diff --git a/apps/backend/cmd/kandev/adapters.go b/apps/backend/cmd/kandev/adapters.go
index 38ed84b4a8..a051c50b9e 100644
--- a/apps/backend/cmd/kandev/adapters.go
+++ b/apps/backend/cmd/kandev/adapters.go
@@ -341,7 +341,8 @@ func (a *lifecycleAdapter) ResolveAgentProfile(ctx context.Context, profileID st
 }
 
 // GetGitLog retrieves the git log for a session from baseCommit to HEAD.
-func (a *lifecycleAdapter) GetGitLog(ctx context.Context, sessionID, baseCommit string, limit int) (*client.GitLogResult, error) {
+// If targetBranch is provided, uses dynamic merge-base calculation for accurate filtering.
+func (a *lifecycleAdapter) GetGitLog(ctx context.Context, sessionID, baseCommit string, limit int, targetBranch string) (*client.GitLogResult, error) {
 	execution, ok := a.mgr.GetExecutionBySessionID(sessionID)
 	if !ok {
 		return nil, nil // No execution, not an error
@@ -350,7 +351,7 @@ func (a *lifecycleAdapter) GetGitLog(ctx context.Context, sessionID, baseCommit
 	if agentClient == nil {
 		return nil, nil
 	}
-	return agentClient.GitLog(ctx, baseCommit, limit)
+	return agentClient.GitLog(ctx, baseCommit, limit, targetBranch)
 }
 
 // GetCumulativeDiff retrieves the cumulative diff for a session from baseCommit to HEAD.
diff --git a/apps/backend/cmd/kandev/gateway.go b/apps/backend/cmd/kandev/gateway.go
index 66c9b2ee70..76ea3492df 100644
--- a/apps/backend/cmd/kandev/gateway.go
+++ b/apps/backend/cmd/kandev/gateway.go
@@ -67,6 +67,22 @@ func (a *sessionReaderAdapter) GetSessionBaseCommit(ctx context.Context, session
 	return session.BaseCommitSHA
 }
 
+func (a *sessionReaderAdapter) GetSessionBaseBranch(ctx context.Context, sessionID string) string {
+	session, err := a.repo.GetTaskSession(ctx, sessionID)
+	if err != nil {
+		if a.logger != nil {
+			a.logger.Warn("failed to load session for base branch lookup",
+				zap.String("session_id", sessionID),
+				zap.Error(err))
+		}
+		return ""
+	}
+	if session == nil {
+		return ""
+	}
+	return session.BaseBranch
+}
+
 func provideGateway(
 	ctx context.Context,
 	log *logger.Logger,
diff --git a/apps/backend/internal/agent/handlers/git_handlers.go b/apps/backend/internal/agent/handlers/git_handlers.go
index d54fe81995..0a25896ceb 100644
--- a/apps/backend/internal/agent/handlers/git_handlers.go
+++ b/apps/backend/internal/agent/handlers/git_handlers.go
@@ -3,6 +3,7 @@ package handlers
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -25,6 +26,9 @@ type GitOperationFailedCallback func(ctx context.Context, sessionID, taskID, ope
 // ExecutionLookup provides access to running agent executions by session ID.
 type ExecutionLookup interface {
 	GetExecutionBySessionID(sessionID string) (*lifecycle.AgentExecution, bool)
+	// GetOrEnsureExecution returns an existing execution or creates one on-demand.
+	// Use this for workspace-oriented operations that should survive backend restarts.
+	GetOrEnsureExecution(ctx context.Context, sessionID string) (*lifecycle.AgentExecution, error)
 }
 
 // SessionReader is a minimal interface for reading session metadata.
@@ -34,6 +38,11 @@ type SessionReader interface {
 	// GetSessionBaseCommit returns the base commit SHA for a session.
 	// Returns empty string if not set or on error.
 	GetSessionBaseCommit(ctx context.Context, sessionID string) string
+
+	// GetSessionBaseBranch returns the target branch for a session (e.g., "origin/main").
+	// Used for computing merge-base to filter commits accurately after rebases.
+	// Returns empty string if not set or on error.
+	GetSessionBaseBranch(ctx context.Context, sessionID string) string
 }
 
