docs: clarify heartbeat empty file behavior (#1535) (thanks @JustYannicc)

docs/start/clawd.md

@@ -182,6 +182,8 @@ By default, Clawdbot runs a heartbeat every 30 minutes with the prompt:
 `Read HEARTBEAT.md if it exists (workspace context). Follow it strictly. Do not infer or repeat old tasks from prior chats. If nothing needs attention, reply HEARTBEAT_OK.`
 Set `agents.defaults.heartbeat.every: "0m"` to disable.
 
+- If `HEARTBEAT.md` exists but is effectively empty (only blank lines and markdown headers like `# Heading`), Clawdbot skips the heartbeat run to save API calls.
+- If the file is missing, the heartbeat still runs and the model decides what to do.
 - If the agent replies with `HEARTBEAT_OK` (optionally with short padding; see `agents.defaults.heartbeat.ackMaxChars`), Clawdbot suppresses outbound delivery for that heartbeat.
 - Heartbeats run full agent turns — shorter intervals burn more tokens.
 

docs/start/faq.md

@@ -971,6 +971,10 @@ Heartbeats run every **30m** by default. Tune or disable them:
 }
 ```
 
+If `HEARTBEAT.md` exists but is effectively empty (only blank lines and markdown
+headers like `# Heading`), Clawdbot skips the heartbeat run to save API calls.
+If the file is missing, the heartbeat still runs and the model decides what to do.
+
 Per-agent overrides use `agents.list[].heartbeat`. Docs: [Heartbeat](/gateway/heartbeat).
 
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