diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 0000000..4bd5b94
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,7 @@
+# Agent Instructions — First Draft CLI
+
+For release details, follow `RELEASING.md`.
+
+- After merging to `main`, report the exact merged SHA and ask whether to coordinate and promote the three-repository
+  candidate. If the user defers, call the SHA unpromoted. Never publish npm, deploy First Draft, or release the
+  plugin without explicit approval.
diff --git a/RELEASING.md b/RELEASING.md
index 8844e5f..e832663 100644
--- a/RELEASING.md
+++ b/RELEASING.md
@@ -3,6 +3,32 @@
 Publishing is a separate, explicit action after a release-preparation pull request has merged. npm registry bytes
 and package versions cannot be replaced, so do not create or push a release tag as a dry run.
 
+## Coordinated candidate eligibility
+
+`release/compatibility.json` declares this package's SemVer version, the First Draft API-contract range it accepts,
+and the exact Foundation Plan formats it accepts. It is source-only release metadata and is intentionally absent from
+the npm tarball. The normal test suite validates the manifest's shape, keeps its version equal to `package.json`, and
+binds its Foundation Plan format to the implemented CLI constant.
+
+The `script/release_compatibility_check` evaluator in `firstdraft/firstdraft` reads this declaration with the matching
+declarations from exact, clean checkouts of `firstdraft/firstdraft` and `firstdraft/skills`. It implements SemVer 2.0
+precedence. The service API contract is currently the stable `0.1.0` contract line even though this CLI package is a
+prerelease. Comparator arrays form one conjunction, while `foundation_plan_formats` lists alternatives. A
+prerelease satisfies a comparator set only when a comparator explicitly names a prerelease with the same major,
+minor, and patch numbers; Skills therefore names this CLI alpha explicitly. `firstdraft.release-compatibility/1` is
+intentionally closed. The evaluator in `firstdraft/firstdraft` rejects an unrecognized format and unknown keys, so
+adding a key requires a coordinated compatibility-format bump rather than silently changing version 1.
+
+A compatible result establishes candidate eligibility, not authorization or runtime proof. Exact Git SHAs identify
+the three-repository candidate. A merge to `main` is integration only: report the merged SHA and ask the user whether
+to coordinate the three repositories and promote that candidate. If promotion is declined, record the SHA as
+unpromoted.
+
+Promotion is manual and approval-gated. One operator serializes mutations: qualify the exact candidate on staging,
+obtain human approval, and only then promote the approved service revision to production or authorize the
+corresponding npm and plugin releases. Do not publish npm, deploy either environment, or release the plugin merely
+because the compatibility check passes.
+
 ## Repository and registry setup
 
 Before the first release, a repository administrator must:
@@ -78,10 +104,12 @@ Do not move or reuse that tag or version. The first organization-scoped candidat
 
 ## Prepare a release
 
-1. Update `package.json` and `package-lock.json` to the exact release version.
-2. Keep prereleases on the `next` dist-tag. Do not create `latest` until a stable release is intentionally approved.
-3. Update user-facing documentation and release notes for behavior changes.
-4. Run:
+1. Update `package.json`, `package-lock.json`, and `release/compatibility.json` to the exact release version.
+2. When that version changes, coordinate the matching explicit CLI comparator in `firstdraft/skills` before
+   qualification; an old alpha comparator intentionally makes the three-repository candidate ineligible.
+3. Keep prereleases on the `next` dist-tag. Do not create `latest` until a stable release is intentionally approved.
+4. Update user-facing documentation and release notes for behavior changes.
+5. Run:
 
    ```sh
    npm ci --ignore-scripts
@@ -89,7 +117,7 @@ Do not move or reuse that tag or version. The first organization-scoped candidat
    npm run check
    ```
 
-5. Merge the reviewed pull request only after local and hosted checks pass.
+6. Merge the reviewed pull request only after local and hosted checks pass.
 