 // GitHandlers provides WebSocket handlers for git worktree operations.
@@ -635,6 +644,7 @@ type GitCommitsRequest struct {
 // wsGitCommits handles session.git.commits action
 // The base commit SHA is always looked up from the session metadata in the database.
 // This ensures commits are filtered to only those made during the session.
+// When a target branch is available, we use dynamic merge-base calculation for accuracy.
 func (h *GitHandlers) wsGitCommits(ctx context.Context, msg *ws.Message) (*ws.Message, error) {
 	var req GitCommitsRequest
 	if err := msg.ParsePayload(&req); err != nil {
@@ -645,21 +655,36 @@ func (h *GitHandlers) wsGitCommits(ctx context.Context, msg *ws.Message) (*ws.Me
 		return nil, fmt.Errorf("session_id is required")
 	}
 
-	agentClient, err := h.getAgentCtlClient(req.SessionID)
+	// Use GetOrEnsureExecution to recover workspace after backend restarts.
+	// This is a workspace-oriented operation that doesn't require a running agent process.
+	execution, err := h.lifecycleMgr.GetOrEnsureExecution(ctx, req.SessionID)
 	if err != nil {
-		if isSessionNotReadyError(err) {
+		// Check for specific "not ready" errors that indicate the session workspace
+		// is still being prepared. For these, return ready:false so the client can retry.
+		if errors.Is(err, lifecycle.ErrSessionWorkspaceNotReady) || isSessionNotReadyError(err) {
 			return ws.NewResponse(msg.ID, msg.Action, map[string]any{
 				"commits": []any{},
 				"ready":   false,
 			})
 		}
-		return nil, err
+		// For unexpected errors (database failures, etc.), return the error
+		// so the client can display an appropriate error message.
+		return nil, fmt.Errorf("failed to get execution for session %s: %w", req.SessionID, err)
 	}
 
-	// Look up base commit SHA from the session metadata
-	var baseCommit string
+	agentClient := execution.GetAgentCtlClient()
+	if agentClient == nil {
+		return ws.NewResponse(msg.ID, msg.Action, map[string]any{
+			"commits": []any{},
+			"ready":   false,
+		})
+	}
+
+	// Look up base commit SHA and target branch from the session metadata
+	var baseCommit, targetBranch string
 	if h.sessionReader != nil {
 		baseCommit = h.sessionReader.GetSessionBaseCommit(ctx, req.SessionID)
+		targetBranch = h.sessionReader.GetSessionBaseBranch(ctx, req.SessionID)
 	}
 
 	// Fallback: if base_commit_sha is not stored in session, use git merge-base
@@ -675,7 +700,9 @@ func (h *GitHandlers) wsGitCommits(ctx context.Context, msg *ws.Message) (*ws.Me
 		}
 	}
 
-	result, err := agentClient.GitLog(ctx, baseCommit, req.Limit)
+	// Use target branch for dynamic merge-base calculation.
+	// This ensures accurate commit filtering even after rebases.
+	result, err := agentClient.GitLog(ctx, baseCommit, req.Limit, targetBranch)
 	if err != nil {
 		return nil, fmt.Errorf("git log failed: %w", err)
 	}
diff --git a/apps/backend/internal/agent/handlers/git_handlers_test.go b/apps/backend/internal/agent/handlers/git_handlers_test.go
index 73fbb2dda6..e4ba4083cb 100644
--- a/apps/backend/internal/agent/handlers/git_handlers_test.go
+++ b/apps/backend/internal/agent/handlers/git_handlers_test.go
@@ -3,6 +3,7 @@ package handlers
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"sync"
 	"testing"
@@ -16,6 +17,8 @@ import (
 // mockExecutionLookup implements ExecutionLookup for testing.
 type mockExecutionLookup struct {
 	executions map[string]*lifecycle.AgentExecution
+	// ensureErr allows tests to inject specific errors from GetOrEnsureExecution
+	ensureErr error
 }
 
 func (m *mockExecutionLookup) GetExecutionBySessionID(sessionID string) (*lifecycle.AgentExecution, bool) {
@@ -26,9 +29,25 @@ func (m *mockExecutionLookup) GetExecutionBySessionID(sessionID string) (*lifecy
 	return exec, ok
 }
 
