fix(kiro): improve direct session cache reuse

Reshape Kiro direct requests so resumed client sessions reuse Kiro's
cache-affinity fields instead of starting unrelated CodeWhisperer
conversations.

- keep conversationState.conversationId stable when the client sends an
  explicit session id (x-session-id, session_id, conversation_id, Claude
  Code session metadata)
- add a stable conversationState.agentContinuationId per Kiro session
- send conversationState.agentTaskType: "vibe" and agentMode: "vibe",
  matching the normal Kiro CLI/KAS chat path
- move Kiro thinking instructions into Kiro-compatible systemPrompt /
  additionalModelRequestFields instead of generic top-level thinking
- keep volatile timestamp context out of the top-level systemPrompt; it
  remains only in user content fallback
- suppress additionalModelRequestFields for legacy 4.5-era Claude/Kiro
  models that reject it, while defaulting future Claude/Kiro model ids
  to supported
- preserve Kiro meteringEvent credit usage internally for accounting
  without leaking provider-specific fields into OpenAI-compatible usage
- prevent unrelated headerless Kiro requests from sharing one
  connection-wide continuation
- cap/evict continuation sessions so long-running processes do not grow
  the continuation map unbounded
- treat generated headerless Kiro sessions as one-shot so they do not
  evict real explicit-session continuations
- keep credit-only Kiro metering valid for internal persistence when
  token metrics are unavailable

tests/translator/claude-kiro-direct.test.js

@@ -6,8 +6,8 @@ import "./registerAll.js";
 import { translateRequest, translateResponse } from "../../open-sse/translator/index.js";
 import { FORMATS } from "../../open-sse/translator/formats.js";
 
-const C2K = (body) =>
-  translateRequest(FORMATS.CLAUDE, FORMATS.KIRO, "claude-sonnet-4.5", body, true, null, "kiro");
+const C2K = (body, credentials = null, model = "claude-sonnet-4.5") =>
+  translateRequest(FORMATS.CLAUDE, FORMATS.KIRO, model, body, true, credentials, "kiro");
 
 describe("Claude → Kiro (direct route)", () => {
   it("produces a Kiro conversationState payload", () => {
@@ -16,6 +16,27 @@ describe("Claude → Kiro (direct route)", () => {
     expect(out.conversationState.currentMessage.userInputMessage.content).toContain("hello");
   });
 
+  it("keeps conversationId stable from client session headers and replays frozen msg0", () => {
+    const credentials = {
+      rawHeaders: { "x-session-id": "hermes-session-123-claude-replay" },
+      connectionId: "kiro-account-1",
+    };
+    const first = C2K({ messages: [{ role: "user", content: "first" }] }, credentials);
+    const second = C2K({ messages: [{ role: "user", content: "second" }] }, credentials);
+
+    expect(first.conversationState.conversationId).toBe("hermes-session-123-claude-replay");
+    expect(second.conversationState.conversationId).toBe("hermes-session-123-claude-replay");
+    expect(first.conversationState.agentContinuationId).toBeTruthy();
+    expect(second.conversationState.agentContinuationId).toBe(first.conversationState.agentContinuationId);
+    expect(first.conversationState.agentTaskType).toBe("vibe");
+    expect(second.conversationState.history[0].userInputMessage.content).toBe(
+      first.conversationState.currentMessage.userInputMessage.content
+    );
+    expect(second.conversationState.history[0].userInputMessage.modelId).toBe("claude-sonnet-4.5");
+    expect(second.conversationState.currentMessage.userInputMessage.content).toContain("Current time");
+    expect(second.conversationState.currentMessage.userInputMessage.content).toContain("second");
+  });
+
   it("guard 1: with no tools, a dangling tool_result is flattened to text (no structured ref)", () => {
     // Client omitted `tools` but kept a tool_result after compaction.
     const out = C2K({
@@ -60,20 +81,60 @@ describe("Claude → Kiro (direct route)", () => {
       null,
       "kiro"
     );
-    expect(out.conversationState.currentMessage.userInputMessage.content).toContain(
+    expect(out.systemPrompt).toContain(
       "<thinking_mode>enabled</thinking_mode>"
     );
+    expect(out.agentMode).toBe("vibe");
   });
 
-  it("maps output_config.effort high to Kiro max_thinking_length 24576", () => {
+  it("does not send additionalModelRequestFields for Kiro models without effort support", () => {
     const out = C2K({
       output_config: { effort: "high" },
       messages: [{ role: "user", content: "think with adaptive effort" }],
     });
 
