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-shell/src/util/config/persist.rs

@@ -153,9 +153,9 @@ pub(crate) fn atomic_write_string(path: &std::path::Path, content: &str) -> std:
 }
 
 /// Merge `[toolset.ask_user_question]` into the root table. `[toolset]` is
-/// deliberately NOT merged wholesale — it carries runtime-only structs
-/// (`web_search` sampler etc.) whose serialized defaults must never land in
-/// the user file — so only this settings-writable sub-table round-trips.
+/// deliberately NOT merged wholesale — its other sub-tables (`bash` etc.)
+/// carry serialized defaults that must never land in the user file — so only
+/// this settings-writable sub-table round-trips.
 fn merge_ask_user_question_section(
     table: &mut TomlMap<String, TomlValue>,
     ask: &crate::tools::config::AskUserQuestionToolConfig,
@@ -245,7 +245,7 @@ mod tests {
 
     /// The `[toolset.ask_user_question]` settings write merges only that
     /// sub-table: the toggled field lands, hand-written sibling keys survive,
-    /// and no other `[toolset]` defaults (bash/web_search) are splatted into
+    /// and no other `[toolset]` defaults (bash etc.) are splatted into
     /// the user file. All-None leaves the file untouched.
     #[test]
     fn ask_user_question_merge_writes_subtable_without_splatting_toolset() {
@@ -830,7 +830,6 @@ auto_update = true
         if let TomlValue::Table(t) = v {
             assert_eq!(t.len(), 1);
             assert!(t.contains_key("default"));
-            assert!(!t.contains_key("web_search"));
             assert!(!t.contains_key("session_summary"));
             assert!(!t.contains_key("image_description"));
             assert!(!t.contains_key("hidden_models"));
@@ -935,7 +934,10 @@ auto_update = true
     fn merge_section_models_only_updates_set_fields_preserves_others() {
         let mut table = TomlMap::new();
         let mut models = TomlMap::new();
-        models.insert("web_search".into(), TomlValue::String("old-search".into()));
+        models.insert(
+            "session_summary".into(),
+            TomlValue::String("old-title".into()),
+        );
         models.insert("unmodeled_foo".into(), TomlValue::String("keep-me".into()));
         table.insert("models".into(), TomlValue::Table(models));
         let cfg = crate::agent::config::ModelsConfig {
@@ -946,19 +948,19 @@ auto_update = true
         let m = table.get("models").unwrap().as_table().unwrap();
         assert_eq!(m.get("default").and_then(|v| v.as_str()), Some("grok-new"));
         assert_eq!(
-            m.get("web_search").and_then(|v| v.as_str()),
-            Some("old-search")
+            m.get("session_summary").and_then(|v| v.as_str()),
+            Some("old-title")
         );
         assert_eq!(
             m.get("unmodeled_foo").and_then(|v| v.as_str()),
             Some("keep-me")
         );
-        assert!(!m.contains_key("session_summary"));
+        assert!(!m.contains_key("image_description"));
     }
 
     #[test]
     fn persist_preferred_model_flow_roundtrips_via_load_and_new_from_toml_cfg() {
-        let original = "[models]\ndefault = \"grok-old\"\nweb_search = \"some-search\"\n";
+        let original = "[models]\ndefault = \"grok-old\"\n";
         let root: TomlValue = toml::from_str(original).unwrap();
         let mut cfg = load_config_from_toml(&root);
         cfg.models.default = Some("grok-persisted".to_string());