+func (m *mockExecutionLookup) GetOrEnsureExecution(_ context.Context, sessionID string) (*lifecycle.AgentExecution, error) {
+	// Return injected error if set
+	if m.ensureErr != nil {
+		return nil, m.ensureErr
+	}
+	if m.executions == nil {
+		return nil, fmt.Errorf("no execution for session %s", sessionID)
+	}
+	exec, ok := m.executions[sessionID]
+	if !ok {
+		return nil, fmt.Errorf("no execution for session %s", sessionID)
+	}
+	return exec, nil
+}
+
 // mockSessionReader implements SessionReader for testing.
 type mockSessionReader struct {
-	baseCommits map[string]string
+	baseCommits  map[string]string
+	baseBranches map[string]string
 }
 
 func (m *mockSessionReader) GetSessionBaseCommit(_ context.Context, sessionID string) string {
@@ -38,6 +57,13 @@ func (m *mockSessionReader) GetSessionBaseCommit(_ context.Context, sessionID st
 	return m.baseCommits[sessionID]
 }
 
+func (m *mockSessionReader) GetSessionBaseBranch(_ context.Context, sessionID string) string {
+	if m.baseBranches == nil {
+		return ""
+	}
+	return m.baseBranches[sessionID]
+}
+
 func TestNewGitHandlers(t *testing.T) {
 	log := newTestLogger()
 	lookup := &mockExecutionLookup{}
@@ -335,7 +361,10 @@ func TestWsPush_NoExecution(t *testing.T) {
 
 func TestWsGitCommits_NotReady(t *testing.T) {
 	log := newTestLogger()
-	lookup := &mockExecutionLookup{} // no executions → "no agent running" error
+	// Use "no agent running for session" error which matches isSessionNotReadyError
+	lookup := &mockExecutionLookup{
+		ensureErr: fmt.Errorf("no agent running for session session-1"),
+	}
 	h := NewGitHandlers(lookup, nil, log)
 
