[asukaminato0721]

Summary

Fixes #5529

Completion now returns suggestions after as, in, and is at statement starts.

• I am a human, and I fully understand the code I am submitting.

Test Plan

add test

[meta-codesync]

This pull request has been imported. If you are a Meta employee, you can view this in D131272332. (Because this pull request was imported automatically, there will not be any future comments.)

[stroxler]

From an initial AI-assisted review, I think the overall structure here is good but we want a couple of fixes before we merge:

1. P2 — Preserve the typed-prefix completion-list contract. The new fallback supplies a nonempty list marked complete even though later typing enables deferred auto-import candidates absent from that list. Recover/reuse the normal prefix behavior, including isIncomplete when more typing requires a new request.
2. P2 — Cover nested inline-suite statement starts. The boundary condition accepts a newline or semicolon but misses a nested inline suite following a compound-statement colon. This is incomplete intended scope, not a newly introduced regression. Do not simply accept every colon: dictionaries, slices, and annotations also contain colons.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