json resources. | Done: 2026-03-06
-- [x] **E2E/integration test suite** -- 104 vitest tests (layout 30, agent-bridge 11, agent-dispatcher 18, sdk-messages 25, agent-tree 20) + 29 cargo tests. | Done: 2026-03-06
-- [x] **Copy/paste (Ctrl+Shift+C/V)** -- TerminalPane attachCustomKeyEventHandler, C copies selection, V writes clipboard to PTY. | Done: 2026-03-06
-- [x] **Terminal theme hot-swap** -- onThemeChange callback registry in theme.svelte.ts, TerminalPane subscribes. All open terminals update. | Done: 2026-03-06
-- [x] **Tree node click -> scroll to message** -- handleTreeNodeClick in AgentPane, scrollIntoView smooth. | Done: 2026-03-06
-- [x] **Subtree cost display** -- Yellow cost text below each tree node (subtreeCost util, NODE_H 32->40). | Done: 2026-03-06
-- [x] **Session resume** -- Follow-up prompt in AgentPane, resume_session_id passed to SDK. | Done: 2026-03-06
-- [x] **Pane drag-resize handles** -- Splitter overlays in TilingGrid with mouse drag, 10-90% clamping. | Done: 2026-03-06
+- [x] **E2E/integration test suite** -- 114 vitest tests + 29 cargo tests. | Done: 2026-03-06
+- [x] **Set TAURI_SIGNING_PRIVATE_KEY secret** -- Set via `gh secret set` on DexterFromLab/BTerminal. | Done: 2026-03-06