Intellisense for ="" needs Ctrl + Space to wake up

inside a tag, if I have a = before "" or {}, eg: <div if:true="">, or <div if:true={}>, I need Ctrl + Space to wake up intellisense so I can have a autocomplete list for "" or {}. But for tag, I can have a dynamical autocomplete list whenever I type a character, the intellisense is automatically waked up by user typing a character.
Can you point out to me which lines/block of code in this repo that define this behavior? Our team is developing an extended html language server based on this repo, and we want a autocomplete list for {} but without asking user to use Ctrl + Space to trigger the intellisense.

Steps to Reproduce:
1, go to a html file
2, <div if:true=""
3, move your cursor away, then move it back inside ""
4, typing a character does not trigger a autocomplete list
5, using Ctrl + Space, you can see a autocomplete list.

Start by tracing the HTML language service's completion entry points for typing inside tags versus quoted or braced attribute values. Reproduce the steps in an HTML file, then identify where automatic completion triggering differs from Ctrl+Space. Done means typing inside "" or {} opens the appropriate completion list without an explicit trigger, with the existing tag behavior preserved.