feat(login): custom provider logins fetch and select models

After the base URL, name, and key steps, the login now opens a model
selection screen instead of blindly saving. The listing fetch runs
concurrently with a manual-id input — a WAF challenge page or a 404 no
longer passes validation silently: a base without a /vN tail is probed
once as {base}/v1 and the working base is adopted, an anthropic-wire
listing that 401s on x-api-key retries once with Bearer (relays gate
GET /models on Bearer while /messages takes the key header), and a
failed fetch shows its reason while manual add stays usable. The chosen
ids persist as [platforms.<name>] models = [...]; catalog assembly
synthesizes selected ids the listing never served (before [model.*]
overrides so they compose) and filters unselected provider entries
(after overrides, authoritative in the provider namespace). Provider-
owned entries keep their declared wire against donor backend
inheritance, and listing errors quote line/column only — a reflected
body could carry the key.

crates/codegen/kigi-shell/src/agent/custom_providers/selection.rs

@@ -0,0 +1,233 @@
+//! The `[platforms.<name>] models` allowlist: keep the selected, synthesize the manual.
+
+use indexmap::IndexMap;
+
+use super::CredentialedProvider;
+use crate::agent::config::{ModelEntry, PlatformsConfig};
+
+/// Synthesizes selected ids the listing never served; runs before `[model.*]` overrides.
+pub(crate) fn synthesize_selected(
+    resolved: &mut IndexMap<String, ModelEntry>,
+    platforms: &PlatformsConfig,
+    keyed: &[CredentialedProvider],
+) {
+    for credentialed in keyed {
+        let provider = &credentialed.provider;
+        let Some(list) = platforms
+            .entries
+            .get(&provider.name)
+            .and_then(|e| e.models.as_ref())
+        else {
+            continue;
+        };
+        for id in list.iter().map(|m| m.trim()) {
+            if let Err(e) = kigi_models::custom::validate_model_id(id) {
+                tracing::warn!(provider = %provider.name, %e, "skipping an invalid selected model id");
+                continue;
+            }
+            let key = provider.managed_model_key(id);
+            if resolved.contains_key(&key) {
+                continue;
+            }
+            let entry = super::fetch::manual_entry(provider, id);
+            resolved.insert(key, ModelEntry::from_config_entry(&entry));
+        }
+    }
+}
+
+/// Drops `{name}/*` entries outside the provider's selection; runs after `[model.*]` overrides.
+pub(crate) fn filter_unselected(
+    resolved: &mut IndexMap<String, ModelEntry>,
+    platforms: &PlatformsConfig,
+    keyed: &[CredentialedProvider],
+) {
+    for credentialed in keyed {
+        let provider = &credentialed.provider;
+        let Some(list) = platforms
+            .entries
+            .get(&provider.name)
+            .and_then(|e| e.models.as_ref())
+        else {
+            continue;
+        };
+        let list: Vec<&str> = list.iter().map(|m| m.trim()).collect();
+        let prefix = format!("{}/", provider.name);
+        resolved.retain(|key, entry| {
+            let id = entry.info.id.as_deref().unwrap_or(key.as_str());
+            id.strip_prefix(&prefix)
+                .is_none_or(|bare| list.contains(&bare))
+        });
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use kigi_models::custom::{CustomApi, CustomProvider};
+
+    use crate::agent::models::PlatformApiKeys;
+
+    fn provider(name: &str, base: &str) -> CustomProvider {
+        CustomProvider::new(name, CustomApi::OpenAi, base).unwrap()
+    }
+
+    fn fetched_entry(provider: &CustomProvider, id: &str) -> (String, ModelEntry) {
+        let cfg = super::super::fetch::manual_entry(provider, id);
+        let key = cfg.id.clone().unwrap();
+        (key, ModelEntry::from_config_entry(&cfg))
+    }
+
+    fn keyed(provider: CustomProvider) -> Vec<CredentialedProvider> {
+        vec![CredentialedProvider::for_test(provider, "sk-x")]
+    }
+
+    #[test]
+    fn selection_filters_the_listing_and_synthesizes_the_manual() {
+        let proxy = provider("proxy", "https://p.example/v1");
+        let mut resolved = IndexMap::new();
+        for id in ["m1", "m2"] {
+            let (key, entry) = fetched_entry(&proxy, id);
+            resolved.insert(key, entry);
+        }
+        let platforms: PlatformsConfig = toml::from_str(
+            "[proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\nmodels = [\"m2\", \"manual-1\"]\n",
+        )
+        .unwrap();
+
+        synthesize_selected(&mut resolved, &platforms, &keyed(proxy.clone()));
+        filter_unselected(&mut resolved, &platforms, &keyed(proxy));
+
+        let ids: Vec<_> = resolved.keys().map(String::as_str).collect();
+        assert_eq!(ids, ["proxy/m2", "proxy/manual-1"]);
+        assert_eq!(resolved["proxy/manual-1"].info.model, "manual-1");
+    }
+
+    #[test]
+    fn a_provider_without_the_models_key_keeps_its_whole_listing() {
+        let proxy = provider("proxy", "https://p.example/v1");
+        let mut resolved = IndexMap::new();
+        let (key, entry) = fetched_entry(&proxy, "m1");
+        resolved.insert(key, entry);
+        let platforms: PlatformsConfig =
+            toml::from_str("[proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\n")
