feat: add /compact (#289)

Added the ability to compact. Not sure if I should switch the model over
to gpt-4.1 for longer context or if keeping the current model is fine.
Also I'm not sure if setting the compacted to system is best practice,
would love feedback 😄

Mentioned in this issue: https://github.com/openai/codex/issues/230

codex-cli/src/components/chat/terminal-chat-input.tsx

@@ -42,6 +42,7 @@ export default function TerminalChatInput({
   openModelOverlay,
   openApprovalOverlay,
   openHelpOverlay,
+  onCompact,
   interruptAgent,
   active,
 }: {
@@ -61,6 +62,7 @@ export default function TerminalChatInput({
   openModelOverlay: () => void;
   openApprovalOverlay: () => void;
   openHelpOverlay: () => void;
+  onCompact: () => void;
   interruptAgent: () => void;
   active: boolean;
 }): React.ReactElement {
@@ -166,6 +168,12 @@ export default function TerminalChatInput({
         return;
       }
 
+      if (inputValue === "/compact") {
+        setInput("");
+        onCompact();
+        return;
+      }
+
       if (inputValue.startsWith("/model")) {
         setInput("");
         openModelOverlay();
@@ -295,6 +303,7 @@ export default function TerminalChatInput({
       openModelOverlay,
       openHelpOverlay,
       history, // Add history to the dependency array
+      onCompact,
     ],
   );
 
@@ -366,7 +375,8 @@ export default function TerminalChatInput({
                 <>
                   {" — "}
                   <Text color="red">
-                    {Math.round(contextLeftPercent)}% context left
+                    {Math.round(contextLeftPercent)}% context left — send
+                    "/compact" to condense context
                   </Text>
                 </>
               )}

codex-cli/src/components/chat/terminal-chat.tsx

@@ -17,6 +17,7 @@ import { useTerminalSize } from "../../hooks/use-terminal-size.js";
 import { AgentLoop } from "../../utils/agent/agent-loop.js";
 import { isLoggingEnabled, log } from "../../utils/agent/log.js";
 import { ReviewDecision } from "../../utils/agent/review.js";
+import { generateCompactSummary } from "../../utils/compact-summary.js";
 import { OPENAI_BASE_URL } from "../../utils/config.js";
 import { createInputItem } from "../../utils/input-utils.js";
 import { getAvailableModels } from "../../utils/model-utils.js";
@@ -138,6 +139,34 @@ export default function TerminalChat({
     initialApprovalPolicy,
   );
   const [thinkingSeconds, setThinkingSeconds] = useState(0);
+  const handleCompact = async () => {
+    setLoading(true);
+    try {
+      const summary = await generateCompactSummary(items, model);
+      setItems([
+        {
+          id: `compact-${Date.now()}`,
+          type: "message",
+          role: "assistant",
+          content: [{ type: "output_text", text: summary }],
+        } as ResponseItem,
+      ]);
+    } catch (err) {
+      setItems((prev) => [
+        ...prev,
+        {
+          id: `compact-error-${Date.now()}`,
+          type: "message",
+          role: "system",
+          content: [
+            { type: "input_text", text: `Failed to compact context: ${err}` },
+          ],
+        } as ResponseItem,
+      ]);
+    } finally {
+      setLoading(false);
+    }
+  };
   const {
     requestConfirmation,
     confirmationPrompt,
@@ -453,6 +482,7 @@ export default function TerminalChat({
             openModelOverlay={() => setOverlayMode("model")}
             openApprovalOverlay={() => setOverlayMode("approval")}
             openHelpOverlay={() => setOverlayMode("help")}
+            onCompact={handleCompact}
             active={overlayMode === "none"}
             interruptAgent={() => {
               if (!agent) {