-    expect(out.conversationState.currentMessage.userInputMessage.content).toContain(
-      "<max_thinking_length>24576</max_thinking_length>"
-    );
+    expect(out.additionalModelRequestFields).toBeUndefined();
+    expect(out.thinking).toBeUndefined();
+    expect(out.systemPrompt).toContain("<max_thinking_length>24576</max_thinking_length>");
+  });
+
+  it("maps output_config.effort high to Kiro CLI-style additionalModelRequestFields for effort models", () => {
+    const out = C2K({
+      output_config: { effort: "high" },
+      messages: [{ role: "user", content: "think with adaptive effort" }],
+    }, null, "claude-sonnet-5");
+
+    expect(out.additionalModelRequestFields).toEqual({
+      thinking: { type: "adaptive", display: "summarized" },
+      output_config: { effort: "high" },
+    });
+    expect(out.thinking).toBeUndefined();
+    expect(out.systemPrompt).toContain("<max_thinking_length>24576</max_thinking_length>");
+  });
+
+  it("sends Claude system as top-level systemPrompt and keeps a user-content fallback", () => {
+    const out = C2K({
+      system: "system-only instruction",
+      messages: [{ role: "user", content: "hello" }],
+    });
+
+    expect(out.systemPrompt).toContain("system-only instruction");
+    expect(out.conversationState.currentMessage.userInputMessage.content).toContain("system-only instruction");
+  });
+
+  it("keeps top-level systemPrompt stable across turns", () => {
+    const first = C2K({
+      system: "stable instruction",
+      messages: [{ role: "user", content: "first" }],
+    });
+    const second = C2K({
+      system: "stable instruction",
+      messages: [{ role: "user", content: "second" }],
+    });
+
+    expect(first.systemPrompt).toBe(second.systemPrompt);
+    expect(first.systemPrompt).not.toContain("Current time");
+    expect(first.conversationState.currentMessage.userInputMessage.content).toContain("Current time");
   });
 });
 

tests/unit/kiro-thinking-strip.test.js

@@ -1,5 +1,6 @@
 import { describe, it, expect } from "vitest";
 import { KiroExecutor } from "../../open-sse/executors/kiro.js";
+import "../translator/registerAll.js";
 
 function createMockFrame(eventType, payloadObj) {
   const payloadStr = JSON.stringify(payloadObj);
@@ -47,6 +48,13 @@ async function readAllSSE(stream) {
   return result;
 }
 
+async function readNextWithTimeout(reader) {
+  return Promise.race([
+    reader.read(),
+    new Promise((_, reject) => setTimeout(() => reject(new Error("timed out waiting for SSE chunk")), 100)),
+  ]);
+}
+
 describe("KiroExecutor thinking tag stripping", () => {
   it("strips <thinking> tags from assistantResponseEvent", async () => {
     const executor = new KiroExecutor();
@@ -121,4 +129,53 @@ describe("KiroExecutor thinking tag stripping", () => {
     const contentChunks = objects.filter(obj => obj.choices[0].delta.content !== undefined);
     expect(contentChunks.length).toBe(0);
   });
+
+  it("emits a terminal chunk at messageStop before the upstream stream closes", async () => {
+    const executor = new KiroExecutor();
+
+    const f1 = createMockFrame("assistantResponseEvent", { content: "OK" });
+    const f2 = createMockFrame("messageStopEvent", {});
+
+    const readableStream = new ReadableStream({
+      start(controller) {
+        controller.enqueue(f1);
+        controller.enqueue(f2);
+      }
+    });
+
+    const transformedResponse = executor.transformEventStreamToSSE({ body: readableStream }, "claude-test");
+    const reader = transformedResponse.body.getReader();
+    const decoder = new TextDecoder();
+    let output = "";
+    for (let i = 0; i < 4 && !output.includes("\"finish_reason\":\"stop\""); i++) {
+      const { value } = await readNextWithTimeout(reader);
+      output += decoder.decode(value, { stream: true });
+    }
+    await reader.cancel();
+
+    expect(output).toContain("\"finish_reason\":\"stop\"");
+  });
+
+  it("uses tool_calls finish reason for tool streams without messageStop", async () => {
+    const executor = new KiroExecutor();
+
+    const f1 = createMockFrame("toolUseEvent", { toolUseId: "tool-1", name: "read_file", input: { path: "a.txt" } });
+
+    const readableStream = new ReadableStream({
+      start(controller) {
+        controller.enqueue(f1);
+        controller.close();
+      }
+    });
+
+    const transformedResponse = executor.transformEventStreamToSSE({ body: readableStream }, "claude-test");
+    const output = await readAllSSE(transformedResponse.body);
+    const objects = output
+      .split("\n")
+      .filter(line => line.startsWith("data: ") && !line.includes("[DONE]"))
+      .map(line => JSON.parse(line.slice(6)));
+
+    const finalChunk = objects.at(-1);
+    expect(finalChunk.choices[0].finish_reason).toBe("tool_calls");
+  });
 });

