diff --git a/.changeset/chat-completion-tool-calls-608.md b/.changeset/chat-completion-tool-calls-608.md
new file mode 100644
index 00000000..6d362e9f
--- /dev/null
+++ b/.changeset/chat-completion-tool-calls-608.md
@@ -0,0 +1,27 @@
+---
+"ornn-api": patch
+---
+
+NyxLlmClient now normalizes Chat Completions tool-call deltas into the same Responses-API `response.output_item.done` / `function_call` events the playground tool loop already consumes (#608).
+
+Background: #574 routed chat-completion providers to `/chat/completions` and translated text deltas, but the stream parser ignored `choices[].delta.tool_calls`. The playground tool-use loop in `chatService.ts` only matches on Responses-API `response.output_item.done` with `item.type === "function_call"`, so when a chat-completion provider (DeepSeek, Together, any OpenAI-compat gateway) responded with a tool call, no `function_call` event ever reached the loop. The model's `execute_in_sandbox(...)` invocation arrived as plain assistant text and got rendered as JSON in the chat instead of being executed — runtime-based and mixed skills appeared to "respond" without ever running the sandbox.
+
+Fix: `parseChatCompletionStream` keeps a per-index `Map<number, ToolCallAccumulator>` carrying `{id, name, arguments}`. Each `choices[].delta.tool_calls[]` chunk merges into its index buffer (id + name arrive on the first chunk for that call; the `arguments` JSON string accumulates across many chunks). A turn flushes when any of: explicit `finish_reason` (`tool_calls`, `stop`, anything non-null), upstream `[DONE]` sentinel, or stream EOF — whichever fires first. A `flushed` guard makes flush idempotent so we never double-emit if multiple end signals fire.
+
+The synthesized event matches the Responses-API shape `chatService.ts` already validates with Zod (`outputItemDoneEventSchema`):
+
+```js
+{
+  type: "response.output_item.done",
+  item: {
+    type: "function_call",
+    id, call_id, name, arguments,  // arguments is the accumulated JSON string
+  },
+}
+```
+
+This way zero changes are needed in `chatService.ts` — its existing `pendingToolCall` capture + `executeToolCall` dispatch path works for both upstream formats now.
+
+Parallel tool calls within one assistant turn are supported (one done event per index, emitted in index order). Missing `index` falls back to 0 (treated as a single tool call). Streams that close without `[DONE]` or `finish_reason` still flush at EOF so a buffered call is never lost.
+
+Coverage: 6 new tests appended to `src/clients/nyxid/llm.test.ts` — chunked accumulation + finish_reason flush, EOF flush without [DONE], parallel tool calls, idempotent flush across finish_reason+[DONE], intermixed text+tool deltas (correct event order), missing `index` fallback. All 17 tests in the file green; full ornn-api suite has no new regressions.
diff --git a/ornn-api/src/clients/nyxid/llm.test.ts b/ornn-api/src/clients/nyxid/llm.test.ts
index 143dc852..ae73130c 100644
--- a/ornn-api/src/clients/nyxid/llm.test.ts
+++ b/ornn-api/src/clients/nyxid/llm.test.ts
@@ -400,3 +400,211 @@ describe("NyxLlmClient.complete() routing on apiFormat", () => {
     expect(out).toEqual([]);
   });
 });
+
+// ---------------------------------------------------------------------------
+// #608 — chat-completion tool-call delta normalization
+// ---------------------------------------------------------------------------
+
+describe("chat-completion stream tool-call normalization (#608)", () => {
+  function makeClient(): NyxLlmClient {
+    return new NyxLlmClient({
+      resolver: makeResolver({
+        gatewayUrl: "https://api.example.com",
+        apiKey: "sk-x",
+        apiFormat: "chat-completion",
+      }),
+      saTokenProvider: STUB_SA_TOKEN,
+    });
+  }
+
+  it("accumulates tool_calls across chunks and emits one output_item.done on finish_reason=tool_calls", async () => {
+    fetchHandler = () =>
+      sseResponse([
+        JSON.stringify({
+          choices: [{
