feat(mcp): per server deferred mode (#1654)

* feat(mcp): per server deferred mode

* fix deferred behavior

docs/tools_configuration.md

@@ -158,7 +158,7 @@ and injected into the context for a configured number of turns (`ttl`).
 
 | Config               | Type | Default | Description                                                                                                                       |
 |----------------------|------|---------|-----------------------------------------------------------------------------------------------------------------------------------|
-| `enabled`            | bool | false   | If true, MCP tools are hidden and loaded on-demand via search. If false, all tools are loaded                                     |
+| `enabled`            | bool | false   | Global default: if `true`, all MCP tools are hidden and loaded on-demand via search; if `false`, all tools are loaded into context. Individual servers can override this with the per-server `deferred` field. |
 | `ttl`                | int  | 5       | Number of conversational turns a discovered tool remains unlocked                                                                 |
 | `max_search_results` | int  | 5       | Maximum number of tools returned per search query                                                                                 |
 | `use_bm25`           | bool | true    | Enable the natural language/keyword search tool (`tool_search_tool_bm25`). **Warning**: consumes more resources than regex search |
@@ -170,8 +170,9 @@ and injected into the context for a configured number of turns (`ttl`).
 ### Per-Server Config
 
 | Config     | Type    | Required | Description                                                                                                                                                     |
-|------------|--------|----------|--------------------------------------------|
+|------------|---------|----------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `enabled`  | bool    | yes      | Enable this MCP server                                                                                                                                          |
+| `deferred` | bool    | no       | Override deferred mode for this server only. `true` = tools are hidden and discoverable via search; `false` = tools are always visible in context. When omitted, the global `discovery.enabled` value applies. |
 | `type`     | string  | no       | Transport type: `stdio`, `sse`, `http`                                                                                                                          |
 | `command`  | string  | stdio    | Executable command for stdio transport                                                                                                                          |
 | `args`     | array   | no       | Command arguments for stdio transport                                                                                                                           |
@@ -291,6 +292,50 @@ dynamically only when requested by the user.*
 }
 ```
 
+#### 4) Mixed setup: per-server deferred override
+
+*Discovery is enabled globally, but `filesystem` is pinned as always-visible while `context7` follows the global
+default (deferred). `aws` explicitly opts in to deferred mode even though it is the same as the global default.*
+
+```json
+{
+  "tools": {
+    "mcp": {
+      "enabled": true,
+      "discovery": {
+        "enabled": true,
+        "ttl": 5,
+        "max_search_results": 5,
+        "use_bm25": true
+      },
+      "servers": {
+        "filesystem": {
+          "enabled": true,
+          "command": "npx",
+          "args": ["-y", "@modelcontextprotocol/server-filesystem", "/workspace"],
+          "deferred": false
+        },
+        "context7": {
+          "enabled": true,
+          "command": "npx",
+          "args": ["-y", "@upstash/context7-mcp"]
+        },
+        "aws": {
+          "enabled": true,
+          "command": "npx",
+          "args": ["-y", "aws-mcp-server"],
+          "deferred": true
+        }
+      }
+    }
+  }
+}
+```
+
+> **Tip:** `deferred` on a per-server basis is independent of `discovery.enabled`. You can keep
+> `discovery.enabled: false` globally (all tools visible by default) and still mark individual
+> high-volume servers as `"deferred": true` to avoid polluting the context with their tools.
+
 ## Skills Tool
 
 The skills tool configures skill discovery and installation via registries like ClawHub.

pkg/agent/loop_mcp.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"sync"
 
+	"github.com/sipeed/picoclaw/pkg/config"
 	"github.com/sipeed/picoclaw/pkg/logger"