+                .unwrap();
+
+        synthesize_selected(&mut resolved, &platforms, &keyed(proxy.clone()));
+        filter_unselected(&mut resolved, &platforms, &keyed(proxy));
+
+        assert!(resolved.contains_key("proxy/m1"));
+    }
+
+    #[test]
+    fn an_empty_selection_drops_every_fetched_entry() {
+        let proxy = provider("proxy", "https://p.example/v1");
+        let mut resolved = IndexMap::new();
+        let (key, entry) = fetched_entry(&proxy, "m1");
+        resolved.insert(key, entry);
+        let platforms: PlatformsConfig = toml::from_str(
+            "[proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\nmodels = []\n",
+        )
+        .unwrap();
+
+        synthesize_selected(&mut resolved, &platforms, &keyed(proxy.clone()));
+        filter_unselected(&mut resolved, &platforms, &keyed(proxy));
+
+        assert!(resolved.is_empty());
+    }
+
+    #[test]
+    fn invalid_selected_ids_are_skipped_with_a_warning() {
+        let proxy = provider("proxy", "https://p.example/v1");
+        let mut resolved = IndexMap::new();
+        let platforms: PlatformsConfig = toml::from_str(
+            "[proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\nmodels = [\"ok\", \"has space\"]\n",
+        )
+        .unwrap();
+
+        synthesize_selected(&mut resolved, &platforms, &keyed(proxy.clone()));
+        filter_unselected(&mut resolved, &platforms, &keyed(proxy));
+
+        assert!(resolved.contains_key("proxy/ok"));
+        assert_eq!(resolved.len(), 1);
+    }
+
+    #[test]
+    fn selection_applies_through_resolve_model_list_and_gets_the_key() {
+        let raw: toml::Value = toml::from_str(
+            "[platforms.proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\nmodels = [\"manual-1\"]\n",
+        )
+        .unwrap();
+        let cfg = crate::agent::config::Config::new_from_toml_cfg(&raw).unwrap();
+        let proxy = provider("proxy", "https://p.example/v1");
+        let keys =
+            PlatformApiKeys::test_custom(vec![CredentialedProvider::for_test(proxy, "sk-proxy")]);
+
+        let resolved = crate::agent::config::resolve_model_list(&cfg, None, &keys);
+
+        let entry = resolved
+            .get("proxy/manual-1")
+            .expect("a manual model survives without any fetched catalog");
+        assert_eq!(entry.api_key.as_deref(), Some("sk-proxy"));
+        assert!(entry.has_own_credentials());
+        assert_eq!(entry.info.context_window.get(), 256_000);
+    }
+
+    #[test]
+    fn a_model_override_composes_with_the_synthesized_entry() {
+        let raw: toml::Value = toml::from_str(
+            "[platforms.proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\nmodels = [\"manual-1\"]\n\n[model.\"proxy/manual-1\"]\ncontext_window = 1000000\n",
+        )
+        .unwrap();
+        let cfg = crate::agent::config::Config::new_from_toml_cfg(&raw).unwrap();
+        let proxy = provider("proxy", "https://p.example/v1");
+        let keys =
+            PlatformApiKeys::test_custom(vec![CredentialedProvider::for_test(proxy, "sk-proxy")]);
+
+        let resolved = crate::agent::config::resolve_model_list(&cfg, None, &keys);
+
+        let entry = &resolved["proxy/manual-1"];
+        assert_eq!(entry.info.context_window.get(), 1_000_000);
+        assert_eq!(entry.info.base_url, "https://p.example/v1");
+        assert_eq!(entry.api_key.as_deref(), Some("sk-proxy"));
+    }
+
+    #[test]
+    fn the_selection_is_authoritative_in_the_provider_namespace() {
+        // A context-only override cannot resurrect a deselected model.
+        let raw: toml::Value = toml::from_str(
+            "[platforms.proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\nmodels = [\"m2\"]\n\n[model.\"proxy/m1\"]\ncontext_window = 123456\n",
+        )
+        .unwrap();
+        let cfg = crate::agent::config::Config::new_from_toml_cfg(&raw).unwrap();
+        let proxy = provider("proxy", "https://p.example/v1");
+        let (key, entry) = fetched_entry(&proxy, "m1");
+        let prefetched = IndexMap::from([(key, entry)]);
+        let keys =
+            PlatformApiKeys::test_custom(vec![CredentialedProvider::for_test(proxy, "sk-proxy")]);
+
+        let resolved = crate::agent::config::resolve_model_list(&cfg, Some(prefetched), &keys);
+
+        assert!(!resolved.contains_key("proxy/m1"));
+        assert!(resolved.contains_key("proxy/m2"));
+    }
+
+    #[test]
+    fn provider_owned_entries_keep_their_declared_wire_against_donors() {
+        let raw: toml::Value = toml::from_str(
+            "[platforms.proxy]\nbase_url = \"https://p.example/v1\"\napi = \"openai\"\nmodels = [\"shared\"]\n\n[model.donorx]\nmodel = \"shared\"\napi_backend = \"messages\"\ncontext_window = 500000\n",
+        )
+        .unwrap();
+        let cfg = crate::agent::config::Config::new_from_toml_cfg(&raw).unwrap();
+        let proxy = provider("proxy", "https://p.example/v1");
+        let keys =
+            PlatformApiKeys::test_custom(vec![CredentialedProvider::for_test(proxy, "sk-proxy")]);
+
+        let resolved = crate::agent::config::resolve_model_list(&cfg, None, &keys);
+
+        let entry = &resolved["proxy/shared"];
+        assert_eq!(
+            entry.info.api_backend,
+            crate::sampling::ApiBackend::ChatCompletions
+        );
+    }
+}