feat: enable load_image for subagents via MediaResolver in RunToolLoop

Instead of removing load_image from sub-agent tools (28f69e71), inject a
MediaResolver into the legacy RunToolLoop fallback path so media:// refs
are resolved to base64 before each LLM call — matching the main agent
loop behavior.

- Add MediaResolver field to ToolLoopConfig and call it on iteration > 1
- Add SubagentManager.SetMediaResolver() and wire it through runTask
- Remove ToolRegistry.Unregister() (no longer needed)
- Restore load_image in sub-agent tool set (revert Clone+Unregister)
- Add TestSubagentManager_SetMediaResolver_StoresResolver

pkg/agent/loop.go

@@ -299,6 +299,14 @@ func registerSharedTools(
 			subagentManager := tools.NewSubagentManager(provider, agent.Model, agent.Workspace)
 			subagentManager.SetLLMOptions(agent.MaxTokens, agent.Temperature)
 
+			// Inject a media resolver so the legacy RunToolLoop fallback path can
+			// resolve media:// refs in the same way the main AgentLoop does.
+			// This keeps subagent vision support working even when the optimized
+			// sub-turn spawner path is unavailable.
+			subagentManager.SetMediaResolver(func(msgs []providers.Message) []providers.Message {
+				return resolveMediaRefs(msgs, al.mediaStore, cfg.Agents.Defaults.GetMaxMediaSize())
+			})
+
 			// Set the spawner that links into AgentLoop's turnState
 			subagentManager.SetSpawner(func(
 				ctx context.Context,
@@ -363,12 +371,7 @@ func registerSharedTools(
 			// tools registered so far (file, web, etc.) but NOT spawn/
 			// spawn_status which are added below — preventing recursive
 			// subagent spawning.
-			subagentTools := agent.Tools.Clone()
+			subagentManager.SetTools(agent.Tools.Clone())
-			// load_image depends on resolveMediaRefs which only runs in
-			// the main agent loop, not in RunToolLoop. Remove it from
-			// sub-agent tools so the LLM won't call it in vain.
-			subagentTools.Unregister("load_image")
-			subagentManager.SetTools(subagentTools)
 			if spawnEnabled {
 				spawnTool := tools.NewSpawnTool(subagentManager)
 				spawnTool.SetSpawner(NewSubTurnSpawner(al))

pkg/tools/load_image_test.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/sipeed/picoclaw/pkg/config"
 	"github.com/sipeed/picoclaw/pkg/media"
+	"github.com/sipeed/picoclaw/pkg/providers"
 )
 
 func TestLoadImage_PathRequired(t *testing.T) {
@@ -75,3 +76,25 @@ func TestLoadImage_FileTooLarge(t *testing.T) {
 		t.Fatal("expected error for oversized file")
 	}
 }
+
+func TestSubagentManager_SetMediaResolver_StoresResolver(t *testing.T) {
+	manager := NewSubagentManager(nil, "gpt-test", "/tmp")
+
+	called := false
+	manager.SetMediaResolver(func(msgs []providers.Message) []providers.Message {
+		called = true
+		return msgs
+	})
+
+	manager.mu.RLock()
+	got := manager.mediaResolver
+	manager.mu.RUnlock()
+
+	if got == nil {
+		t.Fatal("expected mediaResolver to be set")
+	}
+
+	if called {
+		t.Fatal("resolver should not be called during SetMediaResolver")
+	}
+}

pkg/tools/registry.go

@@ -395,18 +395,6 @@ func (r *ToolRegistry) Clone() *ToolRegistry {
 	return clone
 }
 
