fix(session): 串行化 SQLite 会话写入

[Yumiue]

背景

运行中同一会话可能因为多个工具结果并发回灌、Gateway 管理写入口绕过 Runtime 会话锁等路径，同时竞争 SQLite 写事务，偶发触发 database is locked 并中断当前会话。

当前修改

• 在 SQLiteStore 内增加单 writer 写锁，并将 SQLite 连接池收敛为单连接，避免同一工作区数据库多 writer 抢锁。
• 保留工具执行并发，但将 tool result 的 transcript 持久化改为按原始 tool call 顺序串行回灌。
• 增加 Runtime 会话 mutation 边界，Gateway 的删除、重命名、模型切换、provider/model 同步优先走 Runtime 会话锁。
• 修复两个 Windows 环境敏感测试点：卷根 .git 误判、slash-rooted 路径解析。
• 补充 SQLite 并发写、工具结果顺序回灌、Gateway mutation 边界路由相关测试。

验证

• git diff --check
• go test ./...
• CGO_ENABLED=1 go test -race ./internal/session ./internal/runtime

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[fennoai]

I found 2 noteworthy issues in the changed code. One is a behavior regression in runtime event delivery for concurrent tool calls, and the other is a lock-granularity regression that can stall unrelated session writes during large asset saves.

[fennoai]

Medium: workerWG.Wait() now completes before any call to persistCompletedToolCallResult, which means EventToolResult, todo/facts updates, and remembered-state updates are all held back until every tool finishes. With calls like [slow, fast], the fast tool no longer surfaces its result when it completes; it is delayed behind the slow one. The PR description says only transcript persistence should become ordered, but this change also batches user-visible runtime events and state propagation for the entire tool phase.

[fennoai]

Medium: SaveAsset takes the global writeMu before the full asset write path, including io.Copy, Sync, Close, and the rename. Because r can be slow and assets can be large, one upload now blocks every other session write in the workspace for the entire file I/O duration. The original bug was SQLite writer contention, but this lock scope serializes unrelated non-SQLite work as well and can noticeably stall transcript/title/state updates under load.

[codecov]

Codecov Report

❌ Patch coverage is 79.78142% with 37 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/runtime/runtime.go	78.26%	11 Missing and 9 partials ⚠️
internal/session/sqlite_store.go	73.80%	7 Missing and 4 partials ⚠️
internal/runtime/toolexec.go	88.57%	3 Missing and 1 partial ⚠️
internal/cli/gateway_runtime_bridge.go	80.00%	1 Missing and 1 partial ⚠️

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