fix(volcengine): scope assistant placeholder by endpoint

src/adapters/openai-chat.ts

@@ -672,16 +672,18 @@ const VOLCENGINE_ARK_HOSTNAMES = new Set([
   "ark.ap-southeast.volces.com",
 ]);
 
-function isVolcengineArkTarget(provider: OcxProviderConfig): boolean {
+function isVolcengineArkPaygChatTarget(provider: OcxProviderConfig): boolean {
   try {
-    return VOLCENGINE_ARK_HOSTNAMES.has(new URL(provider.baseUrl).hostname);
+    const url = new URL(provider.baseUrl);
+    const pathname = url.pathname.replace(/\/+$/, "") || "/";
+    return VOLCENGINE_ARK_HOSTNAMES.has(url.hostname) && pathname === "/api/v3";
   } catch {
     return false;
   }
 }
 
 function emptyAssistantContent(provider: OcxProviderConfig): string | { type: "text"; text: string }[] {
-  return isVolcengineArkTarget(provider) ? [{ type: "text", text: "" }] : "";
+  return isVolcengineArkPaygChatTarget(provider) ? [{ type: "text", text: "" }] : "";
 }
 
 function ensureRootObjectType(parameters: unknown): Record<string, unknown> {

structure/04_transports-and-sidecars.md

@@ -587,6 +587,22 @@ adapters advertise the catalog bit only on explicit `true`; cursor keeps its own
 Providers with flaky parallel streaming can be opted out individually. Evidence and provider
 ledger: `devlog/_fin/260709_parallel_tool_calls/`.
 
+## Volcengine Ark assistant continuation shapes
+
+The `openai-chat` adapter keeps Volcengine's pay-as-you-go Chat endpoint and Coding Plan endpoint
+on separate empty-assistant contracts. The pay-as-you-go `/api/v3` route retains the structured
+`[{ "type": "text", "text": "" }]` placeholder inferred for #796, while `/api/coding/v3` uses the
+ordinary empty string accepted by its live tool-call continuation contract (#1571). Matching only
+the shared Ark hostname is too broad because the two endpoint families reject opposite shapes.
+
+[Decision Log]
+- 목적과 의도: Preserve multi-turn tool-call continuations across both Ark Chat endpoint families.
+- 기존 구현 및 제약 조건: The #796 workaround was host-wide and unverified; live Coding Plan evidence shows its structured placeholder returns HTTP 400 while an empty string succeeds.
+- 검토한 주요 대안: Remove the workaround globally, select by model ID, or scope it by endpoint path.
+- 선택한 방식: Apply the structured placeholder only to recognized Ark hosts whose normalized base path is exactly `/api/v3`.
+- 다른 대안 대신 이 방식을 선택한 이유: Global removal would reopen #796, while model IDs can appear behind multiple Ark products and therefore do not identify the wire contract.
+- 장점, 단점 및 영향: Coding Plan regains its accepted continuation shape without changing generic providers; any future Ark endpoint family must provide evidence before inheriting the pay-as-you-go quirk.
+
 ## Chat structured-output compatibility
 
 The `openai-chat` adapter translates Responses `text.format` and Chat Completions

tests/volcengine-ark-assistant-content.test.ts

@@ -9,9 +9,9 @@ import type { OcxMessage, OcxParsedRequest, OcxProviderConfig } from "../src/typ
  * tool-call turn.
  *
  * This cannot be fixed globally. xAI rejects the opposite way -- "Each message must have at least
- * one content element" -- and the existing "" is what satisfies it. So the two contracts conflict
- * and the fix is host-gated, which is exactly what these tests have to prove: every case runs the
- * SAME input through Ark and a generic host and asserts the two diverge.
+ * one content element" -- and the existing "" is what satisfies it. Ark's Coding Plan endpoint
+ * also rejects the structured placeholder while accepting "" (#1571). The contracts therefore
+ * diverge by endpoint family, so these tests pin both the exact host and the exact Ark path.
  *
  * Scope of these tests: they verify the WIRE SHAPE we emit and that the host gate is real. They
  * cannot verify that Ark accepts it -- no request here reaches Volcengine. The array form is
@@ -23,6 +23,7 @@ function providerFor(baseUrl: string): OcxProviderConfig {
 }
 
 const ark = providerFor("https://ark.cn-beijing.volces.com/api/v3");
+const arkCodingPlan = providerFor("https://ark.cn-beijing.volces.com/api/coding/v3");
 const generic = providerFor("https://example.test/v1");
 
 interface ChatMsg {
@@ -80,6 +81,12 @@ describe("Volcengine Ark empty assistant content (#796)", () => {
     expect(assistant.content).toBe("");
   });
 
+  test("Ark Coding Plan keeps the accepted empty-string continuation", () => {
+    const [assistant] = assistantsOf(wire(arkCodingPlan, history));
+    expect(assistant.tool_calls).toHaveLength(1);
+    expect(assistant.content).toBe("");
+  });
+
   test("a synthesized orphan tool-call assistant follows the same rule", () => {
     // A tool result with no matching call: the adapter fabricates the assistant turn, and that
     // fabricated message hits the same Ark validator.
@@ -93,14 +100,20 @@ describe("Volcengine Ark empty assistant content (#796)", () => {
     expect(genericOrphan?.content).toBe("");
   });
 
-  test("the gate matches the host, not the path or a substring of it", () => {
-    // A lookalike host must not inherit the quirk: the fix keys on an exact hostname set, so a
-    // provider merely mentioning the string in its path stays on the default contract.
+  test("the gate matches the host and pay-as-you-go path, not a substring", () => {
+    // A lookalike host must not inherit the quirk: a provider merely mentioning the Ark hostname
+    // in its path stays on the default contract.
     const lookalike = providerFor("https://example.test/ark.cn-beijing.volces.com/v1");
     const [assistant] = assistantsOf(wire(lookalike, history));
     expect(assistant.content).toBe("");
   });
 
+  test("an unrelated path on the real Ark host does not inherit the pay-as-you-go quirk", () => {
+    const unrelatedArkPath = providerFor("https://ark.cn-beijing.volces.com/api/custom/v3");
+    const [assistant] = assistantsOf(wire(unrelatedArkPath, history));
+    expect(assistant.content).toBe("");
+  });
+
   test("Ark's regional sibling endpoint gets the same treatment", () => {
     const sea = providerFor("https://ark.ap-southeast.volces.com/api/v3");
     const [assistant] = assistantsOf(wire(sea, history));