-// Unregister removes a tool by name. Returns true if the tool was found and removed.
-func (r *ToolRegistry) Unregister(name string) bool {
-	r.mu.Lock()
-	defer r.mu.Unlock()
-	if _, exists := r.tools[name]; !exists {
-		return false
-	}
-	delete(r.tools, name)
-	r.version.Add(1)
-	return true
-}
-
 // Count returns the number of registered tools.
 func (r *ToolRegistry) Count() int {
 	r.mu.RLock()

pkg/tools/subagent.go

@@ -67,6 +67,12 @@ type SubagentManager struct {
 	hasTemperature bool
 	nextID         int
 	spawner        SpawnSubTurnFunc
+
+	// mediaResolver resolves media:// refs in tool-loop messages before
+	// each LLM call in the legacy RunToolLoop fallback path.
+	// This lets subagents reuse the same media handling behavior as the
+	// main agent loop without importing pkg/agent and creating a cycle.
+	mediaResolver func([]providers.Message) []providers.Message
 }
 
 func NewSubagentManager(
@@ -90,6 +96,17 @@ func (sm *SubagentManager) SetSpawner(spawner SpawnSubTurnFunc) {
 	sm.spawner = spawner
 }
 
+// SetMediaResolver injects a message preprocessor that resolves media:// refs
+// into LLM-ready content before each tool-loop iteration.
+// This is only used by the legacy RunToolLoop fallback path.
+func (sm *SubagentManager) SetMediaResolver(
+	resolver func([]providers.Message) []providers.Message,
+) {
+	sm.mu.Lock()
+	defer sm.mu.Unlock()
+	sm.mediaResolver = resolver
+}
+
 // SetLLMOptions sets max tokens and temperature for subagent LLM calls.
 func (sm *SubagentManager) SetLLMOptions(maxTokens int, temperature float64) {
 	sm.mu.Lock()
@@ -177,6 +194,7 @@ func (sm *SubagentManager) runTask(
 	temperature := sm.temperature
 	hasMaxTokens := sm.hasMaxTokens
 	hasTemperature := sm.hasTemperature
+	mediaResolver := sm.mediaResolver
 	sm.mu.RUnlock()
 
 	var result *ToolResult
@@ -223,6 +241,7 @@ After completing the task, provide a clear summary of what was done.`
 			Tools:         tools,
 			MaxIterations: maxIter,
 			LLMOptions:    llmOptions,
+			MediaResolver: mediaResolver,
 		}, messages, task.OriginChannel, task.OriginChatID)
 
 		if err == nil {

pkg/tools/toolloop.go

@@ -24,6 +24,11 @@ type ToolLoopConfig struct {
 	Tools         *ToolRegistry
 	MaxIterations int
 	LLMOptions    map[string]any
+
+	// MediaResolver resolves media:// refs in messages before each LLM call.
+	// This is optional and is mainly used by subagent legacy fallback execution
+	// so subagents can reuse the same multimodal media handling as the main loop.
+	MediaResolver func(messages []providers.Message) []providers.Message
 }
 
 // ToolLoopResult contains the result of running the tool loop.
@@ -63,8 +68,27 @@ func RunToolLoop(
 		if llmOpts == nil {
 			llmOpts = map[string]any{}
 		}
-		// 3. Call LLM
+
-		response, err := config.Provider.Chat(ctx, messages, providerToolDefs, config.Model, llmOpts)
+		// 3. Resolve media:// refs and Call LLM.
+		// Tools like load_image produce media:// refs in their result messages.
+		// Without this step, the LLM would receive raw "media://uuid" strings
+		// instead of base64-encoded image data URLs.
+		//
+		// We build a separate callMessages slice so that:
+		//   (a) the resolver output is used for the LLM call only,
+		//   (b) the original `messages` slice keeps the unresolved refs for
+		//       subsequent iterations — the resolver is idempotent but working
+		//       on the original avoids double-encoding issues.
+		//
+		// On iteration 1 the initial user messages typically have no media://
+		// refs (they come from plain text), so this is effectively a no-op;
+		// it becomes relevant from iteration 2 onward when tool results may
+		// contain media refs.
+		callMessages := messages
+		if config.MediaResolver != nil && iteration > 1 {
+			callMessages = config.MediaResolver(messages)
+		}
+		response, err := config.Provider.Chat(ctx, callMessages, providerToolDefs, config.Model, llmOpts)
 		if err != nil {
 			logger.ErrorCF("toolloop", "LLM call failed",
 				map[string]any{