feat(cli): invite-link parsing + join flow + keypair generation

End-to-end join: user runs `claudemesh join ic://join/<base64>` and
walks away with a signed member record + persistent keypair.

new modules:
- src/crypto/keypair.ts: libsodium ed25519 keypair generation. Format
  is crypto_sign_keypair raw bytes, hex-encoded (32-byte pub, 64-byte
  secret = seed || pub). Same format libsodium will need in Step 18
  for sign/verify.
- src/invite/parse.ts: ic://join/<base64url(JSON)> parser with Zod
  shape validation + expiry check. encodeInviteLink helper for tests.
- src/invite/enroll.ts: POST /join to broker, converts ws:// to http://
  transparently.

rewritten join command wires them together:
  1. parse invite → 2. generate keypair → 3. POST /join → 4. persist
  config → 5. print success.

state/config.ts: saveConfig now chmods the file to 0600 after write,
since it holds ed25519 secret keys. No-op on Windows.

signature verification (step 18) + invite-token one-time-use tracking
are deferred. For now the invite link is a plain bearer token; any
client with the link can join.

verified end-to-end via apps/cli/scripts/join-roundtrip.ts:
  build invite → run join subprocess → load new config → connect as
  new member → send A→B → receive push. Flow passes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/cli/src/commands/join.ts

@@ -1,30 +1,90 @@
 /**
- * `claudemesh join <invite-link>` — parse a mesh invite link and
- * join the mesh.
+ * `claudemesh join <invite-link>` — full join flow.
  *
- * STUB: real invite-link parsing + keypair generation + broker
- * enrollment lands in Step 17. For now this just validates the link
- * shape and tells the user what's coming.
+ * 1. Parse + validate the ic://join/... link
+ * 2. Generate a fresh ed25519 keypair (libsodium)
+ * 3. POST /join to the broker → get member_id
+ * 4. Persist the mesh + keypair to ~/.claudemesh/config.json (0600)
+ * 5. Print success
+ *
+ * Signature verification + invite-token one-time-use land in Step 18.
  */
 
-export function runJoin(args: string[]): void {
+import { parseInviteLink } from "../invite/parse";
+import { enrollWithBroker } from "../invite/enroll";
+import { generateKeypair } from "../crypto/keypair";
+import { loadConfig, saveConfig, getConfigPath } from "../state/config";
+import { hostname } from "node:os";
+
+export async function runJoin(args: string[]): Promise<void> {
   const link = args[0];
   if (!link) {
     console.error("Usage: claudemesh join <invite-link>");
     console.error("");
-    console.error("Example: claudemesh join ic://join/BASE64URL...");
+    console.error("Example: claudemesh join ic://join/eyJ2IjoxLC4uLn0");
     process.exit(1);
   }
-  if (!link.startsWith("ic://join/")) {
+
+  // 1. Parse.
+  let invite;
+  try {
+    invite = parseInviteLink(link);
+  } catch (e) {
     console.error(
-      `claudemesh: invalid invite link. Expected ic://join/... got "${link}"`,
+      `claudemesh: ${e instanceof Error ? e.message : String(e)}`,
     );
     process.exit(1);
   }
-  console.log("claudemesh: join not yet implemented (Step 17).");
-  console.log(`  Invite link parsed: ${link.slice(0, 40)}...`);
-  console.log(
-    "  Real flow will: verify sig, generate keypair, enroll member, persist to ~/.claudemesh/config.json",
+  const { payload } = invite;
+  console.log(`Joining mesh "${payload.mesh_slug}" (${payload.mesh_id})…`);
+
+  // 2. Generate keypair.
+  const keypair = await generateKeypair();
+
+  // 3. Enroll with broker.
+  const displayName = `${hostname()}-${process.pid}`;
+  let enroll;
+  try {
+    enroll = await enrollWithBroker({
+      brokerWsUrl: payload.broker_url,
+      meshId: payload.mesh_id,
+      peerPubkey: keypair.publicKey,
+      displayName,
+      role: payload.role,
+    });
+  } catch (e) {
+    console.error(
+      `claudemesh: broker enrollment failed: ${e instanceof Error ? e.message : String(e)}`,
+    );
+    process.exit(1);
+  }
+
+  // 4. Persist.
+  const config = loadConfig();
+  config.meshes = config.meshes.filter(
+    (m) => m.slug !== payload.mesh_slug,
   );
-  process.exit(0);
+  config.meshes.push({
+    meshId: payload.mesh_id,
+    memberId: enroll.memberId,
+    slug: payload.mesh_slug,
+    name: payload.mesh_slug,
+    pubkey: keypair.publicKey,
+    secretKey: keypair.secretKey,
+    brokerUrl: payload.broker_url,
+    joinedAt: new Date().toISOString(),
+  });
+  saveConfig(config);
+
+  // 5. Report.
+  console.log("");
+  console.log(
+    `✓ Joined "${payload.mesh_slug}" as ${displayName}${enroll.alreadyMember ? " (already a member — re-enrolled with same pubkey)" : ""}`,
+  );
+  console.log(`  member id: ${enroll.memberId}`);
+  console.log(`  pubkey:    ${keypair.publicKey.slice(0, 16)}…`);
+  console.log(`  broker:    ${payload.broker_url}`);
+  console.log(`  config:    ${getConfigPath()}`);
+  console.log("");
+  console.log("Restart Claude Code to pick up the new mesh.");
 }

