Spike: Changing LMS GUID breaks existing annotations

[mattdricker]

This isn't so much a bug, but a statement of problem that sometimes occurs, which me may be able to find a better method of coping with.

Hypothesis LMS app uses the LTI parameter tool_consumer_instance_guid to uniquely identify the LMS instance. Occasionally an LMS instance will change the value of this parameter internally, breaking that's school's existing Hypothesis assignments and rendering all previous annotations made under the old GUID no longer visible.

There are a few circumstances where I've seen this occur:

• Sometimes an LMS has a blank tool_consumer_instance_guid; IMS considers this parameter "recommended" and not every LMS instance has this parameter populated. If Hypothesis finds a blank tool_consumer_instance_guid, it will define its own unique GUID to use for that LMS instance. If later the LMS populates tool_consumer_instance_guid (perhaps as part of a system upgrade), Hypothesis will begin using the actual value in tool_consumer_instance_guid and no longer identify annotations made under the previous GUID as connected to that LMS instance.
• A school will upgrade their LMS and the existing value of tool_consumer_instance_guid is replaced with a new value.

There may be other scenarios where the tool_consumer_instance_guid will change.

Ideally, Hypothesis would be able to weather a change of tool_consumer_instance_guid without losing that LMS's connection to previous annotations.