refactor: remove deprecated AITaskPromptParameterName constant (#21023)

This removes the deprecated AITaskPromptParameterName constant and all
backward compatibility code that was added for v2.28.

- Remove AITaskPromptParameterName constant from codersdk/aitasks.go
- Remove backward compatibility code in coderd/aitasks.go that populated
  the "AI Prompt" parameter for templates that defined it
- Remove the backward compatibility test (OK AIPromptBackCompat)
- Update dbfake to no longer set the AI Prompt parameter
- Remove AITaskPromptParameterName from frontend TypeScript types
- Remove preset prompt read-only feature from TaskPrompt component
- Update docs to reflect that pre-2.28 definition is no longer supported

Task prompts are now exclusively stored in the tasks.prompt database
column, as introduced in the migration that added the tasks table.

site/src/api/typesGenerated.ts

@@ -108,22 +108,6 @@ export interface AIConfig {
 	readonly bridge?: AIBridgeConfig;
 }
 
-// From codersdk/aitasks.go
-/**
- * AITaskPromptParameterName is the name of the parameter used to pass prompts
- * to AI tasks.
- *
- * Deprecated: This constant is deprecated and maintained only for backwards
- * compatibility with older templates. Task prompts are now stored directly
- * in the tasks.prompt database column. New code should access prompts via
- * the Task.InitialPrompt field returned from task endpoints.
- *
- * This constant will be removed in a future major version. Templates should
- * not rely on this parameter name, as the backend will continue to create it
- * automatically for compatibility but reads from tasks.prompt.
- */
-export const AITaskPromptParameterName = "AI Prompt";
-
 // From codersdk/allowlist.go
 /**
  * APIAllowListTarget represents a single allow-list entry using the canonical

site/src/modules/tasks/TaskPrompt/TaskPrompt.stories.tsx

@@ -1,7 +1,7 @@
 import {
-	MockAIPromptPresets,
 	MockPresets,
 	MockTask,
+	MockTaskPresets,
 	MockTasks,
 	MockTemplate,
 	MockTemplateVersion,
@@ -72,11 +72,9 @@ export const WithPresets: Story = {
 	},
 };
 
-export const ReadOnlyPresetPrompt: Story = {
+export const WithAIPresets: Story = {
 	beforeEach: () => {
-		spyOn(API, "getTemplateVersionPresets").mockResolvedValue(
-			MockAIPromptPresets,
-		);
+		spyOn(API, "getTemplateVersionPresets").mockResolvedValue(MockTaskPresets);
 	},
 };
 

site/src/modules/tasks/TaskPrompt/TaskPrompt.tsx

@@ -7,7 +7,6 @@ import type {
 	Template,
 	TemplateVersionExternalAuth,
 } from "api/typesGenerated";
-import { AITaskPromptParameterName } from "api/typesGenerated";
 import { ErrorAlert } from "components/Alert/ErrorAlert";
 import { Button } from "components/Button/Button";
 import { ExternalImage } from "components/ExternalImage/ExternalImage";
@@ -162,19 +161,6 @@ const CreateTaskForm: FC<CreateTaskFormProps> = ({ templates, onSuccess }) => {
 		const defaultPreset = presets?.find((p) => p.Default);
 		setSelectedPresetId(defaultPreset?.ID ?? presets?.[0]?.ID);
 	}, [presets]);
-	const selectedPreset = presets?.find((p) => p.ID === selectedPresetId);
-
-	// Read-only prompt if defined in preset
-	const presetPrompt = selectedPreset?.Parameters?.find(
-		(param) => param.Name === AITaskPromptParameterName,
-	)?.Value;
-	const isPromptReadOnly = !!presetPrompt;
-	useEffect(() => {
-		if (presetPrompt) {
-			setPrompt(presetPrompt);
-		}
-	}, [presetPrompt]);
-
 	// External Auth
 	const {
 		externalAuth,
@@ -250,21 +236,13 @@ const CreateTaskForm: FC<CreateTaskFormProps> = ({ templates, onSuccess }) => {
 				className="border border-border border-solid rounded-3xl p-3 bg-surface-secondary"
 				disabled={createTaskMutation.isPending}
 			>
-				<label
-					htmlFor="prompt"
-					className={
-						isPromptReadOnly
-							? "text-xs font-medium text-content-primary block px-3 pt-2"
-							: "sr-only"
-					}
-				>
-					{isPromptReadOnly ? "Prompt defined by preset" : "Prompt"}
+				<label htmlFor="prompt" className="sr-only">
+					Prompt
 				</label>
 				<PromptTextarea
 					required
 					value={prompt}
 					onChange={(e) => setPrompt(e.target.value)}
-					readOnly={isPromptReadOnly}
 					isSubmitting={createTaskMutation.isPending}
 					onKeyDown={handleKeyDown}
 				/>

site/src/testHelpers/entities.ts

@@ -4977,14 +4977,13 @@ export const MockPresets: TypesGen.Preset[] = [
 	},
 ];
 
-export const MockAIPromptPresets: TypesGen.Preset[] = [
+export const MockTaskPresets: TypesGen.Preset[] = [
 	{
 		ID: "ai-preset-1",
 		Name: "Code Review",
 		Description: "",
 		Icon: "",
 		Parameters: [
-			{ Name: "AI Prompt", Value: "Review the code for best practices" },
 			{ Name: "cpu", Value: "4" },
 			{ Name: "memory", Value: "8GB" },
 		],