Add commit_tree_hash to checkpoint metadata

cmd/entire/cli/checkpoint/checkpoint.go

@@ -204,6 +204,10 @@ type WriteCommittedOptions struct {
 	// Branch is the branch name where the checkpoint was created (empty if detached HEAD)
 	Branch string
 
+	// CommitTreeHash is the git tree hash of HEAD at condensation time.
+	// Used as a content-addressable anchor for re-linking after history rewrites (rebase, squash).
+	CommitTreeHash string
+
 	// Transcript is the session transcript content (full.jsonl)
 	Transcript []byte
 
@@ -338,7 +342,8 @@ type CommittedMetadata struct {
 	SessionID        string          `json:"session_id"`
 	Strategy         string          `json:"strategy"`
 	CreatedAt        time.Time       `json:"created_at"`
-	Branch           string          `json:"branch,omitempty"` // Branch where checkpoint was created (empty if detached HEAD)
+	Branch           string          `json:"branch,omitempty"`           // Branch where checkpoint was created (empty if detached HEAD)
+	CommitTreeHash   string          `json:"commit_tree_hash,omitempty"` // Git tree hash of HEAD at condensation time
 	CheckpointsCount int             `json:"checkpoints_count"`
 	FilesTouched     []string        `json:"files_touched"`
 
@@ -416,6 +421,7 @@ type CheckpointSummary struct {
 	CheckpointID     id.CheckpointID    `json:"checkpoint_id"`
 	Strategy         string             `json:"strategy"`
 	Branch           string             `json:"branch,omitempty"`
+	CommitTreeHash   string             `json:"commit_tree_hash,omitempty"`
 	CheckpointsCount int                `json:"checkpoints_count"`
 	FilesTouched     []string           `json:"files_touched"`
 	Sessions         []SessionFilePaths `json:"sessions"`

cmd/entire/cli/checkpoint/checkpoint_test.go

@@ -579,6 +579,117 @@ func TestWriteCommitted_BranchField(t *testing.T) {
 	})
 }
 
