fix(service): enhance message filtering to drop empty chat messages while retaining tool requests

docs/api.md

@@ -239,10 +239,10 @@ file (`episode-<YYYY-MM-DD>.md` etc.).
 
 **`content`** — The message body.
 - A bare **string** is shorthand for a single text content item.
-- An **array of `ContentItem`** is for mixed-modality input (text +
-  image / pdf / audio / ...); non-text items are parsed by the
-  multimodal LLM configured via `EVEROS_MULTIMODAL__*` env vars. See
-  [ContentItem](#contentitem).
+- An **array of `ContentItem`** is for mixed input (`text` / `md` +
+  image / pdf / audio / ...). `md` items are read as UTF-8 text;
+  media/document items are parsed by the multimodal LLM configured via
+  `EVEROS_MULTIMODAL__*` env vars. See [ContentItem](#contentitem).
 
 **`tool_calls`** — When `role: "assistant"`, the tool calls the
 assistant emitted in this turn (OpenAI Chat Completions shape).
@@ -252,34 +252,38 @@ message is the response to.
 
 ### ContentItem
 
-Mixed-modality message-body element. Carry the payload in exactly one
-of `text` / `uri` / `base64`; the others must be `null`. For
-`type: "text"` use `text`; for every **non-text** type use `uri`
-(`http(s)://`) or `base64` (with `ext`). Non-text items are routed
-through the multimodal parser, which needs a fetchable or decodable
-payload — a non-text item carrying only `text` returns `415`.
+Mixed message-body element. Carry the payload in exactly one of `text` /
+`uri` / `base64`; the others must be `null`. For `type: "text"` use
+`text`. For `type: "md"` use `text`, a server-local `file://` URI, or
+`base64` UTF-8 bytes. For every **non-text, non-md** type use `uri`
+(`http(s)://`) or `base64` (with `ext`). Non-text, non-md items are
+routed through the multimodal parser, which needs a fetchable or
+decodable payload — passing only `text` returns `415`.
 
 | Field | Type | Required | Default | Notes |
 |---|---|---|---|---|
-| `type` | `"text" \| "image" \| "audio" \| "doc" \| "pdf" \| "html" \| "email"` | yes | — | — |
-| `text` | `string \| null` | no | `null` | Required when `type: "text"` |
+| `type` | `"text" \| "md" \| "image" \| "audio" \| "doc" \| "pdf" \| "html" \| "email"` | yes | — | — |
+| `text` | `string \| null` | no | `null` | Required when `type: "text"`; optional inline Markdown when `type: "md"` |
 | `uri` | `string \| null` | no | `null` | `http(s)://` (fetched server-side) or `file://` (read from the server's local fs, guardrailed) pointer |
 | `base64` | `string \| null` | no | `null` | Inline payload, plain base64 (no `data:` prefix) |
 | `ext` | `string \| null` | no | `null` | File-extension hint when `uri` lacks one |
 | `name` | `string \| null` | no | `null` | Display filename, used in logs |
 | `extras` | `object \| null` | no | `null` | Provider-specific metadata, opaque to EverOS |
 
-**`type`** — The content kind. Each non-text type is dispatched to the
-multimodal LLM. If the multimodal endpoint cannot handle the supplied
-payload, `/add` returns `415 Unsupported Media Type`.
+**`type`** — The content kind. `text` and `md` are treated as text.
+Each other type is dispatched to the multimodal LLM. If the multimodal
+endpoint cannot handle the supplied payload, `/add` returns
+`415 Unsupported Media Type`.
 
-**`text`** — The literal text payload; valid **only** for
-`type: "text"`. A non-text type (including `"html"`) is always routed
-to the parser and must carry `uri` or `base64`; passing only `text` on
-a non-text item returns `415`. To inline HTML as plain text, send it
-as `type: "text"`.
+**`text`** — The literal text payload; valid for `type: "text"` and
+inline `type: "md"`. A non-text, non-md type (including `"html"`) is
+always routed to the parser and must carry `uri` or `base64`; passing
+only `text` on those items returns `415`. To inline HTML as plain text,
+send it as `type: "text"`.
 
-**`uri`** — `http(s)://` or `file://` pointer to the asset. An
+**`uri`** — `http(s)://` or `file://` pointer to the asset. For
+`type: "md"`, only `file://` is supported and the file is decoded as
+UTF-8 text. For parser-backed content, an
 `http(s)` uri is fetched by the server and dispatched by the response
 Content-Type (use it for assets hosted elsewhere — S3 / OSS presigned
 URL, http server). A `file://` uri is read from the **server's** local

docs/openapi.json

@@ -251,6 +251,7 @@
             "type": "string",
             "enum": [
               "text",
+              "md",
               "image",
               "audio",
               "doc",