Prompt loop reloads all messages from DB every iteration, breaking prompt cache byte-identity #31525

Describe the bug

filterCompactedEffect(sessionID) reloads ALL messages from the DB at the start of every prompt loop iteration. Between reloads, the DB can return rows with different object identity (new allocations), even though the message content hasn't changed. This breaks Anthropic's prompt cache, which relies on byte-identical prefixes to avoid reprocessing cached content.

Steps to reproduce

1. Start a session with many messages
2. Observe that each prompt loop iteration reloads all messages from the DB
3. Prompt cache hit rate drops because message object identity changes between iterations

Expected behavior

Messages should be cached across prompt loop iterations, with only new messages appended. A full reload should only happen after operations that modify the message list (subtasks, compaction, overflow).

System info

• OpenCode version: v1.15.3
• OS: Linux