feat(session,viewer): record review mode and diff refs in session

Store ReviewMode, DiffFrom, DiffTo, and DiffCommit in SessionHistory
and persist them to JSONL (conditionally, only when non-empty). Display
mode in viewer list page and show version details (from/to or commit)
on the session detail page based on review mode.

internal/agent/agent.go

@@ -56,6 +56,10 @@ type Args struct {
 	// Commit is a single commit hash to review (vs its parent).
 	Commit string
 
+	// ReviewMode is one of "workspace", "range", or "commit".
+	// When empty, it is derived from From/To/Commit at session creation time.
+	ReviewMode string
+
 	// Template loaded from YAML config file.
 	Template template.Template
 
@@ -230,7 +234,16 @@ func New(args Args) *Agent {
 	}
 	if args.Session == nil {
 		gitBranch := detectGitBranch(args.RepoDir)
-		args.Session = session.New(args.RepoDir, gitBranch, args.Model)
+		mode := args.ReviewMode
+		if mode == "" {
+			mode = reviewModeString(args.From, args.To, args.Commit)
+		}
+		args.Session = session.New(args.RepoDir, gitBranch, args.Model, session.SessionOptions{
+			ReviewMode: mode,
+			DiffFrom:   args.From,
+			DiffTo:     args.To,
+			DiffCommit: args.Commit,
+		})
 	}
 	return &Agent{
 		args:    args,
@@ -1302,6 +1315,16 @@ func buildMessageXML(msgs []llm.Message) string {
 	return sb.String()
 }
 
+func reviewModeString(from, to, commit string) string {
+	if commit != "" {
+		return session.ReviewModeCommit
+	}
+	if from != "" && to != "" {
+		return session.ReviewModeRange
+	}
+	return session.ReviewModeWorkspace
+}
+
 // detectGitBranch returns the current git branch name for the given repo, or empty string on failure.
 func detectGitBranch(repoDir string) string {
 	cmd := exec.Command("git", "-C", repoDir, "rev-parse", "--abbrev-ref", "HEAD")

internal/session/history.go

@@ -22,6 +22,12 @@ const (
 	ReLocationTask        TaskType = "re_location_task"
 )
 
+const (
+	ReviewModeWorkspace = "workspace"
+	ReviewModeRange     = "range"
+	ReviewModeCommit    = "commit"
+)
+
 // SessionHistory is the top-level container for an entire CR run.
 // It is safe for concurrent use by multiple goroutines.
 type SessionHistory struct {
@@ -30,6 +36,10 @@ type SessionHistory struct {
 	RepoDir      string
 	GitBranch    string
 	Model        string
+	ReviewMode   string
+	DiffFrom     string
+	DiffTo       string
+	DiffCommit   string
 	StartTime    time.Time
 	EndTime      time.Time
 	persist      *jsonlWriter
@@ -81,19 +91,31 @@ type ToolResultRecord struct {
 	Result    string
 }
 
+// SessionOptions holds optional metadata for a new session.
+type SessionOptions struct {
+	ReviewMode string
+	DiffFrom   string
+	DiffTo     string
+	DiffCommit string
+}
+
 // New creates a new SessionHistory with the given repo directory.
-func New(repoDir, gitBranch, model string) *SessionHistory {
+func New(repoDir, gitBranch, model string, opts SessionOptions) *SessionHistory {
 	sessionID := generateUUID()
 	sh := &SessionHistory{
 		SessionID:    sessionID,
 		RepoDir:      repoDir,
 		GitBranch:    gitBranch,
 		Model:        model,
+		ReviewMode:   opts.ReviewMode,
+		DiffFrom:     opts.DiffFrom,
+		DiffTo:       opts.DiffTo,
+		DiffCommit:   opts.DiffCommit,
 		StartTime:    time.Now(),
 		FileSessions: make(map[string]*FileSession),
 	}
 
