Partial unique indices that overlap with an existing foreign key silently overwrite the existing foreign key connection

[pawarren]

Describe the bug
When I have a table that has a foreign key reference, and then I create a unique partial index on the same field, the

To Reproduce
I have a table called "works" and a table called "readthroughs". Each work can have many readthroughs. I want to ensure there is at most one in progress readthrough per work at a given time.

Create tables and insert the initial values:

CREATE TABLE IF NOT EXISTS public.works (
    work_id INTEGER,
    PRIMARY KEY (work_id)
);

CREATE TABLE IF NOT EXISTS public.readthroughs (
    readthrough_id INTEGER NOT NULL,
    work_id INTEGER NOT NULL,
    status TEXT NOT NULL,
    PRIMARY KEY (readthrough_id),
    FOREIGN KEY (work_id) REFERENCES public.works (work_id) ON DELETE CASCADE ON UPDATE CASCADE
);

INSERT INTO public.works (work_id) VALUES (1);

INSERT INTO public.readthroughs (readthrough_id, work_id, status)
VALUES (1, 1, 'in_progress');

COMMENT ON TABLE public.readthroughs IS E'@graphql({"totalCount": {"enabled": true}})';

When I look at the GraphiQL docs, I see:

I can run queries like this successfully:

{
  worksCollection(filter: {work_id: {eq: 1}}) {
    edges {
      node {
        work_id
        readthroughsCollection {
          totalCount
        }
      }
    }
  }
}

Now I add a unique partial index:

CREATE UNIQUE INDEX idx_unique_active_readthrough ON public.readthroughs (work_id)
WHERE status IN ('in_progress');

The GraphiQL docs now look like this:

And I can no longer use readthroughsCollection in my GraphQL queries.

This feels like it might be related to #541 and #502, i.e. pg_graphql generating readthroughCollection based on the foreign key but then overwriting it because of the index.

Expected behavior
Creating a unique partial index shouldn't screw with existing Collections