Add --json support to gh agent-task view

Add --json, --jq, and --template flags to `gh agent-task view`,
consistent with the pattern used by `gh pr view --json`,
`gh issue view --json`, etc.

This reuses the same ExportData interface and SessionFields defined
for list, applying them to the single-session view output.

Closes https://github.com/cli/cli/issues/12805 (partial)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

pkg/cmd/agent-task/capi/sessions.go

@@ -102,6 +102,58 @@ type SessionError struct {
 	Message string
 }
 
+// SessionFields defines the available fields for JSON export of a Session.
+var SessionFields = []string{
+	"id",
+	"name",
+	"status",
+	"repository",
+	"createdAt",
+	"updatedAt",
+	"pullRequestNumber",
+	"pullRequestUrl",
+}
+
+// ExportData implements the exportable interface for JSON output.
+func (s *Session) ExportData(fields []string) map[string]interface{} {
+	data := make(map[string]interface{}, len(fields))
+	for _, f := range fields {
+		switch f {
+		case "id":
+			data[f] = s.ID
+		case "name":
+			data[f] = s.Name
+		case "status":
+			data[f] = s.State
+		case "repository":
+			if s.PullRequest != nil && s.PullRequest.Repository != nil {
+				data[f] = s.PullRequest.Repository.NameWithOwner
+			} else {
+				data[f] = nil
+			}
+		case "createdAt":
+			data[f] = s.CreatedAt
+		case "updatedAt":
+			data[f] = s.LastUpdatedAt
+		case "pullRequestNumber":
+			if s.PullRequest != nil {
+				data[f] = s.PullRequest.Number
+			} else {
+				data[f] = nil
+			}
+		case "pullRequestUrl":
+			if s.PullRequest != nil {
+				data[f] = s.PullRequest.URL
+			} else {
+				data[f] = nil
+			}
+		default:
+			data[f] = nil
+		}
+	}
+	return data
+}
+
 type resource struct {
 	ID                   string            `json:"id"`
 	UserID               uint64            `json:"user_id"`

pkg/cmd/agent-task/view/view.go

@@ -37,6 +37,7 @@ type ViewOptions struct {
 	Finder     prShared.PRFinder
 	Prompter   prompter.Prompter
 	Browser    browser.Browser
+	Exporter   cmdutil.Exporter
 
 	LogRenderer func() shared.LogRenderer
 	Sleep       func(d time.Duration)
@@ -125,6 +126,8 @@ func NewCmdView(f *cmdutil.Factory, runF func(*ViewOptions) error) *cobra.Comman
 	cmd.Flags().BoolVar(&opts.Log, "log", false, "Show agent session logs")
 	cmd.Flags().BoolVar(&opts.Follow, "follow", false, "Follow agent session logs")
 
+	cmdutil.AddJSONFlags(cmd, &opts.Exporter, capi.SessionFields)
+
 	return cmd
 }
 
@@ -289,6 +292,10 @@ func viewRun(opts *ViewOptions) error {
 		return printLogs(opts, capiClient, session.ID)
 	}
 
+	if opts.Exporter != nil {
+		return opts.Exporter.Write(opts.IO, session)
+	}
+
 	printSession(opts, session)
 	return nil
 }

pkg/cmd/agent-task/view/view_test.go

@@ -168,6 +168,7 @@ func Test_viewRun(t *testing.T) {
 		promptStubs      func(*testing.T, *prompter.MockPrompter)
 		capiStubs        func(*testing.T, *capi.CapiClientMock)
 		logRendererStubs func(*testing.T, *shared.LogRendererMock)
+		jsonFields       []string
 		wantOut          string
 		wantErr          error
 		wantStderr       string
@@ -1209,6 +1210,41 @@ func Test_viewRun(t *testing.T) {
 				(rendered:) <raw-logs-two>
 			`),
 		},
+		{
+			name: "json output (tty)",
+			tty:  true,
+			opts: ViewOptions{
+				SelectorArg: "some-session-id",
+				SessionID:   "some-session-id",
+			},
+			capiStubs: func(t *testing.T, m *capi.CapiClientMock) {
+				m.GetSessionFunc = func(_ context.Context, id string) (*capi.Session, error) {
+					return &capi.Session{
+						ID:            "some-session-id",
+						Name:          "Fix login bug",
+						State:         "completed",
+						CreatedAt:     sampleDate,
+						LastUpdatedAt: sampleDate,
+						CompletedAt:   sampleCompletedAt,
+						ResourceType:  "pull",
+						PullRequest: &api.PullRequest{
+							Number: 42,
+							URL:    "https://github.com/OWNER/REPO/pull/42",
+							Title:  "Fix login bug",
+							State:  "OPEN",
+							Repository: &api.PRRepository{
+								NameWithOwner: "OWNER/REPO",
+							},
+						},
+						User: &api.GitHubUser{
+							Login: "testuser",
+						},
+					}, nil
+				}
+			},
+			wantOut: "{\"id\":\"some-session-id\",\"name\":\"Fix login bug\",\"pullRequestNumber\":42,\"pullRequestUrl\":\"https://github.com/OWNER/REPO/pull/42\",\"repository\":\"OWNER/REPO\",\"status\":\"completed\"}\n",
+			jsonFields: []string{"id", "name", "status", "repository", "pullRequestNumber", "pullRequestUrl"},
+		},
 	}
 
 	for _, tt := range tests {
@@ -1244,6 +1280,12 @@ func Test_viewRun(t *testing.T) {
 				return logRenderer
 			}
 
+			if tt.jsonFields != nil {
+				exporter := cmdutil.NewJSONExporter()
+				exporter.SetFields(tt.jsonFields)
+				opts.Exporter = exporter
+			}
+
 			err := viewRun(&opts)
 			if tt.wantErr != nil {
 				assert.Error(t, err)