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cherry-pick(pr-9733): fix(executors): repair DuckDuckGo AI Chat challenge solver (418 ERR_CHALLENGE) #9866

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Merged
diegosouzapw merged 1 commit into from
Aug 9, 2026
Merged

cherry-pick(pr-9733): fix(executors): repair DuckDuckGo AI Chat challenge solver (418 ERR_CHALLENGE) #9866

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52 changes: 12 additions & 40 deletions open-sse/executors/duckduckgo-web.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -251,11 +251,14 @@ export function normalizeDuckDuckGoModel(model: string | undefined): string {
}

function getDuckDuckGoModelCapabilities(model: string): DuckDuckGoModelCapabilities {
// Per duckchat/v1/models (2026-07-22): claude-haiku-4-5 and gpt-oss-120b take a "low"
// reasoningEffort on the free tier; the others omit it (duck.ai applies its own default).
// `reasoningEffort` is REQUIRED on every duckchat/v1/chat request. Omitting it
// returns 400 ERR_BAD_REQUEST — A/B verified live against duck.ai with an
// otherwise byte-identical payload (200 with the field, 400 without, repeated).
// The live duck.ai bundle always sends one, so there is no "let the server
// pick a default" path any more.
if (model === "claude-haiku-4-5") return { reasoningEffort: "low" };
if (model === "tinfoil/gpt-oss-120b") return { reasoningEffort: "low" };
return { reasoningEffort: null };
return { reasoningEffort: "none" };
}

function extractDuckDuckGoFeVersion(html: string): string | null {
Expand Down Expand Up @@ -353,7 +356,6 @@ export class DuckDuckGoWebExecutor extends BaseExecutor {
}

private warmed = false;
private seeded = false;
private feVersion = DEFAULT_FE_VERSION;
private pendingVqdHash1: string | null = null;
private readonly cookieJar = new Map<string, string>();
Expand Down Expand Up @@ -561,7 +563,12 @@ export class DuckDuckGoWebExecutor extends BaseExecutor {
}

await this.warmSession(mergedSignal);
await this.seedChallengeChain(upstreamModel, mergedSignal);
// NOTE: the throwaway "seed" chat POST that used to run here has been removed.
// It existed to coax a usable challenge out of the upstream while the solver
// was broken; now that the solver reproduces a real browser's probe vectors
// exactly, the first real request succeeds on its own. Keeping it only doubled
// the chat calls per user request against an IP-rate-limited endpoint, which
// showed up as spurious 429 ERR_RATE_LIMIT.
const vqdHeaders = await this.acquireAuthHeaders(mergedSignal);
if (!vqdHeaders.vqd4 && !vqdHeaders.vqdHash1) {
clearTimeout(timeout);
Expand Down Expand Up @@ -770,41 +777,6 @@ export class DuckDuckGoWebExecutor extends BaseExecutor {
);
}

private async seedChallengeChain(model: string, signal: AbortSignal): Promise<void> {
if (this.seeded || signal.aborted) return;
this.seeded = true;
const seedMessages = [{ role: "user", content: "hi" }];
const previousPending = this.pendingVqdHash1;
try {
const vqdHeaders = await this.acquireAuthHeaders(signal);
if (!vqdHeaders.vqd4 && !vqdHeaders.vqdHash1) {
this.pendingVqdHash1 = previousPending;
return;
}
const response = await fetch(CHAT_URL, {
method: "POST",
headers: mergeHeadersCaseInsensitive(this.buildRequestHeaders(), {
Accept: "text/event-stream",
"Content-Type": "application/json",
"x-ddg-journey-id": randomUUID().replaceAll("-", ""),
"x-fe-signals": makeDuckDuckGoFeSignals(),
"x-fe-version": this.feVersion,
...(vqdHeaders.vqd4 ? { "x-vqd-4": vqdHeaders.vqd4 } : {}),
...(vqdHeaders.vqdHash1 ? { "x-vqd-hash-1": vqdHeaders.vqdHash1 } : {}),
}),
body: JSON.stringify(buildDuckDuckGoPayload(model, seedMessages, false)),
signal,
});
this.rememberResponseCookies(response);
if (response.ok) this.rememberChallengeHeader(response);
else this.pendingVqdHash1 = previousPending;
await response.body?.cancel().catch(() => {});
} catch (error) {
void error;
this.pendingVqdHash1 = previousPending;
}
}

private async processResponse(
response: Response,
streaming: boolean,
Expand Down
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