refactor: remove ~275 lines of dead code and enable stricter tsconfig

- Delete unused src/cli/ui.ts, remove zod dependency, drop 4 dead functions (logError, handleToolError, getRetryDelay, displayTimingSummary)
- Remove 8 unused types/interfaces and 3 duplicate formatting utils from audit/utils.ts
- Narrow export surface: make 7 message-handler functions private, remove unused audit re-exports, unexport AgentDefinition and path constants
- Remove unused runClaudePrompt params (sessionMetadata, attemptNumber) and update caller
- Enable tsconfig noUnusedLocals, noUnusedParameters, noImplicitReturns, noImplicitOverride, noFallthroughCasesInSwitch

src/ai/types.ts

@@ -13,22 +13,6 @@ export interface ExecutionContext {
   agentKey: string;
 }
 
-interface ProcessingState {
-  turnCount: number;
-  result: string | null;
-  apiErrorDetected: boolean;
-  totalCost: number;
-  partialCost: number;
-  lastHeartbeat: number;
-}
-
-interface ProcessingResult {
-  result: string | null;
-  turnCount: number;
-  apiErrorDetected: boolean;
-  totalCost: number;
-}
-
 export interface AssistantResult {
   content: string;
   cleanedContent: string;
@@ -110,15 +94,6 @@ export interface ApiErrorDetection {
   shouldThrow?: Error;
 }
 
-// Message types from SDK stream
-type SdkMessage =
-  | AssistantMessage
-  | ResultMessage
-  | ToolUseMessage
-  | ToolResultMessage
-  | SystemInitMessage
-  | UserMessage;
-
 export interface SystemInitMessage {
   type: 'system';
   subtype: 'init';
@@ -131,16 +106,3 @@ export interface UserMessage {
   type: 'user';
 }
 
-// Dispatch result types for message processing
-type MessageDispatchResult =
-  | { action: 'continue' }
-  | { action: 'break'; result: string | null; cost: number }
-  | { action: 'throw'; error: Error };
-
-interface MessageDispatchContext {
-  turnCount: number;
-  execContext: ExecutionContext;
-  description: string;
-  colorFn: (text: string) => string;
-  useCleanOutput: boolean;
-}