 	msg, _ := ws.NewRequest("test-1", ws.ActionSessionGitCommits, GitCommitsRequest{SessionID: "session-1"})
@@ -411,3 +440,76 @@ func TestIsSessionNotReadyError(t *testing.T) {
 		})
 	}
 }
+
+func TestWsGitCommits_WorkspaceNotReadyError(t *testing.T) {
+	// Test that ErrSessionWorkspaceNotReady returns ready:false gracefully
+	log := newTestLogger()
+	lookup := &mockExecutionLookup{
+		ensureErr: lifecycle.ErrSessionWorkspaceNotReady,
+	}
+	h := NewGitHandlers(lookup, nil, log)
+
+	msg, _ := ws.NewRequest("test-1", ws.ActionSessionGitCommits, GitCommitsRequest{SessionID: "session-1"})
+
+	resp, err := h.wsGitCommits(context.Background(), msg)
+	if err != nil {
+		t.Fatalf("expected graceful response for workspace not ready, got error: %v", err)
+	}
+	if resp == nil {
+		t.Fatal("expected non-nil response")
+	}
+
+	var payload map[string]any
+	if err := json.Unmarshal(resp.Payload, &payload); err != nil {
+		t.Fatalf("failed to parse payload: %v", err)
+	}
+	if ready, ok := payload["ready"].(bool); !ok || ready {
+		t.Errorf("expected ready=false, got %v", payload["ready"])
+	}
+}
+
+func TestWsGitCommits_UnexpectedError(t *testing.T) {
+	// Test that unexpected errors (not workspace-not-ready) are returned as errors
+	log := newTestLogger()
+	lookup := &mockExecutionLookup{
+		ensureErr: errors.New("database connection failed"),
+	}
+	h := NewGitHandlers(lookup, nil, log)
+
+	msg, _ := ws.NewRequest("test-1", ws.ActionSessionGitCommits, GitCommitsRequest{SessionID: "session-1"})
+
+	_, err := h.wsGitCommits(context.Background(), msg)
+	if err == nil {
+		t.Fatal("expected error for unexpected failure")
+	}
+	if !errors.Is(err, lookup.ensureErr) && err.Error() != "failed to get execution for session session-1: database connection failed" {
+		t.Errorf("expected wrapped database error, got: %v", err)
+	}
+}
+
+func TestWsGitCommits_WrappedWorkspaceNotReadyError(t *testing.T) {
+	// Test that wrapped ErrSessionWorkspaceNotReady is still detected
+	log := newTestLogger()
+	lookup := &mockExecutionLookup{
+		ensureErr: fmt.Errorf("some context: %w", lifecycle.ErrSessionWorkspaceNotReady),
+	}
+	h := NewGitHandlers(lookup, nil, log)
+
+	msg, _ := ws.NewRequest("test-1", ws.ActionSessionGitCommits, GitCommitsRequest{SessionID: "session-1"})
+
+	resp, err := h.wsGitCommits(context.Background(), msg)
+	if err != nil {
+		t.Fatalf("expected graceful response for wrapped workspace not ready, got error: %v", err)
+	}
+	if resp == nil {
+		t.Fatal("expected non-nil response")
+	}
+
+	var payload map[string]any
+	if err := json.Unmarshal(resp.Payload, &payload); err != nil {
+		t.Fatalf("failed to parse payload: %v", err)
+	}
+	if ready, ok := payload["ready"].(bool); !ok || ready {
+		t.Errorf("expected ready=false, got %v", payload["ready"])
+	}
+}
diff --git a/apps/backend/internal/agentctl/client/git.go b/apps/backend/internal/agentctl/client/git.go
index 237de7be0d..0cf7cf6cbf 100644
--- a/apps/backend/internal/agentctl/client/git.go
+++ b/apps/backend/internal/agentctl/client/git.go
@@ -326,8 +326,13 @@ type GitCommitInfo struct {
 
 // GitLog gets the commit log from baseCommit to HEAD.
 // If baseCommit is empty, returns recent commits (limited by limit).
-func (c *Client) GitLog(ctx context.Context, baseCommit string, limit int) (*GitLogResult, error) {
-	reqURL := fmt.Sprintf("%s/api/v1/git/log?since=%s&limit=%d", c.baseURL, url.QueryEscape(baseCommit), limit)
+// If targetBranch is provided, computes merge-base dynamically for accurate filtering.
+func (c *Client) GitLog(ctx context.Context, baseCommit string, limit int, targetBranch string) (*GitLogResult, error) {
+	reqURL := fmt.Sprintf("%s/api/v1/git/log?since=%s&limit=%d",
+		c.baseURL, url.QueryEscape(baseCommit), limit)
+	if targetBranch != "" {
+		reqURL += "&target_branch=" + url.QueryEscape(targetBranch)
+	}
 
 	req, err := http.NewRequestWithContext(ctx, "GET", reqURL, nil)
 	if err != nil {
diff --git a/apps/backend/internal/agentctl/server/api/git.go b/apps/backend/internal/agentctl/server/api/git.go
index 3363c4f03d..b422746780 100644
--- a/apps/backend/internal/agentctl/server/api/git.go
+++ b/apps/backend/internal/agentctl/server/api/git.go
@@ -89,8 +89,9 @@ type GitResetRequest struct {
 
 // GitLogRequest for GET /api/v1/git/log
 type GitLogRequest struct {
-	Since string `form:"since"` // Base commit SHA (exclusive)
-	Limit int    `form:"limit"` // Max commits to return
+	Since        string `form:"since"`         // Base commit SHA (exclusive)
+	TargetBranch string `form:"target_branch"` // Target branch for merge-base calculation (e.g., "origin/main")
+	Limit        int    `form:"limit"`         // Max commits to return
 }
 
