diff --git a/agent/agent.go b/agent/agent.go
index 78a76b8..c734557 100644
--- a/agent/agent.go
+++ b/agent/agent.go
@@ -319,6 +319,35 @@ func (ag *Agent) RenamePreamble(old, new string) {
 	}
 }
 
+// refreshToolListing replaces the "# Available Tools" section in the preamble
+// with an updated listing. Called when tool_list detects directory changes.
+func (ag *Agent) refreshToolListing(listing string) {
+	if ag.runtime == nil {
+		return
+	}
+	const marker = "\n# Available Tools\n\n"
+	if idx := strings.Index(ag.runtime.Preamble, marker); idx >= 0 {
+		ag.runtime.Preamble = ag.runtime.Preamble[:idx]
+	}
+	if listing != "" {
+		ag.runtime.Preamble += marker + listing
+	}
+}
+
+// wireToolsChanged sets the OnToolsChanged callback on the tool server
+// so the preamble stays in sync when tools are added/removed from disk.
+func (ag *Agent) wireToolsChanged() {
+	if ag.runtime == nil || ag.runtime.ToolServer == nil {
+		return
+	}
+	type hasHook interface {
+		SetOnToolsChanged(func(string))
+	}
+	if srv, ok := ag.runtime.ToolServer.(hasHook); ok {
+		srv.SetOnToolsChanged(ag.refreshToolListing)
+	}
+}
+
 // SaveFull persists the full session state (history + metadata) to the given path.
 func (ag *Agent) SaveFull(path, sessionID, cwd, remote string) error {
 	if ag.history == nil {
diff --git a/agent/commands.go b/agent/commands.go
index e0af3db..cf820bd 100644
--- a/agent/commands.go
+++ b/agent/commands.go
@@ -203,6 +203,7 @@ func (ag *Agent) cmdAgent(_ context.Context, args []string) {
 	ag.runtime = rt
 	ag.agentName = name
 	ag.history = nil
+	ag.wireToolsChanged()
 	ag.notifyChange()
 	for _, msg := range rt.Messages {
 		ag.emit(infoEvent(msg))
diff --git a/agent/new.go b/agent/new.go
index 2674d41..a638285 100644
--- a/agent/new.go
+++ b/agent/new.go
@@ -56,5 +56,6 @@ func NewAgent(cfg AgentCfg) *Agent {
 	}
 	ag.changeCond = sync.NewCond(&ag.changeMu)
 	ag.turnError = ag.defaultTurnError
+	ag.wireToolsChanged()
 	return ag
 }
diff --git a/tools/tool.go b/tools/tool.go
index 7bf1e27..d4ed254 100644
--- a/tools/tool.go
+++ b/tools/tool.go
@@ -28,6 +28,19 @@ func ToolList(ctx context.Context, srv *toolsrv.Server, args json.RawMessage) (s
 		}
 		out.WriteString("\n")
 	}
+
+	// Notify the agent that the tool listing may have changed so the
+	// preamble stays in sync with the directory contents.
+	if srv.OnToolsChanged != nil {
+		var listing strings.Builder
+		for _, s := range summaries {
+			if s.Description != "" {
+				fmt.Fprintf(&listing, "- **%s** — %s\n", s.Name, s.Description)
+			}
+		}
+		srv.OnToolsChanged(listing.String())
+	}
+
 	return strings.TrimRight(out.String(), "\n"), nil
 }
 
diff --git a/toolsrv/accessors.go b/toolsrv/accessors.go
index 1debffe..b2e0521 100644
--- a/toolsrv/accessors.go
+++ b/toolsrv/accessors.go
@@ -30,6 +30,11 @@ func (e *Server) InjectContent(content string) {
 	}
 }
 
