fix(coderd): require ssh access for workspace chats (#23094)

### Motivation
- The chat creation flow associated a workspace agent for a chat if the requester could read the workspace, enabling privilege escalation where users without SSH/app-connect permissions could cause the daemon to open privileged agent connections and execute commands.
- The intent is to ensure that attaching a workspace agent to a chat only happens when the requester has the workspace SSH permission so the chat daemon cannot be abused to bypass RBAC.

### Description
- Require request-scoped authorization for workspace agent usage by changing `validateCreateChatWorkspaceSelection` to accept the `*http.Request` and calling `api.Authorize(r, policy.ActionSSH, workspace)` before selecting the workspace for a chat.
- Pass the HTTP request into the validator from `postChats` so authorization is evaluated in the request context (`postChats` now calls `validateCreateChatWorkspaceSelection(ctx, r, req)`).
- Add a regression test `WorkspaceAccessibleButNoSSH` in `coderd/chats_test.go` which creates an org-admin-scoped user (read access but no `ActionSSH`) and asserts that creating a chat with `WorkspaceID` is denied.

### Testing
- Ran `gofmt -w coderd/chats.go coderd/chats_test.go` which succeeded.
- Attempted to run repository pre-commit checks (`make pre-commit`) and targeted `go test` invocations; these checks could not be completed in this environment due to missing local tooling and environment constraints (protobuf include resolution, containerized DB access via Docker socket, and long-running golden generation tasks), so full CI/pre-commit verification and end-to-end test runs did not complete here.
- Added a focused regression unit test (`WorkspaceAccessibleButNoSSH`) to prevent reintroduction of the authorization bypass; this test is included in the change and should be executed in CI where the full toolchain and test environment are available.

------
[Codex Task](https://chatgpt.com/codex/tasks/task_b_69b432502670832e91d14e937745de46)

coderd/chats.go

@@ -237,7 +237,7 @@ func (api *API) postChats(rw http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	workspaceSelection, validationStatus, validationError := api.validateCreateChatWorkspaceSelection(ctx, req)
+	workspaceSelection, validationStatus, validationError := api.validateCreateChatWorkspaceSelection(ctx, r, req)
 	if validationError != nil {
 		httpapi.Write(ctx, rw, validationStatus, *validationError)
 		return
@@ -1899,6 +1899,7 @@ type createChatWorkspaceSelection struct {
 
 func (api *API) validateCreateChatWorkspaceSelection(
 	ctx context.Context,
+	r *http.Request,
 	req codersdk.CreateChatRequest,
 ) (
 	createChatWorkspaceSelection,
@@ -1927,6 +1928,12 @@ func (api *API) validateCreateChatWorkspaceSelection(
 		Valid: true,
 	}
 
+	if !api.Authorize(r, policy.ActionSSH, workspace) {
+		return selection, http.StatusBadRequest, &codersdk.Response{
+			Message: "Workspace not found or you do not have access to this resource",
+		}
+	}
+
 	return selection, 0, nil
 }
 

coderd/chats_test.go

@@ -23,6 +23,7 @@ import (
 	"github.com/coder/coder/v2/coderd/database/dbfake"
 	"github.com/coder/coder/v2/coderd/externalauth"
 	coderdpubsub "github.com/coder/coder/v2/coderd/pubsub"
+	"github.com/coder/coder/v2/coderd/rbac"
 	"github.com/coder/coder/v2/codersdk"
 	"github.com/coder/coder/v2/testutil"
 	"github.com/coder/websocket"
@@ -162,6 +163,41 @@ func TestPostChats(t *testing.T) {
 		)
 	})
 
+	t.Run("WorkspaceAccessibleButNoSSH", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+		adminClient, db := newChatClientWithDatabase(t)
+		firstUser := coderdtest.CreateFirstUser(t, adminClient)
+		orgAdminClient, _ := coderdtest.CreateAnotherUser(
+			t,
+			adminClient,
+			firstUser.OrganizationID,
+			rbac.ScopedRoleOrgAdmin(firstUser.OrganizationID),
+		)
+
+		workspaceBuild := dbfake.WorkspaceBuild(t, db, database.WorkspaceTable{
+			OrganizationID: firstUser.OrganizationID,
+			OwnerID:        firstUser.UserID,
+		}).WithAgent().Do()
+
+		_, err := orgAdminClient.CreateChat(ctx, codersdk.CreateChatRequest{
+			Content: []codersdk.ChatInputPart{
+				{
+					Type: codersdk.ChatInputPartTypeText,
+					Text: "hello",
+				},
+			},
+			WorkspaceID: &workspaceBuild.Workspace.ID,
+		})
+		sdkErr := requireSDKError(t, err, http.StatusBadRequest)
+		require.Equal(
+			t,
+			"Workspace not found or you do not have access to this resource",
+			sdkErr.Message,
+		)
+	})
+
 	t.Run("WorkspaceNotFound", func(t *testing.T) {
 		t.Parallel()