fix(fe): handle JSON-stringified fields from backend in message deserialization

Backend returns metadata, ai_moderation_flags, and ai_categories as raw
JSON strings (PostgreSQL JSONB cast to string). Frontend expected parsed
structs/arrays, causing serde to fail silently — entire PageResult parse
failed and user saw empty message list with no error indicator.

Add custom deserialize_with handler (from_json_string_or_value) that
transparently handles null / direct value / JSON-string cases for the
three affected fields.

services/frontend/Cargo.lock

@@ -1883,6 +1883,7 @@ name = "shared-types"
 version = "0.1.0"
 dependencies = [
  "serde",
+ "serde_json",
 ]
 
 [[package]]

services/frontend/shared-types/Cargo.toml

@@ -5,3 +5,4 @@ edition = "2021"
 
 [dependencies]
 serde = { version = "1", features = ["derive"] }
+serde_json = "1"

services/frontend/shared-types/src/message.rs

@@ -1,3 +1,4 @@
+use serde::de::{self, DeserializeOwned, Deserializer};
 use serde::{Deserialize, Serialize};
 
 // ── AI Status ─────────────────────────────────────────────
@@ -93,6 +94,50 @@ pub struct ChannelRef {
     pub thread_name: Option<String>,
 }
 
+// ── Helpers: deserialize JSON-string fields ────────────────
+//
+// The backend stores certain fields as raw JSON strings in PostgreSQL.
+// The JSON response therefore contains *stringified* JSON for these fields
+// (e.g. `"metadata":"{\"stickers\":[]}"`) instead of the actual JSON value.
+// These helpers transparently parse the string when present, so the frontend
+// works with the native Rust type regardless of whether the backend ships
+// a parsed value or a stringified one.
+
+/// Deserialize a `T` from a JSON value that may be:
+///   - `null` → `None`
+///   - a plain JSON value → `Some(T)` (direct serde)
+///   - a JSON *string* whose *contents* are JSON for `T`
+fn from_json_string_or_value<'de, T, D>(d: D) -> Result<Option<T>, D::Error>
+where
+    T: DeserializeOwned,
+    D: Deserializer<'de>,
+{
+    // Intermediate Value to distinguish null / object / array / string
+    let v = Option::<serde_json::Value>::deserialize(d)?;
+    match v {
+        None => Ok(None),
+        Some(serde_json::Value::String(s)) => {
+            serde_json::from_str(&s).map(Some).map_err(de::Error::custom)
+        }
+        Some(json) => serde_json::from_value(json).map(Some).map_err(de::Error::custom),
+    }
+}
+
+/// Concrete wrapper for `metadata: Option<MessageMetadata>`.
+pub(crate) fn deser_msg_meta<'de, D: Deserializer<'de>>(
+    d: D,
+) -> Result<Option<MessageMetadata>, D::Error> {
+    from_json_string_or_value(d)
+}
+
+/// Concrete wrapper for `Option<Vec<String>>` fields
+/// (ai_moderation_flags, ai_categories, etc.).
+pub(crate) fn deser_str_vec<'de, D: Deserializer<'de>>(
+    d: D,
+) -> Result<Option<Vec<String>>, D::Error> {
+    from_json_string_or_value(d)
+}
+
 // ── Message Record ────────────────────────────────────────
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
 pub struct MessageRecord {
@@ -121,13 +166,19 @@ pub struct MessageRecord {
     pub ai_severity: Option<AiSeverity>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub ai_confidence: Option<f64>,
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(
+        deserialize_with = "deser_str_vec",
+        skip_serializing_if = "Option::is_none"
+    )]
     pub ai_moderation_flags: Option<Vec<String>>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub ai_moderation_score: Option<f64>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub ai_analysis: Option<String>,
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(
+        deserialize_with = "deser_str_vec",
+        skip_serializing_if = "Option::is_none"
+    )]
     pub ai_categories: Option<Vec<String>>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub ai_recommended_action: Option<AiRecommendedAction>,
@@ -135,7 +186,10 @@ pub struct MessageRecord {
     pub ai_error: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub ai_analyzed_at: Option<i64>,
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(
+        deserialize_with = "deser_msg_meta",
+        skip_serializing_if = "Option::is_none"
+    )]
     pub metadata: Option<MessageMetadata>,
 }