+// TestWriteCommitted_CommitTreeHashField verifies that the CommitTreeHash field
+// is correctly stored in both session-level and root-level metadata.json.
+func TestWriteCommitted_CommitTreeHashField(t *testing.T) {
+	t.Run("present", func(t *testing.T) {
+		repo, commitHash := setupBranchTestRepo(t)
+
+		// Get the tree hash of the initial commit
+		commit, err := repo.CommitObject(commitHash)
+		if err != nil {
+			t.Fatalf("failed to get commit: %v", err)
+		}
+		expectedTreeHash := commit.TreeHash.String()
+
+		checkpointID := id.MustCheckpointID("d1e2f3a4b5c6")
+		store := NewGitStore(repo)
+		err = store.WriteCommitted(context.Background(), WriteCommittedOptions{
+			CheckpointID:   checkpointID,
+			SessionID:      "test-session-treehash",
+			Strategy:       "manual-commit",
+			CommitTreeHash: expectedTreeHash,
+			Transcript:     []byte("test transcript content"),
+			AuthorName:     "Test Author",
+			AuthorEmail:    "test@example.com",
+		})
+		if err != nil {
+			t.Fatalf("WriteCommitted() error = %v", err)
+		}
+
+		// Verify in session-level metadata (CommittedMetadata)
+		metadata := readLatestSessionMetadata(t, repo, checkpointID)
+		if metadata.CommitTreeHash != expectedTreeHash {
+			t.Errorf("CommittedMetadata.CommitTreeHash = %q, want %q", metadata.CommitTreeHash, expectedTreeHash)
+		}
+
+		// Verify in root-level metadata (CheckpointSummary)
+		summary, err := store.ReadCommitted(context.Background(), checkpointID)
+		if err != nil {
+			t.Fatalf("ReadCommitted() error = %v", err)
+		}
+		if summary.CommitTreeHash != expectedTreeHash {
+			t.Errorf("CheckpointSummary.CommitTreeHash = %q, want %q", summary.CommitTreeHash, expectedTreeHash)
+		}
+	})
+
+	t.Run("omitted when empty", func(t *testing.T) {
+		repo, _ := setupBranchTestRepo(t)
+
+		checkpointID := id.MustCheckpointID("e2f3a4b5c6d7")
+		store := NewGitStore(repo)
+		err := store.WriteCommitted(context.Background(), WriteCommittedOptions{
+			CheckpointID: checkpointID,
+			SessionID:    "test-session-no-treehash",
+			Strategy:     "manual-commit",
+			Transcript:   []byte("test transcript content"),
+			AuthorName:   "Test Author",
+			AuthorEmail:  "test@example.com",
+		})
+		if err != nil {
+			t.Fatalf("WriteCommitted() error = %v", err)
+		}
+
+		// Verify field is empty
+		metadata := readLatestSessionMetadata(t, repo, checkpointID)
+		if metadata.CommitTreeHash != "" {
+			t.Errorf("CommittedMetadata.CommitTreeHash = %q, want empty", metadata.CommitTreeHash)
+		}
+
+		// Verify omitted from JSON (omitempty)
+		ref, err := repo.Reference(plumbing.NewBranchReferenceName(paths.MetadataBranchName), true)
+		if err != nil {
+			t.Fatalf("failed to get metadata branch: %v", err)
+		}
+		commitObj, err := repo.CommitObject(ref.Hash())
+		if err != nil {
+			t.Fatalf("failed to get commit: %v", err)
+		}
+		tree, err := commitObj.Tree()
+		if err != nil {
+			t.Fatalf("failed to get tree: %v", err)
+		}
+
+		// Check session-level metadata JSON
+		sessionPath := checkpointID.Path() + "/0/" + paths.MetadataFileName
+		file, err := tree.File(sessionPath)
+		if err != nil {
+			t.Fatalf("failed to find session metadata: %v", err)
+		}
+		content, err := file.Contents()
+		if err != nil {
+			t.Fatalf("failed to read session metadata: %v", err)
+		}
+		if strings.Contains(content, `"commit_tree_hash"`) {
+			t.Errorf("session metadata should not contain 'commit_tree_hash' when empty (omitempty)")
+		}
+
+		// Check root-level metadata JSON
+		rootPath := checkpointID.Path() + "/" + paths.MetadataFileName
+		rootFile, err := tree.File(rootPath)
+		if err != nil {
+			t.Fatalf("failed to find root metadata: %v", err)
+		}
+		rootContent, err := rootFile.Contents()
+		if err != nil {
+			t.Fatalf("failed to read root metadata: %v", err)
+		}
+		if strings.Contains(rootContent, `"commit_tree_hash"`) {
+			t.Errorf("root metadata should not contain 'commit_tree_hash' when empty (omitempty)")
+		}
+	})
+}
+
 // TestUpdateSummary verifies that UpdateSummary correctly updates the summary
 // field in an existing checkpoint's metadata.
 func TestUpdateSummary(t *testing.T) {

cmd/entire/cli/checkpoint/committed.go

@@ -336,6 +336,7 @@ func (s *GitStore) writeSessionToSubdirectory(opts WriteCommittedOptions, sessio
 		Strategy:                    opts.Strategy,
 		CreatedAt:                   time.Now().UTC(),
 		Branch:                      opts.Branch,
+		CommitTreeHash:              opts.CommitTreeHash,
 		CheckpointsCount:            opts.CheckpointsCount,
 		FilesTouched:                opts.FilesTouched,
 		Agent:                       opts.Agent,
@@ -383,6 +384,7 @@ func (s *GitStore) writeCheckpointSummary(opts WriteCommittedOptions, basePath s
 		CLIVersion:       buildinfo.Version,
 		Strategy:         opts.Strategy,
 		Branch:           opts.Branch,
+		CommitTreeHash:   opts.CommitTreeHash,
 		CheckpointsCount: checkpointsCount,
 		FilesTouched:     filesTouched,
 		Sessions:         sessions,

cmd/entire/cli/integration_test/hooks_test.go

@@ -7,7 +7,7 @@ import (
 	"path/filepath"
 	"testing"
 
