F5: web search/fetch on the Kimi services (kimi-cli parity)

web_search now speaks the Kimi search service (kimi-cli tools/web/search.py,
wire-verified against api.kimi.com):
- POST {coding_base}/search with {text_query, limit 1-20 (default 5),
  enable_page_crawling, timeout_seconds: 30}, OAuth bearer +
  X-Msh-Tool-Call-Id; results render in kimi-cli's Title/Date/URL/Summary
  schema with result URLs as citations.
- The old implementation called the xAI Responses API with a search model;
  that client is fully replaced and the entire model-based config surface
  is excised root-and-branch: web_search_model config keys/env/CLI plumbing,
  resolve_web_search_sampling_config, toolset web_search SamplerConfig,
  RemoteSettings.web_search_model, default_web_search_model.
- Enablement is now purely structural: the service exists only on the Kimi
  Code subscription channel, so OAuth sessions get Enabled and API-key-only
  sessions get Disabled (tool absent) — per PRD F5.

web_fetch gains the Kimi fetch service as its primary path (kimi-cli
tools/web/fetch.py): POST {coding_base}/fetch with {url}, Accept:
text/markdown, OAuth bearer + X-Msh-Tool-Call-Id; the 200 body is the
extracted markdown (still overflow-budgeted). Any service failure falls
back to the existing local pipeline (SSRF guards, cache, extraction).
The tool gate defaults ON now (kimi-cli always offers FetchURL) and the
egress User-Agent no longer claims grok-agent/x.ai.

Verified end-to-end against the scripted mock service: a headless session
drove web_search (limit/crawling/call-id observed on the wire) then
web_fetch (Accept + call-id observed) to completion.

crates/codegen/kigi-workspace/src/session/tool_config.rs

@@ -428,11 +428,9 @@ impl SessionContextFactory for WorkspaceSessionContextFactory {
                                 tier_restricted: false,
                             },
                             WebSearchConfig::Enabled {
+                                search_url: format!("{}/search", url.trim_end_matches('/')),
                                 api_key: token,
-                                base_url: url.clone(),
-                                model: default_web_search_model(),
                                 extra_headers: headers,
-                                alpha_test_key: None,
                             },
                             AppBuilderDeployerConfig::default(),
                         )
@@ -515,9 +513,6 @@ fn build_web_fetch_config() -> kigi_tools::implementations::grok_build::web_fetc
     }
     WebFetchConfig::Enabled { params }
 }
-fn default_web_search_model() -> String {
-    std::env::var("KIGI_WEB_SEARCH_MODEL").unwrap_or_else(|_| "grok-4.20-multi-agent".to_string())
-}
 #[cfg(any(test, feature = "test-support"))]
 pub mod test_support {
     use crate::config::SessionContextFactory;