[FEATURE] suggest starting a new conversation when resuming a large/stale session

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Long-running sessions accumulate a large transcript file (JSONL under .claude/projects/...), especially when tool outputs are large (e.g. notebook executions, big file reads). Once that file grows large enough (observed around ~1GB), the UI becomes slow to load or fails to load the session at all when resuming it.

There's currently no proactive signal to the user that a session has grown too large before they hit this — they only find out when resume is already slow/broken.

Proposed Solution

When resuming a session (e.g. reopening after being idle for a long time, such as >10 hours):

Check the transcript file size for the session being resumed.
If it exceeds some threshold (configurable, e.g. a few hundred MB), show a suggestion in the UI that the user may want to start a fresh conversation instead of continuing this one.
Optionally, offer to generate a short "carry-over" prompt summarizing the key state (current task, relevant files/paths, decisions made) so the user can paste it into a new conversation with minimal loss of context — similar to what /compact already produces, but oriented at kicking off a brand-new session rather than compacting the current one.
Why this matters

Without this, users only discover a session is unmanageably large when the UI already fails to load it, at which point recovering context is harder. A size/idle-time-based nudge, paired with an auto-generated hand-off prompt, would let users switch sessions proactively before hitting that failure mode.

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

Interactive mode (TUI)

Use Case Example

_No response_

Additional Context

Environment

Observed in the VSCode extension.