refactor: extract instance.go fork fields into instanceExt embedded struct

Move fork-specific AgentInstance fields and worktree methods to instance_ext.go:
- SubagentMgr, Subagents, SkillsFilter
- Interview staleness tracking fields
- Per-session worktree isolation (worktrees map, all worktree methods)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/agent/instance.go

@@ -7,7 +7,6 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
-	"sync"
 
 	"github.com/sipeed/picoclaw/pkg/config"
 	"github.com/sipeed/picoclaw/pkg/git"
@@ -20,6 +19,8 @@ import (
 // AgentInstance represents a fully configured agent with its own workspace,
 // session manager, context builder, and tool registry.
 type AgentInstance struct {
+	instanceExt // fork-specific fields (see instance_ext.go)
+
 	ID                        string
 	Name                      string
 	Model                     string
@@ -37,8 +38,6 @@ type AgentInstance struct {
 	Sessions                  *session.LegacyAdapter
 	ContextBuilder            *ContextBuilder
 	Tools                     *tools.ToolRegistry
-	Subagents                 *config.SubagentsConfig
-	SkillsFilter              []string
 	Candidates                []providers.FallbackCandidate
 	PlanModel                 string
 	PlanFallbacks             []string
@@ -51,18 +50,6 @@ type AgentInstance struct {
 	// LightCandidates holds the resolved provider candidates for the light model.
 	// Pre-computed at agent creation to avoid repeated model_list lookups at runtime.
 	LightCandidates []providers.FallbackCandidate
-
-	// SubagentMgr is set during registerSharedTools when orchestration is enabled.
-	// Used by runAgentLoop to wait for spawned subagents before worktree cleanup.
-	SubagentMgr *tools.SubagentManager
-
-	// Interview staleness tracking: consecutive turns where MEMORY.md was not updated.
-	interviewStaleCount int
-	interviewMemoryLen  int
-
-	// Per-session worktree isolation
-	worktrees  map[string]*git.WorktreeInfo // sessionKey → worktree
-	worktreeMu sync.RWMutex
 }
 
 // Close releases resources held by the agent instance.
@@ -295,6 +282,10 @@ func NewAgentInstance(
 	}
 
 	return &AgentInstance{
+		instanceExt: instanceExt{
+			Subagents:    subagents,
+			SkillsFilter: skillsFilter,
+		},
 		ID:                        agentID,
 		Name:                      agentName,
 		Model:                     model,
@@ -312,8 +303,6 @@ func NewAgentInstance(
 		Sessions:                  sessionsManager,
 		ContextBuilder:            contextBuilder,
 		Tools:                     toolsRegistry,
-		Subagents:                 subagents,
-		SkillsFilter:              skillsFilter,
 		Candidates:                candidates,
 		PlanModel:                 planModel,
 		PlanFallbacks:             planFallbacks,
@@ -370,94 +359,6 @@ func resolvePlanFallbacks(agentCfg *config.AgentConfig, defaults *config.AgentDe
 	return defaults.PlanModelFallbacks
 }
 
-// ActivateWorktree creates a worktree for a session.
-// projectDir is the git repository to create the worktree in.
-// If empty, falls back to ai.Workspace.
-// Worktree path: <workspace>/.worktrees/<branch-basename>/
-func (ai *AgentInstance) ActivateWorktree(sessionKey, taskName, projectDir string) (*git.WorktreeInfo, error) {
-	if projectDir == "" {
-		projectDir = ai.Workspace
-	}
-
-	repoRoot := git.FindRepoRoot(projectDir)
-	if repoRoot == "" {
-		return nil, fmt.Errorf("directory is not a git repository: %s", projectDir)
-	}
-
-	branchName := git.SanitizeBranchName(taskName)
-	baseName := git.BranchBaseName(branchName)
-	wtPath := filepath.Join(ai.Workspace, ".worktrees", baseName)
-
-	wt, err := git.CreateWorktree(repoRoot, wtPath, branchName)
-	if err != nil {
-		return nil, err
-	}
-
-	ai.worktreeMu.Lock()
-	if ai.worktrees == nil {
-		ai.worktrees = make(map[string]*git.WorktreeInfo)
-	}
-	ai.worktrees[sessionKey] = wt
-	ai.worktreeMu.Unlock()
-
-	return wt, nil
-}
-
-// DeactivateWorktree safe-disposes the session's worktree.
-func (ai *AgentInstance) DeactivateWorktree(sessionKey, commitMsg string, discard bool) (*git.DisposeResult, error) {
-	ai.worktreeMu.Lock()
-	wt, ok := ai.worktrees[sessionKey]
-	if ok {
-		delete(ai.worktrees, sessionKey)
-	}
-	ai.worktreeMu.Unlock()
-
-	if !ok || wt == nil {
-		return nil, nil
-	}
-
-	repoRoot := git.FindRepoRoot(ai.Workspace)
-	if repoRoot == "" {
-		return nil, fmt.Errorf("workspace is not a git repository")
-	}
-
-	// Even on discard, SafeDispose auto-commits first for safety
-	if commitMsg != "" && git.HasUncommittedChanges(wt.Path) {
-		_ = git.AutoCommit(wt.Path, commitMsg)
-	}
-
-	result := git.SafeDispose(repoRoot, wt)
-	return &result, nil
-}
-
-// GetWorktree returns the session's active worktree, or nil.
-func (ai *AgentInstance) GetWorktree(sessionKey string) *git.WorktreeInfo {
-	ai.worktreeMu.RLock()
-	defer ai.worktreeMu.RUnlock()
-	return ai.worktrees[sessionKey]
-}
-
-// IsInWorktree returns true if the session has an active worktree.
-func (ai *AgentInstance) IsInWorktree(sessionKey string) bool {
-	return ai.GetWorktree(sessionKey) != nil
-}
-
-// EffectiveWorkspace returns worktree path for session, or original Workspace.
-func (ai *AgentInstance) EffectiveWorkspace(sessionKey string) string {
-	if wt := ai.GetWorktree(sessionKey); wt != nil {
-		return wt.Path
-	}
-	return ai.Workspace
-}
-
-// GetWorktreeBranch returns the branch name for the session's worktree, or "".
-func (ai *AgentInstance) GetWorktreeBranch(sessionKey string) string {
-	if wt := ai.GetWorktree(sessionKey); wt != nil {
-		return wt.Branch
-	}
-	return ""
-}
-
 func compilePatterns(patterns []string) []*regexp.Regexp {
 	compiled := make([]*regexp.Regexp, 0, len(patterns))
 	for _, p := range patterns {

