diff --git a/src/adapters/channel/api-server/ApiServerChannel.ts b/src/adapters/channel/api-server/ApiServerChannel.ts
index e17634cb1..1e7ea969d 100644
--- a/src/adapters/channel/api-server/ApiServerChannel.ts
+++ b/src/adapters/channel/api-server/ApiServerChannel.ts
@@ -275,6 +275,13 @@ export class ApiServerChannel implements ChannelAdapter {
     }
 
     this.activeChats.add(chatId);
+    // Expose the session id on every response for this turn, including
+    // buffered failures. An inline `/new <message>` creates the session
+    // binding before the gateway is contacted; when such a turn fails
+    // without this header the caller never learns the chat id, the
+    // retained binding becomes unreachable, and headerless retries fork
+    // into fresh `:general` sessions instead of the reset one.
+    res.setHeader("X-Hermes-Session-Id", chatId);
     try {
       if (streaming) {
         await this.streamTurn(res, chatId, mapped.sessionKey, mapped.message);
@@ -303,7 +310,6 @@ export class ApiServerChannel implements ChannelAdapter {
     res.setHeader("Content-Type", "text/event-stream");
     res.setHeader("Cache-Control", "no-cache");
     res.setHeader("Connection", "keep-alive");
-    res.setHeader("X-Hermes-Session-Id", chatId);
     res.statusCode = 200;
     res.flushHeaders?.();
 
@@ -401,7 +407,6 @@ export class ApiServerChannel implements ChannelAdapter {
     }
     clearTimeout(timeout);
 
