feat(imap): add IMAP_READONLY_MODE feature flag to safeguard shared mailboxes

When enabled, IMAP processing will fetch and process attachments but
will NOT modify the mailbox state (no starring, labeling, deleting,
or flag changes). This allows preprod instances to safely share a
Gmail inbox with production without interfering with production
email processing.

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/utils/config_validator/settings_display.py

@@ -121,6 +121,7 @@ def get_settings_for_display(show_values: bool = False) -> dict[str, list[dict[s
             "imap2_ssl",
             "imap2_poll_interval_minutes",
             "imap2_delete_after_process",
+            "imap_readonly_mode",
         ],
         "Dropbox": ["dropbox_app_key", "dropbox_app_secret", "dropbox_folder", "dropbox_refresh_token"],
         "NextCloud": ["nextcloud_upload_url", "nextcloud_username", "nextcloud_password", "nextcloud_folder"],

app/utils/settings_service.py

@@ -1015,6 +1015,18 @@ SETTING_METADATA = {
         "required": False,
         "restart_required": False,
     },
+    "imap_readonly_mode": {
+        "category": "IMAP",
+        "description": (
+            "When enabled, IMAP processing fetches and processes attachments but does NOT modify "
+            "the mailbox (no starring, labeling, deleting, or flag changes). "
+            "Use for preprod instances sharing a mailbox with production."
+        ),
+        "type": "boolean",
+        "sensitive": False,
+        "required": False,
+        "restart_required": False,
+    },
     # Monitoring - Uptime Kuma
     "uptime_kuma_url": {
         "category": "Monitoring",