-	p, err := newJSONLWriter(sessionID, repoDir, gitBranch, model)
+	p, err := newJSONLWriter(sessionID, repoDir, gitBranch, model, opts)
 	if err != nil {
 		fmt.Printf("[ocr session] warning: failed to create session writer: %v\n", err)
 	} else {

internal/session/persist.go

@@ -17,23 +17,31 @@ import (
 // $HOME/.opencodereview/sessions/<encoded-repo-path>/<session-id>.jsonl.
 // It is safe for concurrent use by multiple goroutines.
 type jsonlWriter struct {
-	mu        sync.Mutex
-	sessionID string
-	repoDir   string
-	gitBranch string
-	model     string
-	file      *os.File
-	writer    *bufio.Writer
-	lastUUID  string // tracks chain of records via parentUuid
+	mu         sync.Mutex
+	sessionID  string
+	repoDir    string
+	gitBranch  string
+	model      string
+	reviewMode string
+	diffFrom   string
+	diffTo     string
+	diffCommit string
+	file       *os.File
+	writer     *bufio.Writer
+	lastUUID   string // tracks chain of records via parentUuid
 }
 
 // newJSONLWriter creates and opens a new JSONL writer for the given session.
-func newJSONLWriter(sessionID, repoDir, gitBranch, model string) (*jsonlWriter, error) {
+func newJSONLWriter(sessionID, repoDir, gitBranch, model string, opts SessionOptions) (*jsonlWriter, error) {
 	jw := &jsonlWriter{
-		sessionID: sessionID,
-		repoDir:   repoDir,
-		gitBranch: gitBranch,
-		model:     model,
+		sessionID:  sessionID,
+		repoDir:    repoDir,
+		gitBranch:  gitBranch,
+		model:      model,
+		reviewMode: opts.ReviewMode,
+		diffFrom:   opts.DiffFrom,
+		diffTo:     opts.DiffTo,
+		diffCommit: opts.DiffCommit,
 	}
 	if err := jw.open(); err != nil {
 		return nil, err
@@ -126,6 +134,18 @@ func (jw *jsonlWriter) WriteSessionStart(startTime time.Time) string {
 		"gitBranch":  jw.gitBranch,
 		"model":      jw.model,
 	}
+	if jw.reviewMode != "" {
+		rec["reviewMode"] = jw.reviewMode
+	}
+	if jw.diffFrom != "" {
+		rec["diffFrom"] = jw.diffFrom
+	}
+	if jw.diffTo != "" {
+		rec["diffTo"] = jw.diffTo
+	}
+	if jw.diffCommit != "" {
+		rec["diffCommit"] = jw.diffCommit
+	}
 
 	jw.mu.Lock()
 	defer jw.mu.Unlock()

internal/session/persist_test.go

@@ -154,7 +154,7 @@ func TestSetErrorIncrementsCounter(t *testing.T) {
 
 func TestSetErrorWritesJSONL(t *testing.T) {
 	repoDir := t.TempDir()
-	sh := New(repoDir, "main", "test-model")
+	sh := New(repoDir, "main", "test-model", SessionOptions{ReviewMode: ReviewModeWorkspace})
 	defer sh.Finalize()
 
 	fs := sh.GetOrCreateFileSession("foo.go")
@@ -193,7 +193,7 @@ func TestSetErrorWritesJSONL(t *testing.T) {
 
 func TestSessionEndIncludesFailures(t *testing.T) {
 	repoDir := t.TempDir()
-	sh := New(repoDir, "main", "test-model")
+	sh := New(repoDir, "main", "test-model", SessionOptions{ReviewMode: ReviewModeWorkspace})
 
