fix: honor explicit OpenAI TTS speed values

Landed from contributor PR #39318 by @ql-wade.

Co-authored-by: ql-wade <wade@openclaw.ai>

CHANGELOG.md

@@ -71,6 +71,7 @@ Docs: https://docs.openclaw.ai
 - TUI/session isolation for `/new`: make `/new` allocate a unique `tui-<uuid>` session key instead of resetting the shared agent session, so multiple TUI clients on the same agent stop receiving each other’s replies; also sanitize `/new` and `/reset` failure text before rendering in-terminal. Landed from contributor PR #39238 by @widingmarcus-cyber. Thanks @widingmarcus-cyber.
 - Synology Chat/rate-limit env parsing: honor `SYNOLOGY_RATE_LIMIT=0` as an explicit value while still falling back to the default limit for malformed env values instead of partially parsing them. Landed from contributor PR #39197 by @scoootscooob. Thanks @scoootscooob.
 - Voice-call/OpenAI Realtime STT config defaults: honor explicit `vadThreshold: 0` and `silenceDurationMs: 0` instead of silently replacing them with defaults. Landed from contributor PR #39196 by @scoootscooob. Thanks @scoootscooob.
+- Voice-call/OpenAI TTS speed config: honor explicit `speed: 0` instead of silently replacing it with the default speed. Landed from contributor PR #39318 by @ql-wade. Thanks @ql-wade.
 - Cron/file permission hardening: enforce owner-only (`0600`) cron store/backup/run-log files and harden cron store + run-log directories to `0700`, including pre-existing directories from older installs. (#36078) Thanks @aerelune.
 - Gateway/remote WS break-glass hostname support: honor `OPENCLAW_ALLOW_INSECURE_PRIVATE_WS=1` for `ws://` hostname URLs (not only private IP literals) across onboarding validation and runtime gateway connection checks, while still rejecting public IP literals and non-unicast IPv6 endpoints. (#36930) Thanks @manju-rn.
 - Routing/binding lookup scalability: pre-index route bindings by channel/account and avoid full binding-list rescans on channel-account cache rollover, preventing multi-second `resolveAgentRoute` stalls in large binding configurations. (#36915) Thanks @songchenghao.

extensions/voice-call/src/providers/tts-openai.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it } from "vitest";
+import type { OpenAITTSConfig } from "./tts-openai.js";
+import { OpenAITTSProvider } from "./tts-openai.js";
+
+type ProviderInternals = OpenAITTSProvider & {
+  speed: number;
+};
+
+function createProvider(config: OpenAITTSConfig): ProviderInternals {
+  return new OpenAITTSProvider(config) as ProviderInternals;
+}
+
+describe("OpenAITTSProvider constructor defaults", () => {
+  it("uses speed: 0 when explicitly configured", () => {
+    const provider = createProvider({
+      apiKey: "sk-test",
+      speed: 0,
+    });
+
+    expect(provider.speed).toBe(0);
+  });
+
+  it("falls back to speed default when undefined", () => {
+    const provider = createProvider({
+      apiKey: "sk-test",
+    });
+
+    expect(provider.speed).toBe(1.0);
+  });
+});

extensions/voice-call/src/providers/tts-openai.ts

@@ -82,7 +82,7 @@ export class OpenAITTSProvider {
     this.model = config.model || "gpt-4o-mini-tts";
     // Default to coral - good balance of quality and natural tone
     this.voice = (config.voice as OpenAITTSVoice) || "coral";
-    this.speed = config.speed || 1.0;
+    this.speed = config.speed ?? 1.0;
     this.instructions = config.instructions;
 
     if (!this.apiKey) {