M6.5: enroll cryptpad (recipe #3, stateful/no-DB) + generic per-recipe EXTRA_ENV

Adds a shared-harness EXTRA_ENV mechanism (recipe_meta.py dict or domain-callable),
applied in deploy_app at every deploy path — no per-recipe harness surgery (D5).
cryptpad uses it for its required distinct SANDBOX_DOMAIN. Tests assert data
survival via a marker file in the backed-up cryptpad_data volume (exec_in_app,
since cryptpad data isn't HTTP-served).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/cryptpad/test_backup.py

@@ -0,0 +1,32 @@
+"""cryptpad — backup/restore stage (D2): write a marker into the backed-up cryptpad_data volume,
+backup, mutate, restore, assert the restored state matches the pre-mutation (backed-up) state.
+
+The cryptpad `app` service is labelled `backupbot.backup=true`, so its volumes (incl. cryptpad_data)
+are backed up. Marker is checked via `exec_in_app` (data isn't HTTP-served)."""
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+MARKER = "/cryptpad/data/ci-marker.txt"
+
+
+def test_backup_mutate_restore(deployed, meta):
+    domain = deployed
+
+    # 1) establish original state in the backed-up volume, then back it up
+    lifecycle.exec_in_app(domain, ["sh", "-c", f"echo original > {MARKER}"])
+    assert lifecycle.exec_in_app(domain, ["cat", MARKER]).strip() == "original"
+    lifecycle.backup_app(domain)
+
+    # 2) mutate state (diverge from the backup)
+    lifecycle.exec_in_app(domain, ["sh", "-c", f"echo mutated > {MARKER}"])
+    assert lifecycle.exec_in_app(domain, ["cat", MARKER]).strip() == "mutated"
+
+    # 3) restore -> state returns to the backed-up "original"
+    lifecycle.restore_app(domain)
+    lifecycle.wait_healthy(domain, ok_codes=tuple(meta["HEALTH_OK"]), path=meta["HEALTH_PATH"],
+                           deploy_timeout=meta["DEPLOY_TIMEOUT"], http_timeout=meta["HTTP_TIMEOUT"])
+    assert lifecycle.exec_in_app(domain, ["cat", MARKER]).strip() == "original", \
+        "restore did not return the pre-mutation state"