tests/unit/openai-to-kiro.test.js

@@ -11,6 +11,7 @@ import { openaiToKiroRequest } from "../../open-sse/translator/request/openai-to
 
 const contentOf = (result) =>
   result.conversationState.currentMessage.userInputMessage.content;
+const systemPromptOf = (result) => result.systemPrompt || "";
 
 describe("openaiToKiroRequest", () => {
   describe("basic message conversion", () => {
@@ -293,7 +294,11 @@ describe("openaiToKiroRequest", () => {
 
       const result = openaiToKiroRequest("claude-sonnet-4.6", body, true, {});
 
-      expect(contentOf(result)).toContain("<max_thinking_length>1024</max_thinking_length>");
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>1024</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toEqual({
+        thinking: { type: "adaptive", display: "summarized" },
+        output_config: { effort: "low" },
+      });
     });
 
     it("maps reasoning_effort high to max_thinking_length 24576", () => {
@@ -304,7 +309,97 @@ describe("openaiToKiroRequest", () => {
 
       const result = openaiToKiroRequest("claude-sonnet-4.6", body, true, {});
 
-      expect(contentOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toEqual({
+        thinking: { type: "adaptive", display: "summarized" },
+        output_config: { effort: "high" },
+      });
+    });
+
+    it("does not send additionalModelRequestFields for legacy Kiro model ids", () => {
+      const body = {
+        reasoning_effort: "high",
+        messages: [{ role: "user", content: "Legacy model id should not get adaptive fields" }]
+      };
+
+      const result = openaiToKiroRequest("claude-sonnet-4.5", body, true, {});
+
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toBeUndefined();
+    });
+
+    it("does not send additionalModelRequestFields for date-suffixed Claude 4 model ids", () => {
+      const body = {
+        reasoning_effort: "high",
+        messages: [{ role: "user", content: "Date-suffixed Claude 4 should stay legacy" }]
+      };
+
+      const result = openaiToKiroRequest("claude-sonnet-4-20250514", body, true, {});
+
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toBeUndefined();
+    });
+
+    it("does not send additionalModelRequestFields for pre-4 legacy Kiro model ids", () => {
+      const body = {
+        reasoning_effort: "high",
+        messages: [{ role: "user", content: "Older model id should not get adaptive fields" }]
+      };
+
+      const result = openaiToKiroRequest("claude-sonnet-3.7", body, true, {});
+
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toBeUndefined();
+    });
+
+    it("does not send additionalModelRequestFields for prefixed pre-4 legacy Kiro model ids", () => {
+      const body = {
+        reasoning_effort: "high",
+        messages: [{ role: "user", content: "Prefixed older model id should not get adaptive fields" }]
+      };
+
+      const result = openaiToKiroRequest("kiro/claude-3-7-sonnet-20250219", body, true, {});
+
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toBeUndefined();
+    });
+
+    it("does not send Claude-specific additionalModelRequestFields for prefixed non-Claude aliases", () => {
+      const body = {
+        reasoning_effort: "high",
+        messages: [{ role: "user", content: "Prefixed non-Claude alias should not get adaptive fields" }]
+      };
+
+      const result = openaiToKiroRequest("kiro/gpt-4o", body, true, {});
+
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toBeUndefined();
+    });
+
+    it("does not send Claude-specific additionalModelRequestFields for non-Claude aliases", () => {
+      const body = {
+        reasoning_effort: "high",
+        messages: [{ role: "user", content: "Non-Claude aliases should not get Claude adaptive fields" }]
+      };
+
+      const result = openaiToKiroRequest("gpt-4o", body, true, {});
+
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
+      expect(result.additionalModelRequestFields).toBeUndefined();
+    });
+
+    it("defaults future Kiro model ids to additionalModelRequestFields support", () => {
+      const body = {
+        reasoning_effort: "high",
+        messages: [{ role: "user", content: "Future model id should get adaptive fields" }]
+      };
+
+      const result = openaiToKiroRequest("claude-sonnet-4.60", body, true, {});
+
+      expect(result.additionalModelRequestFields).toEqual({
+        thinking: { type: "adaptive", display: "summarized" },
+        output_config: { effort: "high" },
+      });
     });
 
     it("clamps reasoning_effort max to Kiro max_thinking_length 32000", () => {
@@ -315,7 +410,8 @@ describe("openaiToKiroRequest", () => {
 
       const result = openaiToKiroRequest("claude-sonnet-4.6", body, true, {});
 
