browserrot: Phase A-tier-1 site-side rotation engine (go-rod)

Deterministic, headless browser-driven password rotation:
discover change page via RFC 8615 / links, inject old+new over CDP
(no model in the loop), submit, and re-login to verify the new
password before commit. Implements rotate.Rotator so the mandatory
backup gate, verify-before-revoke ordering, and proof gate apply
unchanged; RevokeOld is a no-op (the site invalidates the old pw).

Proof-as-data per Site: the engine is LIVE-VM (real headless
Chromium vs a real local change-password form, via
lab-provision-browserrot.sh / TestIntegration_realBrowserRotation);
real-site selector tables stay UNPROVEN and nothing auto-registers
into production rotate yet. 14 packages, -race clean.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lab/lab-provision-browserrot.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+# LIVE-VM proof for the Phase A-tier-1 site-side rotation ENGINE (internal/browserrot),
+# inside the sandbox VM. FAKE credential only, against a throwaway in-process website —
+# nothing real is touched.
+#
+# What this proves is the deterministic browser-drive machinery that would run against a
+# real change-password page:
+#
+#   * discover the change page via RFC 8615 /.well-known/change-password (real redirect)
+#   * inject the OLD + a freshly-minted NEW password into the form over CDP, with NO
+#     language model in the loop
+#   * submit and read the site's SUCCESS marker
+#   * VERIFY the new password authenticates by re-logging-in (hard rule 2), and confirm
+#     the OLD password no longer works (the rotation is real, not a no-op)
+#
+# The engine is exercised by the CHROME_BIN-gated integration test
+# (TestIntegration_realBrowserRotation) driving a REAL headless Chromium. This is what
+# earns browserrot's LIVE-VM proof level for the ENGINE; a specific real-site selector
+# table stays UNPROVEN until it is run against that real site.
+#
+# It does NOT rotate any real account: only the user's own accounts, with explicit
+# per-credential authorization, may ever be driven against a real provider.
+set -euo pipefail
+export PATH=/usr/local/bin:$PATH
+
+# Locate a usable, NON-snap Chromium (snap chromium fights CDP + can't read /tmp).
+find_chrome() {
+  for c in \
+    "${CHROME_BIN:-}" \
+    "$HOME"/.cache/ms-playwright/chromium-*/chrome-linux64/chrome \
+    "$HOME"/.cache/ms-playwright/chromium-*/chrome-linux/chrome \
+    /usr/bin/google-chrome /usr/bin/chromium /opt/google/chrome/chrome ; do
+    [ -n "$c" ] && [ -x "$c" ] && { echo "$c"; return 0; }
+  done
+  return 1
+}
+
+CHROME_BIN="$(find_chrome || true)"
+if [ -z "${CHROME_BIN:-}" ]; then
+  echo "FAIL: no usable Chromium found. Install Chrome-for-Testing / google-chrome, or"
+  echo "      set CHROME_BIN to a chromium executable (a Playwright-managed one is ideal)."
+  echo "      hint: npx playwright install chromium"
+  exit 1
+fi
+echo "== using Chromium: $CHROME_BIN"
+"$CHROME_BIN" --version 2>/dev/null | sed 's/^/   /' || true
+
+# Run from the repo root (the dir containing go.mod).
+cd "$(git -C "$(dirname "$0")" rev-parse --show-toplevel 2>/dev/null || echo "$(dirname "$0")/..")"
+
+echo "== running the LIVE-VM browser-rotation proof =="
+CHROME_BIN="$CHROME_BIN" go test -run TestIntegration_realBrowserRotation -v ./internal/browserrot/
+
+echo
+echo "LIVE-VM BROWSER-ROTATION ENGINE PROOF PASSED"