Harden audio transcription arg hydration and add rewrite audit event

src/audit/logger.ts

@@ -8,6 +8,7 @@ import type {
   ToolErrorEvent,
   ToolDeniedEvent,
   ToolApprovalEvent,
+  ToolArgsRewrittenEvent,
   SkillsInstallerExecutionBlockedEvent,
   SkillsInstallerCommandResultEvent,
   SkillsScanEvent,
@@ -104,6 +105,11 @@ export class AuditLogger {
     this.write({ level: 'debug', event_type: 'tool.approval', event: event as unknown as Record<string, unknown> });
   }
 
+  toolArgsRewritten(event: ToolArgsRewrittenEvent): void {
+    if (!this.shouldLog('tools', 'debug')) {return;}
+    this.write({ level: 'debug', event_type: 'tool.args_rewritten', event: event as unknown as Record<string, unknown> });
+  }
+
   skillsInstallerExecutionBlocked(event: SkillsInstallerExecutionBlockedEvent): void {
     if (!this.shouldLog('tools', 'warn')) {return;}
     this.write({

src/audit/types.ts

@@ -2,7 +2,7 @@ export type AuditLevel = 'debug' | 'info' | 'warn' | 'error';
 
 export type AuditEventType =
   // Tool execution
-  | 'tool.start' | 'tool.success' | 'tool.error' | 'tool.denied' | 'tool.approval'
+  | 'tool.start' | 'tool.success' | 'tool.error' | 'tool.denied' | 'tool.approval' | 'tool.args_rewritten'
   // Security
   | 'security.elevation.enabled' | 'security.elevation.disabled' | 'security.elevation.expired'
   // Skills scan
@@ -110,6 +110,17 @@ export interface ToolApprovalEvent {
   session_id?: string;
 }
 
+export interface ToolArgsRewrittenEvent {
+  tool_name: string;
+  session_id?: string;
+  source: 'latest_turn' | 'persisted' | 'history';
+  reason: 'latest_audio_preferred' | 'voice_turn_fallback' | 'invalid_model_args' | 'missing_model_args';
+  original_has_data: boolean;
+  original_has_url: boolean;
+  original_mime_type?: string;
+  final_mime_type?: string;
+}
+
 export interface SkillsInstallerExecutionBlockedEvent {
   skill_name: string;
   phase: 'install' | 'execute';