fix(stage-tamagotchi): replace streaming caption corrections (#2263)

packages/stage-shared/src/caption.ts

@@ -0,0 +1,9 @@
+/** A caption update sent through the cross-window caption channel. */
+export interface CaptionChannelEvent {
+  /** Controls whether the overlay appends text or replaces the current source text. */
+  operation?: 'append' | 'replace'
+  /** Text rendered by the caption overlay. Empty text clears this source. */
+  text: string
+  /** Identifies the speaker that owns this caption text. */
+  type: 'caption-speaker' | 'caption-assistant'
+}

packages/stage-shared/src/index.ts

@@ -1,4 +1,5 @@
 export * from './artistry'
+export * from './caption'
 export * from './env-vars'
 export * from './environment'
 export * from './error-message'