feat(cli): add dynamic completions for ssh command (#20171)

Adds CompletionHandler to the ssh command that dynamically suggests
workspace and agent targets based on the user's running workspaces.

Features:
- Suggests workspace name for single-agent workspaces
- Suggests agent.workspace format for all agents in multi-agent
workspaces
- Only shows running workspaces (matches immediate availability)
- Alphabetically sorted completions for better UX

Tests cover single-agent, multi-agent, and network error scenarios.

Amp-Thread-ID:
https://ampcode.com/threads/T-d137d343-53f3-4ece-be5a-584249bbd9e8

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closes #20158

Demo:


https://github.com/user-attachments/assets/e1000463-ded6-4bc9-b013-61780453f019

---------

Co-authored-by: Ethan Dickson <ethan@coder.com>

cli/ssh.go

@@ -109,6 +109,51 @@ func (r *RootCmd) ssh() *serpent.Command {
 				}
 			},
 		),
+		CompletionHandler: func(inv *serpent.Invocation) []string {
+			client, err := r.InitClient(inv)
+			if err != nil {
+				return []string{}
+			}
+
+			res, err := client.Workspaces(inv.Context(), codersdk.WorkspaceFilter{
+				Owner: codersdk.Me,
+			})
+			if err != nil {
+				return []string{}
+			}
+
+			var mu sync.Mutex
+			var completions []string
+			var wg sync.WaitGroup
+			for _, ws := range res.Workspaces {
+				wg.Add(1)
+				go func() {
+					defer wg.Done()
+					resources, err := client.TemplateVersionResources(inv.Context(), ws.LatestBuild.TemplateVersionID)
+					if err != nil {
+						return
+					}
+					var agents []codersdk.WorkspaceAgent
+					for _, resource := range resources {
+						agents = append(agents, resource.Agents...)
+					}
+
+					mu.Lock()
+					defer mu.Unlock()
+					if len(agents) == 1 {
+						completions = append(completions, ws.Name)
+					} else {
+						for _, agent := range agents {
+							completions = append(completions, fmt.Sprintf("%s.%s", ws.Name, agent.Name))
+						}
+					}
+				}()
+			}
+			wg.Wait()
+
+			slices.Sort(completions)
+			return completions
+		},
 		Handler: func(inv *serpent.Invocation) (retErr error) {
 			client, err := r.InitClient(inv)
 			if err != nil {

cli/ssh_test.go

@@ -2447,3 +2447,99 @@ func tempDirUnixSocket(t *testing.T) string {
 
 	return t.TempDir()
 }
+
+func TestSSH_Completion(t *testing.T) {
+	t.Parallel()
+
+	t.Run("SingleAgent", func(t *testing.T) {
+		t.Parallel()
+
+		client, workspace, agentToken := setupWorkspaceForAgent(t)
+		_ = agenttest.New(t, client.URL, agentToken)
+		coderdtest.AwaitWorkspaceAgents(t, client, workspace.ID)
+
+		var stdout bytes.Buffer
+		inv, root := clitest.New(t, "ssh", "")
+		inv.Stdout = &stdout
+		inv.Environ.Set("COMPLETION_MODE", "1")
+		clitest.SetupConfig(t, client, root)
+
+		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitMedium)
+		defer cancel()
+
+		err := inv.WithContext(ctx).Run()
+		require.NoError(t, err)
+
+		// For single-agent workspaces, the only completion should be the
+		// bare workspace name.
+		output := stdout.String()
+		t.Logf("Completion output: %q", output)
+		require.Contains(t, output, workspace.Name)
+	})
+
+	t.Run("MultiAgent", func(t *testing.T) {
+		t.Parallel()
+
+		client, store := coderdtest.NewWithDatabase(t, nil)
+		first := coderdtest.CreateFirstUser(t, client)
+		userClient, user := coderdtest.CreateAnotherUserMutators(t, client, first.OrganizationID, nil, func(r *codersdk.CreateUserRequestWithOrgs) {
+			r.Username = "multiuser"
+		})
+
+		r := dbfake.WorkspaceBuild(t, store, database.WorkspaceTable{
+			Name:           "multiworkspace",
+			OrganizationID: first.OrganizationID,
+			OwnerID:        user.ID,
+		}).WithAgent(func(agents []*proto.Agent) []*proto.Agent {
+			return []*proto.Agent{
+				{
+					Name: "agent1",
+					Auth: &proto.Agent_Token{},
+				},
+				{
+					Name: "agent2",
+					Auth: &proto.Agent_Token{},
+				},
+			}
+		}).Do()
+
+		var stdout bytes.Buffer
+		inv, root := clitest.New(t, "ssh", "")
+		inv.Stdout = &stdout
+		inv.Environ.Set("COMPLETION_MODE", "1")
+		clitest.SetupConfig(t, userClient, root)
+
+		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitMedium)
+		defer cancel()
+
+		err := inv.WithContext(ctx).Run()
+		require.NoError(t, err)
+
+		// For multi-agent workspaces, completions should include the
+		// workspace.agent format but NOT the bare workspace name.
+		output := stdout.String()
+		t.Logf("Completion output: %q", output)
+		lines := strings.Split(strings.TrimSpace(output), "\n")
+		require.NotContains(t, lines, r.Workspace.Name)
+		require.Contains(t, output, r.Workspace.Name+".agent1")
+		require.Contains(t, output, r.Workspace.Name+".agent2")
+	})
+
+	t.Run("NetworkError", func(t *testing.T) {
+		t.Parallel()
+
+		var stdout bytes.Buffer
+		inv, _ := clitest.New(t, "ssh", "")
+		inv.Stdout = &stdout
+		inv.Environ.Set("COMPLETION_MODE", "1")
+
+		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)
+		defer cancel()
+
+		err := inv.WithContext(ctx).Run()
+		require.NoError(t, err)
+
+		output := stdout.String()
+		require.Empty(t, output)
+	})
+}