diff --git a/AGENTS.md b/AGENTS.md
index 68673ad..18beb97 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -79,16 +79,18 @@ Use these terms as the default implementation contract for Video Workbench slide
 
 | User term | Meaning | Default carrier |
 | --- | --- | --- |
-| `子会话` / `session` | A user-visible separate Codex session for brief / orchestration work. | `codex_app.fork_thread` to create, `codex_app.send_message_to_thread` to continue, `codex_app.read_thread` to inspect. |
+| `子会话` / `session` | A user-visible separate Codex session for brief / orchestration work, started from a clean prompt rather than inherited orchestration history. | `codex_app.create_thread` to create, `codex_app.send_message_to_thread` to continue, `codex_app.read_thread` to inspect. |
 | `继续前子会话` | Continue the already recorded visible child session instead of creating a new one. | Send the next instruction to the recorded `threadId`. |
 | `Agent` / `SubAgent` | An internal one-shot worker owned by the child session; it should not appear as a separate user-visible Codex session. | `multi_agent_v1.spawn_agent(agent_type="worker")`; one worker handles exactly one slide. |
 | `无 review` | Review is disabled for the named scope. | Do not write `sNN-vN-review.md`; record only packet / return / ledger / task-log evidence. |
 
-If the default tools are not already exposed in a new session, use `tool_search` to expose `fork_thread`, `send_message_to_thread`, `read_thread`, and `spawn_agent` by name, then proceed with this contract.
+Do not use `codex_app.fork_thread` as the default carrier for production child sessions. Forking copies completed orchestration history from the parent thread and can contaminate the child session's context. Use `fork_thread` only when the user explicitly wants an inherited-context branch.
+
+If the default tools are not already exposed in a new session, use `tool_search` to expose `create_thread`, `send_message_to_thread`, `read_thread`, and `spawn_agent` by name, then proceed with this contract.
 
 Default preflight for a slide/session run:
 
-- confirm the target visible session id or create exactly one new visible session;
+- confirm the target visible session id or create exactly one new clean visible session with `create_thread`;
 - scan the target slide folder for the next unused `sNN-vN-*` version;
 - set `Overwrite allowed: no`;
 - record whether review is disabled or enabled;