diff --git a/nix/templates/harness-base.nix b/nix/templates/harness-base.nix
index f6c7c01a..eb921254 100644
--- a/nix/templates/harness-base.nix
+++ b/nix/templates/harness-base.nix
@@ -828,6 +828,34 @@ in
     '';
   };
 
+  options.hyperhive.mcp.httpPort = lib.mkOption {
+    type = lib.types.nullOr lib.types.port;
+    default = null;
+    example = 8790;
+    description = ''
+      Serve the built-in hyperhive MCP surface as a persistent
+      streamable-http daemon on this loopback port instead of the
+      default per-turn stdio child.
+
+      When null (the default) claude spawns a fresh `hive … mcp` stdio
+      subprocess every turn — the shape that carries the per-turn MCP
+      re-registration race (a resumed turn can emit its first tool call
+      before that turn's async `initialize`/`tools-list` completes,
+      stranding the agent with `No such tool`). When set, a long-lived
+      `hive-mcp-http` systemd unit runs `hive mcp --http 127.0.0.1:<port>`
+      and `render_claude_config` points claude at the stable
+      `http://127.0.0.1:<port>/mcp` URL, which survives the per-turn
+      claude re-spawn (and a host-side hive-c0re restart — each tool call
+      dials the control socket fresh). Extra MCP servers (matrix/bash)
+      stay stdio bridges regardless.
+
+      Bound loopback-only; the rmcp streamable-http transport's default
+      `allowed_hosts` (`localhost` / `127.0.0.1` / `::1`) rejects Host
+      headers from anywhere else, so no auth token is required for a
+      container-local endpoint.
+    '';
+  };
+
   config = {
     warnings = lib.optional (config.hyperhive.allowedBashPatterns != [ ]) ''
       hyperhive.allowedBashPatterns is deprecated and has no effect.
@@ -1709,6 +1737,33 @@ in
       };
     };
 
+    # Persistent streamable-http MCP daemon for the built-in hyperhive
+    # surface. Only wired when `hyperhive.mcp.httpPort` is set; otherwise
+    # the surface stays the default per-turn stdio child (rendered by
+    # `render_claude_config`). Long-lived so claude reconnects to the
+    # stable URL each turn instead of respawning + re-registering a stdio
+    # subprocess (the per-turn MCP registration race). It dials the
+    # control socket (`/run/hive/mcp.sock`, the `hive` binary default)
+    # fresh on every tool call, so a host-side hive-c0re restart is
+    # transparent. `before = hive-ag3nt` so the URL is already listening
+    # by the time the harness renders the first turn's config; the
+    # harness/claude also reconnect on their own, so ordering is a
+    # latency nicety not a hard correctness dep.
+    systemd.services.hive-mcp-http = lib.mkIf (config.hyperhive.mcp.httpPort != null) {
+      description = "persistent streamable-http MCP daemon for the hyperhive surface";
+      wantedBy = [ "multi-user.target" ];
+      before = [ "hive-ag3nt.service" ];
+      environment.RUST_LOG = "info";
+      serviceConfig = {
+        ExecStart = "${pkgs.hyperhive}/bin/hive mcp --http 127.0.0.1:${toString config.hyperhive.mcp.httpPort}";
+        SyslogIdentifier = "hive-mcp-http";
+        Restart = "on-failure";
+        RestartSec = 3;
+        User = userName;
+        Group = userName;
+      };
+    };
+
     # Re-fire the daemon when the matrix token appears (hive-c0re
     # provisions it after agent containers come up). Without this
     # the daemon would exit 0 silently on first boot and the MCP
@@ -1802,6 +1857,13 @@ in
           # bind-mounts and gateway upstream config stay in sync.
           HIVE_WEB_SOCKET = "/run/hive-agent/${userName}/web.sock";
         }
+        // lib.optionalAttrs (config.hyperhive.mcp.httpPort != null) {
+          # Presence tells `render_claude_config` to point claude at the
+          # persistent `hive-mcp-http` daemon's loopback URL instead of a
+          # per-turn stdio child. Kept in sync with the `hive-mcp-http`
+          # unit's `--http` port above via the same option.
+          HYPERHIVE_MCP_HTTP_PORT = toString config.hyperhive.mcp.httpPort;
+        }
         // lib.optionalAttrs config.hyperhive.gui.enable {
           # Tells the harness which fixed VNC port weston bound, and (by
           # its presence) that gui is enabled — the harness `/screen/ws`