+            delta: {
+              tool_calls: [{
+                index: 0,
+                id: "call_abc",
+                type: "function",
+                function: { name: "execute_in_sandbox", arguments: "" },
+              }],
+            },
+          }],
+        }),
+        JSON.stringify({
+          choices: [{
+            delta: { tool_calls: [{ index: 0, function: { arguments: "{\"scr" } }] },
+          }],
+        }),
+        JSON.stringify({
+          choices: [{
+            delta: { tool_calls: [{ index: 0, function: { arguments: "ipt\":\"x\"}" } }] },
+          }],
+        }),
+        JSON.stringify({ choices: [{ delta: {}, finish_reason: "tool_calls" }] }),
+      ]);
+
+    const events: ResponsesApiStreamEvent[] = [];
+    for await (const e of makeClient().stream({
+      model: "deepseek-v4",
+      input: [{ role: "user", content: "run x" }],
+      tools: [{
+        type: "function",
+        name: "execute_in_sandbox",
+        description: "run",
+        parameters: { type: "object" },
+      }],
+    })) events.push(e);
+
+    const done = events.filter((e) => e.type === "response.output_item.done");
+    expect(done).toHaveLength(1);
+    expect(done[0]).toEqual({
+      type: "response.output_item.done",
+      item: {
+        type: "function_call",
+        id: "call_abc",
+        call_id: "call_abc",
+        name: "execute_in_sandbox",
+        arguments: "{\"script\":\"x\"}",
+      },
+    });
+  });
+
+  it("flushes a buffered tool call when stream ends without [DONE] or finish_reason", async () => {
+    // Body has no [DONE] sentinel and no finish_reason — just an EOF.
+    fetchHandler = () =>
+      new Response(
+        `data: ${JSON.stringify({
+          choices: [{
+            delta: {
+              tool_calls: [{
+                index: 0,
+                id: "call_z",
+                function: { name: "t", arguments: "{\"a\":1}" },
+              }],
+            },
+          }],
+        })}\n\n`,
+        { status: 200, headers: { "Content-Type": "text/event-stream" } },
+      );
+
+    const events: ResponsesApiStreamEvent[] = [];
+    for await (const e of makeClient().stream({
+      model: "m",
+      input: [{ role: "user", content: "go" }],
+    })) events.push(e);
+
+    const done = events.find((e) => e.type === "response.output_item.done");
+    expect(done).toEqual({
+      type: "response.output_item.done",
+      item: {
+        type: "function_call",
+        id: "call_z",
+        call_id: "call_z",
+        name: "t",
+        arguments: "{\"a\":1}",
+      },
+    });
+  });
+
+  it("supports parallel tool calls — one done event per index", async () => {
+    fetchHandler = () =>
+      sseResponse([
+        JSON.stringify({
+          choices: [{
+            delta: {
+              tool_calls: [
+                { index: 0, id: "call_a", function: { name: "fn_a", arguments: "{}" } },
+                { index: 1, id: "call_b", function: { name: "fn_b", arguments: "{}" } },
+              ],
+            },
+          }],
+        }),
+        JSON.stringify({ choices: [{ delta: {}, finish_reason: "tool_calls" }] }),
+      ]);
+
+    const events: ResponsesApiStreamEvent[] = [];
+    for await (const e of makeClient().stream({
+      model: "m",
+      input: [{ role: "user", content: "go" }],
+    })) events.push(e);
+
+    const done = events.filter((e) => e.type === "response.output_item.done");
+    expect(done).toHaveLength(2);
+    expect((done[0]!.item as { id: string }).id).toBe("call_a");
+    expect((done[1]!.item as { id: string }).id).toBe("call_b");
+  });
+
+  it("only flushes once when finish_reason and [DONE] both arrive", async () => {
+    fetchHandler = () =>
+      sseResponse([
+        JSON.stringify({
+          choices: [{
+            delta: {
+              tool_calls: [{ index: 0, id: "call_x", function: { name: "fn", arguments: "{}" } }],
+            },
+            finish_reason: "tool_calls",
+          }],
+        }),
