Free per-user homepages at <name>.<host> (wildcard subdomains)

- sites.AskHandler now approves <name>.AGENTBBS_HOST on-demand-TLS when <name>
  is a registered member (so only real users mint subdomain certs).
- Caddyfile: *.${DOMAIN} block serving users/<name>/public_html with on_demand
  TLS; unknown users 404. Needs a wildcard DNS record *.${DOMAIN} -> host.
- Test: TestAskUserSubdomain.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/sites/sites.go

@@ -48,6 +48,7 @@ type Manager struct {
 	st       store.Store
 	usersDir string // <data>/users
 	domDir   string // <data>/domains  (the symlink farm Caddy serves)
+	baseHost string // AGENTBBS_HOST, e.g. bbs.profullstack.com (for <name>.<host>)
 }
 
 // NewManager prepares the symlink farm under dataDir/domains.
@@ -60,6 +61,7 @@ func NewManager(st store.Store, dataDir string) (*Manager, error) {
 		st:       st,
 		usersDir: filepath.Join(dataDir, "users"),
 		domDir:   domDir,
+		baseHost: strings.ToLower(strings.TrimSpace(os.Getenv("AGENTBBS_HOST"))),
 	}, nil
 }
 
@@ -132,6 +134,20 @@ func (m *Manager) AskHandler() http.Handler {
 			http.Error(w, "bad domain", http.StatusBadRequest)
 			return
 		}
+		// Free user-homepage subdomain: <name>.<baseHost> for any registered
+		// member (e.g. alice.bbs.profullstack.com). Single label only.
+		if m.baseHost != "" && strings.HasSuffix(d, "."+m.baseHost) {
+			label := strings.TrimSuffix(d, "."+m.baseHost)
+			if label != "" && !strings.Contains(label, ".") {
+				if _, ok, err := m.st.UserByName(label); err != nil {
+					http.Error(w, "lookup error", http.StatusInternalServerError)
+					return
+				} else if ok {
+					w.WriteHeader(http.StatusOK)
+					return
+				}
+			}
+		}
 		if _, ok, err := m.st.DomainUser(d); err != nil {
 			http.Error(w, "lookup error", http.StatusInternalServerError)
 			return

internal/sites/sites_test.go

@@ -110,3 +110,39 @@ func TestManagerAddRemoveSyncAsk(t *testing.T) {
 		t.Error("expected domain unmapped in store")
 	}
 }
+
+func TestAskUserSubdomain(t *testing.T) {
+	t.Setenv("AGENTBBS_HOST", "bbs.profullstack.com")
+	dir := t.TempDir()
+	st, err := store.Open(filepath.Join(dir, "test.db"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer st.Close()
+	if _, err := st.EnsureUser("alice", "member", "SHA256:aaa"); err != nil {
+		t.Fatal(err)
+	}
+
+	m, err := NewManager(st, dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	h := m.AskHandler()
+
+	for _, c := range []struct {
+		domain string
+		code   int
+	}{
+		{"alice.bbs.profullstack.com", http.StatusOK},        // registered member → cert allowed
+		{"nobody.bbs.profullstack.com", http.StatusNotFound}, // no such user
+		{"a.b.bbs.profullstack.com", http.StatusNotFound},    // multi-label, not a user subdomain
+		{"bbs.profullstack.com", http.StatusNotFound},        // apex is not a user subdomain
+	} {
+		rec := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/check?domain="+c.domain, nil)
+		h.ServeHTTP(rec, req)
+		if rec.Code != c.code {
+			t.Errorf("ask %q = %d, want %d", c.domain, rec.Code, c.code)
+		}
+	}
+}