refactor: rename teacher/student to optimizer/target, remove best skills, fix slow update

- Rename teacher -> optimizer, student -> target across all code, configs, docs, prompts
- CLI: --teacher_model -> --optimizer_model, --student_model -> --target_model
- Remove best_skill files, keep only initial skills
- Fix slow update gate (force write into skill)
- Fix SLOW_UPDATE marker stripping
- Remove deep_reflect and meta_reflect mechanisms
- Update .env.example with export prefix and azure_cli docs
- Add endpoint empty validation in azure_openai.py

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

configs/_base_/default.yaml

@@ -3,10 +3,10 @@
 
 model:
   backend: azure_openai
-  teacher: gpt-5.5
-  student: gpt-5.5
-  teacher_backend: openai_chat
-  student_backend: openai_chat
+  optimizer: gpt-5.5
+  target: gpt-5.5
+  optimizer_backend: openai_chat
+  target_backend: openai_chat
   reasoning_effort: medium
   rewrite_reasoning_effort: ""
   rewrite_max_completion_tokens: 64000
@@ -24,25 +24,25 @@ model:
   claude_code_exec_use_sdk: auto
   claude_code_exec_effort: medium
   claude_code_exec_max_thinking_tokens: 16384
-  codex_trace_to_teacher: true
+  codex_trace_to_optimizer: true
   azure_openai_endpoint: ""           # e.g. "https://your-resource.openai.azure.com/"
   azure_openai_api_version: "2024-12-01-preview"
   azure_openai_api_key: ""       # Fill locally if you do not export AZURE_OPENAI_API_KEY
   azure_openai_auth_mode: azure_cli
   azure_openai_ad_scope: "https://cognitiveservices.azure.com/.default"
   azure_openai_managed_identity_client_id: ""
-  teacher_azure_openai_endpoint: ""   # e.g. "https://your-resource.openai.azure.com/"
-  teacher_azure_openai_api_version: "2024-12-01-preview"
-  teacher_azure_openai_api_key: ""
-  teacher_azure_openai_auth_mode: azure_cli
-  teacher_azure_openai_ad_scope: "https://cognitiveservices.azure.com/.default"
-  teacher_azure_openai_managed_identity_client_id: ""
-  student_azure_openai_endpoint: ""   # e.g. "https://your-resource.openai.azure.com/"
-  student_azure_openai_api_version: "2024-12-01-preview"
-  student_azure_openai_api_key: ""
-  student_azure_openai_auth_mode: azure_cli
-  student_azure_openai_ad_scope: "https://cognitiveservices.azure.com/.default"
-  student_azure_openai_managed_identity_client_id: ""
+  optimizer_azure_openai_endpoint: ""   # e.g. "https://your-resource.openai.azure.com/"
+  optimizer_azure_openai_api_version: "2024-12-01-preview"
+  optimizer_azure_openai_api_key: ""
+  optimizer_azure_openai_auth_mode: azure_cli
+  optimizer_azure_openai_ad_scope: "https://cognitiveservices.azure.com/.default"
+  optimizer_azure_openai_managed_identity_client_id: ""
+  target_azure_openai_endpoint: ""   # e.g. "https://your-resource.openai.azure.com/"
+  target_azure_openai_api_version: "2024-12-01-preview"
+  target_azure_openai_api_key: ""
+  target_azure_openai_auth_mode: azure_cli
+  target_azure_openai_ad_scope: "https://cognitiveservices.azure.com/.default"
+  target_azure_openai_managed_identity_client_id: ""
 
 train:
   num_epochs: 4
@@ -57,9 +57,6 @@ gradient:
   analyst_workers: 16
   max_analyst_rounds: 3
   failure_only: false
-  use_deep_reflect: false
-  deep_reflect_failures: 4
-  deep_reflect_successes: 2
 
 optimizer:
   learning_rate: 4          # max edits per step (edit_budget)
@@ -67,8 +64,6 @@ optimizer:
   lr_scheduler: cosine      # constant / linear / cosine / autonomous
   lr_control_mode: fixed    # fixed / autonomous / none
   skill_update_mode: patch  # patch / rewrite_from_suggestions / full_rewrite_minibatch
-  use_meta_reflect: false
-  meta_learning_rate: 4     # max edits per epoch-level meta-reflect
   use_slow_update: true
   slow_update_samples: 20
   longitudinal_pair_policy: mixed  # mixed / changed / unchanged
@@ -89,5 +84,5 @@ env:
   split_dir: ""
   data_path: ""
   split_output_dir: ""
-  exec_timeout: 120      # per student model/code-agent call timeout in seconds
+  exec_timeout: 120      # per target model/code-agent call timeout in seconds
   out_root: ""

configs/alfworld/default.yaml

@@ -10,7 +10,6 @@ gradient:
 
 optimizer:
   learning_rate: 4
-  use_meta_reflect: false
 
 evaluation:
   sel_env_num: 0