web: Referrer-Policy same-origin; a password shown once emptied on pagehide

D-B3. Fetch Standard § 3.2 "append a request `Origin` header": under
Referrer-Policy no-referrer a request that is not GET/HEAD and not CORS -
a form POST, a navigation - gets Origin "null". originAllowed() refuses
"null" whenever Sec-Fetch-Site is absent, and Fetch Metadata § 3 sends
Sec-Fetch-Site only to a potentially trustworthy URL: every form,
sign-in included, failed in Safari before 16.4 and in any browser on a
plain-HTTP panel at a name. same-origin nulls Origin only for a request
not same origin with its URL and still sends no referrer to another
site. The comments of the origin check say so.

D-B13. noStore keeps the page out of HTTP caches (RFC 9111 § 5.2.2.5);
a history mechanism "might honor" it (§ 6), and Pragma in a response
"was never specified" (§ 5.4) - it goes. CopyField.Secret marks the
password of out-app-created data-secret, and panel.js empties such
fields on pagehide (HTML § 7.5.9, "unload a Document", step 10.2: fired
whether or not the document is kept for history traversal).

Measured 2026-10-15 in Chrome 152 (the desktop app's browser), a local
probe page with Cache-Control: no-store and a data-secret field: Back
reloads it (pageshow persisted=false, a new load), so this browser keeps
no-store pages out of its back/forward cache; the handler, fired on the
same page, empties the field. Firefox and Safari not measured.

Tests: the header value; the created page has the password data-secret
and the login not, no Pragma. Stand (2026-10-15, make e2e, exit 0): new
form_post_with_the_browsers_origin - Referrer-Policy: same-origin on a
page; a POST carrying the page's own Origin and no Sec-Fetch-Site, what
a browser sends now, passes; one carrying Origin: null, what it sent
before, is 403. (A first run failed where the e2e client and a view test
scraped the old input markup; both read data-secret now.) go vet and go
test ./... pass on the server (24 packages).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/e2e/health_served_test.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"math/big"
 	"net"
+	"net/http"
 	"os"
 	"path/filepath"
 	"strings"
@@ -137,3 +138,41 @@ func writeCertWithoutItsKey(certPath string, notAfter time.Time) error {
 	}
 	return os.WriteFile(certPath, pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der}), 0o644)
 }
+
+// testFormPostWithTheBrowsersOrigin: a browser on a plain-HTTP panel at a
+// name sends no Sec-Fetch-Site (Fetch Metadata § 3: only for a potentially
+// trustworthy URL), and its form POST - a navigation - carries Origin by the
+// page's Referrer-Policy (Fetch Standard § 3.2): its own origin under the
+// panel's same-origin, which passes; "null" under no-referrer, which the
+// panel sent until 2.5.2 and which the origin check refuses (assumptions
+// D-B3). The client here is not a browser: it sends what one would.
+func testFormPostWithTheBrowsersOrigin(t *testing.T, sc *scenario) {
+	resp, _, err := sc.panel.get("/server/health")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := resp.Header.Get("Referrer-Policy"); got != "same-origin" {
+		t.Fatalf("Referrer-Policy %q, want same-origin", got)
+	}
+	post := func(origin string) int {
+		t.Helper()
+		req, err := http.NewRequest(http.MethodPost, panelBaseURL+"/server/health/recheck", strings.NewReader(""))
+		if err != nil {
+			t.Fatal(err)
+		}
+		req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+		req.Header.Set("Origin", origin)
+		resp, err := sc.panel.http.Do(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp.Body.Close()
+		return resp.StatusCode
+	}
+	if code := post(panelBaseURL); code != http.StatusOK {
+		t.Fatalf("POST with the page's own Origin: status %d, want 200 after the redirect", code)
+	}
+	if code := post("null"); code != http.StatusForbidden {
+		t.Fatalf("POST with Origin: null: status %d, want 403", code)
+	}
+}