Add M4 orchestration: broadcast, idle notifications, palette

tree.ts
- LeafNode gains broadcast?: boolean
- walkLeaves(root) generator; toggleBroadcast helper

ops.ts (PaneOps)
- toggleBroadcast, broadcastFrom, setActivePane, registerPaneId,
  notify; activeLeafId data field.

XtermPane.svelte
- onSpawn(paneId), onInput(b64), onDataReceived(),
  and focusTrigger prop. All optional; backward-compatible.

LeafPane.svelte
- 📡 broadcast toggle; 5s idle detection -> ops.notify (once per
  idle cycle); active + broadcasting border colors; click-to-focus
  via setActivePane + focusTrigger bump.

New Notifications.svelte
- Top-right toast stack, slide-in, 5s auto-dismiss + click ×.

New Palette.svelte
- Modal overlay, backdrop, filtered leaf list with ↑/↓ + Enter,
  Escape to close.

App.svelte
- paneIdByLeaf Map for routing; notifications array + auto-dismiss;
  activeLeafId; Ctrl+K global listener; broadcastFrom routes via
  walkLeaves + writeToPane to all other broadcast leaves; ⌘K button
  in titlebar.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

memory.md

@@ -17,15 +17,23 @@ Durable memory for this project. Read at session start, update before session en
 - **Pane operations bundled into a `PaneOps` interface** in `lib/layout/ops.ts`. Pane and SplitNode just pass `ops` through; LeafPane consumes it. Replaces M2's per-callback prop drilling (would have been split + close + setDistro + setLabel + distros = 5 separate props). Easier to grow as M4 adds broadcast / palette ops.
 - **Per-pane distro change forces a remount via id swap.** `changeDistro` in `tree.ts` assigns a new id to the leaf; `Pane.svelte`'s `{#key leaf.id}` unmounts XtermPane (which kills the old PTY) and mounts a fresh one with the new distro. Same mechanism we already use for split/close.
 - **Split inherits parent's distro AND cwd** (not label — label is a per-pane name, not a hierarchy thing). So "split right" while in a project keeps both panes in that project.
+- **Broadcast input is frontend-routed, not a backend command.** Each LeafPane reports its backend `PaneId` to App via `ops.registerPaneId`. When a broadcasting pane's `XtermPane.onInput` fires, App's `broadcastFrom` walks all other leaves with `broadcast === true` and calls `writeToPane(theirPaneId, b64)`. No Rust changes needed; the existing per-pane write path does the work N times. Origin pane writes to its own PTY normally — broadcast is purely about mirroring to others.
+- **Idle detection lives in LeafPane.** Each pane tracks `lastDataTime` (reset on every `XtermPane.onDataReceived`) and a `setInterval` that fires `ops.notify` after `IDLE_THRESHOLD_MS` (5000ms) of silence, once per idle cycle. No backend involvement — purely observes the existing PTY data stream. The "is foreground process claude" filter is **deferred** (would need a Rust-side foreground-process probe); for now every pane notifies after 5s of quiet.
+- **In-app toasts (top-right stack), 5s auto-dismiss.** Lives in `Notifications.svelte`; App owns the array + auto-dismiss timer. Not native OS notifications — defer `tauri-plugin-notification` if/when we want desktop alerts that work when the app is backgrounded.
+- **Ctrl+K palette: modal overlay with text filter on `label | distro | cwd`**, arrow-key nav, Enter to focus. Activating a pane sets `activeLeafId`; `LeafPane` has a `$derived` `active = ops.activeLeafId === leaf.id` and a `$effect` that bumps a `focusTrigger` counter when active flips true; `XtermPane` watches `focusTrigger` and calls `term.focus()`. Active pane gets a blue 1px border; broadcasting pane gets orange.
 
