Session disappears from /resume picker while transcript file still exists on disk

Environment

• Claude Code on macOS 25.5.0 (Darwin)
• Shell: zsh
• Session ID affected: 4282779e-bc10-4105-9c20-861f5de4f606
• Project cwd: /Users/klaus
• Date observed: 2026-05-22

Description

A long-running session (~13h, 1747 transcript lines, 3.7MB jsonl) became invisible in the /resume picker between 04:28 and 04:33 UTC even though the on-disk transcript at ~/.claude/projects/-Users-klaus/<sid>.jsonl was intact and the last assistant message wrote successfully at 04:28:22.

The session has zero session-start / session-resume events in its transcript, despite many turns. Sibling sessions in the same project dir were also missing from listings — mcp__ccd_session_mgmt__list_sessions returned "No other sessions found" while ls ~/.claude/projects/-Users-klaus/ showed 6 jsonl files modified that day.

Reproduce

Unclear — possibly correlates with sessions that never logged a session-start event. Common factor in this case: heavy MCP/tool usage (~100 pr-link events, multi-agent dispatch over a long-running session).

Suggested investigation: check whether the resume index is built from session-start event records rather than from scanning transcript files on disk. If so, any session whose session-start event was never persisted will be invisible to /resume even though its transcript is complete.

Expected

Any session with a transcript file in ~/.claude/projects/<project>/<sid>.jsonl should appear in /resume and in list_sessions results.

Actual

Session was undiscoverable through the normal UI. Only claude --resume <sid> worked, and only because the user already knew the session ID (recovered by inspecting ~/.claude/projects/ manually).

Impact

User loses access to in-progress work mid-task, may start a fresh session, fragmenting context. Without a way to discover the lost session ID from the UI, the only recovery path is filesystem archaeology.