website/docs/developer-guide/cron-internals.md

---
sidebar_position: 11
title: "Cron Internals"
description: "How Hermes stores, schedules, edits, pauses, skill-loads, and delivers cron jobs"
---

# Cron Internals

The cron subsystem provides scheduled task execution — from simple one-shot delays to recurring cron-expression jobs with skill injection and cross-platform delivery.

## Key Files

| File | Purpose |
|------|---------|
| `cron/jobs.py` | Job model, storage, atomic read/write to `jobs.json` |
| `cron/scheduler.py` | Scheduler loop — due-job detection, execution, repeat tracking |
| `tools/cronjob_tools.py` | Model-facing `cronjob` tool registration and handler |
| `gateway/run.py` | Gateway integration — cron ticking in the long-running loop |
| `hermes_cli/cron.py` | CLI `hermes cron` subcommands |

## Scheduling Model

Four schedule formats are supported:

| Format | Example | Behavior |
|--------|---------|----------|
| **Relative delay** | `30m`, `2h`, `1d` | One-shot, fires after the specified duration |
| **Interval** | `every 2h`, `every 30m` | Recurring, fires at regular intervals |
| **Cron expression** | `0 9 * * *` | Standard 5-field cron syntax (minute, hour, day, month, weekday) |
| **ISO timestamp** | `2025-01-15T09:00:00` | One-shot, fires at the exact time |

The model-facing surface is a single `cronjob` tool with action-style operations: `create`, `list`, `update`, `pause`, `resume`, `run`, `remove`.

## Job Storage

Jobs are stored in `~/.hermes/cron/jobs.json` with atomic write semantics (write to temp file, then rename). Each job record contains:

```json
{
  "id": "a1b2c3d4e5f6",
  "name": "Daily briefing",
  "prompt": "Summarize today's AI news and funding rounds",
  "schedule": {
    "kind": "cron",
    "expr": "0 9 * * *",
    "display": "0 9 * * *"
  },
  "skills": ["ai-funding-daily-report"],
  "deliver": "telegram:-1001234567890",
  "repeat": {
    "times": null,
    "completed": 42
  },
  "state": "scheduled",
  "enabled": true,
  "next_run_at": "2025-01-16T09:00:00Z",
  "last_run_at": "2025-01-15T09:00:00Z",
  "last_status": "ok",
  "created_at": "2025-01-01T00:00:00Z",
  "model": null,
  "provider": null,
  "script": null
}
```

### Job Lifecycle States

| State | Meaning |
|-------|---------|
| `scheduled` | Active, will fire at next scheduled time |
| `paused` | Suspended — won't fire until resumed |
| `completed` | Repeat count exhausted or one-shot that has fired |
| `running` | Currently executing (transient state) |

### Backward Compatibility

Older jobs may have a single `skill` field instead of the `skills` array. The scheduler normalizes this at load time — single `skill` is promoted to `skills: [skill]`.

## Scheduler Runtime

### Tick Cycle

The scheduler runs on a periodic tick (default: every 60 seconds):

```text
tick()
  1. Acquire scheduler lock (prevents overlapping ticks)
  2. Load all jobs from jobs.json
  3. Filter to due jobs (next_run <= now AND state == "scheduled")
  4. For each due job:
     a. Set state to "running"
     b. Create fresh AIAgent session (no conversation history)
     c. Load attached skills in order (injected as user messages)
     d. Run the job prompt through the agent
     e. Deliver the response to the configured target
     f. Update run_count, compute next_run
     g. If repeat count exhausted → state = "completed"
     h. Otherwise → state = "scheduled"
  5. Write updated jobs back to jobs.json
  6. Release scheduler lock
```

### Gateway Integration

In gateway mode, the scheduler tick is integrated into the gateway's main event loop. The gateway calls `scheduler.tick()` on its periodic maintenance cycle, which runs alongside message handling.

In CLI mode, cron jobs only fire when `hermes cron` commands are run or during active CLI sessions.

