Resolves#641
## Problem
When a VM migrates between Proxmox nodes, Pulse was treating it as a new
resource and discarding custom alert threshold overrides. This occurred
because guest IDs included the node name (e.g., `instance-node-VMID`),
causing the ID to change when the VM moved to a different node.
Users reported that after migrating a VM, previously disabled alerts
(e.g., memory threshold set to 0) would resume firing.
## Root Cause
Guest IDs were constructed as:
- Standalone: `node-VMID`
- Cluster: `instance-node-VMID`
When a VM migrated from node1 to node2, the ID changed from
`instance-node1-100` to `instance-node2-100`, causing:
- Alert threshold overrides to be orphaned (keyed by old ID)
- Guest metadata (custom URLs, descriptions) to be orphaned
- Active alerts to reference the wrong resource ID
## Solution
Changed guest ID format to be stable across node migrations:
- New format: `instance-VMID` (for both standalone and cluster)
- Retains uniqueness across instances while being node-independent
- Allows VMs to migrate freely without losing configuration
## Implementation
### Backend Changes
1. **Guest ID Construction** (`monitor_polling.go`):
- Simplified to always use `instance-VMID` format
- Removed node from the ID construction logic
2. **Alert Override Migration** (`alerts.go`):
- Added lazy migration in `getGuestThresholds()`
- Detects legacy ID formats and migrates to new format
- Preserves user configurations automatically
3. **Guest Metadata Migration** (`guest_metadata.go`):
- Added `GetWithLegacyMigration()` helper method
- Called during VM/container polling to migrate metadata
- Preserves custom URLs and descriptions
4. **Active Alerts Migration** (`alerts.go`):
- Added migration logic in `LoadActiveAlerts()`
- Translates legacy alert resource IDs to new format
- Preserves alert acknowledgments across restarts
### Frontend Changes
5. **ID Construction Updates**:
- `ThresholdsTable.tsx`: Updated fallback from `instance-node-vmid` to `instance-vmid`
- `Dashboard.tsx`: Simplified guest ID construction
- `GuestRow.tsx`: Updated `buildGuestId()` helper
## Migration Strategy
- **Lazy Migration**: Configs are migrated as guests are discovered
- **Backwards Compatible**: Old IDs are detected and automatically converted
- **Zero Downtime**: No manual intervention required
- **Persisted**: Migrated configs are saved on next config write cycle
## Testing Recommendations
After deployment:
1. Verify existing alert overrides still apply
2. Test VM migration - confirm thresholds persist
3. Check guest metadata (custom URLs) survive migration
4. Verify active alerts maintain acknowledgment state
## Related
- Addresses similar issues with guest metadata and active alert tracking
- Lays groundwork for any future guest-specific configuration features
- Aligns with project philosophy: correctness and UX over implementation complexity
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