refactor(core): ignore the recorded thinking level when resuming a session (#72)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/docs/content/omni-message.en.md

@@ -50,7 +50,7 @@ interface ToolDefinition {
 }
 ```
 
-session_meta holds **per-session invariants only** — the model, system prompt and Workspace are immutable for the Session's lifetime; on resume, the engine takes this Trace line as the runtime config. See [Sessions & Traces](/sessions-and-traces). The thinking level is a per-turn parameter (sent with each Task) and is not recorded here; legacy Traces may still carry a `thinking_level` field in their meta, which resume keeps honoring for back-compat.
+session_meta holds **per-session invariants only** — the model, system prompt and Workspace are immutable for the Session's lifetime; on resume, the engine takes this Trace line as the runtime config. See [Sessions & Traces](/sessions-and-traces). The thinking level is a per-turn parameter (sent with each Task) and is not recorded here; a `thinking_level` field still present in a legacy Trace's meta is ignored on resume — the resumed Session reads the Agent's current config instead.
 
 ## model_msg: complete payloads
 

packages/docs/content/omni-message.zh.md

@@ -50,7 +50,7 @@ interface ToolDefinition {
 }
 ```
 
-session_meta 只承载**会话级不变量**——模型、系统提示词、Workspace 在 Session 生命周期内不可变；恢复 Session 时引擎直接以 Trace 中的这条消息为运行时配置，见 [Session 与 Trace](/sessions-and-traces)。思考等级是逐轮参数（随每次 Task 下发），不记录在此；旧版 Trace 的 meta 里可能仍带 `thinking_level` 字段，恢复时按兼容逻辑继续生效。
+session_meta 只承载**会话级不变量**——模型、系统提示词、Workspace 在 Session 生命周期内不可变；恢复 Session 时引擎直接以 Trace 中的这条消息为运行时配置，见 [Session 与 Trace](/sessions-and-traces)。思考等级是逐轮参数（随每次 Task 下发），不记录在此；旧版 Trace 的 meta 里可能仍带 `thinking_level` 字段，恢复时会被忽略——恢复后的 Session 直接读取 Agent 当前配置。
 
 ## model_msg：完整消息