chore: import upstream snapshot with attribution

open-sse/services/compression/resolveCompressionPlan.ts

@@ -0,0 +1,28 @@
+import { deriveDefaultPlan, type DerivedPlan } from "./deriveDefaultPlan.ts";
+
+export interface ResolveCtx {
+  comboId?: string | null;
+  combos?: Record<string, Array<{ engine: string; intensity?: string }>>; // named combo pipelines by id
+}
+
+export function resolveCompressionPlan(config: any, ctx: ResolveCtx): DerivedPlan {
+  if (config?.enabled === false) return { mode: "off", stackedPipeline: [] };
+
+  // routing-combo override
+  const ov = ctx.comboId ? config?.comboOverrides?.[ctx.comboId] : undefined;
+  if (ov) return modeToPlan(ov, config);
+
+  // active named combo
+  if (config?.activeComboId && ctx.combos?.[config.activeComboId]) {
+    return { mode: "stacked", stackedPipeline: ctx.combos[config.activeComboId] };
+  }
+
+  // derived default
+  return deriveDefaultPlan(config?.engines ?? {}, config?.enabled !== false);
+}
+
+function modeToPlan(mode: string, config: any): DerivedPlan {
+  return mode === "stacked"
+    ? { mode: "stacked", stackedPipeline: config?.stackedPipeline ?? [] }
+    : { mode, stackedPipeline: [] };
+}