-      expect(contentOf(result)).toContain("<max_thinking_length>32000</max_thinking_length>");
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>32000</max_thinking_length>");
+      expect(result.additionalModelRequestFields?.output_config?.effort).toBe("high");
     });
 
     it("clamps OpenAI Responses reasoning.effort xhigh to max_thinking_length 32000", () => {
@@ -326,7 +422,8 @@ describe("openaiToKiroRequest", () => {
 
       const result = openaiToKiroRequest("claude-sonnet-4.6", body, true, {});
 
-      expect(contentOf(result)).toContain("<max_thinking_length>32000</max_thinking_length>");
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>32000</max_thinking_length>");
+      expect(result.additionalModelRequestFields?.output_config?.effort).toBe("high");
     });
 
     it("uses Claude thinking.budget_tokens as max_thinking_length", () => {
@@ -337,7 +434,7 @@ describe("openaiToKiroRequest", () => {
 
       const result = openaiToKiroRequest("claude-sonnet-4.6", body, true, {});
 
-      expect(contentOf(result)).toContain("<max_thinking_length>4096</max_thinking_length>");
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>4096</max_thinking_length>");
     });
 
     it("uses the default budget for synthetic -thinking models with no explicit config", () => {
@@ -347,7 +444,54 @@ describe("openaiToKiroRequest", () => {
 
       const result = openaiToKiroRequest("claude-sonnet-4.6-thinking", body, true, {});
 
-      expect(contentOf(result)).toContain("<max_thinking_length>16000</max_thinking_length>");
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>16000</max_thinking_length>");
+    });
+
+    it("keeps top-level systemPrompt stable across turns", () => {
+      const first = openaiToKiroRequest(
+        "claude-sonnet-4.6-thinking",
+        { messages: [{ role: "user", content: "first" }] },
+        true,
+        {}
+      );
+      const second = openaiToKiroRequest(
+        "claude-sonnet-4.6-thinking",
+        { messages: [{ role: "user", content: "second" }] },
+        true,
+        {}
+      );
+
+      expect(first.systemPrompt).toBe(second.systemPrompt);
+      expect(first.systemPrompt).not.toContain("Current time");
+      expect(first.conversationState.currentMessage.userInputMessage.content).toContain("Current time");
+    });
+
+    it("replays frozen msg0 for explicit Kiro sessions while keeping current time fresh", () => {
+      const credentials = {
+        connectionId: "kiro-account-openai-replay",
+        rawHeaders: { "x-session-id": "hermes-session-openai-replay" },
+      };
+      const first = openaiToKiroRequest(
+        "claude-sonnet-4.6",
+        { messages: [{ role: "user", content: "first turn" }] },
+        true,
+        credentials
+      );
+      const second = openaiToKiroRequest(
+        "claude-sonnet-4.6",
+        { messages: [{ role: "user", content: "second turn" }] },
+        true,
+        credentials
+      );
+
+      expect(second.conversationState.conversationId).toBe("hermes-session-openai-replay");
+      expect(second.conversationState.agentContinuationId).toBe(first.conversationState.agentContinuationId);
+      expect(second.conversationState.history[0].userInputMessage.content).toBe(
+        first.conversationState.currentMessage.userInputMessage.content
+      );
+      expect(second.conversationState.history[0].userInputMessage.modelId).toBe("claude-sonnet-4.6");
+      expect(second.conversationState.currentMessage.userInputMessage.content).toContain("Current time");
+      expect(second.conversationState.currentMessage.userInputMessage.content).toContain("second turn");
     });
 
     it("does not inject thinking prefix for reasoning_effort none", () => {
@@ -358,8 +502,9 @@ describe("openaiToKiroRequest", () => {
 
       const result = openaiToKiroRequest("claude-sonnet-4.6", body, true, {});
 