### Fresh Session Isolation

Each cron job runs in a completely fresh agent session:

- No conversation history from previous runs
- No memory of previous cron executions (unless persisted to memory/files)
- The prompt must be self-contained — cron jobs cannot ask clarifying questions
- The `cronjob` toolset is disabled (recursion guard)

## Skill-Backed Jobs

A cron job can attach one or more skills via the `skills` field. At execution time:

1. Skills are loaded in the specified order
2. Each skill's SKILL.md content is injected as context
3. The job's prompt is appended as the task instruction
4. The agent processes the combined skill context + prompt

This enables reusable, tested workflows without pasting full instructions into cron prompts. For example:

```
Create a daily funding report → attach "ai-funding-daily-report" skill
```

### Script-Backed Jobs

Jobs can also attach a Python script via the `script` field. The script runs *before* each agent turn, and its stdout is injected into the prompt as context. This enables data collection and change detection patterns:

```python
# ~/.hermes/scripts/check_competitors.py
import requests, json
# Fetch competitor release notes, diff against last run
# Print summary to stdout — agent analyzes and reports
```

The script timeout defaults to 120 seconds. `_get_script_timeout()` resolves the limit through a three-layer chain:

1. **Module-level override** — `_SCRIPT_TIMEOUT` (for tests/monkeypatching). Only used when it differs from the default.
2. **Environment variable** — `HERMES_CRON_SCRIPT_TIMEOUT`
3. **Config** — `cron.script_timeout_seconds` in `config.yaml` (read via `load_config()`)
4. **Default** — 120 seconds

### Provider Recovery

`run_job()` passes the user's configured fallback providers and credential pool into the `AIAgent` instance:

- **Fallback providers** — reads `fallback_providers` (list) or `fallback_model` (legacy dict) from `config.yaml`, matching the gateway's `_load_fallback_model()` pattern. Passed as `fallback_model=` to `AIAgent.__init__`, which normalizes both formats into a fallback chain.
- **Credential pool** — loads via `load_pool(provider)` from `agent.credential_pool` using the resolved runtime provider name. Only passed when the pool has credentials (`pool.has_credentials()`). Enables same-provider key rotation on 429/rate-limit errors.

This mirrors the gateway's behavior — without it, cron agents would fail on rate limits without attempting recovery.

## Delivery Model

Cron job results can be delivered to any supported platform:

| Target | Syntax | Example |
|--------|--------|---------|
| Origin chat | `origin` | Deliver to the chat where the job was created |
| Local file | `local` | Save to `~/.hermes/cron/output/` |
| Telegram | `telegram` or `telegram:<chat_id>` | `telegram:-1001234567890` |
| Discord | `discord` or `discord:#channel` | `discord:#engineering` |
| Slack | `slack` | Deliver to Slack home channel |
| WhatsApp | `whatsapp` | Deliver to WhatsApp home |
| Signal | `signal` | Deliver to Signal |
| Matrix | `matrix` | Deliver to Matrix home room |
| Mattermost | `mattermost` | Deliver to Mattermost home |
| Email | `email` | Deliver via email |
| SMS | `sms` | Deliver via SMS |
| Home Assistant | `homeassistant` | Deliver to HA conversation |
| DingTalk | `dingtalk` | Deliver to DingTalk |
| Feishu | `feishu` | Deliver to Feishu |
| WeCom | `wecom` | Deliver to WeCom |
| Weixin | `weixin` | Deliver to Weixin (WeChat) |
| BlueBubbles | `bluebubbles` | Deliver to iMessage via BlueBubbles |
| QQ Bot | `qqbot` | Deliver to QQ (Tencent) via Official API v2 |

For Telegram topics, use the format `telegram:<chat_id>:<thread_id>` (e.g., `telegram:-1001234567890:17585`).

### Response Wrapping

By default (`cron.wrap_response: true`), cron deliveries are wrapped with:
- A header identifying the cron job name and task
- A footer noting the agent cannot see the delivered message in conversation

The `[SILENT]` prefix in a cron response suppresses delivery entirely — useful for jobs that only need to write to files or perform side effects.

### Session Isolation

Cron deliveries are NOT mirrored into gateway session conversation history. They exist only in the cron job's own session. This prevents message alternation violations in the target chat's conversation.

## Recursion Guard

Cron-run sessions have the `cronjob` toolset disabled. This prevents:
- A scheduled job from creating new cron jobs
- Recursive scheduling that could explode token usage
- Accidental mutation of the job schedule from within a job

## Locking

The scheduler uses file-based locking to prevent overlapping ticks from executing the same due-job batch twice. This is important in gateway mode where multiple maintenance cycles could overlap if a previous tick takes longer than the tick interval.

## CLI Interface

The `hermes cron` CLI provides direct job management:

```bash
hermes cron list                    # Show all jobs
hermes cron create                  # Interactive job creation (alias: add)
hermes cron edit <job_id>           # Edit job configuration
hermes cron pause <job_id>          # Pause a running job
hermes cron resume <job_id>         # Resume a paused job
hermes cron run <job_id>            # Trigger immediate execution
hermes cron remove <job_id>         # Delete a job
```

## Related Docs

- [Cron Feature Guide](/docs/user-guide/features/cron)
- [Gateway Internals](./gateway-internals.md)
- [Agent Loop Internals](./agent-loop.md)