[BUG] Exit hint prints `claude --resume "<title>"` for sessions the resume list hides (first user message is a slash command)

What happened

On exit, Claude Code printed:

Resume this session with:
  claude --resume "product - new"

Running that exact command does not resume. It opens the session picker with product - new pre-filled in the search box and no match. The same session is also missing from claude -r's list entirely. Resuming it by UUID works fine.

So the exit hint emits a command that can never succeed for this class of session.

Root cause (bisected)

The session list that backs both claude -r and title-based --resume excludes sessions whose first user message is a slash-command invocation. The exit hint, however, is generated from the custom title without checking that the title is resolvable.

The session in question was started with /loop (args /ap), so its first type:"user" record is:

{"role":"user","content":"<command-message>loop</command-message>\n<command-name>/loop</command-name>\n<command-args>/ap</command-args>"}

A/B that isolates it

Copied the same 65 MB transcript twice into a throwaway project directory, rewriting only sessionId and cwd so both are valid for that project:

| fixture | first user message | appears in claude -r |
|---|---|---|
| unmodified copy | <command-name>/loop</command-name> | no |
| identical copy, only that one record's content replaced with plain text | plain text | yes — product - new · 65.5MB |

Controls that rule out size / record count (both synthetic, plain-text first message, both listed fine):

| fixture | size | records | appears |
|---|---|---|---|
| few huge records | 76.3 MB | 81 | yes |
| many small records | 11.4 MB | 25,001 | yes |

An unrelated control also confirms title resume itself works: a fixture with custom-title.json = ZZZ-custom-name and a plain first message resumes correctly via claude --resume "ZZZ-custom-name", while claude --resume "<its auto-generated title>" returns No sessions match.

Repro

1. Start a session whose first user message is a slash command (e.g. claude then /loop <something> as the very first prompt).
2. Give it a custom title (Ctrl+R in the resume picker, or rename in-session).
3. Exit — note the printed claude --resume "<title>" hint.
4. Run that exact command → picker opens with the title pre-filled and no match. The session is also absent from claude -r.
5. claude --resume <uuid> works.

Expected

Either:

• the session list should not exclude sessions whose first message is a slash command (they are ordinary user-started sessions), or
• the exit hint should print claude --resume <uuid> when the title is not resolvable.

The current combination is the worst case: the product tells you a command and the same product then cannot act on it.

Environment

• Claude Code 2.1.277 (native install), macOS 15.6 / Darwin 25.6.0
• Session was created by 2.1.273; transcript 23,389 records, 68 MB
• The custom-title.json sidecar existed and contained the exact string that was printed