 ## Open questions / TODOs
 
 - [x] ~~**M2 — splits-tree layout component.** Two panes side by side, draggable divider, both panes alive. Save/restore layout as JSON.~~ Done 2026-05-22.
 - [x] ~~**M3 — workspace persistence + preset layouts + per-pane distro + pane labels.**~~ Done 2026-05-22.
+- [x] ~~**M4 — orchestration.** Broadcast input, idle notifications, Ctrl+K palette.~~ Done 2026-05-22.
 - [x] ~~**Auto-save debouncing.**~~ 500ms timer in `App.svelte` `$effect`.
-- [x] ~~**HMR distro picker reset.**~~ No longer an issue — per-pane distro selection via in-toolbar popover; titlebar `default:` only seeds new splits.
+- [x] ~~**HMR distro picker reset.**~~ No longer an issue — per-pane distro selection.
+- [ ] **Idle detection: filter by "claude is foreground."** Currently every pane notifies after 5s silence, which fires too eagerly when the user is reading a `claude` response. Want to detect that `claude` (or any user-specified process) is actually running in the pane's shell before notifying. Needs a Rust-side probe over WSL: `wsl.exe -d <distro> ps --ppid <shell_pid> -o comm=`. Defer to a future polish pass.
+- [ ] **Native OS notifications.** Right now toasts only show while the app is focused. `tauri-plugin-notification` would push to Windows Action Center; useful for "claude finished" when the app is minimized. Worth adding if/when the user actually backgrounds the app while waiting for sessions.
+- [ ] **Configurable idle threshold.** Hardcoded 5000ms in `LeafPane.svelte`. Should move into a settings panel; M5 territory.
 - [ ] **Multi-workspace tabs.** Several independent layouts the user can switch between. Saved as `workspaces.json` with `{ current: id, list: [{ id, name, tree }] }`. Not on the M0–M5 critical path; either bolt on after M5 ship or fold into a "tabs" minor milestone.
-- [ ] **M4 — orchestration.** Broadcast input groups (write same bytes to N PTYs flagged into a group), idle/finish notifications (detect when a `claude` pane stops emitting output for >Ns → toast), Ctrl+K fuzzy palette over `label / distro / cwd`. Will extend `PaneOps` with a couple more methods + add a "broadcast group" concept to the leaf type.
+- [ ] **M5 — Ship.** Replace placeholder icons, NSIS installer, Forgejo release. Copy `claude-usage-widget`'s release scripts.
 - [ ] **M5 — Ship.** Replace placeholder icons, NSIS installer, Forgejo release. Copy `claude-usage-widget`'s release scripts.
 - [ ] **Native Windows shells (cmd / pwsh)?** `portable-pty` supports them for free; keep the option open. Decide whether to expose in UI at M3.
 - [ ] **Persistent scrollback across app restarts.** Would need an out-of-process mux daemon. Big scope creep; explicitly deferred past v1.
@@ -33,6 +41,17 @@ Durable memory for this project. Read at session start, update before session en
 
 ## Session log
 
+### 2026-05-22 — M4 orchestration (broadcast + notifications + palette)
+
+- `tree.ts`: added `broadcast?: boolean` to LeafNode; `walkLeaves` generator; `toggleBroadcast` helper (metadata-only, no id swap).
+- `ops.ts`: extended `PaneOps` with `toggleBroadcast`, `broadcastFrom`, `setActivePane`, `registerPaneId`, `notify`, plus `activeLeafId` data field.
+- `XtermPane.svelte`: added optional callbacks `onSpawn`, `onInput` (called after each writeToPane on user keypress), `onDataReceived` (called per PTY output chunk), and a `focusTrigger` prop (counter; bumping it refocuses the terminal). All optional; pre-M4 callers untouched.
+- `LeafPane.svelte`: 📡 broadcast toggle in toolbar; idle detection (5s threshold, 1s polling, fires once per idle cycle); active/broadcasting border colors; click anywhere on the leaf sets it active; on active=true bumps focusTrigger so XtermPane refocuses.
+- New `Notifications.svelte`: top-right toast stack, slide-in animation, 5s auto-dismiss + manual ×.
+- New `Palette.svelte`: modal overlay with backdrop, autofocused text input, filtered list (label/distro/cwd substring), ↑/↓ navigation, Enter/click to pick, Escape to close.
+- `App.svelte`: paneIdByLeaf Map (non-reactive lookup); notifications $state with auto-dismiss; activeLeafId; paletteOpen with global Ctrl+K listener; broadcastFrom routes via walkLeaves + writeToPane; ⌘K button in titlebar.
+- `pnpm check` clean (111 files).
+
 ### 2026-05-22 — M3 persistence + presets + per-pane distro/label
 
 - Backend: added `save_workspace(json)` and `load_workspace()` Tauri commands. Atomic write via tmp + rename. Path resolved from `app.path().app_config_dir()`.