 	"github.com/sipeed/picoclaw/pkg/mcp"
 	"github.com/sipeed/picoclaw/pkg/tools"
@@ -111,6 +112,12 @@ func (al *AgentLoop) ensureMCPInitialized(ctx context.Context) error {
 
 		for serverName, conn := range servers {
 			uniqueTools += len(conn.Tools)
+
+			// Determine whether this server's tools should be deferred (hidden).
+			// Per-server "deferred" field takes precedence over the global Discovery.Enabled.
+			serverCfg := al.cfg.Tools.MCP.Servers[serverName]
+			registerAsHidden := serverIsDeferred(al.cfg.Tools.MCP.Discovery.Enabled, serverCfg)
+
 			for _, tool := range conn.Tools {
 				for _, agentID := range agentIDs {
 					agent, ok := al.registry.GetAgent(agentID)
@@ -120,7 +127,7 @@ func (al *AgentLoop) ensureMCPInitialized(ctx context.Context) error {
 
 					mcpTool := tools.NewMCPTool(mcpManager, serverName, tool)
 
-					if al.cfg.Tools.MCP.Discovery.Enabled {
+					if registerAsHidden {
 						agent.Tools.RegisterHidden(mcpTool)
 					} else {
 						agent.Tools.Register(mcpTool)
@@ -133,6 +140,7 @@ func (al *AgentLoop) ensureMCPInitialized(ctx context.Context) error {
 							"server":   serverName,
 							"tool":     tool.Name,
 							"name":     mcpTool.Name(),
+							"deferred": registerAsHidden,
 						})
 				}
 			}
@@ -198,3 +206,18 @@ func (al *AgentLoop) ensureMCPInitialized(ctx context.Context) error {
 
 	return al.mcp.getInitErr()
 }
+
+// serverIsDeferred reports whether an MCP server's tools should be registered
+// as hidden (deferred/discovery mode).
+//
+// The per-server Deferred field takes precedence over the global discoveryEnabled
+// default. When Deferred is nil, discoveryEnabled is used as the fallback.
+func serverIsDeferred(discoveryEnabled bool, serverCfg config.MCPServerConfig) bool {
+	if !discoveryEnabled {
+		return false
+	}
+	if serverCfg.Deferred != nil {
+		return *serverCfg.Deferred
+	}
+	return true
+}

pkg/agent/loop_mcp_test.go

@@ -0,0 +1,75 @@
+// PicoClaw - Ultra-lightweight personal AI agent
+// Inspired by and based on nanobot: https://github.com/HKUDS/nanobot
+// License: MIT
+//
+// Copyright (c) 2026 PicoClaw contributors
+
+package agent
+
+import (
+	"testing"
+
+	"github.com/sipeed/picoclaw/pkg/config"
+)
+
+func boolPtr(b bool) *bool { return &b }
+
+func TestServerIsDeferred(t *testing.T) {
+	tests := []struct {
+		name             string
+		discoveryEnabled bool
+		serverDeferred   *bool
+		want             bool
+	}{
+		// --- global false always wins: per-server deferred is ignored ---
+		{
+			name:             "global false: per-server deferred=true is ignored",
+			discoveryEnabled: false,
+			serverDeferred:   boolPtr(true),
+			want:             false,
+		},
+		{
+			name:             "global false: per-server deferred=false stays false",
+			discoveryEnabled: false,
+			serverDeferred:   boolPtr(false),
+			want:             false,
+		},
+		// --- global true: per-server override applies ---
+		{
+			name:             "global true: per-server deferred=false opts out",
+			discoveryEnabled: true,
+			serverDeferred:   boolPtr(false),
+			want:             false,
+		},
+		{
+			name:             "global true: per-server deferred=true stays true",
+			discoveryEnabled: true,
+			serverDeferred:   boolPtr(true),
+			want:             true,
+		},
+		// --- no per-server override: fall back to global ---
+		{
+			name:             "no per-server field, global discovery enabled",
+			discoveryEnabled: true,
+			serverDeferred:   nil,
+			want:             true,
+		},
+		{
+			name:             "no per-server field, global discovery disabled",
+			discoveryEnabled: false,
+			serverDeferred:   nil,
+			want:             false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			serverCfg := config.MCPServerConfig{Deferred: tt.serverDeferred}
+			got := serverIsDeferred(tt.discoveryEnabled, serverCfg)
+			if got != tt.want {
+				t.Errorf("serverIsDeferred(discoveryEnabled=%v, deferred=%v) = %v, want %v",
+					tt.discoveryEnabled, tt.serverDeferred, got, tt.want)
+			}
+		})
+	}
+}

pkg/config/config.go

@@ -806,6 +806,10 @@ type ClawHubRegistryConfig struct {
 type MCPServerConfig struct {
 	// Enabled indicates whether this MCP server is active
 	Enabled bool `json:"enabled"`
+	// Deferred controls whether this server's tools are registered as hidden (deferred/discovery mode).
+	// When nil, the global Discovery.Enabled setting applies.
+	// When explicitly set to true or false, it overrides the global setting for this server only.
+	Deferred *bool `json:"deferred,omitempty"`
 	// Command is the executable to run (e.g., "npx", "python", "/path/to/server")
 	Command string `json:"command"`
 	// Args are the arguments to pass to the command