turn loop: pin to haiku 4.5 (todo: per-agent override)

hive-ag3nt/src/bin/hive-ag3nt.rs

@@ -178,8 +178,13 @@ async fn invoke_claude(prompt: &str, mcp_config: &Path) -> Result<String> {
     // plus the hyperhive MCP surface so there's no permission prompt
     // mid-turn. A finer-grained allow-list system for Bash command
     // patterns is on the backlog (PLAN.md polish).
+    // Hard-coded to Haiku 4.5 for now to keep cost predictable while we
+    // iterate. TODO: make this overridable per-agent — op via dashboard,
+    // manager via `request_apply_commit` setting on the agent's flake.
     let out = Command::new("claude")
         .arg("--print")
+        .arg("--model")
+        .arg("claude-haiku-4-5-20251001")
         .arg("--mcp-config")
         .arg(mcp_config)
         .arg("--tools")