-  "github.com/entireio/cli/cmd/entire/cli/strategy"
+	"github.com/entireio/cli/cmd/entire/cli/strategy"
 )
 
 func TestHookRunner_SimulateUserPromptSubmit(t *testing.T) {

cmd/entire/cli/strategy/auto_commit.go

@@ -243,8 +243,9 @@ func (s *AutoCommitStrategy) commitMetadataToMetadataBranch(repo *git.Repository
 	// Extract session ID from metadata dir
 	sessionID := filepath.Base(ctx.MetadataDir)
 
-	// Get current branch name
+	// Get current branch name and tree hash
 	branchName := GetCurrentBranchName(repo)
+	commitTreeHash := GetHeadTreeHash(repo)
 
 	// Combine all file changes into FilesTouched (same as manual-commit)
 	filesTouched := mergeFilesTouched(nil, ctx.ModifiedFiles, ctx.NewFiles, ctx.DeletedFiles)
@@ -255,6 +256,7 @@ func (s *AutoCommitStrategy) commitMetadataToMetadataBranch(repo *git.Repository
 		SessionID:                   sessionID,
 		Strategy:                    StrategyNameAutoCommit, // Use new strategy name
 		Branch:                      branchName,
+		CommitTreeHash:              commitTreeHash,
 		MetadataDir:                 ctx.MetadataDirAbs, // Copy all files from metadata dir
 		AuthorName:                  ctx.AuthorName,
 		AuthorEmail:                 ctx.AuthorEmail,
@@ -643,15 +645,17 @@ func (s *AutoCommitStrategy) commitTaskMetadataToMetadataBranch(repo *git.Reposi
 		messageSubject = FormatSubagentEndMessage(ctx.SubagentType, ctx.TaskDescription, shortToolUseID)
 	}
 
-	// Get current branch name
+	// Get current branch name and tree hash
 	branchName := GetCurrentBranchName(repo)
+	commitTreeHash := GetHeadTreeHash(repo)
 
 	// Write committed checkpoint using the checkpoint store
 	err = store.WriteCommitted(context.Background(), checkpoint.WriteCommittedOptions{
 		CheckpointID:           checkpointID,
 		SessionID:              ctx.SessionID,
 		Strategy:               StrategyNameAutoCommit,
 		Branch:                 branchName,
+		CommitTreeHash:         commitTreeHash,
 		IsTask:                 true,
 		ToolUseID:              ctx.ToolUseID,
 		AgentID:                ctx.AgentID,

cmd/entire/cli/strategy/common.go

@@ -1468,6 +1468,20 @@ func GetCurrentBranchName(repo *git.Repository) string {
 	return head.Name().Short()
 }
 
+// GetHeadTreeHash returns the hex string of HEAD's tree hash.
+// Returns an empty string if HEAD or its commit cannot be read (e.g., empty repository).
+func GetHeadTreeHash(repo *git.Repository) string {
+	head, err := repo.Head()
+	if err != nil {
+		return ""
+	}
+	commit, err := repo.CommitObject(head.Hash())
+	if err != nil {
+		return ""
+	}
+	return commit.TreeHash.String()
+}
+
 // getMainBranchHash returns the hash of the main branch (main or master).
 // Returns ZeroHash if no main branch is found.
 func GetMainBranchHash(repo *git.Repository) plumbing.Hash {

cmd/entire/cli/strategy/manual_commit_condensation.go

@@ -137,8 +137,9 @@ func (s *ManualCommitStrategy) CondenseSession(repo *git.Repository, checkpointI
 	// Get author info
 	authorName, authorEmail := GetGitAuthorFromRepo(repo)
 	attribution := calculateSessionAttributions(repo, ref, sessionData, state)
-	// Get current branch name
+	// Get current branch name and tree hash
 	branchName := GetCurrentBranchName(repo)
+	commitTreeHash := GetHeadTreeHash(repo)
 
 	// Generate summary if enabled
 	var summary *cpkg.Summary
@@ -179,6 +180,7 @@ func (s *ManualCommitStrategy) CondenseSession(repo *git.Repository, checkpointI
 		SessionID:                   state.SessionID,
 		Strategy:                    StrategyNameManualCommit,
 		Branch:                      branchName,
+		CommitTreeHash:              commitTreeHash,
 		Transcript:                  sessionData.Transcript,
 		Prompts:                     sessionData.Prompts,
 		Context:                     sessionData.Context,