`PasswordExecCommand` silently ignored for shared-server non-owners in SERVER_MODE despite `ENABLE_SERVER_PASS_EXEC_CMD=True` (regression in 9.15)

[krook1024]

pgAdmin version: 9.15
Regression from: 9.14
Deployment type: Container / SERVER_MODE with OAuth2

Description

Since 9.15 (PR #9830 / CVE-2026-7813), manager.passexec is unconditionally set to None for any non-owner of a shared server in connection_manager() and _restore_connections_from_session() in web/pgadmin/utils/driver/psycopg3/__init__.py:

if config.SERVER_MODE and server_data.shared and \
        server_data.user_id != current_user.id:
    manager.passexec = None  # PasswordExecCommand never runs

This silently breaks any container deployment that:

• Uses PGADMIN_SERVER_JSON_FILE / servers.json with "Shared": true to pre-configure servers for all OAuth users
• Sets "PasswordExecCommand" in the server definition to supply the shared DB user's password
• Has PGADMIN_CONFIG_ENABLE_SERVER_PASS_EXEC_CMD=True explicitly configured by the system administrator

The ENABLE_SERVER_PASS_EXEC_CMD config flag is now meaningless for shared servers — it is checked on startup/UI but the suppression in connection_manager fires regardless, with no log message or error surfaced to the user. The connection silently has no password.

Expected behaviour

When ENABLE_SERVER_PASS_EXEC_CMD=True is explicitly set by the system administrator, PasswordExecCommand should be honoured for shared-server non-owners. The system admin has consciously opted into this feature and is responsible for the command's content — the privilege-escalation concern (malicious owner targeting users) does not apply when the admin and the server owner are the same entity (i.e., the deployment administrator).

A reasonable middle ground: honour passexec_cmd from the SharedServer record (already added as a column in #9835) for non-owners, while still blocking inheritance from the owner's Server record. Currently _owner_only_fields prevents non-owners from ever setting passexec_cmd on their SharedServer via the API, and create_shared_server() seeds it as None, making the new column unreachable.

Steps to reproduce

1. Deploy pgAdmin container with:

   PGADMIN_CONFIG_SERVER_MODE=True
   PGADMIN_CONFIG_ENABLE_SERVER_PASS_EXEC_CMD=True
   PGADMIN_SERVER_JSON_FILE=/path/to/servers.json
   

2. servers.json contains a server entry with "Shared": true and "PasswordExecCommand": "<cmd>"
3. Log in as any non-admin OAuth user
4. Attempt to connect to the shared server

Result: The exec command is never run; the connection has no password and fails (or prompts interactively).
Expected: The exec command runs and supplies the password, as it did in 9.14.

Relevant source locations

• web/pgadmin/utils/driver/psycopg3/__init__.py — connection_manager() and _restore_connections_from_session(): unconditional manager.passexec = None for non-owners
• web/pgadmin/browser/server_groups/servers/__init__.py — _set_valid_attr_value(): _owner_only_fields blocks non-owners from setting passexec_cmd on their SharedServer
• web/pgadmin/browser/server_groups/servers/__init__.py — create_shared_server(): seeds passexec_cmd=None with no path to set it legitimately