fix(patches): validator portability, clearer docs, broader hook trigger

.superpowers/handoff/task-B5-brief.md

@@ -0,0 +1,21 @@
+### Task B5: Document the feature in the README
+
+**Files:**
+- Modify: `README.md`
+
+**Interfaces:**
+- Produces: a short "Patching packages" section explaining the registry and linking the design spec.
+
+- [ ] **Step 1: Add a README section**
+
+Add a `## Patching packages` section after the "Build Process" section describing: why patching exists (compiler/OS-specific failures cascading via shared deps like RcppParallel), where the registry lives (`local/patches/registry.json`), the two tiers (env/configure/Makevars overrides vs source diffs), and that bincraft pre-builds patched binaries served to pak. Link `specs/2026-06-30-package-patching-design.md`.
+
+- [ ] **Step 2: Commit**
+
+```bash
+git add README.md
+git commit -m "docs(patches): document the package patching workflow"
+```
+
+---
+