 // GitCumulativeDiffRequest for GET /api/v1/git/cumulative-diff
@@ -541,7 +542,24 @@ func (s *Server) handleGitLog(c *gin.Context) {
 	}
 
 	gitOp := s.procMgr.GitOperator()
-	result, err := gitOp.GetLog(c.Request.Context(), req.Since, limit)
+
+	// If target_branch is provided, compute merge-base dynamically.
+	// This ensures we only show commits not yet merged into the target branch,
+	// which is accurate even after rebases.
+	baseCommit := req.Since
+	if req.TargetBranch != "" {
+		mergeBase, err := gitOp.GetMergeBase(c.Request.Context(), "HEAD", req.TargetBranch)
+		if err != nil {
+			s.logger.Warn("failed to compute merge-base, falling back to since",
+				zap.String("target_branch", req.TargetBranch),
+				zap.Error(err))
+			// Fall back to the provided base commit
+		} else if mergeBase != "" {
+			baseCommit = mergeBase
+		}
+	}
+
+	result, err := gitOp.GetLog(c.Request.Context(), baseCommit, limit)
 	if err != nil {
 		s.logger.Error("git log failed", zap.Error(err))
 		c.JSON(http.StatusInternalServerError, process.GitLogResult{
diff --git a/apps/backend/internal/agentctl/server/process/git_log.go b/apps/backend/internal/agentctl/server/process/git_log.go
index b48007705e..06e02a988a 100644
--- a/apps/backend/internal/agentctl/server/process/git_log.go
+++ b/apps/backend/internal/agentctl/server/process/git_log.go
@@ -342,3 +342,13 @@ func (g *GitOperator) parseCommitDiff(output string) map[string]interface{} {
 
 	return files
 }
+
+// GetMergeBase returns the merge-base commit SHA between two refs (e.g., HEAD and origin/main).
+// This is used to determine the common ancestor for filtering commits.
+func (g *GitOperator) GetMergeBase(ctx context.Context, ref1, ref2 string) (string, error) {
+	output, err := g.runGitCommand(ctx, "merge-base", ref1, ref2)
+	if err != nil {
+		return "", fmt.Errorf("failed to compute merge-base: %w", err)
+	}
+	return strings.TrimSpace(output), nil
+}
diff --git a/apps/backend/internal/integration/simulated_agent_manager_test.go b/apps/backend/internal/integration/simulated_agent_manager_test.go
index 7083b0c9f1..13079decbe 100644
--- a/apps/backend/internal/integration/simulated_agent_manager_test.go
+++ b/apps/backend/internal/integration/simulated_agent_manager_test.go
@@ -452,7 +452,7 @@ func (s *SimulatedAgentManagerClient) GetExecutionIDForSession(_ context.Context
 	}
 	return "", fmt.Errorf("no execution found for session %s", sessionID)
 }
-func (s *SimulatedAgentManagerClient) GetGitLog(_ context.Context, _, _ string, _ int) (*client.GitLogResult, error) {
+func (s *SimulatedAgentManagerClient) GetGitLog(_ context.Context, _, _ string, _ int, _ string) (*client.GitLogResult, error) {
 	return nil, nil
 }
 func (s *SimulatedAgentManagerClient) GetCumulativeDiff(_ context.Context, _, _ string) (*client.CumulativeDiffResult, error) {
diff --git a/apps/backend/internal/orchestrator/event_handlers_test.go b/apps/backend/internal/orchestrator/event_handlers_test.go
index 365c47e22b..777775df3d 100644
--- a/apps/backend/internal/orchestrator/event_handlers_test.go
+++ b/apps/backend/internal/orchestrator/event_handlers_test.go
@@ -219,7 +219,7 @@ func (m *mockAgentManager) EnsureWorkspaceExecutionForSession(_ context.Context,
 func (m *mockAgentManager) GetExecutionIDForSession(_ context.Context, _ string) (string, error) {
 	return "", fmt.Errorf("no execution found")
 }
-func (m *mockAgentManager) GetGitLog(_ context.Context, _, _ string, _ int) (*client.GitLogResult, error) {
+func (m *mockAgentManager) GetGitLog(_ context.Context, _, _ string, _ int, _ string) (*client.GitLogResult, error) {
 	return nil, nil
 }
 func (m *mockAgentManager) GetCumulativeDiff(_ context.Context, _, _ string) (*client.CumulativeDiffResult, error) {
diff --git a/apps/backend/internal/orchestrator/executor/executor.go b/apps/backend/internal/orchestrator/executor/executor.go
index 3e3aef7090..45c82493cb 100644
--- a/apps/backend/internal/orchestrator/executor/executor.go
+++ b/apps/backend/internal/orchestrator/executor/executor.go
@@ -165,8 +165,9 @@ type AgentManagerClient interface {
 	GetExecutionIDForSession(ctx context.Context, sessionID string) (string, error)
 
