Assert the scan that must not happen, not the index that won

The per-computer grant listing test named the index it expected in the
plan. Two indexes can answer that predicate, the table is empty in the
test database, and their estimated costs are near-identical — so the
planner was free to pick the other one, and did. The test was red on
main for a choice that was never wrong.

It now asserts the property worth holding: the listing does not
degrade to a sequential scan. That stays true whichever index the
planner picks, and still fails when the indexes are gone.

The sibling assertions were read the same way and kept, because in
those two cases only one index can serve the predicate at all — the
others lead on a column the filter does not name. Each now says so in
a comment, so the next reader knows which kind of assertion they are
looking at.

Mutation-checked before landing: dropping both usable indexes turns
the test red, restoring them returns it to green.

Built by a Devin child through the openagents coder's delegate tool;
the mutation proof was run in review, after installing the worktree's
dependencies the child could not.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GoYpb8FEmdxVErsv7ABCYi

Co-Authored-By

Claude Fable 5 <noreply@anthropic.com>

Claude-Session

https://claude.ai/code/session_01GoYpb8FEmdxVErsv7ABCYi

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pushed

by user · WAL seq 351 · 2026-08-25T06:57:11.759938Z

Changed files

• modified test/openagents/machines/index_reach_test.exs

Diff

1 file changed, +11 -6

        Inference.revoke_active_for_machine(Ecto.UUID.generate())

      end)

    # The only index that can answer `machine_id = ?` on this table is the

    # `machine_id` index; the other indexes lead on `token_digest` or

    # `conversation_id`, which the predicate does not name.

    assert plan =~ "inference_grants_machine_id_index", plan

  end

  test "the per-computer grant listing is served by repository_machine_grants_machine_id_index" do

  test "the per-computer grant listing avoids a sequential scan on repository_machine_grants" do

    owner = owner()

    machine = computer(owner)

        Repositories.list_machine_grants(owner, machine.id)

      end)

    # The composite unique index leads on `repository_id`, which this filter

    # does not name, so it cannot serve here — which is why the single-column

    # index stopped being redundant the moment the listing landed.

    assert plan =~ "repository_machine_grants_machine_id_index", plan

    refute plan =~ "repository_machine_grants_repository_id_machine_id_index"

    # The planner may use the single-column `machine_id` index or the

    # composite unique index to satisfy the predicate, depending on the

    # table's shape and the join shape. The property that matters is that

    # the listing does not degrade to a sequential scan on the table.

    refute plan =~ ~r/Seq Scan\s+on\s+repository_machine_grants/, plan

  end

  test "the pairing sweep is served by machine_pairings_expires_at_index" do

        OpenAgents.Machines.expire_elapsed_pairings()

      end)

    # The sweep's predicate is `expires_at <= ?` plus a `status` filter; the

    # only index with `expires_at` is `machine_pairings_expires_at_index`.

    assert plan =~ "machine_pairings_expires_at_index", plan

  end