fix(sse): keep a numeric delta.content as string text in the OpenAI passthrough

changelog.d/fixes/16614-numeric-delta-content.md

@@ -0,0 +1 @@
+- **fix(sse):** some Cloudflare Workers AI models stream a digit as a JSON number (`"delta": {"content": 7}`). Only string content counted as text in the passthrough, so those chunks were dropped and the digits vanished from the reply («ABC123» came out as «ABC»). A finite numeric `delta.content` is now turned into its string before the chunk is forwarded, recorded or counted ([#16614](https://github.com/diegosouzapw/OmniRoute/pull/16614)) — thanks @pacocartones. Refs #16554.

open-sse/utils/arrayContentDelta.ts

@@ -11,7 +11,8 @@
  * which strict Responses clients reject ("malformed response.output_text.delta delta").
  *
  * These helpers fold such a delta back into the OpenAI shape in place: text parts
- * become the `content` string, thinking parts are appended to `reasoning_content`.
+ * become the `content` string, thinking parts are appended to `reasoning_content`. A numeric
+ * `content` (some Cloudflare Workers AI models stream digits as JSON numbers) becomes its string.
  */
 
 type JsonRecord = Record<string, unknown>;
@@ -30,6 +31,14 @@ function partsText(value: unknown): string {
 
 /** Normalize one `delta` object. Returns true when it was changed. */
 export function normalizeArrayContentDelta(delta: JsonRecord): boolean {
+  // Cloudflare Workers AI sometimes streams a digit as a JSON number (`"content": 7`). Keep it as
+  // the text it stands for: a non-string content is not counted as text further down the
+  // pipeline, so the digit would be dropped (OmniRoute#16554).
+  if (typeof delta.content === "number") {
+    if (!Number.isFinite(delta.content)) return false;
+    delta.content = String(delta.content);
+    return true;
+  }
   if (!Array.isArray(delta.content)) return false;
 
   let text = "";

tests/unit/openai-numeric-delta-content.test.ts

@@ -0,0 +1,105 @@
+/**
+ * Cloudflare Workers AI (for example `@cf/mistralai/mistral-small-3.1-24b-instruct`) sometimes
+ * streams `choices[].delta.content` as a JSON number instead of a string:
+ *
+ *   {"delta":{"content":"A"}} {"delta":{"content":7}} {"delta":{"content":"."}}
+ *
+ * The passthrough only counted string content as text, so those chunks were dropped and the
+ * digits disappeared from the reply (OmniRoute#16554).
+ */
+
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-numeric-delta-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+const core = await import("../../src/lib/db/core.ts");
+
+const { createSSEStream } = await import("../../open-sse/utils/stream.ts");
+const { FORMATS } = await import("../../open-sse/translator/formats.ts");
+const { normalizeArrayContentDelta } = await import("../../open-sse/utils/arrayContentDelta.ts");
+
+const textEncoder = new TextEncoder();
+
+test.after(() => {
+  core.resetDbInstance();
+  if (fs.existsSync(TEST_DATA_DIR)) {
+    fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true, maxRetries: 5, retryDelay: 100 });
+  }
+});
+
+function chunk(delta: Record<string, unknown>, finishReason: string | null = null) {
+  return `data: ${JSON.stringify({
+    id: "cmpl_cf",
+    object: "chat.completion.chunk",
+    created: 1,
+    model: "@cf/mistralai/mistral-small-3.1-24b-instruct",
+    choices: [{ index: 0, delta, finish_reason: finishReason }],
+  })}\n\n`;
+}
+
+// "A", "B", 7, ".", 1, ".", 9, then a zero, which must not be mistaken for an empty delta.
+const STREAM = [
+  chunk({ role: "assistant", content: "" }),
+  chunk({ content: "A" }),
+  chunk({ content: "B" }),
+  chunk({ content: 7 }),
+  chunk({ content: "." }),
+  chunk({ content: 1 }),
+  chunk({ content: "." }),
+  chunk({ content: 9 }),
+  chunk({ content: 0 }),
+  chunk({}, "stop"),
+  "data: [DONE]\n\n",
+];
+
+async function run(options: object): Promise<string> {
+  const source = new ReadableStream({
+    start(controller) {
+      for (const c of STREAM) controller.enqueue(textEncoder.encode(c));
+      controller.close();
+    },
+  });
+  return new Response(source.pipeThrough(createSSEStream(options))).text();
+}
+
+test("passthrough keeps numeric delta.content as string text", async () => {
+  const text = await run({
+    mode: "passthrough",
+    provider: "cloudflare-ai",
+    model: "@cf/mistralai/mistral-small-3.1-24b-instruct",
+    clientResponseFormat: FORMATS.OPENAI,
+    body: { messages: [{ role: "user", content: "copy 7.1.9" }] },
+  });
+  const deltas = text
+    .split("\n")
+    .filter((l) => l.startsWith("data: ") && !l.includes("[DONE]"))
+    .map((l) => JSON.parse(l.slice(6)))
+    .flatMap((e) =>
+      ((e.choices as Array<{ delta?: Record<string, unknown> }>) ?? []).map((c) => c.delta ?? {})
+    );
+  for (const d of deltas) {
+    if ("content" in d) assert.equal(typeof d.content, "string", JSON.stringify(d));
+  }
+  assert.equal(deltas.map((d) => d.content ?? "").join(""), "AB7.1.9" + "0");
+});
+
+test("normalizeArrayContentDelta turns a finite number into its decimal string", () => {
+  const seven: Record<string, unknown> = { content: 7 };
+  assert.equal(normalizeArrayContentDelta(seven), true);
+  assert.deepEqual(seven, { content: "7" });
+
+  const zero: Record<string, unknown> = { content: 0 };
+  assert.equal(normalizeArrayContentDelta(zero), true);
+  assert.deepEqual(zero, { content: "0" });
+
+  const notFinite: Record<string, unknown> = { content: Number.NaN };
+  assert.equal(normalizeArrayContentDelta(notFinite), false);
+
+  const plain = { content: "x" };
+  assert.equal(normalizeArrayContentDelta(plain), false);
+  assert.deepEqual(plain, { content: "x" });
+});