feat: add proper BuiltinTool support for both websearch providers

- Add web_search to BuiltinTool enum for consistency with brave_search
- Add WEB_SEARCH_BRAVE_TOOL constant following existing patterns
- Update agent logic to properly map both websearch tools:
  * web_search → BuiltinTool.web_search → WEB_SEARCH_TOOL → Tavily
  * web_search_brave → BuiltinTool.brave_search → WEB_SEARCH_BRAVE_TOOL → Brave
- Add tool encoding support for BuiltinTool.web_search in Llama model
- Replace hardcoded strings with constants for maintainability
- Fix tool conflicts that caused non-deterministic provider selection

This resolves the architectural issues where both websearch providers
exposed the same tool name, causing unpredictable behavior and making
it impossible for users to reliably choose their preferred provider.

Fixes #2606

llama_stack/models/llama/datatypes.py

@@ -24,6 +24,7 @@ class Role(Enum):
 
 
 class BuiltinTool(Enum):
+    web_search = "web_search"
     brave_search = "brave_search"
     wolfram_alpha = "wolfram_alpha"
     photogen = "photogen"

llama_stack/models/llama/llama3/tool_utils.py

@@ -220,7 +220,10 @@ class ToolUtils:
 
     @staticmethod
     def encode_tool_call(t: ToolCall, tool_prompt_format: ToolPromptFormat) -> str:
-        if t.tool_name == BuiltinTool.brave_search:
+        if t.tool_name == BuiltinTool.web_search:
+            q = t.arguments["query"]
+            return f'web_search.call(query="{q}")'
+        elif t.tool_name == BuiltinTool.brave_search:
             q = t.arguments["query"]
             return f'brave_search.call(query="{q}")'
         elif t.tool_name == BuiltinTool.wolfram_alpha:

llama_stack/providers/inline/agents/meta_reference/agent_instance.py

@@ -80,6 +80,7 @@ def make_random_string(length: int = 8):
 TOOLS_ATTACHMENT_KEY_REGEX = re.compile(r"__tools_attachment__=(\{.*?\})")
 MEMORY_QUERY_TOOL = "knowledge_search"
 WEB_SEARCH_TOOL = "web_search"
+WEB_SEARCH_BRAVE_TOOL = "web_search_brave"
 RAG_TOOL_GROUP = "builtin::rag"
 
 logger = get_logger(name=__name__, category="agents")
@@ -817,9 +818,12 @@ class ChatAgent(ShieldRunnerMixin):
             for tool_def in tools.data:
                 if toolgroup_name.startswith("builtin") and toolgroup_name != RAG_TOOL_GROUP:
                     identifier: str | BuiltinTool | None = tool_def.identifier
-                    if identifier == "web_search":
+                    # Map tool identifiers to BuiltinTool enum values
+                    if identifier == WEB_SEARCH_TOOL:
+                        identifier = BuiltinTool.web_search
+                    elif identifier == WEB_SEARCH_BRAVE_TOOL:
                         identifier = BuiltinTool.brave_search
-                    else:
+                    elif identifier in [e.value for e in BuiltinTool]:
                         identifier = BuiltinTool(identifier)
                 else:
                     # add if tool_name is unspecified or the tool_def identifier is the same as the tool_name
@@ -880,8 +884,10 @@ class ChatAgent(ShieldRunnerMixin):
                 f"Tool {tool_name} not found in provided tools, registered tools: {', '.join([str(x) for x in registered_tool_names])}"
             )
         if isinstance(tool_name, BuiltinTool):
-            if tool_name == BuiltinTool.brave_search:
+            if tool_name == BuiltinTool.web_search:
                 tool_name_str = WEB_SEARCH_TOOL
+            elif tool_name == BuiltinTool.brave_search:
+                tool_name_str = WEB_SEARCH_BRAVE_TOOL
             else:
                 tool_name_str = tool_name.value
         else: