Concurrent opencode processes on one database fail prompts with "Failed to execute statement" (SQLITE_BUSY)

Description

Running several opencode processes against the same shared data directory makes them contend for the single SQLite write lock. Statements that wait longer than busy_timeout (5s) fail with database is locked and the error propagates as "Failed to execute statement" / "Unexpected server error", killing the whole prompt even though the statement itself is fine and would succeed on retry.

Observed on a busy VM with ~10 concurrent sessions sharing one opencode.db: 43 lock failures in one day, at Session.updateMessage, createUserMessage, and cleanup paths.

Steps to reproduce

1. Start multiple long-running opencode sessions writing to the same opencode.db (WAL mode)
2. Prompt them concurrently under enough IO/CPU load that some writes exceed 5s
3. Watch server log for SqlError/LockTimeoutError: database is locked and failed prompts

OpenCode version

1.18.29