ddg: x-vqd-hash-1 protocol rewrite (plugin v0.2.0) — FEAT-10 closed

[VTSTech]

DDG retired the x-vqd-4 token AND the 2025 model catalog. This is the full rewrite to the challenge-based protocol (reverse-engineered 2026-10-09, cross-validated against benoitpetit/duckduckgo-chat-cli):

• Proof lifecycle: /status (x-vqd-accept: 1) returns a base64 JS challenge in x-vqd-hash-1; solved by the bundled Node helper (ddg_vqd.js, DDG_SOLVE_UA in lockstep with the request UA); post-processed like the page bundle (client_hashes -> base64(SHA256(String(value))), meta origin/stack/duration) -> the X-Vqd-Hash-1 REQUEST header; per-turn rotation via the /chat response header.
• Chat body: canUseTools/canUseApproxLocation/reasoningEffort/ durableStream (client-minted RSA-2048 JWK via bundled ddg_durable.js).
• SSE: role-based grammar (assistant/source/tool-invocation/ ui-component) + legacy action fallback + bracketed markers.
• Catalog rotated: 8 live wire IDs (gpt-6-luna, gpt-5.6-luna, gpt-5.4-nano/mini, claude-haiku-4-5, mistral-small-2603, tinfoil/gpt-oss-120b, tinfoil/gemma4-31b) with forward-resolving legacy aliases; live discovery via fetch_capabilities() (/duckchat/v1/capabilities, proof-gated retry).
• generate_stream() TRUE incremental (FEAT-10 closed) with full error-taxonomy parity.
• Fixes over the first rewrite pass: is_cloud=True restored (BaseBackend defaults direct subclasses to local), tool/function roles fold to user (DDG only understands user/assistant), mixed-case legacy alias keys never matched the lowercased lookup, stream limit/403/429/5xx wrapping.
• Tests: 49 -> 99 (proof lifecycle, wire shape, SSE grammar, stream, capabilities, taxonomy, alias table, node plumbing). Suite 3,433 passed / 20 skipped. ruff + black clean.
• scripts/probe_duckduckgo.py rewritten for the new protocol (--live drives the backend end-to-end; TEST-13 automation).
• audit: FEAT-10 CLOSED; TEST-13 partially closed (handshake live-verified via ddg-challenge-solver; one live 200 SSE turn remains). Register 136 findings / 18 OPEN.