Allow disabling the built-in default personality/tone

Feature request

Please provide an option to disable Codex's built-in default personality/tone and use a neutral/none setting instead.

The current base instructions include a default tone such as concise, direct, and friendly. That is reasonable as a general default, but some users already define their preferred personality and communication style in AGENTS.md.

In that setup, a built-in personality becomes another instruction that the user's own style rules have to counteract or work around. This can make custom personas less predictable and can cause unnecessary style conflicts.

Requested behavior

Please allow one of the following:

• a neutral / none personality mode that removes built-in personality/tone directives, or
• a config option that disables only the default personality/tone layer.

Ideally, users who opt out would still receive all normal Codex system instructions related to coding behavior, tools, safety, task completion, etc. Only the conversational personality/tone defaults should be disabled.

This would make AGENTS.md the clean source of truth for users who intentionally manage personality there, without requiring them to fight an additional built-in style.

Start by locating where Codex assembles its base instructions and where configuration or personality modes are defined. Trace how AGENTS.md guidance is combined with the built-in personality, then define and test an opt-out path that preserves coding, tool, safety, and task-completion instructions while removing only the default tone directives.