pkg/agent/instance_ext.go

@@ -0,0 +1,122 @@
+package agent
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/sipeed/picoclaw/pkg/config"
+	"github.com/sipeed/picoclaw/pkg/git"
+	"github.com/sipeed/picoclaw/pkg/tools"
+)
+
+// instanceExt holds fork-specific fields for AgentInstance.
+// Embedded in AgentInstance so existing field access continues to work.
+type instanceExt struct {
+	// SubagentMgr is set during registerSharedTools when orchestration is enabled.
+	// Used by runAgentLoop to wait for spawned subagents before worktree cleanup.
+	SubagentMgr *tools.SubagentManager
+
+	Subagents    *config.SubagentsConfig
+	SkillsFilter []string
+
+	// Interview staleness tracking: consecutive turns where MEMORY.md was not updated.
+	interviewStaleCount int
+	interviewMemoryLen  int
+
+	// Per-session worktree isolation
+	worktrees  map[string]*git.WorktreeInfo // sessionKey → worktree
+	worktreeMu sync.RWMutex
+}
+
+// ActivateWorktree creates a worktree for a session.
+// projectDir is the git repository to create the worktree in.
+// If empty, falls back to ai.Workspace.
+// Worktree path: <workspace>/.worktrees/<branch-basename>/
+func (ai *AgentInstance) ActivateWorktree(sessionKey, taskName, projectDir string) (*git.WorktreeInfo, error) {
+	if projectDir == "" {
+		projectDir = ai.Workspace
+	}
+
+	repoRoot := git.FindRepoRoot(projectDir)
+	if repoRoot == "" {
+		return nil, fmt.Errorf("directory is not a git repository: %s", projectDir)
+	}
+
+	branchName := git.SanitizeBranchName(taskName)
+	baseName := git.BranchBaseName(branchName)
+	wtPath := ai.worktreePath(baseName)
+
+	wt, err := git.CreateWorktree(repoRoot, wtPath, branchName)
+	if err != nil {
+		return nil, err
+	}
+
+	ai.worktreeMu.Lock()
+	if ai.worktrees == nil {
+		ai.worktrees = make(map[string]*git.WorktreeInfo)
+	}
+	ai.worktrees[sessionKey] = wt
+	ai.worktreeMu.Unlock()
+
+	return wt, nil
+}
+
+// worktreePath returns the standard path for a worktree under the workspace.
+func (ai *AgentInstance) worktreePath(baseName string) string {
+	return ai.Workspace + "/.worktrees/" + baseName
+}
+
+// DeactivateWorktree safe-disposes the session's worktree.
+func (ai *AgentInstance) DeactivateWorktree(sessionKey, commitMsg string, discard bool) (*git.DisposeResult, error) {
+	ai.worktreeMu.Lock()
+	wt, ok := ai.worktrees[sessionKey]
+	if ok {
+		delete(ai.worktrees, sessionKey)
+	}
+	ai.worktreeMu.Unlock()
+
+	if !ok || wt == nil {
+		return nil, nil
+	}
+
+	repoRoot := git.FindRepoRoot(ai.Workspace)
+	if repoRoot == "" {
+		return nil, fmt.Errorf("workspace is not a git repository")
+	}
+
+	// Even on discard, SafeDispose auto-commits first for safety
+	if commitMsg != "" && git.HasUncommittedChanges(wt.Path) {
+		_ = git.AutoCommit(wt.Path, commitMsg)
+	}
+
+	result := git.SafeDispose(repoRoot, wt)
+	return &result, nil
+}
+
+// GetWorktree returns the session's active worktree, or nil.
+func (ai *AgentInstance) GetWorktree(sessionKey string) *git.WorktreeInfo {
+	ai.worktreeMu.RLock()
+	defer ai.worktreeMu.RUnlock()
+	return ai.worktrees[sessionKey]
+}
+
+// IsInWorktree returns true if the session has an active worktree.
+func (ai *AgentInstance) IsInWorktree(sessionKey string) bool {
+	return ai.GetWorktree(sessionKey) != nil
+}
+
+// EffectiveWorkspace returns worktree path for session, or original Workspace.
+func (ai *AgentInstance) EffectiveWorkspace(sessionKey string) string {
+	if wt := ai.GetWorktree(sessionKey); wt != nil {
+		return wt.Path
+	}
+	return ai.Workspace
+}
+
+// GetWorktreeBranch returns the branch name for the session's worktree, or "".
+func (ai *AgentInstance) GetWorktreeBranch(sessionKey string) string {
+	if wt := ai.GetWorktree(sessionKey); wt != nil {
+		return wt.Branch
+	}
+	return ""
+}