[Bug] Claude makes assumptions without reading full files before providing suggestions

Bug Description
A message I sent to some other devs:
Has anyone else noticed issues since the release of Opus 4.6 where it'll make a ton of assumptions and read snippets of files, or lean on docs/claude.md instead of actually reading the whole file?
I thought the issue was Opus 4.6, so I switched back to 4.5, but it still has the same issue.
It's almost like it used to read a file before telling you things, and now it feels like it'll assume a lot based on whatever's in it's head.

Any suggestions for how to fix it? It's caused a lot of issues for me where it thinks there's a bug or insists on implementing something a specific way, but as soon as I push back it's like "let me go read the actual code and get back to you"
Or it'll tell you how to fix an issue and it makes sense so I tell it to go fix the issue, and then it's like "let me read through all the related files and make a plan" and I'm just like "what? How could you give a suggestion on anything without reading through the related files?"

I did some research and apparently other devs online are complaining that Opus 4.6 will read too many files and fill up the context quickly.
I also had issues with 4.6 with the context filling up quickly, and when I switched to 4.5, those issues did seem to go away, but it still didn't fix the issue of it making assumptions without actually reading the code.

Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.1.50
• Feedback ID: 9e284d84-b867-4efb-b524-1bf77c687976