-      expect(contentOf(result)).not.toContain("<thinking_mode>enabled</thinking_mode>");
-      expect(contentOf(result)).not.toContain("<max_thinking_length>");
+      expect(systemPromptOf(result)).not.toContain("<thinking_mode>enabled</thinking_mode>");
+      expect(systemPromptOf(result)).not.toContain("<max_thinking_length>");
+      expect(result.additionalModelRequestFields).toBeUndefined();
     });
   });
 });

tests/unit/session-manager.test.js

@@ -1,13 +1,15 @@
 // A2: locks resolveSessionId priority/stickiness (codex/kiro/antigravity centralization).
 import { describe, it, expect, beforeEach } from "vitest";
-import { resolveSessionId, deriveSessionId, clearSessionStore } from "../../open-sse/utils/sessionManager.js";
+import { resolveContinuationId, resolveSessionId, resolveSessionIdentity, deriveSessionId, clearSessionStore } from "../../open-sse/utils/sessionManager.js";
 
 // Assistant text must reach ASSISTANT_MIN_LEN (80) to use assistant anchor; else first user message.
 const longAssistant = "x".repeat(80);
 const bodyWithAssistant = { messages: [{ role: "assistant", content: longAssistant }] };
 const bodyWithUserOnly = { messages: [{ role: "user", content: "hello from first user message anchor" }] };
 
-beforeEach(() => clearSessionStore());
+beforeEach(() => {
+  clearSessionStore();
+});
 
 describe("resolveSessionId", () => {
   it("stickiness: same body+connectionId+scope -> same id", () => {
@@ -55,8 +57,170 @@ describe("resolveSessionId", () => {
     expect(got).toBe("client-sess-123");
   });
 
