feat(compact-basic): baseline compaction backend (squashed from compact-basic)

Collapses the per-round review churn of the prior compact-basic branch into a
single clean baseline on top of compact-interface, so the upcoming retention
refactor lands as fresh, well-scoped commits rather than stacking on a history
of fixes that are being superseded.

packages/compact/compact-basic/tsconfig.json

@@ -0,0 +1,16 @@
+{
+  "extends": "../../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "lib/types"
+  },
+  "include": ["src"],
+  "references": [
+    { "path": "../../../vendor/cosmokit" },
+    { "path": "../../../vendor/cordis" },
+    { "path": "../../llm/llm" },
+    { "path": "../../core/session" },
+    { "path": "../../core/agent" },
+    { "path": "../compact" }
+  ]
+}