adds attachment support

docs/api/streaming-chat.md

@@ -9,6 +9,7 @@ Transport:
 - HTTP response uses `Content-Type: text/event-stream; charset=utf-8`
 - Events are emitted in SSE format (`event: ...`, `data: ...`)
 - Request body is JSON
+- Request body supports the same inline attachment schema and limits documented in `docs/api/rest.md`.
 
 Authentication:
 - Same as REST endpoints (`Authorization: Bearer <token>` when token mode is enabled)
@@ -21,7 +22,30 @@ Authentication:
   "provider": "openai|anthropic|xai",
   "model": "string",
   "messages": [
-    { "role": "system|user|assistant|tool", "content": "string", "name": "optional" }
+    {
+      "role": "system|user|assistant|tool",
+      "content": "string",
+      "name": "optional",
+      "attachments": [
+        {
+          "kind": "image",
+          "id": "attachment-id",
+          "filename": "photo.jpg",
+          "mimeType": "image/jpeg",
+          "sizeBytes": 12345,
+          "dataUrl": "data:image/jpeg;base64,..."
+        },
+        {
+          "kind": "text",
+          "id": "attachment-id",
+          "filename": "notes.md",
+          "mimeType": "text/markdown",
+          "sizeBytes": 4567,
+          "text": "# Notes\\n...",
+          "truncated": false
+        }
+      ]
+    }
   ],
   "temperature": 0.2,
   "maxTokens": 256
@@ -32,6 +56,7 @@ Notes:
 - If `chatId` is omitted, backend creates a new chat.
 - If `chatId` is provided, backend validates it exists.
 - Backend stores only new non-assistant input history rows to avoid duplicates.
+- Attachments are optional and are persisted under `message.metadata.attachments` on stored user messages.
 
 ## Event Stream Contract
 
@@ -103,8 +128,9 @@ Event order:
 ## Provider Streaming Behavior
 
 - `openai`: backend may execute internal tool calls (`web_search`, `fetch_url`) before producing final text.
+- `openai`: image attachments are sent as chat-completions content parts; text attachments are inlined as text parts.
 - `xai`: same tool-enabled behavior as OpenAI.
-- `anthropic`: streamed via event stream; emits `delta` from `content_block_delta` with `text_delta`.
+- `anthropic`: streamed via event stream; emits `delta` from `content_block_delta` with `text_delta`. Image attachments are sent as base64 `image` blocks and text attachments are appended as `text` blocks.
 - `web_search` uses `CHAT_WEB_SEARCH_ENGINE` (`exa` default, or `searxng` with `SEARXNG_BASE_URL` set). SearXNG mode requires the instance to allow `format=json`. This only affects chat-mode tool calls, not search-mode endpoints.
 
 Tool-enabled streaming notes (`openai`/`xai`):