diff --git a/hive-agent/src/web_ui/actions.rs b/hive-agent/src/web_ui/actions.rs
index 56c7ea8d..f05905e0 100644
--- a/hive-agent/src/web_ui/actions.rs
+++ b/hive-agent/src/web_ui/actions.rs
@@ -7,7 +7,7 @@ use axum::{
     http::StatusCode,
     response::{IntoResponse, Response},
 };
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 
 use super::{AppState, SigintOutcome, error_response};
 
@@ -202,5 +202,10 @@ pub(super) async fn post_mark_todos_done(Form(form): Form<MarkTodosDoneForm>) ->
             acked += count;
         }
     }
-    axum::Json(serde_json::json!({ "acked": acked })).into_response()
+    axum::Json(MarkTodosDoneBody { acked }).into_response()
+}
+
+#[derive(Serialize)]
+struct MarkTodosDoneBody {
+    acked: u64,
 }
diff --git a/hive-agent/src/web_ui/stats.rs b/hive-agent/src/web_ui/stats.rs
index f2f83614..9dd6796d 100644
--- a/hive-agent/src/web_ui/stats.rs
+++ b/hive-agent/src/web_ui/stats.rs
@@ -2,7 +2,7 @@
 
 use axum::extract::State;
 use axum::response::{IntoResponse, Response};
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 
 use super::AppState;
 
@@ -40,6 +40,11 @@ async fn fetch_reminder_stats(window_secs: u64) -> Option<hive_sh4re::approvals:
     }
 }
 
+#[derive(Serialize)]
+struct TodosBody {
+    todos: Vec<hive_sh4re::inbox::LooseEnd>,
+}
+
 /// `GET /api/todos` — snapshot of this agent's local todos (loose-ends v2).
 ///
 /// Connects to the in-agent harness socket (`HIVE_AGENT_SOCKET`) and calls
@@ -54,5 +59,5 @@ pub(super) async fn api_todos() -> Response {
             Some(hive_agent_sock::Response::LooseEnds { loose_ends }) => loose_ends,
             _ => Vec::new(),
         };
-    axum::Json(serde_json::json!({ "todos": todos })).into_response()
+    axum::Json(TodosBody { todos }).into_response()
 }
diff --git a/hive-agent/src/web_ui/stream.rs b/hive-agent/src/web_ui/stream.rs
index 3c881cd4..89c4ba31 100644
--- a/hive-agent/src/web_ui/stream.rs
+++ b/hive-agent/src/web_ui/stream.rs
@@ -5,11 +5,23 @@ use std::convert::Infallible;
 use axum::Json;
 use axum::extract::{Query, State};
 use axum::response::sse::{Event, KeepAlive, Sse};
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 use tokio_stream::{Stream, StreamExt, wrappers::BroadcastStream};
 
 use super::AppState;
 
+/// Response body for `GET /api/events/history`. `seq` is omitted from the
+/// wire entirely on a paginated (non-initial) load — matches the old
+/// `json!` shape, which only ever set the `"seq"` key when `Some`.
+#[derive(Serialize)]
+pub(super) struct EventsHistoryBody {
+    events: Vec<crate::events::StoredEvent>,
+    min_id: Option<i64>,
+    has_more: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    seq: Option<u64>,
+}
+
 /// Query params for the paginated history endpoint.
 #[derive(Debug, Deserialize)]
 pub(super) struct HistoryParams {
@@ -23,7 +35,7 @@ pub(super) struct HistoryParams {
 pub(super) async fn events_history(
     State(state): State<AppState>,
     Query(params): Query<HistoryParams>,
-) -> Json<serde_json::Value> {
+) -> Json<EventsHistoryBody> {
     use crate::events::HISTORY_CAPACITY;
     let limit = params.limit.unwrap_or(100).min(HISTORY_CAPACITY);
     let before = params.before;
@@ -51,15 +63,12 @@ pub(super) async fn events_history(
             se
         })
         .collect();
-    let mut resp = serde_json::json!({
-        "events": events,
-        "min_id": min_id,
-        "has_more": has_more,
-    });
-    if let Some(s) = seq {
-        resp["seq"] = serde_json::json!(s);
-    }
-    Json(resp)
+    Json(EventsHistoryBody {
+        events,
+        min_id,
+        has_more,
+        seq,
+    })
 }
 
 pub(super) async fn events_stream(