diff --git a/local/patches/README.md b/local/patches/README.md
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+# Patch Registry
+
+This directory contains the curated registry of per-package build-time patches consumed by bincraft's `patches` argument.
+
+## Schema
+
+The registry is defined in `registry.json` as an array of patch entries. Each entry specifies lightweight build-time overrides (environment variables, configure arguments, Makevars) and optionally a source diff to apply before building.
+
+### Field semantics
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `package` | string | yes | CRAN package name. |
+| `versions` | string | yes | `"*"` for any, a constraint such as `">=5.1.0"`, or an exact version `"5.1.11-2"`. Env-tier fixes are typically `"*"`; source diffs are normally exact or lower-bounded because a diff is pinned to the source it was generated against. |
+| `platforms` | array of strings | yes | Matched against the running build's platform tokens — distro family (`alpine`, `ubuntu`, `redhat`), codename (`ubuntu-2604`, `alpine-324`), and arch (`amd64`, `arm64`). An entry matches if any listed token matches any build token. `["*"]` matches all platforms. |
+| `env` | object | no | Environment variables exported only for this package's isolated build. |
+| `configure_args` | array | no | Arguments passed as `--configure-args` to the isolated build. |
+| `makevars` | object | no | Key/value pairs written into a package-local Makevars for the isolated build. |
+| `patch` | string or null | no | Path (relative to `local/patches/`) to a unified diff applied to the unpacked CRAN source before building. |
+| `reason` | string | yes | Human explanation, surfaced in logs and metadata. |
+
+## Adding an entry
+
+To add a new patch entry:
+
+1. Add an object to the array in `registry.json` with the fields documented above.
+   Start with lightweight overrides (environment variables, configure arguments, Makevars) before resorting to source diffs.
+
+2. If a source diff is needed, place it in `local/patches/<package>/<file>.patch` and reference its path in the `patch` field.
+   For example, a diff for `RcppParallel` would go in `local/patches/RcppParallel/fix.patch` and be referenced as `"patch": "RcppParallel/fix.patch"`.
+
+3. The `reason` field should clearly explain why the patch is needed and what problem it solves.
+
+## Validation
+
+The registry is validated and applied by bincraft during the build process.
+For manual validation, use:
+
+```r
+x <- jsonlite::fromJSON("local/patches/registry.json", simplifyVector = FALSE)
+```
+
+This loads the registry; inspect the structure to verify correctness.
diff --git a/local/patches/registry.json b/local/patches/registry.json
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+[
+  {
+    "package": "RcppParallel",
+    "versions": "*",
+    "platforms": ["alpine", "ubuntu-2604"],
+    "env": { "RCPP_PARALLEL_USE_TBB": "0" },
+    "configure_args": [],
+    "makevars": {},
+    "patch": null,
+    "reason": "bundled Intel TBB fails to build on musl and on newer toolchains (e.g. g++ 15 on ubuntu-2604); disabling TBB falls back to TinyThread"
+  }
+]