feat: per-role tool lists and system prompt overlays

Each role in model_registry.json can now carry two optional keys:
  system_append — injected into the system prompt at position 7 (after
                  memory, closest to the turn) for the active chat_role
  tools         — explicit tool allow-list; intersected with the user's
                  access-level filter so it can only restrict, never elevate

No changes needed for existing users — missing keys fall back to current
behavior. Add keys to a role to give it a specialty focus:

  "coder": {
    "primary": "claude_cli",
    "system_append": "You are in code-specialist mode...",
    "tools": ["web_search", "file_read", "shell_exec", "scratch_write"]
  }

Changes:
- model_registry.py: get_role_config() returns system_append + tools
- context_loader.py: role_append param appended as "--- Role Context ---"
- tools/__init__.py: get_tools_for_role/get_openai_tools_for_role accept
  optional tool_list and intersect with access-level filter
- orchestrator_engine.py: tool_list threaded through run/resume/checkpoint
- openai_orchestrator.py: tool_list threaded through run/resume/checkpoint;
  _build_client now calls get_openai_tools_for_role instead of returning
  unfiltered OPENAI_TOOL_SCHEMAS
- routers/orchestrator.py: pulls role_cfg for chat_role, passes both
  role_append and tool_list to context loader and engine

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/orchestrator_engine.py

@@ -65,6 +65,7 @@ class OrchestrateCheckpoint:
     respond_with_final: bool = True
     # Common
     user_role: str = "user"
+    tool_list: list[str] | None = None
     confirm_allow: frozenset = field(default_factory=frozenset)
     confirm_deny: frozenset = field(default_factory=frozenset)
     rounds_used: int = 0
@@ -88,6 +89,7 @@ async def run(
     model_name: str | None = None,
     response_role: str = "chat",
     user_role: str = "user",
+    tool_list: list[str] | None = None,
     confirm_allow: set[str] | None = None,
     confirm_deny: set[str] | None = None,
 ) -> OrchestratorResult:
@@ -101,6 +103,8 @@ async def run(
         respond_with_claude: If False, return Gemini's summary as the response (useful for
                              background/cron tasks where a polished reply isn't needed)
         gemini_api_key:     Per-user Gemini API key (falls back to GEMINI_API_KEY in .env)
+        tool_list:          Optional explicit tool allow-list from role config; intersected
+                            with user_role access-level filter (cannot elevate privileges)
         confirm_allow:      Tools to bypass the confirmation gate for this user
         confirm_deny:       Tools to always block for this user
 
@@ -124,7 +128,7 @@ async def run(
     contents: list[types.Content] = [
         types.Content(role="user", parts=[types.Part(text=task_with_context)])
     ]
-    tool_declarations, tool_callables = get_tools_for_role(user_role)
+    tool_declarations, tool_callables = get_tools_for_role(user_role, tool_list)
     tool_call_log: list[dict] = []
 
     gemini_summary, checkpoint = await _run_from_contents(
@@ -141,6 +145,7 @@ async def run(
         respond_with_claude=respond_with_claude,
         response_role=response_role,
         user_role=user_role,
+        tool_list=tool_list,
         confirm_allow=_confirm_allow,
         confirm_deny=_confirm_deny,
         starting_round=0,
@@ -171,7 +176,7 @@ async def resume(checkpoint: OrchestrateCheckpoint, confirmed: bool) -> Orchestr
     """Continue a job that was paused at a confirmation gate."""
     api_key = checkpoint.gemini_api_key or settings.gemini_api_key
     client = genai.Client(api_key=api_key)
-    tool_declarations, tool_callables = get_tools_for_role(checkpoint.user_role)
+    tool_declarations, tool_callables = get_tools_for_role(checkpoint.user_role, checkpoint.tool_list)
 
     effective_confirm = (CONFIRM_REQUIRED - set(checkpoint.confirm_allow)) | set(checkpoint.confirm_deny)
 
@@ -215,6 +220,7 @@ async def resume(checkpoint: OrchestrateCheckpoint, confirmed: bool) -> Orchestr
         respond_with_claude=checkpoint.respond_with_claude,
         response_role=checkpoint.response_role,
         user_role=checkpoint.user_role,
+        tool_list=checkpoint.tool_list,
         confirm_allow=checkpoint.confirm_allow,
         confirm_deny=checkpoint.confirm_deny,
         starting_round=checkpoint.rounds_used,
@@ -259,6 +265,7 @@ async def _run_from_contents(
     confirm_deny: frozenset,
     starting_round: int = 0,
     gemini_api_key: str | None = None,
+    tool_list: list[str] | None = None,
 ) -> tuple[str, OrchestrateCheckpoint | None]:
     """
     Run the ReAct loop from the current contents state.
@@ -364,6 +371,7 @@ async def _run_from_contents(
                 respond_with_claude=respond_with_claude,
                 response_role=response_role,
                 user_role=user_role,
+                tool_list=tool_list,
                 confirm_allow=confirm_allow,
                 confirm_deny=confirm_deny,
                 rounds_used=round_num + 2,