Problem

isHeartbeatEnabledForAgent in src/infra/heartbeat-runner.ts has two bugs:

Bug 1: Default agent gets heartbeat with zero configuration

When no heartbeat is configured anywhere (no agents.defaults.heartbeat, no per-agent heartbeat), the fallback returns true for the default agent:

return resolvedAgentId === resolveDefaultAgentId(cfg);

This silently enables heartbeat at the default interval for the default agent even though nobody asked for it. If no heartbeat is configured, heartbeat should be disabled for all agents.

Bug 2: agents.defaults.heartbeat is ignored for enabled/disabled decision

When agents.defaults.heartbeat IS configured but no individual agent has a per-agent heartbeat property, hasExplicitHeartbeatAgents() returns false (it only scans list[].heartbeat, not defaults). The function then falls through to the same default-agent-only fallback, meaning only the default agent gets heartbeat — even though the user explicitly configured heartbeat defaults intending it for all agents.

Affected code

• hasExplicitHeartbeatAgents(): Only checks per-agent heartbeat, ignores agents.defaults.heartbeat
• isHeartbeatEnabledForAgent(): Fallback logic unconditionally enables heartbeat for default agent

Expected behavior

Existing tests encode the bug

The test "falls back to default agent when no explicit heartbeat entries" asserts the broken behavior as correct — it expects only the default agent to be enabled when agents.defaults.heartbeat is set without per-agent entries.

Also tracked downstream: remoteclaw#623