fix: make heartbeat interval configurable and reduce researcher max_iterations

Two related issues with autonomous Hand agents:

1. heartbeat_interval_secs was hardcoded at 30s (the AutonomousConfig default)
   for all Hands, with no way to override it from HAND.toml. For agents that
   make long LLM calls, 30s causes false-positive recovery triggers during
   normal operation. Add heartbeat_interval_secs to HandAgentConfig so each
   Hand can declare an appropriate interval.

2. The researcher Hand shipped with max_iterations = 80 and a system prompt
   instructing exhaustive research (50+ sources). This combination was designed
   for cloud LLMs with 200K context windows. On any model with a 32K or smaller
   context window, 80 iterations × growing history guarantees context overflow
   before the task completes. Reduce to 25, which is sufficient for thorough
   research within a 32K budget.

researcher/HAND.toml changes:
- max_iterations: 80 → 25
- heartbeat_interval_secs: 120 (new field; 30s default was triggering false
  recovery during normal multi-minute LLM calls)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/openfang-hands/bundled/researcher/HAND.toml

@@ -161,7 +161,10 @@ provider = "default"
 model = "default"
 max_tokens = 16384
 temperature = 0.3
-max_iterations = 80
+max_iterations = 25
+# Researcher makes long LLM calls; 30s (kernel default) causes false-positive
+# recovery triggers. 120s matches typical deep-research call latency.
+heartbeat_interval_secs = 120
 system_prompt = """You are Researcher Hand — an autonomous deep research agent that conducts exhaustive investigations, cross-references sources, fact-checks claims, and produces comprehensive structured reports.
 
 ## Phase 0 — Platform Detection & Context (ALWAYS DO THIS FIRST)

crates/openfang-hands/src/lib.rs

@@ -288,6 +288,11 @@ pub struct HandAgentConfig {
     pub system_prompt: String,
     #[serde(default)]
     pub max_iterations: Option<u32>,
+    /// Heartbeat interval in seconds for autonomous agents. Overrides the
+    /// AutonomousConfig default (30s), which is too aggressive for agents
+    /// making long LLM calls. Omit to use the kernel default.
+    #[serde(default)]
+    pub heartbeat_interval_secs: Option<u64>,
 }
 
 fn default_module() -> String {

crates/openfang-kernel/src/kernel.rs

@@ -3252,6 +3252,10 @@ impl OpenFangKernel {
             ],
             autonomous: def.agent.max_iterations.map(|max_iter| AutonomousConfig {
                 max_iterations: max_iter,
+                // Use the hand-declared heartbeat interval if provided.
+                // The kernel default (30s) is too aggressive for hands making long LLM calls;
+                // HAND.toml authors should set this to reflect expected call latency.
+                heartbeat_interval_secs: def.agent.heartbeat_interval_secs.unwrap_or(30),
                 ..Default::default()
             }),
             // Autonomous hands must run in Continuous mode so the background loop picks them up.