 	fs := sh.GetOrCreateFileSession("bar.go")
 	for i := 0; i < 3; i++ {

internal/viewer/store.go

@@ -80,6 +80,10 @@ type SessionSummary struct {
 	CWD           string
 	GitBranch     string
 	Model         string
+	ReviewMode    string
+	DiffFrom      string
+	DiffTo        string
+	DiffCommit    string
 	FilesReviewed []string
 	DurationSec   float64
 	FileCount     int
@@ -149,6 +153,18 @@ func peekSession(path string) (SessionSummary, error) {
 			if model, ok := rec["model"].(string); ok {
 				summary.Model = model
 			}
+			if rm, ok := rec["reviewMode"].(string); ok {
+				summary.ReviewMode = rm
+			}
+			if v, ok := rec["diffFrom"].(string); ok {
+				summary.DiffFrom = v
+			}
+			if v, ok := rec["diffTo"].(string); ok {
+				summary.DiffTo = v
+			}
+			if v, ok := rec["diffCommit"].(string); ok {
+				summary.DiffCommit = v
+			}
 		}
 	}
 
@@ -274,6 +290,18 @@ func LoadSession(root, encodedRepo, sessionID string) (*ViewSession, error) {
 			if model, ok := rec["model"].(string); ok {
 				vs.Summary.Model = model
 			}
+			if rm, ok := rec["reviewMode"].(string); ok {
+				vs.Summary.ReviewMode = rm
+			}
+			if v, ok := rec["diffFrom"].(string); ok {
+				vs.Summary.DiffFrom = v
+			}
+			if v, ok := rec["diffTo"].(string); ok {
+				vs.Summary.DiffTo = v
+			}
+			if v, ok := rec["diffCommit"].(string); ok {
+				vs.Summary.DiffCommit = v
+			}
 
 		case "llm_request":
 			fp, _ := rec["filePath"].(string)

internal/viewer/templates/session.html

@@ -14,6 +14,14 @@
     <div class="meta">
         <span><strong>CWD:</strong> {{.Session.Summary.CWD}}</span>
         <span><strong>Branch:</strong> {{.Session.Summary.GitBranch}}</span>
+        <span><strong>Mode:</strong> {{if .Session.Summary.ReviewMode}}{{.Session.Summary.ReviewMode}}{{else}}-{{end}}</span>
+        {{if eq .Session.Summary.ReviewMode "range"}}
+        <span><strong>From:</strong> <code>{{.Session.Summary.DiffFrom}}</code></span>
+        <span><strong>To:</strong> <code>{{.Session.Summary.DiffTo}}</code></span>
+        {{end}}
+        {{if eq .Session.Summary.ReviewMode "commit"}}
+        <span><strong>Commit:</strong> <code>{{.Session.Summary.DiffCommit}}</code></span>
+        {{end}}
         <span><strong>Model:</strong> <code>{{.Session.Summary.Model}}</code></span>
         <span><strong>Duration:</strong> {{formatDuration .Session.Summary.DurationSec}}</span>
         <span><strong>Files:</strong> {{.Session.Summary.FileCount}}</span>

internal/viewer/templates/sessions.html

@@ -12,12 +12,13 @@
 <h2>Sessions: {{.RepoName}}</h2>
 {{if .Sessions}}
 <table class="table">
-    <thead><tr><th>Session ID</th><th>Branch</th><th>Model</th><th>Files</th><th>Duration</th><th>Started At</th></tr></thead>
+    <thead><tr><th>Session ID</th><th>Branch</th><th>Mode</th><th>Model</th><th>Files</th><th>Duration</th><th>Started At</th></tr></thead>
     <tbody>
     {{range .Sessions}}
         <tr>
             <td><a href="/r/{{$.EncodedRepo}}/{{.SessionID}}">{{.SessionID | printf "%.8s"}}…</a></td>
             <td>{{.GitBranch}}</td>
+            <td>{{if .ReviewMode}}{{.ReviewMode}}{{else}}-{{end}}</td>
             <td><code>{{.Model}}</code></td>
             <td>{{.FileCount}}</td>
             <td>{{formatDuration .DurationSec}}</td>