I built https://pribrain.com for this and I'm happy to share a free trial with anyone who's interested.
Effectively I just need to connect the MCP and set the preferences/rules in the agent (codex, claude, opencode, etc.) to: "Read instructions and rules from PriBrain before doing anything." Its pricing is targeted at startups/SMBs, not freelancers, though (but we could arrange something if you're interested).
You can achieve a similar result with a markdown file and change "PriBrain" to that file path, then you just need to manage the core rules/instructions in a single place.
A great thing I leverage with PriBrain is using different PriBrain accounts per client, so each agent only gets the core rules/information for each client.
To your specific questions:
1. Just what's necessary. If it is a long wall of text I'll finish with "Read PriBrain first." just to make sure that initial instruction won't be ignored, because sometimes Claude and Codex will ignore them.
2. Yes. Similar answer, the shared brain.
3. I use separate Spaces (think of them as directories or some other kind of taxonomy).
4. Happens many times, but it's not related to the shared brain and that's why I verify work.
5. I used gbrain before and it still caused a lot of hallucinations, so I built my own solution.
Effectively I just need to connect the MCP and set the preferences/rules in the agent (codex, claude, opencode, etc.) to: "Read instructions and rules from PriBrain before doing anything." Its pricing is targeted at startups/SMBs, not freelancers, though (but we could arrange something if you're interested).
You can achieve a similar result with a markdown file and change "PriBrain" to that file path, then you just need to manage the core rules/instructions in a single place.
A great thing I leverage with PriBrain is using different PriBrain accounts per client, so each agent only gets the core rules/information for each client.
To your specific questions:
1. Just what's necessary. If it is a long wall of text I'll finish with "Read PriBrain first." just to make sure that initial instruction won't be ignored, because sometimes Claude and Codex will ignore them.
2. Yes. Similar answer, the shared brain.
3. I use separate Spaces (think of them as directories or some other kind of taxonomy).
4. Happens many times, but it's not related to the shared brain and that's why I verify work.
5. I used gbrain before and it still caused a lot of hallucinations, so I built my own solution.
Hopefully that helps.