+  it("does not treat request-scoped x-client-request-id as a session override", () => {
+    const first = resolveSessionId({
+      headers: { "x-client-request-id": "req-1" },
+      body: bodyWithUserOnly,
+      connectionId: "conn1",
+      scope: "kiro",
+    });
+    const second = resolveSessionId({
+      headers: { "x-client-request-id": "req-2" },
+      body: bodyWithUserOnly,
+      connectionId: "conn1",
+      scope: "kiro",
+    });
+
+    expect(first).not.toBe("req-1");
+    expect(second).not.toBe("req-2");
+    expect(first).not.toBe(second);
+  });
+
+  it("does not treat request-scoped previous_response_id as a Kiro session override", () => {
+    const first = resolveSessionId({
+      body: { ...bodyWithUserOnly, previous_response_id: "resp-1" },
+      connectionId: "conn1",
+      scope: "kiro",
+    });
+    const second = resolveSessionId({
+      body: { ...bodyWithUserOnly, previous_response_id: "resp-2" },
+      connectionId: "conn1",
+      scope: "kiro",
+    });
+
+    expect(first).not.toBe("resp-1");
+    expect(second).not.toBe("resp-2");
+    expect(first).not.toBe(second);
+  });
+
+  it("does not treat raw metadata.user_id as a Kiro conversation session", () => {
+    const first = resolveSessionId({
+      body: {
+        metadata: { user_id: "user-123" },
+        messages: [{ role: "user", content: "new chat about invoices" }],
+      },
+      connectionId: "conn1",
+      scope: "kiro",
+    });
+    const second = resolveSessionId({
+      body: {
+        metadata: { user_id: "user-123" },
+        messages: [{ role: "user", content: "unrelated new chat about refunds" }],
+      },
+      connectionId: "conn1",
+      scope: "kiro",
+    });
+
+    expect(first).not.toBe("user-123");
+    expect(second).not.toBe("user-123");
+    expect(first).not.toBe(second);
+  });
+
+  it("keeps Claude Code session_id metadata as a Kiro conversation session", () => {
+    const body = {
+      metadata: { user_id: JSON.stringify({ session_id: "claude-code-session-123" }) },
+      messages: [{ role: "user", content: "same Claude Code session" }],
+    };
+
+    expect(resolveSessionId({ body, connectionId: "conn1", scope: "kiro" })).toBe("claude:claude-code-session-123");
+  });
+
+  it("keeps raw metadata.user_id as a non-Kiro session fallback", () => {
+    const got = resolveSessionId({
+      body: {
+        metadata: { user_id: "user-123" },
+        messages: [{ role: "user", content: "non-Kiro provider" }],
+      },
+      connectionId: "conn1",
+      scope: "codex",
+    });
+
+    expect(got).toBe("user-123");
+  });
+
+  it("keeps x-client-request-id as a session override outside Kiro scope", () => {
+    const got = resolveSessionId({
+      headers: { "x-client-request-id": "req-1" },
+      body: bodyWithAssistant,
+      connectionId: "conn1",
+      scope: "codex",
+    });
+
+    expect(got).toBe("req-1");
+  });
+
+
   it("workspaceId path: empty body + workspaceId set -> normalized workspaceId", () => {
     const got = resolveSessionId({ body: {}, connectionId: "conn1", workspaceId: "ws-abc" });
     expect(got).toBe("ws-abc");
   });
+
+  it("uses fresh Kiro sessions for unrelated headerless requests on the same connection", () => {
+    const a = resolveSessionId({ body: bodyWithUserOnly, connectionId: "conn1", scope: "kiro" });
+    const b = resolveSessionId({ body: bodyWithUserOnly, connectionId: "conn1", scope: "kiro" });
+    expect(a).not.toBe(b);
+  });
+
+  it("marks generated headerless Kiro sessions as ephemeral", () => {
+    const generated = resolveSessionIdentity({ body: bodyWithUserOnly, connectionId: "conn1", scope: "kiro" });
+    const explicit = resolveSessionIdentity({
+      headers: { "x-session-id": "client-sess-123" },
+      body: bodyWithUserOnly,
+      connectionId: "conn1",
+      scope: "kiro",
+    });
+
+    expect(generated.ephemeral).toBe(true);
+    expect(explicit).toEqual({ sessionId: "client-sess-123", ephemeral: false });
+  });
+
+  it("does not switch Kiro headerless requests to assistant-text session ids mid-conversation", () => {
+    const withAssistant = { messages: [{ role: "user", content: "same user" }, { role: "assistant", content: "y".repeat(80) }] };
+    const a = resolveSessionId({ body: withAssistant, connectionId: "conn1", scope: "kiro" });
+    const b = resolveSessionId({ body: withAssistant, connectionId: "conn1", scope: "kiro" });
+    expect(a).not.toBe(b);
+  });
+});
+
+describe("resolveContinuationId", () => {
+  it("keeps continuation id stable for the same Kiro session", () => {
+    const opts = { sessionId: "kiro-session-1", connectionId: "conn1", scope: "kiro" };
+    expect(resolveContinuationId(opts)).toBe(resolveContinuationId(opts));
+  });
+
+  it("uses a different continuation id for a different Kiro session", () => {
+    const a = resolveContinuationId({ sessionId: "kiro-session-1", connectionId: "conn1", scope: "kiro" });
+    const b = resolveContinuationId({ sessionId: "kiro-session-2", connectionId: "conn1", scope: "kiro" });
+    expect(a).not.toBe(b);
+  });
+
+  it("does not evict a recently used continuation id when the store exceeds its cap", () => {
+    const first = resolveContinuationId({ sessionId: "kiro-session-0", connectionId: "conn1", scope: "kiro" });
+    for (let i = 1; i < 5000; i++) {
+      resolveContinuationId({ sessionId: `kiro-session-${i}`, connectionId: "conn1", scope: "kiro" });
+    }
+    expect(resolveContinuationId({ sessionId: "kiro-session-0", connectionId: "conn1", scope: "kiro" })).toBe(first);
+    resolveContinuationId({ sessionId: "kiro-session-5000", connectionId: "conn1", scope: "kiro" });
+
+    expect(resolveContinuationId({ sessionId: "kiro-session-0", connectionId: "conn1", scope: "kiro" })).toBe(first);
+  });
+
+  it("evicts old continuation ids when the store exceeds its cap", () => {
+    const first = resolveContinuationId({ sessionId: "kiro-session-0", connectionId: "conn1", scope: "kiro" });
+    for (let i = 1; i <= 5000; i++) {
+      resolveContinuationId({ sessionId: `kiro-session-${i}`, connectionId: "conn1", scope: "kiro" });
+    }
+
+    const afterEviction = resolveContinuationId({ sessionId: "kiro-session-0", connectionId: "conn1", scope: "kiro" });
+    expect(afterEviction).not.toBe(first);
+  });
+
+  it("does not let ephemeral Kiro continuations evict explicit session continuations", () => {
+    const stable = resolveContinuationId({ sessionId: "explicit-session", connectionId: "conn1", scope: "kiro" });
+    for (let i = 0; i <= 5000; i++) {
+      resolveContinuationId({ sessionId: `ephemeral-session-${i}`, connectionId: "conn1", scope: "kiro", ephemeral: true });
+    }
+
+    expect(resolveContinuationId({ sessionId: "explicit-session", connectionId: "conn1", scope: "kiro" })).toBe(stable);
+  });
 });