fix(browse): CLI always sends explicit pair scopes via shared DEFAULT_PAIR_SCOPES

The effective pairing default lived in two places: the CLI omitted scopes
unless --restrict was passed, and the server filled in its own literal.
handlePairAgent now always sends an explicit scopes list and both sides
reference one exported constant, DEFAULT_PAIR_SCOPES, so the default cannot
silently drift again (pinned by a server-auth source tripwire).

Three input traps closed in the same surface:
- Bare --restrict (or --restrict swallowing the next flag) parsed as "no
  restriction" and silently granted FULL access, the opposite of the user's
  intent. validatePairAgentFlags rejects it pre-server, before any consent
  gate, so an arg error never boots a daemon.
- A scopes list could smuggle the control scope past the explicit flag:
  --restrict "read,control" minted a control-scoped session with no
  --control. /pair now 400s on control in a scopes list without the control
  flag, and the CLI points the user at --control.
- Option typos validated only at exchange time: createSetupKey stored any
  scope string and any rateLimit, so /pair returned 200 with a poisoned
  setup key whose failure surfaced to the REMOTE agent at /connect as a
  misleading "Invalid request body". Shared validation now runs in both
  creators and throws typed InvalidScopeError; /pair and /token 400 with the
  message, naming the bad scope or negative rateLimit. Also
  `opts.rateLimit || 10` became `?? 10` so the documented "0 = unlimited"
  survives the /pair path.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

browse/test/pair-agent-e2e.test.ts

@@ -194,6 +194,76 @@ describe('pair-agent flow end-to-end (HTTP only, no ngrok)', () => {
     expect(Array.isArray(scopes)).toBe(true);
   });
 
+  // ─── Pair scope contract: defaults, explicit lists, typo naming ───────
+
+  test('default /connect scopes are exactly read,write,admin,meta', async () => {
+    const pairResp = await fetch(`${daemon.baseUrl}/pair`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${daemon.token}` },
+      body: JSON.stringify({ clientId: 'default-scopes' }),
+    });
+    const { setup_key, scopes: pairScopes } = await pairResp.json() as any;
+    expect(pairScopes).toEqual(['read', 'write', 'admin', 'meta']);
+    const connectResp = await fetch(`${daemon.baseUrl}/connect`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ setup_key }),
+    });
+    const { scopes } = await connectResp.json() as any;
+    expect(scopes).toEqual(['read', 'write', 'admin', 'meta']);
+  });
+
+  test('explicit scopes are honored end-to-end (the --restrict wire contract)', async () => {
+    const pairResp = await fetch(`${daemon.baseUrl}/pair`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${daemon.token}` },
+      body: JSON.stringify({ clientId: 'restricted-scopes', scopes: ['read'] }),
+    });
+    const { setup_key } = await pairResp.json() as any;
+    const connectResp = await fetch(`${daemon.baseUrl}/connect`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ setup_key }),
+    });
+    const { scopes } = await connectResp.json() as any;
+    expect(scopes).toEqual(['read']);
+  });
+
+  test('POST /pair with a scope typo fails fast, naming the scope', async () => {
+    // Regression: pre-fix this returned 200 with a poisoned setup key whose
+    // failure surfaced at /connect as a misleading "Invalid request body".
+    const resp = await fetch(`${daemon.baseUrl}/pair`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${daemon.token}` },
+      body: JSON.stringify({ clientId: 'typo-agent', scopes: ['raed'] }),
+    });
+    expect(resp.status).toBe(400);
+    const body = await resp.json() as any;
+    expect(body.error).toContain('Invalid scope: raed');
+  });
+
+  test('POST /token with a scope typo names the scope too', async () => {
+    const resp = await fetch(`${daemon.baseUrl}/token`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${daemon.token}` },
+      body: JSON.stringify({ clientId: 'typo-token', scopes: ['wirte'] }),
+    });
+    expect(resp.status).toBe(400);
+    const body = await resp.json() as any;
+    expect(body.error).toContain('Invalid scope: wirte');
+  });
+
+  test('control cannot ride in through a /pair scopes list without the control flag', async () => {
+    const resp = await fetch(`${daemon.baseUrl}/pair`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${daemon.token}` },
+      body: JSON.stringify({ clientId: 'sneaky', scopes: ['read', 'control'] }),
+    });
+    expect(resp.status).toBe(400);
+    const body = await resp.json() as any;
+    expect(body.error).toContain('control');
+  });
+
   // ─── Revocation e2e: revoke-all + the /agents verification surface ────
 
   test('DELETE /token revokes session AND setup keys; agent leaves /agents; token 401s; re-connect fails', async () => {