Missing unknown identifier code action in specific situation

Prerequisites

Please put an X between the brackets as you perform the following steps:

• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

Consider a file A.lean containing

namespace A.B

structure C.D where
  foo : Nat

end A.B

Now consider a file Basic.lean containing

namespace A.B.E

structure F.C where
  cd : C.D

end A.B.E

C.D is an unknown identifier, so I would like to do Ctrl+. and get an offer to import A.lean. This usually works, but in this specific situation it doesn't: no code action is offered. If the structure isn't called F.C but something else (like F.H), then the code action works.

Context

I ran into this while working on Grove.

Steps to Reproduce

1. https://github.com/TwoFX/import-autocomplete-test
2. Navigate to the C.D in line 4 of Basic.lean
3. Press Ctrl+.
4. Nothing happens

Expected behavior: Code action offers to import A.lean

Actual behavior: Nothing happens

Versions

4.20.1 and nightly-2025-06-09.

Impact

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Start by reproducing the issue in the linked import-autocomplete-test project, using A.lean and Basic.lean as shown and invoking Ctrl+. on C.D. Then trace Lean 4's unknown-identifier code action handling for this case; done means the action offers to import A.lean when C.D is selected.