refactor: reduce cyclomatic complexity of settings, tool data and layout sanitizers

Add characterization tests first, then split the hot spots into small helpers:
- STT/TTS settings updates move to extensions/piagentui-speech-settings.ts (rule tables)
- defaultExtractData is split into diff/diagnostic/output extractors
- getToolSummaryCategory becomes an ordered rule table (toolSummary.ts)
- sanitizePersistedTerminalLayoutMap is split per level
- duplicated diff stats helpers are merged into utils/diffStats.ts

extensions/piagentui-speech-settings.ts

@@ -0,0 +1,126 @@
+import { validateSttBaseUrl } from './piagentui-server-core.js'
+import type { StoredSttSettings, StoredTtsSettings } from './piagentui-settings-store.js'
+
+export type SettingsUpdateResult<T> = { ok: true; next: T } | { ok: false; error: string }
+
+type Fields = Record<string, unknown>
+/** Assigns a validated value to `next`; returns false when the value is invalid. */
+type FieldRule = (value: unknown, next: Fields) => boolean
+
+const TTS_RESPONSE_FORMATS = ['mp3', 'opus', 'aac', 'flac', 'wav', 'pcm'] as const
+
+export function isTtsResponseFormat(value: unknown): value is NonNullable<StoredTtsSettings['responseFormat']> {
+  return typeof value === 'string' && (TTS_RESPONSE_FORMATS as readonly string[]).includes(value)
+}
+
+const booleanField =
+  (key: string): FieldRule =>
+  (value, next) => {
+    next[key] = value === true
+    return true
+  }
+
+const oneOfField =
+  (key: string, allowed: readonly string[]): FieldRule =>
+  (value, next) => {
+    if (typeof value !== 'string' || !allowed.includes(value)) return false
+    next[key] = value
+    return true
+  }
+
+const endpointField =
+  (key: string): FieldRule =>
+  (value, next) => {
+    if (typeof value !== 'string' || !value.startsWith('/')) return false
+    next[key] = value
+    return true
+  }
+
+const trimmedField =
+  (key: string): FieldRule =>
+  (value, next) => {
+    if (typeof value !== 'string' || !value.trim()) return false
+    next[key] = value.trim()
+    return true
+  }
+
+const baseUrlField: FieldRule = (value, next) => {
+  if (typeof value !== 'string' || !validateSttBaseUrl(value)) return false
+  next.baseUrl = value.replace(/\/+$/, '')
+  return true
+}
+
+const languageField: FieldRule = (value, next) => {
+  if (value === null || value === '') delete next.language
+  else if (typeof value === 'string') next.language = value.trim()
+  else return false
+  return true
+}
+
+const speedField: FieldRule = (value, next) => {
+  if (typeof value !== 'number' || value < 0.25 || value > 4) return false
+  next.speed = value
+  return true
+}
+
+const PROVIDER_KINDS = ['openai', 'openai-compatible'] as const
+
+const STT_RULES: Array<[string, FieldRule]> = [
+  ['enabled', booleanField('enabled')],
+  ['providerKind', oneOfField('providerKind', PROVIDER_KINDS)],
+  ['mode', oneOfField('mode', ['file', 'realtime'])],
+  ['baseUrl', baseUrlField],
+  ['apiKeyRequired', booleanField('apiKeyRequired')],
+  ['transcriptionEndpoint', endpointField('transcriptionEndpoint')],
+  ['transcriptionModel', trimmedField('transcriptionModel')],
+  ['language', languageField],
+  ['insertMode', oneOfField('insertMode', ['append', 'replace'])],
+]
+
+const TTS_RULES: Array<[string, FieldRule]> = [
+  ['enabled', booleanField('enabled')],
+  ['providerKind', oneOfField('providerKind', PROVIDER_KINDS)],
+  ['baseUrl', baseUrlField],
+  ['apiKeyRequired', booleanField('apiKeyRequired')],
+  ['speechEndpoint', endpointField('speechEndpoint')],
+  ['model', trimmedField('model')],
+  ['voice', trimmedField('voice')],
+  ['responseFormat', oneOfField('responseFormat', TTS_RESPONSE_FORMATS)],
+  ['speed', speedField],
+]
+
+function applyUpdate<T extends object>(
+  existing: T,
+  update: Record<string, unknown>,
+  rules: Array<[string, FieldRule]>,
+): SettingsUpdateResult<T> {
+  const next: Fields = { ...(existing as Fields) }
+
+  for (const [field, rule] of rules) {
+    if (update[field] === undefined) continue
+    if (!rule(update[field], next)) return { ok: false, error: `Invalid ${field}` }
+  }
+
+  if (Object.prototype.hasOwnProperty.call(update, 'apiKey')) {
+    if (update.apiKey === null) delete next.apiKey
+    else if (typeof update.apiKey === 'string' && update.apiKey.trim()) next.apiKey = update.apiKey.trim()
+  }
+
+  return { ok: true, next: next as T }
+}
+
+/** Validates a PATCH-style STT update against the stored settings. Pure: does not persist anything. */
+export function applySttSettingsUpdate(
+  existing: StoredSttSettings,
+  update: Record<string, unknown>,
+): SettingsUpdateResult<StoredSttSettings> {
+  return applyUpdate(existing, update, STT_RULES)
+}
+
+/** Validates a PATCH-style TTS update against the stored settings. Pure: does not persist anything. */
+export function applyTtsSettingsUpdate(
+  existing: StoredTtsSettings,
+  update: Record<string, unknown>,
+): SettingsUpdateResult<StoredTtsSettings> {
+  return applyUpdate(existing, update, TTS_RULES)
+}