docs: add optional-integration loader shim to roadmap

Record the zero-dependency loader package (@r3b1s/pi-repair-layer-loader) as an
unscheduled item: it would own the dynamic import and absence discrimination so
consumers stop hand-rolling (and drifting from) the recipe.

Author: r3b1s

ROADMAP.md

@@ -0,0 +1,26 @@
+# Roadmap
+
+Longer-horizon items that are not yet scheduled into an OpenSpec change.
+
+## Optional-integration loader shim package
+
+Ship a tiny, zero-runtime-dependency loader package (working name
+`@r3b1s/pi-repair-layer-loader`) that consumers hard-depend on instead of
+hand-rolling the optional-integration recipe. The shim owns the dynamic
+`import("@r3b1s/pi-repair-layer/pi")` and the absence discrimination, so the
+fragile classification logic lives in one place we test and version, rather
+than being copy-pasted (and drifting) across every consumer.
+
+- **Consumer surface:** `const adapt = await loadRepairAdapter()` — returns the
+  adapter or `undefined` when the engine is absent.
+- **Why a separate package:** the absence detector can't ship from the main
+  package (you'd have to import it from the thing that might be missing —
+  bootstrap paradox). A zero-dependency shim can't itself be
+  "present-but-broken," so it removes the last copy-paste hazard.
+- **Trade-off:** a second published package plus version coordination; converts
+  "optional heavy dependency" into "required tiny shim + optional heavy
+  engine." Justified once external adoption is broad enough that copy-paste
+  drift becomes a real maintenance cost.
+- **Depends on:** the A+B work (zero-runtime-dep `/pi` entry + robust
+  quoted-specifier matcher), which makes the shim's internal logic trivial and
+  its detection unambiguous.