 ## Publish
 
diff --git a/release/compatibility.json b/release/compatibility.json
new file mode 100644
index 0000000..48cca0b
--- /dev/null
+++ b/release/compatibility.json
@@ -0,0 +1,9 @@
+{
+  "format": "firstdraft.release-compatibility/1",
+  "component": "cli",
+  "version": "0.1.0-alpha.2",
+  "requires": {
+    "api_contract": [">= 0.1.0", "< 0.2.0"],
+    "foundation_plan_formats": ["firstdraft.foundation-plan.sketch/0.19"]
+  }
+}
diff --git a/src/commands/plan-init.js b/src/commands/plan-init.js
index 018c5c2..b4f01ae 100644
--- a/src/commands/plan-init.js
+++ b/src/commands/plan-init.js
@@ -1,6 +1,8 @@
 import { mkdirSync, writeFileSync } from "node:fs";
 import path from "node:path";
 
+import { FOUNDATION_PLAN_FORMAT } from "../compilation-artifact.js";
+
 /**
  * @typedef {object} FileSystem
  * @property {typeof mkdirSync} mkdirSync
@@ -53,7 +55,7 @@ export function initializePlan({
 /** @param {string} applicationKey @param {string} name */
 function emptyPlan(applicationKey, name) {
   return {
-    format: "firstdraft.foundation-plan.sketch/0.19",
+    format: FOUNDATION_PLAN_FORMAT,
     target: {
       id: "rails",
       profile: "rails-sketch/2026-08",
diff --git a/test/release-compatibility.test.js b/test/release-compatibility.test.js
new file mode 100644
index 0000000..e52bfdf
--- /dev/null
+++ b/test/release-compatibility.test.js
@@ -0,0 +1,70 @@
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import test from "node:test";
+
+import { FOUNDATION_PLAN_FORMAT } from "../src/compilation-artifact.js";
+
+const packageMetadata = JSON.parse(
+  await readFile(new URL("../package.json", import.meta.url), "utf8"),
+);
+const compatibility = JSON.parse(
+  await readFile(
+    new URL("../release/compatibility.json", import.meta.url),
+    "utf8",
+  ),
+);
+
+const semverPattern =
+  /^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[A-Za-z-][0-9A-Za-z-]*)(?:\.(?:0|[1-9]\d*|\d*[A-Za-z-][0-9A-Za-z-]*))*))?(?:\+([0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*))?$/;
+
+test("release compatibility declares the coordinated CLI contract", () => {
+  assertExactKeys(compatibility, [
+    "component",
+    "format",
+    "requires",
+    "version",
+  ]);
+  assert.equal(compatibility.format, "firstdraft.release-compatibility/1");
+  assert.equal(compatibility.component, "cli");
+  assert.equal(typeof compatibility.version, "string");
+  assert.match(compatibility.version, semverPattern);
+  assert.equal(compatibility.version, packageMetadata.version);
+
+  assertExactKeys(compatibility.requires, [
+    "api_contract",
+    "foundation_plan_formats",
+  ]);
+  assert.deepEqual(compatibility.requires.api_contract, [
+    ">= 0.1.0",
+    "< 0.2.0",
+  ]);
+  assert.deepEqual(compatibility.requires.foundation_plan_formats, [
+    FOUNDATION_PLAN_FORMAT,
+  ]);
+
+  for (const requirement of compatibility.requires.api_contract) {
+    assert.equal(typeof requirement, "string");
+    const match = /^(?:=|<|<=|>|>=)\s+(.+)$/.exec(requirement);
+
+    assert.ok(match, `invalid SemVer comparator: ${requirement}`);
+    const requiredVersion = match[1];
+
+    assert.ok(requiredVersion !== undefined);
+    assert.match(requiredVersion, semverPattern);
+  }
+
+  for (const format of compatibility.requires.foundation_plan_formats) {
+    assert.equal(typeof format, "string");
+  }
+});
+
+/**
+ * @param {unknown} value
+ * @param {string[]} expectedKeys
+ */
+function assertExactKeys(value, expectedKeys) {
+  assert.ok(
+    value !== null && typeof value === "object" && !Array.isArray(value),
+  );
+  assert.deepEqual(Object.keys(value).sort(), [...expectedKeys].sort());
+}