fix(classroom): add tests, nil guards, and topic filter

- Add comprehensive unit tests for classroom helper functions
  (date/time parsing, error wrapping, profile helpers)
- Add profileEmail() helper for nil-safe email extraction
- Fix nil pointer guards for Profile access (12 locations in
  courses, rosters, and guardians)
- Add --topic filter for coursework and materials list commands
- Update docs/spec.md with new filter options

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: 2 people

docs/spec.md

@@ -185,13 +185,13 @@ Flag aliases:
 - `gog classroom teachers add <courseId> <userId>`
 - `gog classroom teachers remove <courseId> <userId>`
 - `gog classroom roster <courseId> [--students] [--teachers]`
-- `gog classroom coursework <courseId> [--state ...] [--max N] [--page TOKEN]`
+- `gog classroom coursework <courseId> [--state ...] [--topic TOPIC_ID] [--max N] [--page TOKEN]`
 - `gog classroom coursework get <courseId> <courseworkId>`
 - `gog classroom coursework create <courseId> --title TITLE [--type ASSIGNMENT|...]`
 - `gog classroom coursework update <courseId> <courseworkId> [--title ...]`
 - `gog classroom coursework delete <courseId> <courseworkId>`
 - `gog classroom coursework assignees <courseId> <courseworkId> [--mode ...] [--add-student ...]`
-- `gog classroom materials <courseId> [--state ...] [--max N] [--page TOKEN]`
+- `gog classroom materials <courseId> [--state ...] [--topic TOPIC_ID] [--max N] [--page TOKEN]`
 - `gog classroom materials get <courseId> <materialId>`
 - `gog classroom materials create <courseId> --title TITLE`
 - `gog classroom materials update <courseId> <materialId> [--title ...]`

internal/cmd/classroom_courses.go

@@ -423,7 +423,7 @@ func (c *ClassroomCoursesJoinCmd) Run(ctx context.Context, flags *RootFlags) err
 			return outfmt.WriteJSON(os.Stdout, map[string]any{"student": created})
 		}
 		u.Out().Printf("user_id\t%s", created.UserId)
-		u.Out().Printf("email\t%s", created.Profile.EmailAddress)
+		u.Out().Printf("email\t%s", profileEmail(created.Profile))
 		u.Out().Printf("name\t%s", profileName(created.Profile))
 		return nil
 	case "teacher":
@@ -436,7 +436,7 @@ func (c *ClassroomCoursesJoinCmd) Run(ctx context.Context, flags *RootFlags) err
 			return outfmt.WriteJSON(os.Stdout, map[string]any{"teacher": created})
 		}
 		u.Out().Printf("user_id\t%s", created.UserId)
-		u.Out().Printf("email\t%s", created.Profile.EmailAddress)
+		u.Out().Printf("email\t%s", profileEmail(created.Profile))
 		u.Out().Printf("name\t%s", profileName(created.Profile))
 		return nil
 	default:

internal/cmd/classroom_coursework.go

@@ -24,6 +24,7 @@ type ClassroomCourseworkCmd struct {
 type ClassroomCourseworkListCmd struct {
 	CourseID string `arg:"" name:"courseId" help:"Course ID or alias"`
 	States   string `name:"state" help:"Coursework states filter (comma-separated: DRAFT,PUBLISHED,DELETED)"`
+	Topic    string `name:"topic" help:"Filter by topic ID"`
 	OrderBy  string `name:"order-by" help:"Order by (e.g., updateTime desc, dueDate desc)"`
 	Max      int64  `name:"max" aliases:"limit" help:"Max results" default:"100"`
 	Page     string `name:"page" help:"Page token"`
@@ -62,22 +63,35 @@ func (c *ClassroomCourseworkListCmd) Run(ctx context.Context, flags *RootFlags)
 		return wrapClassroomError(err)
 	}
 
+	// Client-side filter by topic (API doesn't support server-side topic filter)
+	topicFilter := strings.TrimSpace(c.Topic)
+	coursework := resp.CourseWork
+	if topicFilter != "" {
+		filtered := make([]*classroom.CourseWork, 0, len(coursework))
+		for _, work := range coursework {
+			if work != nil && work.TopicId == topicFilter {
+				filtered = append(filtered, work)
+			}
+		}
+		coursework = filtered
+	}
+
 	if outfmt.IsJSON(ctx) {
 		return outfmt.WriteJSON(os.Stdout, map[string]any{
-			"coursework":    resp.CourseWork,
+			"coursework":    coursework,
 			"nextPageToken": resp.NextPageToken,
 		})
 	}
 
-	if len(resp.CourseWork) == 0 {
+	if len(coursework) == 0 {
 		u.Err().Println("No coursework")
 		return nil
 	}
 
 	w, flush := tableWriter(ctx)
 	defer flush()
 	fmt.Fprintln(w, "ID\tTITLE\tSTATE\tDUE\tTYPE\tMAX_POINTS")
-	for _, work := range resp.CourseWork {
+	for _, work := range coursework {
 		if work == nil {
 			continue
 		}

internal/cmd/classroom_guardians.go

@@ -72,7 +72,7 @@ func (c *ClassroomGuardiansListCmd) Run(ctx context.Context, flags *RootFlags) e
 		}
 		fmt.Fprintf(w, "%s\t%s\t%s\n",
 			sanitizeTab(guardian.GuardianId),
-			sanitizeTab(guardian.GuardianProfile.EmailAddress),
+			sanitizeTab(profileEmail(guardian.GuardianProfile)),
 			sanitizeTab(profileName(guardian.GuardianProfile)),
 		)
 	}
@@ -116,7 +116,7 @@ func (c *ClassroomGuardiansGetCmd) Run(ctx context.Context, flags *RootFlags) er
 
 	u.Out().Printf("id\t%s", guardian.GuardianId)
 	u.Out().Printf("student_id\t%s", guardian.StudentId)
-	u.Out().Printf("email\t%s", guardian.GuardianProfile.EmailAddress)
+	u.Out().Printf("email\t%s", profileEmail(guardian.GuardianProfile))
 	u.Out().Printf("name\t%s", profileName(guardian.GuardianProfile))
 	return nil
 }

internal/cmd/classroom_helpers.go

@@ -140,6 +140,13 @@ func profileName(profile *classroom.UserProfile) string {
 	return strings.TrimSpace(strings.TrimSpace(profile.Name.GivenName + " " + profile.Name.FamilyName))
 }
 
+func profileEmail(profile *classroom.UserProfile) string {
+	if profile == nil {
+		return ""
+	}
+	return profile.EmailAddress
+}
+
 func formatFloatValue(v float64) string {
 	return strings.TrimRight(strings.TrimRight(fmt.Sprintf("%.2f", v), "0"), ".")
 }