perf(server): stop retaining unused OpenCode tool history - #9684

💭 This diff strips out turn snapshot tracking entirely -- removing the turns field, resolveTurnSnapshot, appendTurnItem, and its call site. It's purely a removal, so I should check whether OpenCodeTurnSnapshot becomes unused or if other code still references context.turns before assuming this violates any service pattern.

1. browse_code — In apps/server/src/provider/Layers/OpenCodeAdapter.ts, where is OpenCodeTurnSnapshot type declared and used? Also show all usages of context.turns, turns, resolveTurnSnapshot, appendTurnItem in the repo. Show surrounding code for lines ~330-360 and ~470-500 and ~2330-2350.

💭 The removal looks clean — the helpers and field are fully gone, this is just dead in-memory retention being removed, and I don't see any Effect service convention violations. Since there's nothing else changed, there are no findings, so I'll report "All clear" as both the title and summary.