backlog: add system clock heartbeat service task (TASK-47)

Server-side clock broadcasting time signals via Event Bus for shapes
to subscribe to periodic events (tick, hourly, daily).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backlog/tasks/task-47 - Implement-System-Clock-heartbeat-service-for-rSpace-canvas.md

@@ -0,0 +1,91 @@
+---
+id: TASK-47
+title: 'Implement System Clock / Heartbeat Service for rSpace canvas'
+status: To Do
+assignee: []
+created_date: '2026-02-18 22:30'
+labels:
+  - feature
+  - infrastructure
+  - ecosystem
+milestone: m-1
+dependencies:
+  - TASK-43
+references:
+  - rspace-online/backlog/tasks/task-43 - Implement-Event-Broadcasting-canvas-wide-pub-sub-system.md
+  - rSpace-website/docs/R-ECOSYSTEM-ARCHITECTURE.md
+priority: high
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Add a server-side System Clock service that broadcasts consistent time signals across the rSpace canvas via the Event Bus (TASK-43). This provides a shared temporal heartbeat that all shapes, modules, and connected r-ecosystem apps can subscribe to.
+
+**Why**: Currently there is no shared sense of time passing in rSpace. Individual shapes have no way to trigger time-based behavior (recurring updates, countdowns, reminders, periodic recalculations). A system clock provides the foundational "pulse" that time-aware features depend on.
+
+### Architecture
+
+New file `server/clock-service.ts`:
+- `SystemClock` class running server-side (not per-client)
+- Emits events on the CanvasEventBus at configurable intervals:
+  - `clock:tick` — every 60 seconds (primary heartbeat)
+  - `clock:minute:5` — every 5 minutes
+  - `clock:hourly` — every hour
+  - `clock:daily` — at midnight UTC (configurable timezone)
+- Payload includes: `{ timestamp, isoString, hour, minute, dayOfWeek, tickCount }`
+- Single authoritative source — server emits, clients receive via CRDT sync
+- Graceful degradation: if server is offline, clients can run a local fallback clock
+
+### Shape Integration
+
+Shapes opt in by subscribing to clock channels:
+```typescript
+// In a Budget shape
+subscriptions: ['clock:hourly']
+onEventReceived(channel: 'clock:hourly', payload) {
+  this.recalculate();
+}
+
+// In a Countdown shape
+subscriptions: ['clock:tick']
+onEventReceived(channel: 'clock:tick', payload) {
+  this.updateRemaining(payload.timestamp);
+}
+```
+
+### Use Cases
+
+- **Timer/Countdown shapes**: Update display every tick
+- **Budget/Finance shapes**: Recalculate on hourly boundaries
+- **Calendar shapes**: Highlight "now" marker, trigger reminders
+- **Presence decay**: Mark users idle after N missed ticks
+- **Backlog surfacing**: External services can subscribe to clock events to trigger task reviews
+- **rTime.space foundation**: This clock becomes the temporal primitive that rTime.space builds on
+- **Workflow triggers**: "Run this workflow every day at 9am"
+
+### Configuration
+
+Server-level config in community settings:
+- `clock.enabled: true` (default true)
+- `clock.timezone: 'UTC'` (for daily boundary)
+- `clock.tickInterval: 60` (seconds, minimum 10)
+- `clock.channels: ['tick', 'minute:5', 'hourly', 'daily']`
+
+### Performance Considerations
+
+- Clock events should NOT flood the CRDT eventLog — use a separate lightweight channel or mark as ephemeral (not persisted in ring buffer)
+- Server-side only emission prevents N clients from emitting N duplicate ticks
+- Tick events are fire-and-forget, no ack required
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 SystemClock emits `clock:tick` every 60s via CanvasEventBus
+- [ ] #2 Configurable intervals: tick, 5-min, hourly, daily
+- [ ] #3 Server-authoritative — only one clock source per canvas
+- [ ] #4 Shapes can subscribe to clock channels and receive time payloads
+- [ ] #5 Clock events are ephemeral (not persisted in CRDT eventLog ring buffer)
+- [ ] #6 Fallback local clock when server connection is lost
+- [ ] #7 Clock can be enabled/disabled per community in settings
+<!-- AC:END -->