apps/cli/src/crypto/keypair.ts

@@ -0,0 +1,36 @@
+/**
+ * Ed25519 keypair generation using libsodium.
+ *
+ * We use libsodium-wrappers even in Step 17 (pre-crypto) so the key
+ * format matches what Step 18's signing/encryption code will expect —
+ * no migration needed later.
+ */
+
+import sodium from "libsodium-wrappers";
+
+let ready = false;
+
+export async function ensureSodium(): Promise<typeof sodium> {
+  if (!ready) {
+    await sodium.ready;
+    ready = true;
+  }
+  return sodium;
+}
+
+export interface Ed25519Keypair {
+  /** 32-byte public key, hex-encoded. */
+  publicKey: string;
+  /** 64-byte secret key (seed || publicKey), hex-encoded. */
+  secretKey: string;
+}
+
+/** Generate a fresh ed25519 keypair. */
+export async function generateKeypair(): Promise<Ed25519Keypair> {
+  const s = await ensureSodium();
+  const kp = s.crypto_sign_keypair();
+  return {
+    publicKey: s.to_hex(kp.publicKey),
+    secretKey: s.to_hex(kp.privateKey),
+  };
+}

apps/cli/src/index.ts

@@ -48,7 +48,7 @@ async function main(): Promise<void> {
       runInstall();
       return;
     case "join":
-      runJoin(args);
+      await runJoin(args);
       return;
     case "list":
       runList();

apps/cli/src/invite/enroll.ts

@@ -0,0 +1,56 @@
+/**
+ * Broker /join HTTP enrollment.
+ *
+ * Takes a parsed invite + freshly generated keypair, POSTs to the
+ * broker, returns the member_id. Converts the broker's WSS URL to
+ * HTTPS for the /join call (same host, different protocol).
+ */
+
+export interface EnrollResult {
+  memberId: string;
+  alreadyMember: boolean;
+}
+
+function wsToHttp(wsUrl: string): string {
+  // wss://host/ws → https://host
+  // ws://host:port/ws → http://host:port
+  const u = new URL(wsUrl);
+  const httpScheme = u.protocol === "wss:" ? "https:" : "http:";
+  return `${httpScheme}//${u.host}`;
+}
+
+export async function enrollWithBroker(args: {
+  brokerWsUrl: string;
+  meshId: string;
+  peerPubkey: string;
+  displayName: string;
+  role: "admin" | "member";
+}): Promise<EnrollResult> {
+  const base = wsToHttp(args.brokerWsUrl);
+  const res = await fetch(`${base}/join`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({
+      mesh_id: args.meshId,
+      peer_pubkey: args.peerPubkey,
+      display_name: args.displayName,
+      role: args.role,
+    }),
+    signal: AbortSignal.timeout(10_000),
+  });
+  const body = (await res.json()) as {
+    ok?: boolean;
+    memberId?: string;
+    error?: string;
+    alreadyMember?: boolean;
+  };
+  if (!res.ok || !body.ok || !body.memberId) {
+    throw new Error(
+      `broker /join failed (${res.status}): ${body.error ?? "unknown"}`,
+    );
+  }
+  return {
+    memberId: body.memberId,
+    alreadyMember: body.alreadyMember ?? false,
+  };
+}

