feat(gemini_oauth): full Cloud Code API integration with project discovery

- Register gemini_oauth as a dedicated backend in config/llm.rs (skip
  registry fallback, preserve backend name, suppress unknown-backend warning)
- Fix app.rs credential guard to exclude backends with dedicated configs
  (gemini_oauth, bedrock) from the provider.is_none() check
- Auto-discover Cloud Code project_id via loadCodeAssist when credentials
  lack it (e.g. created by the original Gemini CLI)
- Persist discovered project_id to credentials file for subsequent runs
- Add safety settings (BLOCK_NONE), gated behind GEMINI_SAFETY_BLOCK_NONE env
- Add thinkingConfig: budget-based for Gemini 2.5, level-based for Gemini 3.x
  (without includeThoughts to avoid empty responses from reasoning.rs stripping)
- Add thought signature injection for Gemini 3.x preview APIs
- Add history curation to filter invalid model outputs before re-sending
- Add extended generationConfig env vars (topP, topK, seed, penalties,
  responseMimeType, responseJsonSchema, cachedContent)
- Add custom headers support via GEMINI_CLI_CUSTOM_HEADERS
- Add API key auth mode (GEMINI_API_KEY + GEMINI_API_KEY_AUTH_MECHANISM)
- Add SSE metadata extraction (modelVersion, credits, promptFeedback,
  groundingMetadata, citationMetadata, cachedContentTokenCount)
- Add countTokens API support
- Add new models to wizard (gemini-3.1-pro-preview-customtools,
  gemini-3-pro-preview, gemini-3.1-flash-lite-preview)
- Update docs/LLM_PROVIDERS.md with new models and routing rules
- Rewrite regression tests with comprehensive coverage (23 unit tests pass)

src/app.rs

@@ -683,10 +683,14 @@ impl AppBuilder {
         self.init_database().await?;
         self.init_secrets().await?;
 
-        // Post-init validation: if a non-nearai backend was selected but
-        // credentials were never resolved (deferred resolution found no keys),
-        // fail early with a clear error instead of a confusing runtime failure.
-        if self.config.llm.backend != "nearai" && self.config.llm.provider.is_none() {
+        // Post-init validation: backends with dedicated config (nearai, gemini_oauth,
+        // bedrock) handle their own credential resolution. For registry-based backends,
+        // fail early if no provider config was resolved.
+        if self.config.llm.backend != "nearai"
+            && self.config.llm.backend != "gemini_oauth"
+            && self.config.llm.backend != "bedrock"
+            && self.config.llm.provider.is_none()
+        {
             let backend = &self.config.llm.backend;
             anyhow::bail!(
                 "LLM_BACKEND={backend} is configured but no credentials were found. \

src/config/llm.rs

@@ -10,7 +10,6 @@ use crate::llm::registry::{ProviderProtocol, ProviderRegistry};
 use crate::llm::session::SessionConfig;
 use crate::settings::Settings;
 
-
 impl LlmConfig {
     /// Create a test-friendly config without reading env vars.
     #[cfg(feature = "libsql")]
@@ -75,8 +74,10 @@ impl LlmConfig {
             backend_lower == "nearai" || backend_lower == "near_ai" || backend_lower == "near";
         let is_bedrock =
             backend_lower == "bedrock" || backend_lower == "aws_bedrock" || backend_lower == "aws";
+        let is_gemini_oauth = backend_lower == "gemini_oauth" || backend_lower == "gemini-oauth";
 
-        if !is_nearai && !is_bedrock && registry.find(&backend_lower).is_none() {
+        if !is_nearai && !is_bedrock && !is_gemini_oauth && registry.find(&backend_lower).is_none()
+        {
             tracing::warn!(
                 "Unknown LLM backend '{}'. Will attempt as openai_compatible fallback.",
                 backend
@@ -124,7 +125,7 @@ impl LlmConfig {
         };
 
         // Resolve registry provider config (for non-NearAI, non-Bedrock backends)
-        let provider = if is_nearai || is_bedrock {
+        let provider = if is_nearai || is_bedrock || is_gemini_oauth {
             None
         } else {
             Some(Self::resolve_registry_provider(
@@ -199,6 +200,8 @@ impl LlmConfig {
                 "nearai".to_string()
             } else if is_bedrock {
                 "bedrock".to_string()
+            } else if is_gemini_oauth {
+                "gemini_oauth".to_string()
             } else if let Some(ref p) = provider {
                 p.provider_id.clone()
             } else {

src/llm/config.rs

@@ -239,6 +239,21 @@ impl NearAiConfig {
 }
 
 /// Configuration for Gemini OAuth integration.
+///
+/// Extended generation config parameters (topP, topK, seed, etc.) are read from
+/// environment variables at request time:
+/// - `GEMINI_TOP_P` — nucleus sampling (0.0–1.0)
+/// - `GEMINI_TOP_K` — top-k sampling (integer)
+/// - `GEMINI_SEED` — deterministic generation seed
+/// - `GEMINI_PRESENCE_PENALTY` — presence penalty (-2.0–2.0)
+/// - `GEMINI_FREQUENCY_PENALTY` — frequency penalty (-2.0–2.0)
+/// - `GEMINI_RESPONSE_MIME_TYPE` — e.g. "application/json"
+/// - `GEMINI_RESPONSE_JSON_SCHEMA` — JSON schema string for structured output
+/// - `GEMINI_CACHED_CONTENT` — cached content resource name
+/// - `GEMINI_CLI_CUSTOM_HEADERS` — custom headers (key:value,key:value)
+/// - `GOOGLE_GENAI_API_VERSION` — API version (default: v1beta)
+/// - `GEMINI_API_KEY` — optional API key for non-OAuth auth mode
+/// - `GEMINI_API_KEY_AUTH_MECHANISM` — "x-goog-api-key" (default) or "bearer"
 #[derive(Debug, Clone)]
 pub struct GeminiOauthConfig {
     pub model: String,

src/setup/wizard.rs

@@ -1708,10 +1708,22 @@ impl SetupWizard {
                         "gemini-3.1-pro-preview".into(),
                         "Gemini 3.1 Pro (Latest, strongest reasoning)".into(),
                     ),
+                    (
+                        "gemini-3.1-pro-preview-customtools".into(),
+                        "Gemini 3.1 Pro Custom Tools (Enhanced tool use)".into(),
+                    ),
+                    (
+                        "gemini-3-pro-preview".into(),
+                        "Gemini 3 Pro (Preview)".into(),
+                    ),
                     (
                         "gemini-3-flash-preview".into(),
                         "Gemini 3 Flash (Fast preview with thinking)".into(),
                     ),
+                    (
+                        "gemini-3.1-flash-lite-preview".into(),
+                        "Gemini 3.1 Flash Lite (Preview, lightweight)".into(),
+                    ),
                     (
                         "gemini-2.5-pro".into(),
                         "Gemini 2.5 Pro (Stable, strong reasoning)".into(),