feat(ai): session-level prompt cache key for openai responses

Closes #9232

apps/desktop/src/components/editor/AiAssistant.vue

@@ -3151,6 +3151,7 @@ async function send() {
         confirmedConnectionId: confirmedTargetConnId,
         confirmedDatabase: confirmedTargetDb,
         confirmedSchema: confirmedTargetSchema,
+        promptCacheKey: conversationId.value || undefined,
       },
       history,
       (event: AgentEvent) => {

apps/desktop/src/lib/ai/ai.ts

@@ -132,6 +132,8 @@ export interface AiRequestInput {
   confirmedConnectionId?: string;
   confirmedDatabase?: string;
   confirmedSchema?: string;
+  /** Stable per-conversation key forwarded to the Responses API. */
+  promptCacheKey?: string;
 }
 
 export interface AiNamespaceSelection {
@@ -194,6 +196,7 @@ export async function runAiAction(input: AiRequestInput, history?: api.AiMessage
     messages,
     taskContract,
     maxTokens,
+    promptCacheKey: input.promptCacheKey,
   });
 }
 
@@ -209,6 +212,7 @@ export async function runAiStream(input: AiRequestInput, history: api.AiMessage[
       messages,
       taskContract,
       maxTokens,
+      promptCacheKey: input.promptCacheKey,
     },
     (chunk) => {
       if (!chunk.done) {
@@ -232,6 +236,7 @@ export async function runAgentStream(input: AiRequestInput, history: api.AiMessa
       messages,
       taskContract,
       maxTokens,
+      promptCacheKey: input.promptCacheKey,
     },
     input.context.connectionId,
     input.context.database,

apps/desktop/src/lib/backend/tauri.ts

@@ -498,6 +498,8 @@ export interface AiCompletionRequest {
   messages: AiMessage[];
   taskContract?: AiTaskContract;
   maxTokens?: number;
+  /** Stable per-conversation key used by the Responses API prompt cache. */
+  promptCacheKey?: string;
 }
 
 export interface AiModelInfo {