copilot --resume or /resume should prefer the copilot sessions spawned by the parent process / tree

### Describe the feature or problem you'd like to solve

When copilot crashes and doesn't emit a sessionId, copilot --resume lists all sessions for that folder, but if there are others running, the right session might not be obvious.

### Proposed solution

If you record the process (tree?) that created the session and prioritize those in the session list, it will make resuming failed sessions easier.

### Example prompts or workflows

_No response_

### Additional context

_No response_

Start by tracing the --resume and /resume entry points, then follow session creation and the code that builds the session list. Determine how the process or parent relationship can be recorded and used for ordering; done means sessions spawned by the relevant parent process tree are prioritized when resuming.

Written by the indexing model from the issue text.