diff --git a/apps/interfaces/tui/src/run.rs b/apps/interfaces/tui/src/run.rs
index 9d3742e..c98df52 100644
--- a/apps/interfaces/tui/src/run.rs
+++ b/apps/interfaces/tui/src/run.rs
@@ -112,9 +112,12 @@ fn run_loop_inner(
         }
 
         // Drain expired toasts exactly once per loop iteration (was being
-        // done here AND in Action::Tick before this fix).
-        let now_ms = chrono::Utc::now().timestamp_millis();
-        state.misc.drain_expired_toasts(now_ms);
+        // done here AND in Action::Tick before this fix). Skip the clock
+        // syscall + Vec scan when there are no toasts at all.
+        if !state.misc.toasts.is_empty() {
+            let now_ms = chrono::Utc::now().timestamp_millis();
+            state.misc.drain_expired_toasts(now_ms);
+        }
 
         // Skip render when nothing has changed — avoids expensive markdown
         // re-parse and layout recalculation every cycle while idle.
diff --git a/apps/interfaces/tui/src/state/misc.rs b/apps/interfaces/tui/src/state/misc.rs
index 6e4bccb..8154e68 100644
--- a/apps/interfaces/tui/src/state/misc.rs
+++ b/apps/interfaces/tui/src/state/misc.rs
@@ -179,16 +179,9 @@ impl MiscState {
         self.toasts.push(toast);
     }
 
-    /// Remove and return all toasts whose lifetime has expired at `now_ms`.
-    pub fn drain_expired_toasts(&mut self, now_ms: i64) -> Vec<Toast> {
-        let expired: Vec<_> = self
-            .toasts
-            .iter()
-            .filter(|t| t.expired(now_ms))
-            .cloned()
-            .collect();
+    /// Remove all toasts whose lifetime has expired at `now_ms`.
+    pub fn drain_expired_toasts(&mut self, now_ms: i64) {
         self.toasts.retain(|t| !t.expired(now_ms));
-        expired
     }
 }
 
diff --git a/apps/interfaces/tui/src/state/mod.rs b/apps/interfaces/tui/src/state/mod.rs
index 363d2e3..4066e90 100644
--- a/apps/interfaces/tui/src/state/mod.rs
+++ b/apps/interfaces/tui/src/state/mod.rs
@@ -103,6 +103,13 @@ pub struct AppStateRest {
     pub last_render_width: u16,
     /// Number of messages that were in the cache when it was last built.
     pub cached_msg_count: usize,
+    /// Cache index where the last message's rendered lines begin. Used to
+    /// splice streaming updates (only re-render the trailing message).
+    pub cached_last_start: usize,
+    /// Content+reasoning byte length of the last message when it was last
+    /// rendered. Guards the streaming branch from re-rendering on ticks
+    /// where no new token arrived (spinner-only frames).
+    pub cached_last_len: usize,
     /// Terminal width at the time of the last full cache build.
     pub render_width_at_cache: u16,
     /// Atomic flag set when the user aborts the current turn.
@@ -180,6 +187,8 @@ impl Default for AppStateRest {
             token_count_dirty: true,
             last_render_width: 0,
             cached_msg_count: 0,
+            cached_last_start: 0,
+            cached_last_len: 0,
             render_width_at_cache: 0,
         }
     }
@@ -230,6 +239,8 @@ impl AppStateRest {
             token_count_dirty: true,
             last_render_width: 0,
             cached_msg_count: 0,
+            cached_last_start: 0,
+            cached_last_len: 0,
             render_width_at_cache: 0,
         }
     }
diff --git a/apps/interfaces/tui/src/view/chat.rs b/apps/interfaces/tui/src/view/chat.rs
index 840e581..490e39b 100644
--- a/apps/interfaces/tui/src/view/chat.rs
+++ b/apps/interfaces/tui/src/view/chat.rs
@@ -190,6 +190,8 @@ impl Component for ChatComponent {
             }
             state.display_lines_cache = all_lines;
             state.cached_msg_count = msg_count;
+            state.cached_last_start = state.display_lines_cache.len();
+            state.cached_last_len = last_msg_len(state);
             state.render_width_at_cache = state.last_render_width;
             state.transcript_cache.dirty = false;
         } else if state.transcript_cache.dirty && msg_count > cached_count {
@@ -205,6 +207,27 @@ impl Component for ChatComponent {
                 state.display_lines_cache.extend(msg_lines);
             }
             state.cached_msg_count = msg_count;
+            state.cached_last_start = state.display_lines_cache.len();
+            state.cached_last_len = last_msg_len(state);
+            state.transcript_cache.dirty = false;
+        } else if state.transcript_cache.dirty {
+            // Streaming update: message count unchanged, but the last
+            // assistant message's content grew (StreamToken). Re-render only
+            // that message and splice its lines back into the cache — this
+            // keeps updates O(new content), not O(whole history) per token.
+            // Without this branch, streamed tokens would never appear (the
+            // cache is only rebuilt on new-message or resize paths).
+            let cur_len = last_msg_len(state);
+            if cur_len != state.cached_last_len {
+                if let Some(last_msg) = state.transcript_cache.messages.back() {
+                    if state.cached_last_start <= state.display_lines_cache.len() {
+                        let new_lines = render_one_message(last_msg, content_width);
+                        state.display_lines_cache.truncate(state.cached_last_start);
+                        state.display_lines_cache.extend(new_lines);
+                    }
+                }
+                state.cached_last_len = cur_len;
+            }
             state.transcript_cache.dirty = false;
         }
 
@@ -326,3 +349,15 @@ fn split_spans_into_lines(spans: Vec<Span<'_>>) -> Vec<Line<'_>> {
     }
     lines
 }
+
+/// Byte length of the last message's content + reasoning. Used as a cheap
+/// change detector for the streaming render branch — avoids re-rendering on
+/// spinner-only ticks where no new token arrived.
+fn last_msg_len(state: &crate::state::AppStateRest) -> usize {
+    state
+        .transcript_cache
+        .messages
+        .back()
+        .map(|m| m.content.len() + m.reasoning.len())
+        .unwrap_or(0)
+}
diff --git a/apps/interfaces/tui/src/view/mod.rs b/apps/interfaces/tui/src/view/mod.rs
index 7cd89b7..a528dac 100644
--- a/apps/interfaces/tui/src/view/mod.rs
+++ b/apps/interfaces/tui/src/view/mod.rs
@@ -86,6 +86,10 @@ pub fn draw(frame: &mut Frame, state: &AppStateRest) {
 }
 
 fn render_toasts(frame: &mut Frame, state: &AppStateRest) {
+    // Fast path: nothing to render.
+    if state.misc.toasts.is_empty() {
+        return;
+    }
     let now_ms = chrono::Utc::now().timestamp_millis();
     let active: Vec<&zesdex_infrastructure::Toast> = state
         .misc