+      ]);
+
+    const events: ResponsesApiStreamEvent[] = [];
+    for await (const e of makeClient().stream({
+      model: "m",
+      input: [{ role: "user", content: "go" }],
+    })) events.push(e);
+
+    const done = events.filter((e) => e.type === "response.output_item.done");
+    expect(done).toHaveLength(1);
+  });
+
+  it("intermixed text + tool_call deltas produce text-delta then done event in order", async () => {
+    fetchHandler = () =>
+      sseResponse([
+        JSON.stringify({ choices: [{ delta: { content: "thinking…" } }] }),
+        JSON.stringify({
+          choices: [{
+            delta: {
+              tool_calls: [{ index: 0, id: "call_q", function: { name: "fn", arguments: "{}" } }],
+            },
+          }],
+        }),
+        JSON.stringify({ choices: [{ delta: {}, finish_reason: "tool_calls" }] }),
+      ]);
+
+    const events: ResponsesApiStreamEvent[] = [];
+    for await (const e of makeClient().stream({
+      model: "m",
+      input: [{ role: "user", content: "go" }],
+    })) events.push(e);
+
+    expect(events.map((e) => e.type)).toEqual([
+      "response.output_text.delta",
+      "response.output_item.done",
+    ]);
+  });
+
+  it("tool_calls.index missing → falls back to index 0", async () => {
+    fetchHandler = () =>
+      sseResponse([
+        JSON.stringify({
+          choices: [{
+            delta: {
+              tool_calls: [{ id: "call_noix", function: { name: "fn", arguments: "{}" } }],
+            },
+            finish_reason: "tool_calls",
+          }],
+        }),
+      ]);
+
+    const events: ResponsesApiStreamEvent[] = [];
+    for await (const e of makeClient().stream({
+      model: "m",
+      input: [{ role: "user", content: "go" }],
+    })) events.push(e);
+
+    const done = events.find((e) => e.type === "response.output_item.done");
+    expect((done?.item as { id: string }).id).toBe("call_noix");
+  });
+});
diff --git a/ornn-api/src/clients/nyxid/llm.ts b/ornn-api/src/clients/nyxid/llm.ts
index 1f958eca..f3e9e681 100644
--- a/ornn-api/src/clients/nyxid/llm.ts
+++ b/ornn-api/src/clients/nyxid/llm.ts
@@ -11,11 +11,10 @@
  * `ResponsesApiStreamEvent`). For chat-completion providers the client
  * translates the request body on the way out and normalizes the SSE
  * stream / completion payload back into Responses-API event shape on
- * the way in, so consumers (skill generation + playground) do not need
- * to branch on apiFormat (#574).
- *
- * Tool-call delta normalization for chat-completion is intentionally
- * out of scope here — tracked in #608.
+ * the way in — both text deltas (#574) and accumulated tool-call
+ * deltas synthesized into `response.output_item.done` /
+ * `function_call` events (#608) — so consumers (skill generation +
+ * playground tool loop) never branch on apiFormat.
  *
  * Authenticates using a Service Account (SA) token obtained via
  * client_credentials grant when the resolved provider has no direct
@@ -185,21 +184,76 @@ async function* parseResponsesStream(
 }
 
 /**
- * Parse Chat Completions SSE and translate text deltas into
- * Responses-API event shape so consumers stay format-agnostic.
+ * Internal accumulator for a single OpenAI Chat Completions tool call
+ * as it streams in. `id` + `name` arrive on the first delta for that
+ * tool-call index; `arguments` is a JSON string that accumulates
+ * across many chunks before the model finishes emitting it.
+ */
+interface ToolCallAccumulator {
+  id: string;
+  name: string;
+  arguments: string;
+}
+
+/**
+ * Parse Chat Completions SSE and translate it into Responses-API
+ * event shape so downstream consumers (skill generation, playground
+ * tool-use loop) stay format-agnostic.
  *
- * For #574, only text deltas (`choices[].delta.content`) are
- * translated — emitted as `response.output_text.delta`. Tool-call
- * delta normalization is tracked in #608.
+ * - `choices[].delta.content` chunks → `response.output_text.delta`
+ *   events (#574).
