feat(web): searxng plugin (search-only, third migration)

Adds plugins/web/searxng/. SearXNG aggregates results from upstream engines
via its JSON API (/search?format=json) — search-only, no extract capability
(supports_extract() returns False).

E2E verified — registry now has ['brave-free', 'ddgs', 'searxng'].

plugins/web/searxng/__init__.py

@@ -0,0 +1,15 @@
+"""SearXNG search plugin — bundled, auto-loaded.
+
+Backed by a user-hosted SearXNG instance (URL configured via ``SEARXNG_URL``).
+Search-only — pair with an extract provider (firecrawl/tavily/exa) for
+``web_extract`` calls.
+"""
+
+from __future__ import annotations
+
+from plugins.web.searxng.provider import SearXNGWebSearchProvider
+
+
+def register(ctx) -> None:
+    """Register the SearXNG provider with the plugin context."""
+    ctx.register_web_search_provider(SearXNGWebSearchProvider())

plugins/web/searxng/plugin.yaml

@@ -0,0 +1,7 @@
+name: web-searxng
+version: 1.0.0
+description: "SearXNG web search — free, self-hosted, privacy-respecting metasearch engine. Requires SEARXNG_URL pointing at your instance."
+author: NousResearch
+kind: backend
+provides_web_providers:
+  - searxng

plugins/web/searxng/provider.py

@@ -0,0 +1,138 @@
+"""SearXNG search — plugin form.
+
+Subclasses :class:`agent.web_search_provider.WebSearchProvider`. Same JSON
+API call (``/search?format=json``), same result normalization as the legacy
+:mod:`tools.web_providers.searxng` module.
+
+Search-only — SearXNG aggregates results from upstream engines but does not
+fetch/extract arbitrary URLs. ``supports_extract()`` returns False.
+
+Config keys this provider responds to::
+
+    web:
+      search_backend: "searxng"     # explicit per-capability
+      backend: "searxng"            # shared fallback
+
+Env var::
+
+    SEARXNG_URL=http://localhost:8080
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+from typing import Any, Dict
+
+from agent.web_search_provider import WebSearchProvider
+
+logger = logging.getLogger(__name__)
+
+
+class SearXNGWebSearchProvider(WebSearchProvider):
+    """Search via a user-hosted SearXNG instance."""
+
+    @property
+    def name(self) -> str:
+        return "searxng"
+
+    @property
+    def display_name(self) -> str:
+        return "SearXNG"
+
+    def is_available(self) -> bool:
+        """Return True when ``SEARXNG_URL`` is set."""
+        return bool(os.getenv("SEARXNG_URL", "").strip())
+
+    def supports_search(self) -> bool:
+        return True
+
+    def supports_extract(self) -> bool:
+        return False
+
+    def search(self, query: str, limit: int = 5) -> Dict[str, Any]:
+        """Execute a search against the configured SearXNG instance."""
+        import httpx
+
+        base_url = os.getenv("SEARXNG_URL", "").strip().rstrip("/")
+        if not base_url:
+            return {"success": False, "error": "SEARXNG_URL is not set"}
+
+        params: Dict[str, Any] = {
+            "q": query,
+            "format": "json",
+            "pageno": 1,
+        }
+
+        try:
+            resp = httpx.get(
+                f"{base_url}/search",
+                params=params,
+                timeout=15,
+                headers={"Accept": "application/json"},
+            )
+            resp.raise_for_status()
+        except httpx.HTTPStatusError as exc:
+            logger.warning("SearXNG HTTP error: %s", exc)
+            return {
+                "success": False,
+                "error": f"SearXNG returned HTTP {exc.response.status_code}",
+            }
+        except httpx.RequestError as exc:
+            logger.warning("SearXNG request error: %s", exc)
+            return {
+                "success": False,
+                "error": f"Could not reach SearXNG at {base_url}: {exc}",
+            }
+
+        try:
+            data = resp.json()
+        except Exception as exc:  # noqa: BLE001
+            logger.warning("SearXNG response parse error: %s", exc)
+            return {
+                "success": False,
+                "error": "Could not parse SearXNG response as JSON",
+            }
+
+        raw_results = data.get("results", [])
+
+        # SearXNG may return a score field; sort descending and cap to limit.
+        sorted_results = sorted(
+            raw_results,
+            key=lambda r: float(r.get("score", 0)),
+            reverse=True,
+        )[:limit]
+
+        web_results = [
+            {
+                "title": str(r.get("title", "")),
+                "url": str(r.get("url", "")),
+                "description": str(r.get("content", "")),
+                "position": i + 1,
+            }
+            for i, r in enumerate(sorted_results)
+        ]
+
+        logger.info(
+            "SearXNG search '%s': %d results (from %d raw, limit %d)",
+            query,
+            len(web_results),
+            len(raw_results),
+            limit,
+        )
+
+        return {"success": True, "data": {"web": web_results}}
+
+    def get_setup_schema(self) -> Dict[str, Any]:
+        return {
+            "name": "SearXNG",
+            "badge": "free · self-hosted",
+            "tag": "Free, privacy-respecting metasearch. Point SEARXNG_URL at your instance.",
+            "env_vars": [
+                {
+                    "key": "SEARXNG_URL",
+                    "prompt": "SearXNG instance URL (e.g. http://localhost:8080)",
+                    "url": "https://searx.space/",
+                },
+            ],
+        }