feat(heartbeat): skip API calls when HEARTBEAT.md is effectively empty (#1535)

* feat: skip heartbeat API calls when HEARTBEAT.md is effectively empty

- Added isHeartbeatContentEffectivelyEmpty() to detect files with only headers/comments
- Modified runHeartbeatOnce() to check HEARTBEAT.md content before polling the LLM
- Returns early with 'empty-heartbeat-file' reason when no actionable tasks exist
- Preserves existing behavior when file is missing (lets LLM decide)
- Added comprehensive test coverage for empty file detection
- Saves API calls/costs when heartbeat file has no meaningful content

* chore: update HEARTBEAT.md template to be effectively empty by default

Changed instruction text to comment format so new workspaces benefit from
heartbeat optimization immediately. Users still get clear guidance on usage.

* fix: only treat markdown headers (# followed by space) as comments, not #TODO etc

* refactor: simplify regex per code review suggestion

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

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

docs/gateway/heartbeat.md

@@ -162,6 +162,10 @@ If a `HEARTBEAT.md` file exists in the workspace, the default prompt tells the
 agent to read it. Think of it as your “heartbeat checklist”: small, stable, and
 safe to include every 30 minutes.
 
+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.
+
 Keep it tiny (short checklist or reminders) to avoid prompt bloat.
 
 Example `HEARTBEAT.md`:

docs/reference/templates/HEARTBEAT.md

@@ -5,4 +5,5 @@ read_when:
 ---
 # HEARTBEAT.md
 
-Keep this file empty unless you want a tiny checklist. Keep it small.
+# Keep this file empty (or with only comments) to skip heartbeat API calls.
+# Add tasks below when you want the agent to check something periodically.

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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