[feature] adds web_search and fetch_url tool calls

docs/api/streaming-chat.md

@@ -37,8 +37,9 @@ Notes:
 
 Event order:
 1. Exactly one `meta`
-2. Zero or more `delta`
-3. Exactly one terminal event: `done` or `error`
+2. Zero or more `tool_call`
+3. Zero or more `delta`
+4. Exactly one terminal event: `done` or `error`
 
 ### `meta`
 
@@ -60,6 +61,23 @@ Event order:
 
 `text` may contain partial words, punctuation, or whitespace.
 
+### `tool_call`
+
+```json
+{
+  "toolCallId": "call_123",
+  "name": "web_search",
+  "status": "completed",
+  "summary": "Performed web search for 'latest CPI release'.",
+  "args": { "query": "latest CPI release" },
+  "startedAt": "2026-03-02T10:00:00.000Z",
+  "completedAt": "2026-03-02T10:00:00.820Z",
+  "durationMs": 820,
+  "error": null,
+  "resultPreview": "{\"ok\":true,...}"
+}
+```
+
 ### `done`
 
 ```json
@@ -84,10 +102,15 @@ Event order:
 
 ## Provider Streaming Behavior
 
-- `openai`: streamed via OpenAI chat completion chunks; emits `delta` from `choices[0].delta.content`.
-- `xai`: uses OpenAI-compatible API, same chunk extraction as OpenAI.
+- `openai`: backend may execute internal tool calls (`web_search`, `fetch_url`) before producing final text.
+- `xai`: same tool-enabled behavior as OpenAI.
 - `anthropic`: streamed via event stream; emits `delta` from `content_block_delta` with `text_delta`.
 
+Tool-enabled streaming notes (`openai`/`xai`):
+- Stream still emits standard `meta`, `delta`, `done|error` events.
+- Stream may emit `tool_call` events before final assistant text.
+- `delta` may arrive as one consolidated chunk after tool execution, rather than many token-level chunks.
+
 ## Persistence + Consistency Model
 
 Backend database remains source of truth.