From acae259967e02c1d151d5f951902f1fc927ab4ab Mon Sep 17 00:00:00 2001
From: Mynacol <git@mynacol.xyz>
Date: Tue, 11 Aug 2026 14:12:41 +0200
Subject: [PATCH] fix(executors): repair DuckDuckGo AI Chat challenge solver
 (418 ERR_CHALLENGE) (#9733)
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Every duckduckgo-web chat request failed with HTTP 418 ERR_CHALLENGE while
duck.ai worked normally in a browser from the same IP. Ground truth was
established by driving a real headful Chromium at duck.ai from that IP (it
returned 200), so the environment was never the problem — the anti-abuse
challenge solver was. Six independent defects were found; the first alone
disabled the solver completely.

1. Module syntax inside the vm sandbox source.
   CHALLENGE_STUBS is executed with vm.runInContext, which compiles in SCRIPT
   mode. A refactor mass-added `export` to the five `function` declarations
   inside that template literal (they read as ordinary top-level TS functions),
   so every solve threw SyntaxError. The executor swallows solve failures and
   posts the raw unsolved challenge, which upstream answers with 418.

2. Double-escaped regex in a String.raw template.
   `\\s` in __parseCssDisplay reached the sandbox as a literal backslash, so the
   display regex never matched and a getComputedStyle probe silently read empty.

3. buildHtmlLookup undercounted descendants by one.
   `count` backs el.querySelectorAll('*').length; that returns DESCENDANTS and
   countHtmlElements already skips the #document-fragment root, so the `- 1` was
   wrong. Chromium reports 3 for '<li><div></li><li></div'; we reported 2, and a
   variant multiplies innerHTML.length by that count.

4. Browser-fidelity probes.
   Newer challenge variants assert JS/DOM invariants a flat stub cannot satisfy:
   real prototype chains (HTMLDivElement -> HTMLElement -> Element), NodeList
   identity, a live body.children HTMLCollection, native-code toString, and
   sloppy-mode `this === window`. Nine of thirteen failed. Notably Math must NOT
   be sealed — Chromium reports Object.isSealed(Math) === false, and sealing it
   made our vector differ by one.

5. The solved payload dropped meta.origin / meta.stack / meta.duration.
   The duck.ai bundle always sends all three; captured browser requests confirm
   it. Without them upstream returns 418 even when every client_hash is correct.

6. reasoningEffort is now mandatory on duckchat/v1/chat.
   An otherwise byte-identical payload returns 200 with the field and 400
   ERR_BAD_REQUEST without it (A/B verified live, repeated).

Also removes the throwaway "seed" chat POST that ran before every real request.
It existed to coax a usable challenge out of the upstream while the solver was
broken; it only doubled chat calls against an IP-rate-limited endpoint, showing
up as spurious 429 ERR_RATE_LIMIT.

Verification: the solver now reproduces real Chromium's probe vectors exactly
for all 8 captured challenge variants, and the executor returns 200 end-to-end
live (non-streaming, streaming, claude-haiku-4-5, and a math prompt returning
"42").

Tests: tests/unit/duckduckgo-challenge-solver-regression.test.ts (32 tests) and
tests/unit/duckduckgo-reasoning-effort-required.test.ts (5 tests), backed by
tests/fixtures/duckduckgo/challenge-variants.json — real captured challenge
programs plus the probe vectors a real browser produced for them, so the suite
asserts against recorded browser behaviour rather than our own output. Each fix
was confirmed to fail its test when individually reverted.