claude-code: the sealed hand-over, the credentials write with the lineage rule, the identity read (hq to-be 40 WP2, in progress)

The parts of the agent module that hold whichever way the console is registered: X25519 +
HKDF + AES-GCM from Node's own library so the bundle carries no dependency; the predecessor's
lineage rule (rotation only if newer, a re-issue adopted, a switch regardless) with its
incidents as tests; an atomic 0600 write that strips any refresh token and keeps keys it does not
know; the account read from the agent's own state file. Manifest and renderer follow.

modules/claude-code/test/seal.test.ts

@@ -0,0 +1,31 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { generateKeyPair, open, seal } from "../dist/seal.js";
+
+test("a box opens with its recipient's key and yields the value", () => {
+  const k = generateKeyPair();
+  assert.equal(open(seal("at-secret", k.publicKey), k.privateKey), "at-secret");
+});
+
+test("a box sealed for one node does not open with another node's key", () => {
+  const a = generateKeyPair();
+  const b = generateKeyPair();
+  assert.throws(() => open(seal("at-secret", a.publicKey), b.privateKey));
+});
+
+test("a tampered box is refused, not opened to garbage", () => {
+  const k = generateKeyPair();
+  const box = seal("at-secret", k.publicKey);
+  const ct = Buffer.from(box.ct, "base64");
+  ct[0] ^= 0xff;
+  assert.throws(() => open({ ...box, ct: ct.toString("base64") }, k.privateKey));
+});
+
+test("two boxes of one value share nothing a reader could compare", () => {
+  const k = generateKeyPair();
+  const x = seal("at-secret", k.publicKey);
+  const y = seal("at-secret", k.publicKey);
+  assert.notEqual(x.ct, y.ct);
+  assert.notEqual(x.eph, y.eph);
+  assert.ok(!JSON.stringify(x).includes("at-secret"));
+});