 	// GetGitLog retrieves the git log for a session from baseCommit to HEAD.
+	// If targetBranch is provided, uses dynamic merge-base calculation for accurate filtering.
 	// Used for archive snapshot capture. Returns nil, nil if no execution exists.
-	GetGitLog(ctx context.Context, sessionID, baseCommit string, limit int) (*client.GitLogResult, error)
+	GetGitLog(ctx context.Context, sessionID, baseCommit string, limit int, targetBranch string) (*client.GitLogResult, error)
 
 	// GetCumulativeDiff retrieves the cumulative diff for a session from baseCommit to the
 	// working tree (including uncommitted/unstaged changes). Used for archive snapshot capture.
diff --git a/apps/backend/internal/orchestrator/executor/executor_mocks_test.go b/apps/backend/internal/orchestrator/executor/executor_mocks_test.go
index d5d7f0a938..440a89e536 100644
--- a/apps/backend/internal/orchestrator/executor/executor_mocks_test.go
+++ b/apps/backend/internal/orchestrator/executor/executor_mocks_test.go
@@ -136,7 +136,7 @@ func (m *mockAgentManager) ResolveAgentProfile(ctx context.Context, profileID st
 	}, nil
 }
 
-func (m *mockAgentManager) GetGitLog(ctx context.Context, sessionID, baseCommit string, limit int) (*client.GitLogResult, error) {
+func (m *mockAgentManager) GetGitLog(ctx context.Context, sessionID, baseCommit string, limit int, targetBranch string) (*client.GitLogResult, error) {
 	return nil, nil
 }
 
diff --git a/apps/backend/internal/orchestrator/scheduler/scheduler_test.go b/apps/backend/internal/orchestrator/scheduler/scheduler_test.go
index 5e55875592..ebcb0b8131 100644
--- a/apps/backend/internal/orchestrator/scheduler/scheduler_test.go
+++ b/apps/backend/internal/orchestrator/scheduler/scheduler_test.go
@@ -133,7 +133,7 @@ func (m *mockAgentManager) ResolveAgentProfile(ctx context.Context, profileID st
 	}, nil
 }
 
-func (m *mockAgentManager) GetGitLog(_ context.Context, _, _ string, _ int) (*client.GitLogResult, error) {
+func (m *mockAgentManager) GetGitLog(_ context.Context, _, _ string, _ int, _ string) (*client.GitLogResult, error) {
 	return nil, nil
 }
 func (m *mockAgentManager) GetCumulativeDiff(_ context.Context, _, _ string) (*client.CumulativeDiffResult, error) {
diff --git a/apps/backend/internal/orchestrator/task_operations.go b/apps/backend/internal/orchestrator/task_operations.go
index 53c47ddefd..79d77c72b3 100644
--- a/apps/backend/internal/orchestrator/task_operations.go
+++ b/apps/backend/internal/orchestrator/task_operations.go
@@ -1189,35 +1189,48 @@ func (s *Service) StopExecution(ctx context.Context, executionID string, reason
 func (s *Service) CaptureArchiveSnapshot(ctx context.Context, sessionID string) error {
 	s.logger.Info("capturing archive snapshot", zap.String("session_id", sessionID))
 
