bug(conversations): Codex no-index fallback loses 0.157 prompts (reads only event_msg:user_message) #1363

Found by reviews A and B of #1354 (Codex 0.157.1 acceptance).

Actual

src/main/conversations/sources/codex.ts:104 (readRolloutHead) takes prompt text only from event_msg:{type:"user_message"}. Codex 0.157 writes none: the prompt is a role-user response_item plus event_msg:item_completed (UserMessage). When state_N.sqlite is missing or fails schema validation (scanEverything(), codex.ts:204-208), or a rollout is not in the index, the row gets userTexts: []. It is then classified empty (catalog/classify.ts:32) and hidden from the default listing (catalog/listing.ts:19,43), or loses its label and user activity.

Evidence

• A census of 233 local 0.157.x rollouts: all have a role-user response item, and none has a legacy user event.
• Today every sampled file is indexed, so this bites only on the degraded path.
• A 0.157.1-shaped test expected ['Check this file'] and got []. The fallback system test checks only that rows exist.

Fix direction

Also read role-user response_item text (skipping Codex's injected context, as the index does), and pin it with a recorded 0.157 slice.