feat(interactions): durable cross-pod settlement for background interaction billing

litellm-proxy-extras/litellm_proxy_extras/migrations/20260915000000_add_background_interaction_settlement/migration.sql

@@ -0,0 +1,16 @@
+-- CreateTable
+CREATE TABLE IF NOT EXISTS "LiteLLM_BackgroundInteractionSettlement" (
+    "interaction_id" TEXT NOT NULL,
+    "custom_llm_provider" TEXT NOT NULL,
+    "create_context" JSONB NOT NULL,
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "claimed_at" TIMESTAMP(3),
+    "claimed_by" TEXT,
+    "settled_at" TIMESTAMP(3),
+    "outcome" TEXT,
+
+    CONSTRAINT "LiteLLM_BackgroundInteractionSettlement_pkey" PRIMARY KEY ("interaction_id")
+);
+
+-- CreateIndex
+CREATE INDEX IF NOT EXISTS "idx_background_interaction_settlement_claimed_at" ON "LiteLLM_BackgroundInteractionSettlement"("claimed_at");

litellm-proxy-extras/litellm_proxy_extras/schema.prisma

@@ -1815,3 +1815,19 @@ model LiteLLM_WorkflowMessage {
   @@unique([run_id, sequence_number])
   @@index([run_id])
 }
+
+// Pending billing settlements for background interactions, keyed by the
+// interaction id so any replica can settle one that another replica created.
+// `claimed_at` is the exactly-once gate: the first conditional update wins.
+model LiteLLM_BackgroundInteractionSettlement {
+  interaction_id      String    @id
+  custom_llm_provider String
+  create_context      Json
+  created_at          DateTime  @default(now())
+  claimed_at          DateTime?
+  claimed_by          String?
+  settled_at          DateTime?
+  outcome             String?
+
+  @@index([claimed_at], map: "idx_background_interaction_settlement_claimed_at")
+}