-	baseCommit, err := s.resolveArchiveBaseCommit(ctx, sessionID)
+	baseCommit, baseBranch, err := s.resolveArchiveBaseCommitAndBranch(ctx, sessionID)
 	if err != nil {
 		return err
 	}
-	if baseCommit == "" {
-		s.logger.Debug("no base_commit available, skipping archive snapshot capture",
+
+	// Skip only if we have neither baseCommit nor baseBranch for merge-base calculation
+	if baseCommit == "" && baseBranch == "" {
+		s.logger.Debug("no base_commit or base_branch available, skipping archive snapshot capture",
 			zap.String("session_id", sessionID))
 		return nil
 	}
 
-	if !s.captureArchiveCommits(ctx, sessionID, baseCommit) {
+	// Capture commits - baseBranch can be used for merge-base even if baseCommit is empty
+	if !s.captureArchiveCommits(ctx, sessionID, baseCommit, baseBranch) {
 		// Agent not running, skip diff capture as well
 		return nil
 	}
 
+	// Diff capture requires baseCommit
+	if baseCommit == "" {
+		s.logger.Debug("no base_commit available, skipping archive diff capture",
+			zap.String("session_id", sessionID))
+		return nil
+	}
+
 	s.captureArchiveDiff(ctx, sessionID, baseCommit)
 	return nil
 }
 
-// resolveArchiveBaseCommit retrieves the base commit for archive snapshot capture.
-// It first checks the session's stored base_commit_sha, falling back to git status if empty.
-func (s *Service) resolveArchiveBaseCommit(ctx context.Context, sessionID string) (string, error) {
+// resolveArchiveBaseCommitAndBranch retrieves the base commit and branch for archive snapshot capture.
+// It first checks the session's stored values, falling back to git status if empty.
+func (s *Service) resolveArchiveBaseCommitAndBranch(ctx context.Context, sessionID string) (string, string, error) {
 	session, err := s.repo.GetTaskSession(ctx, sessionID)
 	if err != nil {
-		return "", fmt.Errorf("failed to get session: %w", err)
+		return "", "", fmt.Errorf("failed to get session: %w", err)
 	}
 
-	if session.BaseCommitSHA != "" {
-		return session.BaseCommitSHA, nil
+	baseCommit := session.BaseCommitSHA
+	baseBranch := session.BaseBranch
+
+	if baseCommit != "" {
+		return baseCommit, baseBranch, nil
 	}
 
 	// Fallback: try to get base commit from git status for legacy sessions
@@ -1226,21 +1239,22 @@ func (s *Service) resolveArchiveBaseCommit(ctx context.Context, sessionID string
 		s.logger.Debug("failed to get git status for base commit fallback",
 			zap.String("session_id", sessionID),
 			zap.Error(err))
-		return "", nil
+		return "", baseBranch, nil
 	}
 	if status != nil && status.BaseCommit != "" {
 		s.logger.Debug("using git status base commit as fallback for archive",
 			zap.String("session_id", sessionID),
 			zap.String("base_commit", status.BaseCommit))
-		return status.BaseCommit, nil
+		return status.BaseCommit, baseBranch, nil
 	}
-	return "", nil
+	return "", baseBranch, nil
 }
 
 // captureArchiveCommits fetches and saves commits from baseCommit to HEAD.
+// If targetBranch is provided, uses dynamic merge-base for accurate filtering.
 // Returns false if the agent is not running (caller should skip remaining capture).
-func (s *Service) captureArchiveCommits(ctx context.Context, sessionID, baseCommit string) bool {
-	logResult, err := s.agentManager.GetGitLog(ctx, sessionID, baseCommit, 0) // 0 = no limit
+func (s *Service) captureArchiveCommits(ctx context.Context, sessionID, baseCommit, targetBranch string) bool {
+	logResult, err := s.agentManager.GetGitLog(ctx, sessionID, baseCommit, 0, targetBranch) // 0 = no limit
 	if err != nil {
 		s.logger.Warn("failed to capture git log for archive",
 			zap.String("session_id", sessionID),