[Fix] Fast mode loses oversized integration results

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote or in the web UI.

What changed

• Intercept oversized Fast native-tool results before OpenCode can write them to its process-global spill directory, returning a bounded preview and opaque conversation-owned handle instead.
• Add a private spill store with per-conversation directories, restrictive permissions, byte and file quotas, expiry, and cleanup tied to Fast session invalidation and eviction.
• Add bounded spill_read and literal spill_grep tools that authorize handles through parent and child OpenCode session bindings without accepting filesystem paths.
• Add a dedicated spill_analysis subagent with only those spill tools while keeping generic filesystem and shell agents unavailable in Fast mode.
• Align Fast, advisor, and judge prompts with the new capability and cover ownership, expiry, quotas, UTF-8 boundaries, cleanup, and upstream spill prevention.

Why this change was made

OpenCode writes oversized custom-tool output to a process-global service-host directory and recommends filesystem exploration. Fast intentionally denies generic filesystem access, and its pooled servers make enabling that access unsafe across conversations. Roomote now owns the spill boundary and exposes only handle-based, conversation-scoped reads.

Impact

Fast conversations can inspect oversized integration and bridge results without triggering OpenCode's native spill writer or exposing service-host paths. Cross-conversation and expired handles are rejected, spill resources are bounded and evicted, and Brain-specific query compaction remains unchanged.

[roomote-community]

No code issues found. See task

_{Reviewed 0985cf6}