refactor: remove dead code and over-broad exports

- Delete unused CacheFile interface (src/types.ts)
- Demote internal-only symbols from export to module scope:
  PROMPT_VERSION, DEFAULT_CLI_TIMEOUT_MS, MIN_STREAMING_TIMEOUT_MS,
  MIN_CLI_TIMEOUT_MS (settings.ts), CliFailureReason (cli.ts),
  GenerationErrorContext (error-ui.ts), AnthropicMessagesBody/
  OpenAiChatBody/OpenAiResponsesBody/GeminiBody (provider-bodies.ts),
  BackendTestDeps (backend-test.ts)

Verified: tsc, esbuild prod build, biome, all 28 test files pass.
Change-Id: I0fc597ee51ec67d509a7f33db39fabcbdb301797

src/backend-test.ts

@@ -14,7 +14,7 @@ const CLI_TEST_TIMEOUT_MS = 60000;
 
 type SpawnImpl = Parameters<typeof runCli>[5];
 
-export interface BackendTestDeps {
+interface BackendTestDeps {
   requestUrlImpl?: RequestUrlFunction;
   spawnImpl?: SpawnImpl;
 }

src/cli.ts

@@ -52,12 +52,7 @@ export function resolveCliPath(name: string, override: string): string {
   return name;
 }
 
-export type CliFailureReason =
-  | 'wall-timeout'
-  | 'exit-nonzero'
-  | 'streams-unavailable'
-  | 'spawn-failure'
-  | 'startup-error';
+type CliFailureReason = 'wall-timeout' | 'exit-nonzero' | 'streams-unavailable' | 'spawn-failure' | 'startup-error';
 
 export interface CliErrorDetails {
   reason: CliFailureReason;

src/error-ui.ts

@@ -6,7 +6,7 @@ import { translate } from './i18n';
 import type { ErrorKind, PluginSettings } from './types';
 import { copyToClipboard } from './ui-helpers';
 
-export interface GenerationErrorContext {
+interface GenerationErrorContext {
   app: App;
   settings: PluginSettings;
   /** Open the plugin settings tab (best-effort; falls back to no-op if unavailable). */

src/provider-bodies.ts

@@ -12,7 +12,7 @@ import type { PluginSettings } from './types';
 
 /* ---------- Body type interfaces ---------- */
 
-export interface AnthropicMessagesBody {
+interface AnthropicMessagesBody {
   model: string;
   max_tokens: number;
   system: string;
@@ -22,7 +22,7 @@ export interface AnthropicMessagesBody {
   stream?: boolean;
 }
 
-export interface OpenAiChatBody {
+interface OpenAiChatBody {
   model: string;
   messages: Array<{ role: string; content: string }>;
   response_format?: unknown;
@@ -30,7 +30,7 @@ export interface OpenAiChatBody {
   [tokenField: string]: unknown;
 }
 
-export interface OpenAiResponsesBody {
+interface OpenAiResponsesBody {
   model: string;
   instructions: string;
   input: string;
@@ -46,7 +46,7 @@ interface GeminiGenerationConfig {
   responseJsonSchema?: unknown;
 }
 
-export interface GeminiBody {
+interface GeminiBody {
   systemInstruction: { parts: Array<{ text: string }> };
   contents: Array<{ role: string; parts: Array<{ text: string }> }>;
   generationConfig: GeminiGenerationConfig;

src/settings.ts

@@ -8,12 +8,12 @@ import type { ApiFormat, ApiProviderPreset, CacheEntry, PluginSettings } from '.
 export { API_PROVIDER_PRESETS } from './provider-presets';
 
 export const MAX_DOC_CHARS = 100000;
-export const PROMPT_VERSION = 2;
+const PROMPT_VERSION = 2;
 export const CACHE_SCHEMA_VERSION = 2;
 export const DEFAULT_MAX_CACHE_ENTRIES = 100;
-export const DEFAULT_CLI_TIMEOUT_MS = 300000;
-export const MIN_STREAMING_TIMEOUT_MS = 1000;
-export const MIN_CLI_TIMEOUT_MS = 1000;
+const DEFAULT_CLI_TIMEOUT_MS = 300000;
+const MIN_STREAMING_TIMEOUT_MS = 1000;
+const MIN_CLI_TIMEOUT_MS = 1000;
 export const PROMPT_LANGUAGES = {
   zh: '中文',
   en: 'English',

src/types.ts

@@ -37,11 +37,6 @@ export interface CacheEntry {
   updatedAt?: string;
 }
 
-export interface CacheFile {
-  version: number;
-  entries: Record<string, CacheEntry>;
-}
-
 /* ---------- Settings types ---------- */
 
 export interface PluginSettings {