auto-install claude plugins at harness boot

new hyperhive.claudePlugins NixOS option (list of strings) rendered
to /etc/hyperhive/claude-plugins.json. both hive-ag3nt and hive-m1nd
shell out 'claude plugin install <spec>' for each entry once at
startup before the turn loop opens. failures log a warning but don't
abort boot.

hive-ag3nt/src/plugins.rs

@@ -0,0 +1,48 @@
+//! Boot-time `claude plugin install` driver. Reads the list declared
+//! via the `hyperhive.claudePlugins` NixOS option (rendered to
+//! `/etc/hyperhive/claude-plugins.json` by the harness module) and
+//! shells out `claude plugin install <spec>` for each entry. Runs once
+//! per harness boot before the turn loop; `claude plugin install`
+//! is expected to be idempotent so reinstalling on each container
+//! recreate is fine. Failures log a warning but do not abort boot —
+//! we'd rather start without a plugin than refuse to serve.
+
+use tokio::process::Command;
+
+const PLUGINS_PATH: &str = "/etc/hyperhive/claude-plugins.json";
+
+pub async fn install_configured() {
+    let raw = match tokio::fs::read_to_string(PLUGINS_PATH).await {
+        Ok(s) => s,
+        Err(_) => return,
+    };
+    let specs: Vec<String> = match serde_json::from_str(&raw) {
+        Ok(v) => v,
+        Err(e) => {
+            tracing::warn!(path = PLUGINS_PATH, error = ?e, "claude-plugins spec parse failed; skipping");
+            return;
+        }
+    };
+    for spec in specs {
+        match Command::new("claude")
+            .args(["plugin", "install", &spec])
+            .output()
+            .await
+        {
+            Ok(out) if out.status.success() => {
+                tracing::info!(spec = %spec, "claude plugin install ok");
+            }
+            Ok(out) => {
+                tracing::warn!(
+                    spec = %spec,
+                    status = ?out.status,
+                    stderr = %String::from_utf8_lossy(&out.stderr),
+                    "claude plugin install failed",
+                );
+            }
+            Err(e) => {
+                tracing::warn!(spec = %spec, error = ?e, "claude plugin install spawn failed");
+            }
+        }
+    }
+}