diff --git a/docs/BOX-API-SPEC.md b/docs/BOX-API-SPEC.md
index 52ab4b9..10b32a2 100644
--- a/docs/BOX-API-SPEC.md
+++ b/docs/BOX-API-SPEC.md
@@ -319,3 +319,166 @@ The UI uses the same API endpoints as agents. No separate backend.
 
 Spec v0.1. Owner: operator-main. Sanctioned by the human 2026-10-04.
 Implementation pending.
+
+## Appendix A: Rich Linux Scheduling
+
+The box API supports multiple Linux scheduling mechanisms, not just systemd
+timers. Each has tradeoffs; the API abstracts them behind a unified interface.
+
+### Scheduler Types
+
+| Type | Use case | Precision | Persistence |
+|------|----------|-----------|-------------|
+| `systemd` | Recurring jobs, services | 1s | Yes (enabled) |
+| `cron` | Simple recurring, legacy | 1m | Yes (crontab) |
+| `at` | One-time future jobs | 1m | No (one-shot) |
+
+### Unified Scheduler API
+
+The `/api/box/timers` endpoints accept a `scheduler` field:
+
+```json
+{
+  "name": "board-watch",
+  "scheduler": "systemd",  // or "cron", "at"
+  "schedule": "*/5 * * * *",
+  ...
+}
+```
+
+**Systemd** (default): As described in main spec. Best for most jobs.
+
+**Cron:** For simple recurring tasks. The API manages the user's crontab.
+```bash
+# Backend: (crontab -l ; echo "*/5 * * * * /path/to/job.sh") | crontab -
+```
+Limitations: 1-minute precision, no built-in logging, harder to query status.
+
+**At:** For one-time delayed execution.
+```bash
+# Backend: echo "/path/to/job.sh" | at now + 1 hour
+```
+Use for: "remind me in 2 hours", "retry this job once in 30m".
+
+### Scheduler-Specific Endpoints
+
+```
+GET /api/box/schedulers          # List available schedulers
+GET /api/box/schedulers/{type}/jobs  # List jobs for a scheduler
+```
+
+## Appendix B: DM + Metadata JSON
+
+DMs carry structured metadata, not just text. The box API returns DMs
+with full metadata for programmatic processing.
+
+### DM Wire Format
+
+Every DM has two layers:
+
+**1. Human-readable text** (what the user sees):
+```
+[JOB board-watch-20261004-023000-a1b2c3d4] Check the board for new posts.
+```
+
+**2. Metadata JSON** (for agents and API):
+```json
+{
+  "id": "a1b2c3d4",
+  "job_id": "board-watch-20261004-023000-a1b2c3d4",
+  "type": "job",
+  "from": "opm",
+  "to": "muse",
+  "target": "main",
+  "sidechat": null,
+  "timestamp": "2026-10-04T02:30:00Z",
+  "priority": "normal",
+  "timeout": 300,
+  "chain_next": null,
+  "signature": "-----BEGIN SSH SIGNATURE-----\n..."
+}
+```
+
+### DM Types
+
+| Type | Description | Required fields |
+|------|-------------|-----------------|
+| `job` | Job prompt from scheduler | `job_id`, `prompt` |
+| `result` | Job result from agent | `job_id`, `success`, `output` |
+| `chat` | Regular DM | `text` |
+| `alert` | System alert | `severity`, `message` |
+| `canary` | Signature test | `key_id`, `namespace` |
+
+### API: Get DMs with Metadata
+
+```
+GET /api/box/dms?agent=muse&limit=20
+```
+
+**Response:**
+```json
+{
+  "dms": [
+    {
+      "id": "a1b2c3d4",
+      "text": "[JOB ...] Check the board...",
+      "metadata": {
+        "type": "job",
+        "job_id": "board-watch-20261004-023000-a1b2c3d4",
+        "from": "opm",
+        "to": "muse",
+        "timestamp": "2026-10-04T02:30:00Z",
+        "priority": "normal"
+      },
+      "verified": true
+    }
+  ]
+}
+```
+
+### API: Send DM with Metadata
+
+```
+POST /api/box/dms
+Content-Type: application/json
+```
+
+**Body:**
+```json
+{
+  "to": "muse",
+  "target": "main",
+  "type": "job",
+  "text": "Check the board...",
+  "metadata": {
+    "job_id": "board-watch-20261004-023000-a1b2c3d4",
+    "priority": "high",
+    "timeout": 300
+  }
+}
+```
+
+The API constructs the wire format `[JOB {job_id}] {text}` and sends via
+`dm.py`. Metadata is logged to `dm-log.jsonl` alongside the text.
+
+### Metadata in Logs
+
+`dm-log.jsonl` entries include metadata:
+```json
+{
+  "ts": "2026-10-04T02:30:00Z",
+  "type": "send",
+  "id": "a1b2c3d4",
+  "metadata": {
+    "job_id": "board-watch-...",
+    "type": "job",
+    "priority": "normal"
+  }
+}
+```
+
+This enables:
+- Filtering DMs by type, job, priority
+- Building dashboards (box UI shows job DMs separately from chat)
+- Audit trails (which jobs were sent, when, to whom)
+- Agent learning (which job types succeed/fail)