Long-lived session shows as corrupted on resume despite valid events.jsonl

[KarnikJain]

(content withdrawn by author)

[KarnikJain]

Update: Session repaired and root cause narrowed

The repair worked. After aggressive trimming, the session resumes successfully.

What fixed it

1. Trimmed events.jsonl from 8,366 lines (18 MB) → 101 lines (183 KB) — kept only the last 5 user messages + their assistant turn events, removing all hook events and earlier segments
2. Cleaned the session.start event — removed extra fields (repaired, originalStartTime, repairNote) and updated copilotVersion from 1.0.9 to 1.0.10

Root cause analysis

The session accumulated 18 MB of events across 3 resume segments (204 premium requests, 34 user messages, 2,103 tool executions, 38 sub-agents). The CLI either:

• OOMs or times out parsing 18 MB of events on resume
• Has a size/line limit that isn't enforced at write time

The repaired 183 KB file resumes instantly and loads all 3 MCP servers + 45 skills successfully.

Recommendations

1. Auto-compact: The CLI should automatically compact/checkpoint events.jsonl when it exceeds a threshold (e.g., 5 MB or 2,000 events)
2. Better error messaging: Instead of "corrupted", say "Session too large to resume (18 MB). Run /compact first or start a new session."
3. Graceful degradation: On resume failure, offer to resume from the last checkpoint or trim to recent turns automatically

[KarnikJain]

Hit this again on a different session (5fecb21a-8cde-4fa1-ac96-934505967671) with v1.0.16. This time it was compounded with #2012 (U+2028 in user message). Filed #2490 with full diagnostics, error progression, and a working manual workaround.

Key new data points:

• 20MB / 10,667 events across 10 segments — even larger than the 18MB session in this issue
• Largest single event: 1.6MB — a hook.start event containing SharePoint binary file data via MCP. Individual event size caps would help.
• The two bugs mask each other: fixing the size issue reveals U+2028, fixing U+2028 reveals missing session.start after trimming. Users need to fix all three in the right order.

[jespinal]

Hello, there:

I stumbled upon this issue too a few minutes ago.

I gave Copilot the session summary title and a link to this Github issue, and it fixed the session file by, according to it, "replacing the raw bytes \xe2\x80\xa8 (U+2028 in UTF-8) with the ASCII bytes for \u2028 (the JSON escape sequence: \, u, 2, 0, 2, 8)". The fix worked.

I was writing in Spanish, and used plenty of accented + UTF8 characters.

GitHub Copilot CLI 1.0.17