feat: unify context compaction

pi-compaction/test/token-accounting.test.ts

@@ -0,0 +1,19 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { shouldCompact } from "../src/token-accounting.ts";
+
+test("raw pressure cannot trigger compaction while effective lower-bound stays below 90%", () => {
+  const config = { hardRatio: 0.9 };
+  const snapshot = { lowerBound: 231_000, contextWindow: 300_000 };
+  assert.equal(shouldCompact("threshold", snapshot, config), false);
+  assert.equal(shouldCompact("manual", snapshot, config), true);
+  assert.equal(shouldCompact("overflow", snapshot, config), true);
+});
+
+test("effective lower-bound at the configured threshold compacts", () => {
+  assert.equal(shouldCompact(
+    "threshold",
+    { lowerBound: 270_000, contextWindow: 300_000 },
+    { hardRatio: 0.9 },
+  ), true);
+});