Session hidden from /resume when first user messages are all IDE metadata

Bug Description

Sessions become invisible in /resume and the past conversations dropdown when the first ~16KB of the JSONL session file contains only IDE metadata messages (<ide_selection>, <ide_opened_file>, empty messages) with no "real" user prompt.

Root Cause

The session discovery code (Xwz/Dwz in the bundled CLI) reads only the first 16KB (pT6=16384 bytes) of a session JSONL file to extract the firstPrompt. It skips messages matching:

• <ide_selection>...</ide_selection>
• <ide_opened_file>...</ide_opened_file>
• <local-command-stdout>
• Empty text content
• tool_result messages
• isMeta messages

If all user messages within that 16KB window are skipped, firstPrompt comes back empty. Then in jwz, the filter:

if (!Y.firstPrompt && !Y.customTitle) return null;

...silently drops the session from the listing entirely.

Reproduction

1. Open a VS Code session with Claude Code
2. Have many IDE selection/opened-file events before typing your first real message (e.g. selecting code, switching files ~25+ times)
3. Have a long conversation
4. Close the tab
5. Try /resume — the session does not appear

In my case, the first real user message was message #28, well past the 16KB read window. The session (21MB, containing extensive conversation) was completely hidden.

Workaround

Appending a customTitle record to the JSONL file makes the session visible again, since customTitle is read from the last 16KB of the file:

{"type": "system", "subtype": "custom_title", "customTitle": "My session title", "sessionId": "...", "timestamp": "..."}

Using /rename within a session also sets customTitle and prevents this issue.

Suggested Fix

Options:

1. Increase the read buffer or do a streaming scan for the first real prompt
2. Don't filter out sessions with no firstPrompt — show them with a fallback title (e.g., the date/time)
3. Write firstPrompt eagerly to a lightweight index when the first real user message arrives, rather than extracting it lazily from the raw JSONL

Option 2 seems safest — a session should never silently disappear from the listing.

Environment

• Claude Code version: 2.1.39
• Platform: macOS (Darwin 24.6.0, Apple Silicon)
• IDE: VS Code extension

🤖 Generated with Claude Code