fix(sse): remove duplicate sseCommentsEnabled import that breaks the production build

The #9378 merge auto-resolve left open-sse/utils/stream.ts importing
sseCommentsEnabled from sseHeartbeat.ts twice (lines 31 and 77). tsx/esbuild
(typecheck + both test runners) silently dedupe the binding, but webpack
fails the release build with "Identifier 'sseCommentsEnabled' has already
been declared" — this is the open-sse-typecheck / build base-red on
release/v3.8.50.

Adds a static regression guard (tests/unit/stream-imports-no-duplicates.test.ts,
RED on the duplicate, GREEN after) so the next merge auto-resolve of this
hot file fails in the unit suite instead of at release-build time. Also
includes the prettier canonicalization of the three style drifts the same
merge introduced (applied by lint-staged either way).

Validated: webpack release build passes on this tree (192.168.0.113 build box).

Refs #9985

open-sse/utils/stream.ts

@@ -74,7 +74,6 @@ import {
   hasUnsupportedReasoningSignal,
 } from "./reasoningFields.ts";
 import { applyThinkTag, flushThink, initThinkState } from "./thinkTagParser.ts";
-import { sseCommentsEnabled } from "./sseHeartbeat.ts";
 import {
   caseInsensitiveToolNameLookup,
   restoreOpenAIToolNames,
@@ -1882,7 +1881,6 @@ export function createSSEStream(options: StreamOptions = {}) {
                     passthroughSawFinishReason = true;
                   }
 
-
                   if (isFinishChunk && passthroughHasToolCalls) {
                     toolFinishTime = now;
                     try {
@@ -2221,7 +2219,8 @@ export function createSSEStream(options: StreamOptions = {}) {
               },
               pushProviderPayload: (payload: unknown) => providerPayloadCollector.push(payload),
               pushClientPayload: (payload: unknown) => clientPayloadCollector.push(payload),
-              sanitizeUsagePayload: (payload: unknown) => sanitizeUsagePayloadForRequest(payload, body, clientResponseFormat),
+              sanitizeUsagePayload: (payload: unknown) =>
+                sanitizeUsagePayloadForRequest(payload, body, clientResponseFormat),
               setPassthroughResponsesId: (value: string) => {
                 passthroughResponsesId = value;
               },
@@ -2282,7 +2281,8 @@ export function createSSEStream(options: StreamOptions = {}) {
               const bufferedPayload = parseSSELine(bufferedLine);
               if (bufferedPayload) {
                 providerPayloadCollector.push(bufferedPayload);
-                if (sanitizeUsagePayloadForRequest(bufferedPayload, body, clientResponseFormat)) output = `data: ${JSON.stringify(bufferedPayload)}\n\n`;
+                if (sanitizeUsagePayloadForRequest(bufferedPayload, body, clientResponseFormat))
+                  output = `data: ${JSON.stringify(bufferedPayload)}\n\n`;
                 if (
                   shouldInjectClaudeEmptyResponseBeforeCurrentEvent(
                     claudeEmptyResponseLifecycle,

tests/unit/stream-imports-no-duplicates.test.ts

@@ -0,0 +1,53 @@
+/**
+ * stream-imports-no-duplicates.test.ts — regression guard for duplicate import
+ * bindings in open-sse/utils/stream.ts.
+ *
+ * A merge auto-resolve (#9378 → commit 9a4cca4bc2) left `sseCommentsEnabled`
+ * imported twice. tsx/esbuild (typecheck + test runners) silently dedupe the
+ * binding, but the webpack production build fails with "Identifier
+ * 'sseCommentsEnabled' has already been declared" — so the defect only
+ * surfaces at release-build time. This static guard fails fast in the unit
+ * suite instead.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import { fileURLToPath } from "node:url";
+
+const STREAM_TS = fileURLToPath(new URL("../../open-sse/utils/stream.ts", import.meta.url));
+
+test("open-sse/utils/stream.ts has no duplicate import bindings", async () => {
+  const source = await readFile(STREAM_TS, "utf8");
+
+  const bindings = new Map<string, number>();
+  const importRegex = /^import\s+(?:type\s+)?(\{[\s\S]*?\}|[A-Za-z0-9_$]+)\s+from\s+/gm;
+
+  for (const match of source.matchAll(importRegex)) {
+    const clause = match[1];
+    const names = clause.startsWith("{")
+      ? clause
+          .slice(1, -1)
+          .split(",")
+          .map(
+            (n) =>
+              n
+                .trim()
+                .split(/\s+as\s+/)
+                .pop()
+                ?.trim() ?? ""
+          )
+          .filter(Boolean)
+      : [clause.trim()];
+    for (const name of names) {
+      bindings.set(name, (bindings.get(name) ?? 0) + 1);
+    }
+  }
+
+  const duplicates = [...bindings.entries()].filter(([, count]) => count > 1).map(([name]) => name);
+
+  assert.deepEqual(
+    duplicates,
+    [],
+    `duplicate import bindings in stream.ts (breaks webpack production build): ${duplicates.join(", ")}`
+  );
+});