Allow unlimited (or higher) prompt history via commandHistoryMaxSize #5159

Describe the feature or problem you'd like to solve

Copilot CLI keeps only the last 50 prompts for Ctrl+R and Up/Down history by default. The commandHistoryMaxSize setting can raise this, but only to 1,000 (docs). Once the limit is reached, older prompts are permanently dropped. For heavy users, 1,000 prompts only covers a short period.

Proposed solution

Raise the maximum allowed value for commandHistoryMaxSize, or support an unlimited option (for example, 0), so users can retain their full prompt history.

Example prompts or workflows

• Set "commandHistoryMaxSize": 0 in ~/.copilot/config.json to keep all prompts indefinitely.
• Use Ctrl+R to find a prompt written weeks or months ago.
• Recall long, carefully crafted prompts without rewriting them.

Additional context

Requested by an enterprise customer. Other agentic CLIs (e.g. Claude Code) don't impose a comparable cap on prompt history.