fix(openai): strict OpenAI wire compatibility — Open WebUI can chat again

/v1/chat/completions answered ordinary client payloads with a bare HTTP 422
(a plain-text body no OpenAI client can parse), so Open WebUI showed neither
an answer nor an error — it just hung. Parse the body leniently instead:
content as string/null/content-part array, tools: null, stream: null, a
string reasoning_effort, max_completion_tokens, messages[].name and
tool_call_id, and a missing Content-Type. Unreadable bodies now come back as
an OpenAI error envelope with 400.

Responses are strict OpenAI JSON: no "tool_calls": null, finish_reason mapped
to the spec's closed set (cortiq serve's max_tokens -> length), never an empty
id, and `model` echoes the id the client requested — the model that actually
answered stays in cortiq.selected_model and X-Cortiq-Selected-Model.

Streaming is re-normalised rather than forwarded verbatim: a leading role
delta, message-shaped chunks converted to delta, one terminal finish_reason,
always a trailing data: [DONE], and an SSE error event when the upstream dies
mid-flight. Adds X-Accel-Buffering: no so a fronting proxy cannot buffer the
stream into a hang.

GET /v1/models now lists managed [[cmf.servers]] models with their live
running/healthy state, so clients can pin a local .cmf directly.

Also strips client bookkeeping keys (chat_id, session_id, metadata, features,
...) from the upstream call and drops the leftover [to_wire] debug prints.

src/model.rs

@@ -15,13 +15,53 @@ pub enum RoutingDirective {
     Pinned { model_id: String },
 }
 
-#[derive(Clone, Debug, Serialize, Deserialize)]
+#[derive(Clone, Debug, Default, Serialize, Deserialize)]
 pub struct Message {
     pub role: String, // system | user | assistant | tool
-    #[serde(default)]
+    /// Always a plain string internally. On the wire OpenAI clients legitimately
+    /// send `null` (assistant turns that only carry tool calls) or an array of
+    /// content parts (Open WebUI and every other multimodal UI), so
+    /// [`de_content`] flattens both shapes instead of rejecting the request.
+    #[serde(default, deserialize_with = "de_content")]
     pub content: String,
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub tool_calls: Vec<serde_json::Value>,
+    /// Speaker name (`messages[].name`) — proxied through when the client sends it.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub name: Option<String>,
+    /// Set on `role = "tool"` replies; dropping it breaks multi-turn tool calling.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub tool_call_id: Option<String>,
+}
+
+/// Deserialize `messages[].content` from any shape an OpenAI-compatible client
+/// may send: a string, `null`, or an array of content parts. Text parts are
+/// concatenated; non-text parts (images, audio, files) are skipped — this
+/// gateway routes text, and a picture must not turn into a 422.
+fn de_content<'de, D>(d: D) -> std::result::Result<String, D::Error>
+where
+    D: serde::Deserializer<'de>,
+{
+    use serde::Deserialize as _;
+    Ok(match serde_json::Value::deserialize(d)? {
+        serde_json::Value::Null => String::new(),
+        serde_json::Value::String(s) => s,
+        serde_json::Value::Array(parts) => {
+            let mut out = String::new();
+            for part in parts {
+                // {"type":"text","text":"..."} / {"type":"input_text","text":"..."}
+                let text = part
+                    .get("text")
+                    .and_then(|t| t.as_str())
+                    .or_else(|| part.as_str());
+                if let Some(t) = text {
+                    out.push_str(t);
+                }
+            }
+            out
+        }
+        other => other.to_string(),
+    })
 }
 
 #[derive(Clone, Debug, Default)]