+// SetOnToolsChanged sets the callback for tool directory changes.
+func (e *Server) SetOnToolsChanged(fn func(string)) {
+	e.OnToolsChanged = fn
+}
+
 // ExecuteInSandbox runs a command in the sandbox. Exported for builtin tools.
 func (e *Server) ExecuteInSandbox(ctx context.Context, cmd, language string, timeout int, sandbox string, trusted bool, stdin string, detach bool) (string, error) {
 	return e.executeWithStdin(ctx, cmd, language, timeout, sandbox, trusted, stdin, detach)
diff --git a/toolsrv/registry.go b/toolsrv/registry.go
index dbb725a..a444f8b 100644
--- a/toolsrv/registry.go
+++ b/toolsrv/registry.go
@@ -2,41 +2,40 @@ package toolsrv
 
 import (
 	"fmt"
-	"strings"
-	"sort"
 	"os"
 	"path/filepath"
+	"sort"
+	"strings"
 	"sync"
-
-	
 )
 
 type Registry struct {
 	mu        sync.RWMutex
-	global    map[string]ToolInfo
 	sessions  map[string]map[string]ToolInfo
 	revisions map[string]uint64
 }
 
 func NewRegistry() (*Registry, error) {
 	r := &Registry{
-		global:    make(map[string]ToolInfo),
 		sessions:  make(map[string]map[string]ToolInfo),
 		revisions: make(map[string]uint64),
 	}
-	if err := r.Discover(); err != nil {
-		return nil, err
+	// Validate that the tools directory is readable.
+	dir := ToolsPath()
+	if _, err := os.ReadDir(dir); err != nil {
+		return nil, fmt.Errorf("read tools dir %s: %w", dir, err)
 	}
 	return r, nil
 }
 
-func (r *Registry) Discover() error {
+// discover scans the tools directory and returns all valid tool infos.
+func (r *Registry) discover() map[string]ToolInfo {
 	dir := ToolsPath()
 	entries, err := os.ReadDir(dir)
 	if err != nil {
-		return fmt.Errorf("read tools dir %s: %w", dir, err)
+		return nil
 	}
-	global := make(map[string]ToolInfo)
+	tools := make(map[string]ToolInfo)
 	for _, e := range entries {
 		if e.IsDir() || e.Name() == "idx" || e.Name()[0] == '.' {
 			continue
@@ -49,19 +48,15 @@ func (r *Registry) Discover() error {
 		if !strings.Contains(script, "ollie:prompt") {
 			continue
 		}
-		global[e.Name()] = ParseToolInfo(e.Name(), script)
+		tools[e.Name()] = ParseToolInfo(e.Name(), script)
 	}
-	r.mu.Lock()
-	r.global = global
-	r.mu.Unlock()
-	return nil
+	return tools
 }
 
 func (r *Registry) Summaries() []ToolInfo {
-	r.mu.RLock()
-	defer r.mu.RUnlock()
+	tools := r.discover()
 	var summaries []ToolInfo
-	for _, info := range r.global {
+	for _, info := range tools {
 		summaries = append(summaries, ToolInfo{
 			Name:        info.Name,
 			Description: info.Description,
@@ -72,9 +67,8 @@ func (r *Registry) Summaries() []ToolInfo {
 }
 
 func (r *Registry) Load(sessionID, name string) error {
-	r.mu.RLock()
-	tool, exists := r.global[name]
-	r.mu.RUnlock()
+	tools := r.discover()
+	tool, exists := tools[name]
 	if !exists {
 		return fmt.Errorf("tool not found: %s", name)
 	}
diff --git a/toolsrv/server.go b/toolsrv/server.go
index 6caf1e2..6b5b84a 100644
--- a/toolsrv/server.go
+++ b/toolsrv/server.go
@@ -58,6 +58,10 @@ type Server struct {
 	// should be injected into the agent's context.
 	OnInjection func(content string)
 
+	// OnToolsChanged is called when tool_list detects the available tools
+	// have changed, providing the updated preamble-format listing.
+	OnToolsChanged func(listing string)
+
 	// rate limiting state (per-Server)
 	rateLimitMu        sync.Mutex
 	validationFailures int