diff --git a/.coderabbit.yaml b/.coderabbit.yaml
new file mode 100644
index 00000000..565174d9
--- /dev/null
+++ b/.coderabbit.yaml
@@ -0,0 +1,39 @@
+# yaml-language-server: $schema=https://storage.googleapis.com/coderabbit_public_assets/schema.v2.json
+
+reviews:
+  path_filters:
+    - "!pnpm-lock.yaml"
+  path_instructions:
+    - path: "**/*.ts"
+      instructions: |
+        When the same diff also changes a `CLAUDE.md`, an `AGENTS.md` or a
+        README, check what it now claims against this code. A sentence that
+        counts call sites, names "the one such site" or describes a signature is
+        a claim that goes stale silently, and one already had.
+
+        Errors are values here (`unthrown`), not exceptions. Suggestions that
+        assume otherwise are wrong rather than debatable:
+
+        - No `try`/`catch` around a `Result` pipeline. Every combinator catches
+          a thrown callback and converts it to a `Defect`; the `defect` arm of
+          the final `match` is the catch. A `try` in the diff is either a
+          boundary around a foreign throwing API — legitimate, and they carry a
+          reason — or a mistake.
+        - There is no `mapErr`. The error combinators are `mapErrCases`,
+          `flatMapErrCases`, `recoverErrCases` and `tapErrCases`, and they are
+          exhaustive by design: `P._` is a lint error outside a helper generic
+          in `E`.
+        - Every async surface returns `AsyncResult`, never a bare `Promise` —
+          the infallible ones included (`AsyncResult<T, never>`).
+        - `Ok(v).toAsync()` is `OkAsync(v)`; `Err(e).toAsync()` is
+          `ErrAsync(e)`. A `flatMap` returning the value it was handed is
+          `ensure`. A nullable lookup is `fromNullable`, not a ternary.
+        - `E` is never `unknown`, `any` or `Error`; a `Defect` never appears
+          in it.
+
+        Comments are sparse by convention: rationale lives in the spec file,
+        not beside the code. Do not ask for more comments, or for TSDoc on a
+        private symbol.
+
+        `type` not `interface`, `unknown` not `any`, and every relative import
+        carries `.js` — `moduleResolution: NodeNext`.