chore: remove MULTI_FILE_APPLY_DIFF experiment (#10925)

* chore: remove MULTI_FILE_APPLY_DIFF experiment

Remove the 'Enable concurrent file edits' experimental feature that
allowed editing multiple files in a single apply_diff call.

- Remove multiFileApplyDiff from experiment types and config
- Delete MultiFileSearchReplaceDiffStrategy class and tests
- Delete MultiApplyDiffTool wrapper and tests
- Remove experiment-specific code paths in Task.ts, generateSystemPrompt.ts, and presentAssistantMessage.ts
- Remove special handling in ExperimentalSettings.tsx
- Remove translations from all 18 locale files

The existing MultiSearchReplaceDiffStrategy continues to handle
multiple SEARCH/REPLACE blocks within a single file.

* fix: remove unused EXPERIMENT_IDS/experiments import from Task.ts

Addresses review feedback: removes the unused imports from
src/core/task/Task.ts that were left over after removing the
MULTI_FILE_APPLY_DIFF experiment routing code.

Author: hannesrudolph

packages/types/src/experiment.ts

@@ -7,7 +7,7 @@ import type { Keys, Equals, AssertEqual } from "./type-fu.js"
  */
 
 export const experimentIds = [
-	"multiFileApplyDiff",
+	"powerSteering",
 	"preventFocusDisruption",
 	"imageGeneration",
 	"runSlashCommand",
@@ -24,7 +24,7 @@ export type ExperimentId = z.infer<typeof experimentIdsSchema>
  */
 
 export const experimentsSchema = z.object({
-	multiFileApplyDiff: z.boolean().optional(),
+	powerSteering: z.boolean().optional(),
 	preventFocusDisruption: z.boolean().optional(),
 	imageGeneration: z.boolean().optional(),
 	runSlashCommand: z.boolean().optional(),

src/core/assistant-message/presentAssistantMessage.ts

@@ -10,7 +10,6 @@ import { t } from "../../i18n"
 
 import { defaultModeSlug, getModeBySlug } from "../../shared/modes"
 import type { ToolParamName, ToolResponse, ToolUse, McpToolUse } from "../../shared/tools"
-import { experiments, EXPERIMENT_IDS } from "../../shared/experiments"
 
 import { AskIgnoredError } from "../task/AskIgnoredError"
 import { Task } from "../task/Task"
@@ -19,7 +18,6 @@ import { fetchInstructionsTool } from "../tools/FetchInstructionsTool"
 import { listFilesTool } from "../tools/ListFilesTool"
 import { readFileTool } from "../tools/ReadFileTool"
 import { writeToFileTool } from "../tools/WriteToFileTool"
-import { applyDiffTool } from "../tools/MultiApplyDiffTool"
 import { searchAndReplaceTool } from "../tools/SearchAndReplaceTool"
 import { searchReplaceTool } from "../tools/SearchReplaceTool"
 import { editFileTool } from "../tools/EditFileTool"
@@ -743,32 +741,14 @@ export async function presentAssistantMessage(cline: Task) {
 						pushToolResult,
 					})
 					break
-				case "apply_diff": {
+				case "apply_diff":
 					await checkpointSaveAndMark(cline)
-
-					// Get the provider and state to check experiment settings
-					const provider = cline.providerRef.deref()
-					let isMultiFileApplyDiffEnabled = false
-
-					if (provider) {
-						const state = await provider.getState()
-						isMultiFileApplyDiffEnabled = experiments.isEnabled(
-							state.experiments ?? {},
-							EXPERIMENT_IDS.MULTI_FILE_APPLY_DIFF,
-						)
-					}
-
-					if (isMultiFileApplyDiffEnabled) {
-						await applyDiffTool(cline, block, askApproval, handleError, pushToolResult)
-					} else {
-						await applyDiffToolClass.handle(cline, block as ToolUse<"apply_diff">, {
-							askApproval,
-							handleError,
-							pushToolResult,
-						})
-					}
+					await applyDiffToolClass.handle(cline, block as ToolUse<"apply_diff">, {
+						askApproval,
+						handleError,
+						pushToolResult,
+					})
 					break
-				}
 				case "search_and_replace":
 					await checkpointSaveAndMark(cline)
 					await searchAndReplaceTool.handle(cline, block as ToolUse<"search_and_replace">, {