SDC context missing in PageManager block tokens

Problem/Motivation

(This may be a pageManager bug. But as pageManager is well-hung and i could not find an issue that remotely smells like this in that queue, tentatively filing it here.)

Somehow my SDC block does not pick up a context.

Steps to reproduce

- Create a "group dashboard" SDC with a "groupId" prop of type string.
- Create a pageManager page with path "/group/{group}/dashboard", and a required context of type group.
- Create a variant.
- On that variant, add the "group dashboard" SDC as block.
- See the block configuration form, and a (token-enabled) text field for groupId.

Expected:
- I see "group" in the token browser.
- I can use [group:id] to populate groupId.

Experienced:
- I do NOT see "group" in the token browser.
- I can NOT use [group:id] to populate groupId ("[group:id]" => "", "foo([group:id])" => "foo()").

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes