Just as a self follow-up here (I hate to do it!), after chatting to Gemini some more more about document creation alternatives, it does seem that Gemini CLI is by far the best way to go, since it's working in similar fashion to Claude Code and making targeted edits (string replacements) to files, rather than regenerating from scratch (unless it has misinterpreted something you said as a request to do that, which would be obvious when it showed you the suggested diff).

Another alternative (not recommended due to potential for "drift") is to use Gemini's Canvas capability where it is working on a document rather than a specification being spread out over Chat, but this document is fully regenerated for every update (unlike Claude's artifacts), so there is potential for it to summarize or drop sections of the document ("drift") rather than just making requested changes. Canvas also doesn't have Artifact's versioning to allow you to go back to undo unwanted drifts/changes.

Yeah, the online Gemini app is not good for long lived conversations that build up a body of decisions. The context window gets too large and things drop.

What I’ve learned is that once you reach that point you’ve got to break that problem down into smaller pieces that the AI can work productively with.

If you’re about to start with Gemini-cli I recommend you look up https://github.com/github/spec-kit. It’s a project out of Microsoft/Github that encodes a rigorous spec-then-implement multi pass workflow. It gets the AI to produce specs, double check the specs for holes and ambiguity, plan out implementation, translate that into small tasks, then check them off as it goes. I don’t use spec-kit all the time, but it taught me that what explicit multi pass prompting can do when the context is held in files on disk, often markdown that I can go in and change as needed. I think it ask basically comes down to enforcing enough structure in the form of codified processes, self checks and/or tests for your code.

Pro tip, tell spec-kit to do TDD in your constitution and the tests will keep it on the rails as you progress. I suspect “vibe coding” can get a bad rap due to lack of testing. With AI coding I think test coverage gets more important.