Draft PR Description

Title: Warn on high-frequency cron schedules (<30m) to reduce session accumulation risk

Summary

High-frequency cron jobs (e.g. every 15m/30m) can silently accumulate sessions and inflate the agent context window until the agent becomes non-responsive (“dispatch succeeds but replies=0”). This PR adds a minimal guardrail: warn when creating cron jobs with --every intervals under 30 minutes.

What this PR does

• CLI warning during openclaw cron add if --every < 30m.
• Gateway log warning on cron.add for schedule.kind="every" and everyMs < 30m.

CLI message:

Warning: High-frequency cron (< 30m) may cause session accumulation and silently exhaust the agent context window. Consider using heartbeat or longer intervals.

Why this is safe

• Does not block cron creation (no breaking change).
• Provides immediate, actionable feedback at the moment of job creation.

Implementation

• src/cli/cron-cli/register.cron-add.ts
• src/gateway/server-methods/cron.ts

Tests

• pnpm vitest src/cli/cron-cli.test.ts --run
• pnpm vitest src/gateway/server.cron.test.ts --run

Closes openclaw#38730