fix(headroom): compress Kiro conversation state (#2488)

Project conversationState history/currentMessage into OpenAI-style
messages for /v1/compress, then write compressed text back into the
original Kiro fields while preserving provider payload shape. Fail open
when the proxy returns malformed or reordered messages.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/headroom.test.js

@@ -31,6 +31,10 @@ describe("compressWithHeadroom", () => {
     expect(body.messages[0].content).toBe("short");
     expect(stats.tokens_saved).toBe(80);
     expect(global.fetch).toHaveBeenCalledWith("http://headroom:8787/v1/compress", expect.objectContaining({ method: "POST" }));
+    expect(JSON.parse(global.fetch.mock.calls[0][1].body)).toMatchObject({
+      model: "gpt-4o",
+      messages: [{ role: "user", content: "long" }],
+    });
   });
 
   it("compresses responses input in-place", async () => {
@@ -44,6 +48,141 @@ describe("compressWithHeadroom", () => {
     expect(body.input[0].content).toBe("short");
   });
 
+  it("compresses Kiro conversationState history/currentMessage in-place", async () => {
+    let requestPayload;
+    global.fetch = vi.fn(async (_url, init) => {
+      requestPayload = JSON.parse(init.body);
+      return new Response(JSON.stringify({
+        messages: [
+          { role: "user", content: "compressed earlier user" },
+          { role: "assistant", content: "compressed assistant", tool_calls: [{ id: "tool_1", type: "function", function: { name: "read_file", arguments: "{\"path\":\"a.js\"}" } }] },
+          { role: "system", content: "compressed system instruction" },
+          { role: "user", content: "compressed current user" },
+          { role: "tool", content: [{ type: "text", text: "compressed tool output" }], tool_call_id: "tool_1" },
+        ],
+        tokens_before: 100,
+        tokens_after: 40,
+        tokens_saved: 60,
+      }), { status: 200 });
+    });
+    const body = {
+      profileArn: "arn:test",
+      conversationState: {
+        chatTriggerType: "MANUAL",
+        conversationId: "conv-1",
+        history: [
+          {
+            userInputMessage: {
+              content: "earlier user",
+              modelId: "claude-sonnet-4.5",
+            },
+          },
+          {
+            assistantResponseMessage: {
+              content: "assistant response",
+              toolUses: [
+                {
+                  toolUseId: "tool_1",
+                  name: "read_file",
+                  input: { path: "a.js" },
+                },
+              ],
+            },
+          },
+        ],
+        currentMessage: {
+          userInputMessage: {
+            content: "current user",
+            modelId: "claude-sonnet-4.5",
+            systemInstruction: "native system instruction",
+            userInputMessageContext: {
+              tools: [{ toolSpecification: { name: "read_file" } }],
+              toolResults: [
+                {
+                  toolUseId: "tool_1",
+                  status: "success",
+                  content: [{ text: "long tool output" }],
+                },
+              ],
+            },
+          },
+        },
+      },
+    };
+
+    const stats = await compressWithHeadroom(body, {
+      enabled: true,
+      url: "http://localhost:8787",
+      model: "claude-sonnet-4.5",
+      format: "kiro",
+      compressUserMessages: true,
+    });
+
+    expect(stats.tokens_saved).toBe(60);
+    expect(requestPayload).toEqual({
+      model: "claude-sonnet-4.5",
+      config: { compress_user_messages: true },
+      messages: [
+        { role: "user", content: "earlier user" },
+        {
+          role: "assistant",
+          content: "assistant response",
+          tool_calls: [
+            {
+              id: "tool_1",
+              type: "function",
+              function: { name: "read_file", arguments: "{\"path\":\"a.js\"}" },
+            },
+          ],
+        },
+        { role: "system", content: "native system instruction" },
+        { role: "user", content: "current user" },
+        { role: "tool", content: "long tool output", tool_call_id: "tool_1" },
+      ],
+    });
+    expect(body.conversationState.history[0].userInputMessage.content).toBe("compressed earlier user");
+    expect(body.conversationState.history[1].assistantResponseMessage.content).toBe("compressed assistant");
+    expect(body.conversationState.currentMessage.userInputMessage.systemInstruction).toBe("compressed system instruction");
+    expect(body.conversationState.currentMessage.userInputMessage.content).toBe("compressed current user");
+    expect(body.conversationState.currentMessage.userInputMessage.userInputMessageContext.toolResults[0].content[0].text)
+      .toBe("compressed tool output");
+    expect(body.profileArn).toBe("arn:test");
+    expect(body.conversationState.currentMessage.userInputMessage.userInputMessageContext.tools)
+      .toEqual([{ toolSpecification: { name: "read_file" } }]);
+  });
+
+  it("fails open when Kiro Headroom output does not preserve message order", async () => {
+    global.fetch = vi.fn(async () => new Response(JSON.stringify({
+      messages: [{ role: "assistant", content: "wrong role" }],
+      tokens_saved: 10,
+    }), { status: 200 }));
+    const body = {
+      conversationState: {
+        currentMessage: {
+          userInputMessage: {
+            content: "original",
+            modelId: "claude-sonnet-4.5",
+          },
+        },
+        history: [],
+      },
+    };
+    const original = structuredClone(body);
+    const diagnostics = {};
+
+    const stats = await compressWithHeadroom(body, {
+      enabled: true,
+      url: "http://localhost:8787",
+      model: "claude-sonnet-4.5",
+      format: "kiro",
+      diagnostics,
+    });
+
+    expect(stats).toBeNull();
+    expect(body).toEqual(original);
+    expect(diagnostics.reason).toBe("proxy response did not preserve Kiro message order");
+  });
+
   it("fails open on bad response", async () => {
     global.fetch = vi.fn(async () => new Response(JSON.stringify({ error: "bad" }), { status: 500 }));
     const body = { messages: [{ role: "user", content: "long" }] };