apps/cli/src/invite/parse.ts

@@ -0,0 +1,81 @@
+/**
+ * Invite-link parser for claudemesh `ic://join/<base64url(JSON)>` links.
+ *
+ * v0.1.0: parses + shape-validates + checks expiry. Signature
+ * verification and one-time-use invite-token tracking land in Step 18.
+ */
+
+import { z } from "zod";
+
+const invitePayloadSchema = z.object({
+  v: z.literal(1),
+  mesh_id: z.string().min(1),
+  mesh_slug: z.string().min(1),
+  broker_url: z.string().min(1),
+  expires_at: z.number().int().positive(),
+  mesh_root_key: z.string().min(1),
+  role: z.enum(["admin", "member"]),
+  signature: z.string().optional(), // ed25519 b64, validated in Step 18
+});
+
+export type InvitePayload = z.infer<typeof invitePayloadSchema>;
+
+export interface ParsedInvite {
+  payload: InvitePayload;
+  raw: string; // the original ic://join/... string
+}
+
+export function parseInviteLink(link: string): ParsedInvite {
+  if (!link.startsWith("ic://join/")) {
+    throw new Error(
+      `invalid invite link: expected prefix "ic://join/", got "${link.slice(0, 20)}…"`,
+    );
+  }
+  const encoded = link.slice("ic://join/".length);
+  if (!encoded) throw new Error("invite link has no payload");
+
+  let json: string;
+  try {
+    json = Buffer.from(encoded, "base64url").toString("utf-8");
+  } catch (e) {
+    throw new Error(
+      `invite link base64 decode failed: ${e instanceof Error ? e.message : e}`,
+    );
+  }
+
+  let obj: unknown;
+  try {
+    obj = JSON.parse(json);
+  } catch (e) {
+    throw new Error(
+      `invite link JSON parse failed: ${e instanceof Error ? e.message : e}`,
+    );
+  }
+
+  const parsed = invitePayloadSchema.safeParse(obj);
+  if (!parsed.success) {
+    throw new Error(
+      `invite link shape invalid: ${parsed.error.issues.map((i) => i.path.join(".") + ": " + i.message).join("; ")}`,
+    );
+  }
+
+  // Expiry check (unix seconds).
+  const nowSeconds = Math.floor(Date.now() / 1000);
+  if (parsed.data.expires_at < nowSeconds) {
+    throw new Error(
+      `invite expired: expires_at=${parsed.data.expires_at}, now=${nowSeconds}`,
+    );
+  }
+
+  return { payload: parsed.data, raw: link };
+}
+
+/**
+ * Encode a payload back to an `ic://join/...` link. Used for testing
+ * + for building links server-side once we add that flow.
+ */
+export function encodeInviteLink(payload: InvitePayload): string {
+  const json = JSON.stringify(payload);
+  const encoded = Buffer.from(json, "utf-8").toString("base64url");
+  return `ic://join/${encoded}`;
+}

apps/cli/src/state/config.ts

@@ -6,7 +6,13 @@
  * and on every join/leave.
  */
 
-import { readFileSync, writeFileSync, existsSync, mkdirSync } from "node:fs";
+import {
+  readFileSync,
+  writeFileSync,
+  existsSync,
+  mkdirSync,
+  chmodSync,
+} from "node:fs";
 import { homedir } from "node:os";
 import { join, dirname } from "node:path";
 import { z } from "zod";
@@ -51,6 +57,12 @@ export function loadConfig(): Config {
 export function saveConfig(config: Config): void {
   mkdirSync(dirname(CONFIG_PATH), { recursive: true });
   writeFileSync(CONFIG_PATH, JSON.stringify(config, null, 2) + "\n", "utf-8");
+  // Config holds ed25519 secret keys — restrict to owner read/write.
+  try {
+    chmodSync(CONFIG_PATH, 0o600);
+  } catch {
+    // Windows filesystems ignore chmod; that's fine.
+  }
 }
 
 export function getConfigPath(): string {