feat: add DeepSeek extreme reasoning tier

docs/architecture.md

@@ -34,6 +34,13 @@ Every run records its model tier, strategy version, scheduler version, context
 policy, model/tool events, failures, and completion. This event stream is the
 foundation for replay, evaluation, and future experiment assignment.
 
+The light, medium, and high tiers use the internal K1412 model endpoint. The
+extreme tier uses DeepSeek V4 Pro with thinking enabled and maximum reasoning
+effort. Provider selection and credentials remain server-side. Thinking state
+is preserved across tool turns because DeepSeek requires the assistant's
+`reasoning_content` to be returned with the following tool results; Work never
+publishes that hidden state as its own user-facing reasoning.
+
 Work completion is evidence-gated. Requests for scripts, reports, code, or
 other concrete artifacts are not accepted as complete until a file mutation
 has succeeded and a later read, diff, or command has verified the latest

docs/operations.md

@@ -39,6 +39,11 @@ listed above. `https://api.k1412.top` remains the external API entrypoint, but
 Runtime must not send long-running Agent inference through the public reverse
 proxy.
 
+Set `DEEPSEEK_API_BASE_URL=https://api.deepseek.com` and place
+`DEEPSEEK_API_KEY` only in the protected deployment `.env`. The key is used
+only by Runtime for the extreme tier and must never be added to a browser,
+Compose file, image, repository, or log.
+
 The SSH override removes `/var/run/docker.sock` from Gateway and mounts the
 dedicated SSH directory read-only at `/root/.ssh`.