It sounds like you're using LLMs directly, instead of a coding agent. Agents are capable of testing their own code and using that to fix issues, which is what makes them so powerful.
Nice. The code I got running from gemini was much much cleaner, it did not work, but after the manual changes it did work. I will hive it a try with the next task: put text and generate primitives like rectangle, circle, polygon, etc…
Using Claude Code, I was able to successfully produce the Hello Triangle you asked for (note that I have never used CL before): https://github.com/philpax/hello-triangle-cl
For reference, here is the transcript of the entire interaction I had with CC (produced with simonw's excellent claude-code-transcripts): https://gisthost.github.io/?7924519b32addbf794c17f4dc7106bc2...
Edit: To better contextualise what it's doing, the detailed transcript page may be useful: https://gisthost.github.io/?7924519b32addbf794c17f4dc7106bc2...