-    res.setHeader("X-Hermes-Session-Id", chatId);
     sendJson(res, 200, buildChatCompletion(this.modelName, replyText.trim()));
   }
 }
diff --git a/tests/adapters/channel/api-server-session-header.spec.ts b/tests/adapters/channel/api-server-session-header.spec.ts
new file mode 100644
index 000000000..0e3ea4e7a
--- /dev/null
+++ b/tests/adapters/channel/api-server-session-header.spec.ts
@@ -0,0 +1,174 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { Readable } from "node:stream";
+
+import { ApiServerChannel } from "../../../src/adapters/channel/api-server/ApiServerChannel.js";
+import { ApiServerSessionMapper } from "../../../src/adapters/channel/api-server/ApiServerSessionMapper.js";
+import type { Gateway, GatewayEvent, GatewaySubmitTurnInput } from "../../../src/gateway/index.js";
+
+type Call = Pick<GatewaySubmitTurnInput, "sessionKey" | "channelKey" | "message">;
+
+class FakeResponse {
+  statusCode = 200;
+  readonly headers = new Map<string, string>();
+  private readonly chunks: string[] = [];
+
+  setHeader(name: string, value: string): void {
+    this.headers.set(name.toLowerCase(), String(value));
+  }
+
+  getHeader(name: string): string | undefined {
+    return this.headers.get(String(name).toLowerCase());
+  }
+
+  write(chunk: string): boolean {
+    this.chunks.push(String(chunk));
+    return true;
+  }
+
+  flushHeaders(): void {}
+
+  end(chunk?: string): void {
+    if (chunk !== undefined) this.chunks.push(String(chunk));
+  }
+
+  get body(): string {
+    return this.chunks.join("");
+  }
+}
+
+function makeRequest(content: string, stream: boolean, sessionId?: string): Readable & {
+  method?: string;
+  url?: string;
+  headers: Record<string, string>;
+} {
+  const headers: Record<string, string> = {
+    host: "fixture.invalid",
+    "content-type": "application/json",
+  };
+  if (sessionId !== undefined) headers["x-hermes-session-id"] = sessionId;
+  const request = Readable.from([Buffer.from(JSON.stringify({
+    model: "fixture-model",
+    messages: [{ role: "user", content }],
+    stream,
+  }))]) as Readable & { method?: string; url?: string; headers: Record<string, string> };
+  request.method = "POST";
+  request.url = "/v1/chat/completions";
+  request.headers = headers;
+  return request;
+}
+
+function makeMapper(): ApiServerSessionMapper {
+  return new ApiServerSessionMapper({ activeByChatId: {} }, () => "00000000-0000-0000-0000-000000000042");
+}
+
+async function post(
+  channel: ApiServerChannel,
+  content: string,
+  stream: boolean,
+  sessionId?: string,
+): Promise<{ status: number; sessionHeader: string | null; body: string }> {
+  const response = new FakeResponse();
+  await (channel as unknown as {
+    handleRequest(req: unknown, res: FakeResponse): Promise<void>;
+  }).handleRequest(makeRequest(content, stream, sessionId), response);
+  return {
+    status: response.statusCode,
+    sessionHeader: response.headers.get("x-hermes-session-id") ?? null,
+    body: response.body,
+  };
+}
+
+function makeGateway(mode: "succeed" | "throw", calls: Call[]): Gateway {
+  return {
+    submitTurn(input: GatewaySubmitTurnInput): AsyncIterable<GatewayEvent> {
+      calls.push({
+        sessionKey: input.sessionKey,
+        channelKey: input.channelKey,
+        message: input.message,
+      });
+      return (async function* (): AsyncGenerator<GatewayEvent> {
+        if (mode === "throw") {
+          throw new Error("synthetic submit failure");
+        }
+        yield { type: "assistant_text_delta", text: "fixture reply" } as GatewayEvent;
+        yield {
+          type: "turn_completed",
+          usage: { inputTokens: 0, outputTokens: 0, totalTokens: 0 },
+          finishReason: "completed",
+        } as GatewayEvent;
+      })();
+    },
+  } as unknown as Gateway;
+}
+
+function installGateway(channel: ApiServerChannel, gateway: Gateway | undefined): void {
+  (channel as unknown as { gateway?: Gateway }).gateway = gateway;
+}
+
+function mapperEntries(channel: ApiServerChannel): Array<[string, string]> {
+  return Object.entries((channel as unknown as {
+    mapper: { snapshot(): { activeByChatId: Record<string, string> } };
+  }).mapper.snapshot().activeByChatId);
+}
+
+function makeChannel(): ApiServerChannel {
+  return new ApiServerChannel({
+    host: "127.0.0.1",
+    port: 0,
+    modelName: "fixture-model",
+    mapper: makeMapper(),
+  });
+}
+
+test("buffered inline /new failure exposes the session id and retries reach the reset session", async () => {
+  const channel = makeChannel();
+  const failedCalls: Call[] = [];
+  installGateway(channel, makeGateway("throw", failedCalls));
+
+  const failed = await post(channel, "/new first prompt", false);
+  assert.equal(failed.status, 500);
+  assert.ok(failed.body.includes("channel_submit_failed"));
+  assert.ok(failed.sessionHeader, "buffered failure must still expose the session id");
+
+  const bindings = mapperEntries(channel);
+  assert.equal(bindings.length, 1);
+  const [, resetSessionKey] = bindings[0]!;
+  assert.ok(resetSessionKey.includes(":s_"));
+
+  const retryCalls: Call[] = [];
+  installGateway(channel, makeGateway("succeed", retryCalls));
+  const retry = await post(channel, "retry with returned token", false, failed.sessionHeader!);
+  assert.equal(retry.status, 200);
+  assert.equal(retryCalls[0]?.sessionKey, resetSessionKey);
+});
+
+test("buffered gateway-unavailable inline /new exposes the session id", async () => {
+  const channel = makeChannel();
+
+  const failed = await post(channel, "/new first prompt", false);
+  assert.equal(failed.status, 503);
+  assert.ok(failed.body.includes("gateway_unavailable"));
+  assert.ok(failed.sessionHeader, "preflight failure must still expose the session id");
+  assert.equal(mapperEntries(channel).length, 1);
+});
+
+test("streaming preflight gateway-unavailable inline /new exposes the session id", async () => {
+  const channel = makeChannel();
+
+  const failed = await post(channel, "/new first prompt", true);
+  assert.equal(failed.status, 503);
+  assert.ok(failed.sessionHeader, "streaming preflight failure must still expose the session id");
+  assert.equal(mapperEntries(channel).length, 1);
+});
+
+test("buffered success still exposes the session id", async () => {
+  const channel = makeChannel();
+  const calls: Call[] = [];
+  installGateway(channel, makeGateway("succeed", calls));
+
+  const ok = await post(channel, "plain message", false);
+  assert.equal(ok.status, 200);
+  assert.ok(ok.sessionHeader);
+  assert.ok(calls[0]?.sessionKey.endsWith(":general"));
+});