diff --git a/AGENTS.md b/AGENTS.md
index c94ee0f..ac9653c 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -4,6 +4,12 @@ Start with `docs/README.md` and follow its task routes. Detailed command semanti
 handled-error recovery in `docs/errors.md`, living release policy in `RELEASING.md`, and dated release observations
 in `docs/release-history.md`. When behavior changes, update its owning document in the same change.
 
+- Verify with `npm run check`, which takes about 30 seconds. A fresh checkout needs `npm ci --ignore-scripts` first.
+- Sibling repositories: `firstdraft/firstdraft` (private) owns the Service API and Plan format; `firstdraft/skills`
+  owns the Skill and plugin packaging.
+- Changes to the accepted API-contract range, accepted Plan formats, command names or flags, handled `error` values,
+  or exit statuses get an independent review through cross-review: `codex-review` from Claude Code, `$claude-review`
+  from Codex.
 - `firstdraft plan compile` defaults to local output in the current directory. GitHub publication requires
   `--github`; Codespaces is a fallback. Keep Skill callers and recovery instructions aligned with this boundary.
 - A coordinated release needs explicit approval once. Reuse an existing approval for its named scope; do not ask
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..43c994c
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1 @@
+@AGENTS.md
diff --git a/docs/README.md b/docs/README.md
index 6ccc64e..f7a2dcd 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -24,6 +24,7 @@ evidence for implemented behavior; if they contradict a document, surface the co
 - [release-history.md](release-history.md) preserves dated release observations. Recheck live tags, package versions,
   and dist-tags before relying on them operationally; publisher configuration is checked when it changes or fails.
 - The source repository's `AGENTS.md` routes agent work; it should stay compact rather than duplicate these documents.
+  Its `CLAUDE.md` only imports `AGENTS.md`, so Claude Code and Codex read the same instructions.
 
 ## Retrieval quality
 
diff --git a/test/documentation.test.js b/test/documentation.test.js
index 0ca902b..336ef04 100644
--- a/test/documentation.test.js
+++ b/test/documentation.test.js
@@ -40,6 +40,14 @@ test("public documentation avoids unavailable destinations", () => {
   }
 });
 
+test("Claude Code imports the shared agent instructions", () => {
+  assert.equal(
+    readFileSync(path.join(repository, "CLAUDE.md"), "utf8"),
+    "@AGENTS.md\n",
+    "CLAUDE.md must only import AGENTS.md so both harnesses read one source",
+  );
+});
+
 test("documentation entrypoints stay lean and route every public topic", () => {
   const entrypointBudgets = new Map([
     [path.join(repository, "AGENTS.md"), 2_048],