chat: route_entry helper separates routing from sync

PaneTarget enum + route_entry() function: given a ConversationEntry,
returns which pane it belongs to (or None to skip). The sync loop
becomes: detect desync → pop, then route new entries.

Routing: User→Conversation, Assistant→ConversationAssistant,
tool_calls→Tools, Tool results→ToolResult, Memory/System→None.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

src/user/chat.rs

@@ -18,6 +18,53 @@ use super::{
 };
 use crate::user::ui_channel::{UiMessage, StreamTarget};
 
+enum PaneTarget {
+    Conversation,
+    ConversationAssistant,
+    Tools,
+    ToolResult,
+}
+
+/// Route an agent entry to the appropriate pane.
+/// Returns None for entries that shouldn't be displayed (memory, system).
+fn route_entry(entry: &crate::agent::context::ConversationEntry) -> Option<(PaneTarget, String, Marker)> {
+    use crate::agent::api::types::Role;
+    use crate::agent::context::ConversationEntry;
+
+    if let ConversationEntry::Memory { .. } = entry {
+        return None;
+    }
+
+    let msg = entry.message();
+    let text = msg.content_text().to_string();
+
+    match msg.role {
+        Role::User => {
+            if text.starts_with("<system-reminder>") { return None; }
+            Some((PaneTarget::Conversation, text, Marker::User))
+        }
+        Role::Assistant => {
+            // Tool calls → tools pane
+            if let Some(ref calls) = msg.tool_calls {
+                for call in calls {
+                    let line = format!("[{}] {}",
+                        call.function.name,
+                        call.function.arguments.chars().take(80).collect::<String>());
+                    // TODO: return multiple targets — for now just return first tool call
+                    return Some((PaneTarget::Tools, line, Marker::None));
+                }
+            }
+            if text.is_empty() { return None; }
+            Some((PaneTarget::ConversationAssistant, text, Marker::Assistant))
+        }
+        Role::Tool => {
+            if text.is_empty() { return None; }
+            Some((PaneTarget::ToolResult, text, Marker::None))
+        }
+        Role::System => None,
+    }
+}
+
 pub(crate) struct InteractScreen {
     pub(crate) autonomous: PaneState,
     pub(crate) conversation: PaneState,
@@ -61,69 +108,38 @@ impl InteractScreen {
 
     /// Sync conversation display from agent entries.
     fn sync_from_agent(&mut self) {
-        use crate::agent::api::types::Role;
-
         let agent = self.agent.blocking_lock();
         let gen = agent.generation;
         let count = agent.entries().len();
 
-        if gen != self.last_generation {
-            // Generation changed — full re-render
+        // Phase 1: detect desync — pop entries from panes to match
+        if gen != self.last_generation || count < self.last_entry_count {
+            // Compaction or mutation happened — full reset
+            // (could be smarter and pop from front, but reset is safe)
             self.conversation = PaneState::new(true);
             self.autonomous = PaneState::new(true);
             self.tools = PaneState::new(false);
             self.last_entry_count = 0;
         }
 
-        // Render new entries
+        // Phase 2: route new entries to panes
         for entry in agent.entries().iter().skip(self.last_entry_count) {
-            let msg = entry.message();
-            let text = msg.content_text();
-
-            // Skip memory/system-reminder entries — they're context, not conversation
-            if let crate::agent::context::ConversationEntry::Memory { .. } = entry {
-                continue;
+            match route_entry(entry) {
+                Some((PaneTarget::Conversation, text, marker)) => {
+                    self.conversation.push_line_with_marker(text, Color::Cyan, marker);
                 }
-
-            match msg.role {
-                Role::User => {
-                    // Skip system-reminder injections
-                    if text.starts_with("<system-reminder>") {
-                        continue;
+                Some((PaneTarget::ConversationAssistant, text, marker)) => {
+                    self.conversation.push_line_with_marker(text, Color::Reset, marker);
                 }
-                    self.conversation.push_line_with_marker(
-                        text.to_string(), Color::Cyan, Marker::User,
-                    );
+                Some((PaneTarget::Tools, text, _)) => {
+                    self.tools.push_line(text, Color::Yellow);
                 }
-                Role::Assistant => {
-                    // Tool calls show in tools pane
-                    if let Some(ref calls) = msg.tool_calls {
-                        for call in calls {
-                            let line = format!("[{}] {}", call.function.name,
-                                call.function.arguments.chars().take(80).collect::<String>());
-                            self.tools.push_line(line, Color::Yellow);
-                        }
-                    }
-                    // Text content to conversation
-                    if !text.is_empty() {
-                        self.conversation.push_line_with_marker(
-                            text.to_string(), Color::Reset, Marker::Assistant,
-                        );
-                    }
-                }
-                Role::Tool => {
-                    // Tool results to tools pane
+                Some((PaneTarget::ToolResult, text, _)) => {
                     for line in text.lines().take(20) {
                         self.tools.push_line(format!("  {}", line), Color::DarkGray);
                     }
-                    if text.lines().count() > 20 {
-                        self.tools.push_line(
-                            format!("  ... ({} more lines)", text.lines().count() - 20),
-                            Color::DarkGray,
-                        );
                 }
-                }
-                Role::System => {} // skip
+                None => {} // skip (memory, system, system-reminder)
             }
         }