+ * - `choices[].delta.tool_calls` chunks are buffered per tool-call
+ *   index (id + name + accumulated JSON arguments). When the turn
+ *   completes (explicit `finish_reason` of `"tool_calls"` /
+ *   `"stop"`, upstream `[DONE]`, or EOF), each buffered tool call is
+ *   emitted as a synthesized `response.output_item.done` event with
+ *   `item.type === "function_call"` — the exact shape the playground
+ *   loop already consumes (#608). Without this the playground never
+ *   sees a tool call from chat-completion providers and renders
+ *   `execute_in_sandbox(...)` as plain text instead of running it.
  */
 async function* parseChatCompletionStream(
   response: Response,
 ): AsyncIterable<ResponsesApiStreamEvent> {
+  const toolCalls = new Map<number, ToolCallAccumulator>();
+  let flushed = false;
+
+  function* flushToolCalls(): Generator<ResponsesApiStreamEvent> {
+    if (flushed) return;
+    flushed = true;
+    const indices = [...toolCalls.keys()].sort((a, b) => a - b);
+    for (const idx of indices) {
+      const tc = toolCalls.get(idx)!;
+      yield {
+        type: "response.output_item.done",
+        item: {
+          type: "function_call",
+          id: tc.id,
+          call_id: tc.id,
+          name: tc.name,
+          arguments: tc.arguments,
+        },
+      };
+    }
+  }
+
   for await (const { data } of parseSSELines(response)) {
-    if (data === "[DONE]") return;
+    if (data === "[DONE]") {
+      yield* flushToolCalls();
+      return;
+    }
     let chunk: {
       choices?: Array<{
-        delta?: { content?: string | null };
+        delta?: {
+          content?: string | null;
+          tool_calls?: Array<{
+            index?: number;
+            id?: string;
+            type?: string;
+            function?: { name?: string; arguments?: string };
+          }>;
+        };
+        finish_reason?: string | null;
       }>;
     };
     try {
@@ -208,11 +262,47 @@ async function* parseChatCompletionStream(
       logger.debug({ data: data.slice(0, 100) }, "Failed to parse chat-completion chunk");
       continue;
     }
-    const delta = chunk.choices?.[0]?.delta?.content;
-    if (typeof delta === "string" && delta.length > 0) {
-      yield { type: "response.output_text.delta", delta };
+
+    const choice = chunk.choices?.[0];
+    if (!choice) continue;
+
+    const text = choice.delta?.content;
+    if (typeof text === "string" && text.length > 0) {
+      yield { type: "response.output_text.delta", delta: text };
+    }
+
+    const deltaToolCalls = choice.delta?.tool_calls;
+    if (Array.isArray(deltaToolCalls)) {
+      for (const piece of deltaToolCalls) {
+        // OpenAI uses `index` to disambiguate parallel tool calls
+        // within one assistant turn. Missing index → assume a single
+        // tool call at index 0.
+        const idx = typeof piece.index === "number" ? piece.index : 0;
+        const acc = toolCalls.get(idx) ?? { id: "", name: "", arguments: "" };
+        if (piece.id) acc.id = piece.id;
+        if (piece.function?.name) acc.name = piece.function.name;
+        if (typeof piece.function?.arguments === "string") {
+          acc.arguments += piece.function.arguments;
+        }
+        toolCalls.set(idx, acc);
+      }
+    }
+
+    // Some providers (DeepSeek, Together, …) terminate a tool-call
+    // turn with finish_reason=tool_calls; others emit
+    // finish_reason=stop alongside the final tool-call delta. Treat
+    // any non-null finish_reason as "no more deltas this turn" and
+    // flush so the playground loop sees the tool call before
+    // [DONE] / EOF.
+    if (choice.finish_reason && toolCalls.size > 0) {
+      yield* flushToolCalls();
     }
   }
+
+  // Stream ended without a [DONE] sentinel (some upstreams just
+  // close the body). Flush any pending tool calls so we don't drop
+  // them on the floor.
+  yield* flushToolCalls();
 }
 
 // ---------------------------------------------------------------------------