Message timestamps lose sender time zone context after profile changes

Context

Slack stores every message timestamp as a UTC Unix epoch value and renders it in each viewer's current time zone setting. The sender's local time zone at the moment of sending is not persisted with the message, so historical messages cannot be displayed in the sender's original local time once either party updates their time zone preference.

Constraint

The users.info API returns only the current tz (IANA identifier) and tz_offset (seconds from UTC) for a user. There is no field capturing the time zone that was in effect when a specific message was sent, and the tz_offset value does not reflect future daylight-saving transitions.

Goal

Determine whether a workspace can reconstruct the sender's local clock time for any historical message without relying on external logs or manual annotation.

Can the sender's original time zone be inferred from any combination of message metadata, user profile history, or audit logs? Does the Enterprise Grid audit log or any SCIM provisioning record retain historical time zone assignments per user? Is there a supported API or export format that includes the effective tz value at message creation time?