feat(site/src/pages/TemplateBuilder): disable create button when no provisioners (#26938)

## Summary

Add provisioner awareness to the Template Builder wizard: disable the
Create Template button when the selected organization has no
provisioners, and reset the customizations step when navigating back.

## Changes

- Query provisioner daemons for the selected org in
`TemplateCustomizationsStep` and show a warning alert when none are
found
- Track `hasProvisioners` in wizard state via `SET_HAS_PROVISIONERS`
action; `computeCanContinue` disables the Create Template button when
`hasProvisioners === false`
- Add `RESET_CUSTOMIZATIONS` action to clear customization fields (name,
displayName, description, icon, organizationId, hasProvisioners) when
navigating back from the customizations step
- Clear the create mutation error on back navigation via
`onClearCreateError` callback

Follows up on #26935 which added the provisioner warning alert to the
Template Builder.

> 🤖 Generated by Coder Agents on behalf of @jeremyruppel

site/src/pages/TemplateBuilder/TemplateBuilderPage.tsx

@@ -62,6 +62,7 @@ const TemplateBuilderPage: FC = () => {
 				onCreateTemplate={handleCreate}
 				createError={createMutation.error}
 				isCreating={createMutation.isPending}
+				onClearCreateError={() => createMutation.reset()}
 			/>
 		</>
 	);

site/src/pages/TemplateBuilder/TemplateBuilderPageView.tsx

@@ -1,4 +1,10 @@
-import { type FC, type ReactNode, useReducer, useState } from "react";
+import {
+	type FC,
+	type ReactNode,
+	useCallback,
+	useReducer,
+	useState,
+} from "react";
 
 import { useQuery } from "react-query";
 import { templateBuilderModules } from "#/api/queries/templateBuilder";
@@ -51,6 +57,7 @@ interface TemplateBuilderPageViewProps {
 	onCreateTemplate: (state: TemplateBuilderWizardState) => void;
 	createError: Error | null;
 	isCreating: boolean;
+	onClearCreateError?: () => void;
 }
 
 export const TemplateBuilderPageView: FC<TemplateBuilderPageViewProps> = ({
@@ -59,6 +66,7 @@ export const TemplateBuilderPageView: FC<TemplateBuilderPageViewProps> = ({
 	onCreateTemplate,
 	createError,
 	isCreating,
+	onClearCreateError,
 }) => {
 	const [state, dispatch] = useReducer(wizardReducer, initialWizardState);
 	const [stepIndex, setStepIndex] = useState(0);
@@ -85,6 +93,10 @@ export const TemplateBuilderPageView: FC<TemplateBuilderPageViewProps> = ({
 	);
 
 	const handleBack = () => {
+		if (currentStep.id === "customizations") {
+			dispatch({ type: "RESET_CUSTOMIZATIONS" });
+			onClearCreateError?.();
+		}
 		window.scrollTo(0, 0);
 		setStepIndex(prevIndex);
 	};
@@ -98,6 +110,13 @@ export const TemplateBuilderPageView: FC<TemplateBuilderPageViewProps> = ({
 		setStepIndex(nextIndex);
 	};
 
+	const handleProvisionerStatusChange = useCallback(
+		(value: boolean | undefined) => {
+			dispatch({ type: "SET_HAS_PROVISIONERS", value });
+		},
+		[],
+	);
+
 	const handleDeselectModule = (moduleId: string) => {
 		// If the only module gets deselected, go back to module selection
 		if (state.modules.length === 1) {
@@ -142,6 +161,7 @@ export const TemplateBuilderPageView: FC<TemplateBuilderPageViewProps> = ({
 							dispatch,
 							moduleVarMap,
 							createError,
+							handleProvisionerStatusChange,
 						)}
 					</div>
 
@@ -193,6 +213,7 @@ function renderStepContent(
 	dispatch: (action: WizardAction) => void,
 	moduleVarMap: Record<string, Record<string, string>>,
 	createError: Error | null,
+	onProvisionerStatusChange: (value: boolean | undefined) => void,
 ): ReactNode {
 	switch (stepId) {
 		case "base-infra":
@@ -253,6 +274,7 @@ function renderStepContent(
 								value,
 							})
 						}
+						onProvisionerStatusChange={onProvisionerStatusChange}
 					/>
 				</>
 			);
@@ -284,7 +306,7 @@ function computeCanContinue(
 				moduleVarMap,
 			);
 		case "customizations":
-			return state.name.trim() !== "";
+			return state.name.trim() !== "" && state.hasProvisioners !== false;
 		default:
 			return true;
 	}

site/src/pages/TemplateBuilder/TemplateCustomizationsStep.tsx

@@ -28,11 +28,12 @@ interface TemplateCustomizationsStepProps {
 		field: "organizationId" | "name" | "displayName" | "description" | "icon",
 		value: string,
 	) => void;
+	onProvisionerStatusChange: (hasProvisioners: boolean | undefined) => void;
 }
 
 export const TemplateCustomizationsStep: FC<
 	TemplateCustomizationsStepProps
-> = ({ state, onChangeField }) => {
+> = ({ state, onChangeField, onProvisionerStatusChange }) => {
 	const permittedOrgsQuery = useQuery(
 		permittedOrganizations({
 			object: { resource_type: "template" },
@@ -47,7 +48,14 @@ export const TemplateCustomizationsStep: FC<
 		...provisionerDaemons(selectedOrg?.id ?? ""),
 		enabled: Boolean(selectedOrg),
 	});
-	const showProvisionerWarning = provisioners ? provisioners.length < 1 : false;
+	const hasProvisioners = provisioners ? provisioners.length > 0 : undefined;
+	const showProvisionerWarning = hasProvisioners === false;
+
+	// Notify parent when provisioner status changes so the wizard can
+	// disable the create button when no provisioners are available.
+	useEffect(() => {
+		onProvisionerStatusChange(hasProvisioners);
+	}, [hasProvisioners, onProvisionerStatusChange]);
 
 	// Auto-select when exactly one org is available.
 	useEffect(() => {

site/src/pages/TemplateBuilder/wizardState.ts

@@ -34,6 +34,7 @@ export type TemplateBuilderWizardState = {
 	baseVariableValues: Record<string, string>;
 	modules: TemplateBuilderComposeModule[];
 	organizationId?: string;
+	hasProvisioners: boolean | undefined;
 	name: string;
 	displayName: string;
 	description: string;
@@ -46,6 +47,7 @@ export const initialWizardState: TemplateBuilderWizardState = {
 	baseTemplateId: null,
 	baseVariableValues: {},
 	modules: [],
+	hasProvisioners: undefined,
 	name: "",
 	displayName: "",
 	description: "",
@@ -72,6 +74,8 @@ export type WizardAction =
 			field: "organizationId" | "name" | "displayName" | "description" | "icon";
 			value: string;
 	  }
+	| { type: "SET_HAS_PROVISIONERS"; value: boolean | undefined }
+	| { type: "RESET_CUSTOMIZATIONS" }
 	| { type: "RESET" };
 
 export function wizardReducer(
@@ -123,6 +127,21 @@ export function wizardReducer(
 				...state,
 				[action.field]: action.value,
 			};
+		case "SET_HAS_PROVISIONERS":
+			return {
+				...state,
+				hasProvisioners: action.value,
+			};
+		case "RESET_CUSTOMIZATIONS":
+			return {
+				...state,
+				organizationId: undefined,
+				hasProvisioners: undefined,
+				name: "",
+				displayName: "",
+				description: "",
+				icon: "",
+			};
 		case "RESET":
 			return initialWizardState;
 		default: