feat: add experimental agents support (#22290)

feat: add AI chat system with agent tools and chat UI

Introduce the chatd subsystem and Agents UI for AI-powered chat
within Coder workspaces.

- Add chatd package with chat loop, message compaction, prompt
  management, and LLM provider integration (OpenAI, Anthropic)
- Add agent tools: create workspace, list/read templates, read/write/
  edit files, execute commands
- Add chat API endpoints with streaming, message editing, and
  durable reconnection
- Add database schema and migrations for chats, chat messages, chat
  providers, and chat model configs
- Add RBAC policies and dbauthz enforcement for chat resources
- Add Agents UI pages with conversation timeline, queued messages
  list, diff viewer, and model configuration panel
- Add comprehensive test coverage including coderd integration tests,
  chatd unit tests, and Storybook stories
- Gate feature behind experiments flag

---------

Co-authored-by: Cian Johnston <cian@coder.com>
Co-authored-by: Danielle Maywood <danielle@themaywoods.com>
Co-authored-by: Jeremy Ruppel <jeremy@coder.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

codersdk/agentsdk/agentsdk.go

@@ -638,6 +638,14 @@ type ExternalAuthRequest struct {
 	ID string
 	// Match is an arbitrary string matched against the regex of the provider.
 	Match string
+	// GitBranch is the current git branch in the working directory.
+	// Sent by the agent so the control plane can resolve diffs
+	// without SSHing into the workspace.
+	GitBranch string
+	// GitRemoteOrigin is the remote origin URL of the git repository.
+	// Sent by the agent so the control plane can resolve diffs
+	// without SSHing into the workspace.
+	GitRemoteOrigin string
 	// Listen indicates that the request should be long-lived and listen for
 	// a new token to be requested.
 	Listen bool
@@ -653,6 +661,12 @@ func (c *Client) ExternalAuth(ctx context.Context, req ExternalAuthRequest) (Ext
 	if req.Listen {
 		q.Set("listen", "true")
 	}
+	if req.GitBranch != "" {
+		q.Set("git_branch", req.GitBranch)
+	}
+	if req.GitRemoteOrigin != "" {
+		q.Set("git_remote_origin", req.GitRemoteOrigin)
+	}
 	reqURL := "/api/v2/workspaceagents/me/external-auth?" + q.Encode()
 	res, err := c.SDK.Request(ctx, http.MethodGet, reqURL, nil)
 	if err != nil {

codersdk/agentsdk/agentsdk_test.go

@@ -153,3 +153,33 @@ func TestRewriteDERPMap(t *testing.T) {
 	require.Equal(t, "coconuts.org", node.HostName)
 	require.Equal(t, 44558, node.DERPPort)
 }
+
+func TestExternalAuthRequestQuery(t *testing.T) {
+	t.Parallel()
+
+	t.Run("IncludesGitRefFieldsAndOmitsWorkdir", func(t *testing.T) {
+		t.Parallel()
+
+		srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			require.Equal(t, "/api/v2/workspaceagents/me/external-auth", r.URL.Path)
+			require.Equal(t, "true", r.URL.Query().Get("listen"))
+			require.Equal(t, "main", r.URL.Query().Get("git_branch"))
+			require.Equal(t, "https://github.com/coder/coder.git", r.URL.Query().Get("git_remote_origin"))
+			require.False(t, r.URL.Query().Has("workdir"))
+			_, _ = w.Write([]byte(`{"type":"github","access_token":"token"}`))
+		}))
+		defer srv.Close()
+
+		parsedURL, err := url.Parse(srv.URL)
+		require.NoError(t, err)
+
+		client := agentsdk.New(parsedURL, agentsdk.WithFixedToken("token"))
+		_, err = client.ExternalAuth(testutil.Context(t, testutil.WaitShort), agentsdk.ExternalAuthRequest{
+			Match:           "github.com",
+			Listen:          true,
+			GitBranch:       "main",
+			GitRemoteOrigin: "https://github.com/coder/coder.git",
+		})
+		require.NoError(t, err)
+	})
+}