feat(llm): wire Atlas Cloud as opt-in last-resort provider

Atlas Cloud was merged as a provider type but wasn't reachable from the
binaries — nothing constructed it, so ATLASCLOUD_API_KEY had no effect.
Add it to ProviderChain::default() after Anthropic, gated on its key, so
it's only active when explicitly configured and never preempts an
already-configured provider. Also add an ATLASCLOUD_MODEL env fallback so
chain users (new(None, None, None)) can override the model, matching the
existing GEMINI_MODEL pattern.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -63,7 +63,7 @@ Three binaries: `webclaw` (CLI), `webclaw-mcp` (MCP server), `webclaw-server` (R
 - `url_security.rs` — SSRF guards + SSRF-safe redirect policy
 
 ### LLM Modules (`webclaw-llm`)
-- Provider chain (`chain.rs`): Ollama (local-first, always added; availability checked at call time) -> OpenAI -> Gemini -> Anthropic. Gemini sits ahead of Anthropic so Google Cloud credits are preferred; Anthropic is the last-resort fallback. Each provider lives in `providers/` (`ollama.rs`, `openai.rs`, `gemini.rs`, `anthropic.rs`).
+- Provider chain (`chain.rs`): Ollama (local-first, always added; availability checked at call time) -> OpenAI -> Gemini -> Anthropic -> Atlas Cloud. Gemini sits ahead of Anthropic so Google Cloud credits are preferred; Anthropic is the last-resort fallback. Atlas Cloud is opt-in and added last — only when `ATLASCLOUD_API_KEY` is set — so it never preempts an already-configured provider (`ATLASCLOUD_MODEL` / `ATLASCLOUD_BASE_URL` override its model/endpoint). Each provider lives in `providers/` (`ollama.rs`, `openai.rs`, `gemini.rs`, `anthropic.rs`, `atlascloud.rs`).
 - JSON schema extraction, prompt-based extraction, summarization
 
 ### PDF Modules (`webclaw-pdf`)

crates/webclaw-llm/src/chain.rs

@@ -1,5 +1,5 @@
 /// Provider chain — tries providers in order until one succeeds.
-/// Default order: Ollama (local, free) -> OpenAI -> Gemini -> Anthropic.
+/// Default order: Ollama (local, free) -> OpenAI -> Gemini -> Anthropic -> Atlas Cloud (opt-in).
 /// Only includes providers that are actually configured/available.
 use async_trait::async_trait;
 use tracing::{debug, warn};
@@ -7,8 +7,8 @@ use tracing::{debug, warn};
 use crate::error::LlmError;
 use crate::provider::{CompletionRequest, LlmProvider};
 use crate::providers::{
-    anthropic::AnthropicProvider, gemini::GeminiProvider, ollama::OllamaProvider,
-    openai::OpenAiProvider,
+    anthropic::AnthropicProvider, atlascloud::AtlasCloudProvider, gemini::GeminiProvider,
+    ollama::OllamaProvider, openai::OpenAiProvider,
 };
 
 pub struct ProviderChain {
@@ -16,11 +16,13 @@ pub struct ProviderChain {
 }
 
 impl ProviderChain {
-    /// Build the default chain: Ollama -> OpenAI -> Gemini -> Anthropic.
+    /// Build the default chain: Ollama -> OpenAI -> Gemini -> Anthropic -> Atlas Cloud.
     /// Ollama is always added (availability checked at call time).
     /// Cloud providers are only added if their API keys are configured.
     /// Gemini sits ahead of Anthropic so Google Cloud credits are preferred,
-    /// with Anthropic as the last-resort fallback.
+    /// with Anthropic as the last-resort fallback. Atlas Cloud is opt-in and
+    /// added last (only when `ATLASCLOUD_API_KEY` is set), so it never preempts
+    /// an already-configured provider.
     pub async fn default() -> Self {
         let mut providers: Vec<Box<dyn LlmProvider>> = Vec::new();
 
@@ -47,6 +49,11 @@ impl ProviderChain {
             providers.push(Box::new(anthropic));
         }
 
+        if let Some(atlas) = AtlasCloudProvider::new(None, None, None) {
+            debug!("atlascloud configured, adding to chain");
+            providers.push(Box::new(atlas));
+        }
+
         Self { providers }
     }
 

crates/webclaw-llm/src/providers/atlascloud.rs

@@ -21,7 +21,9 @@ impl AtlasCloudProvider {
         let base_url = base_url
             .or_else(|| std::env::var("ATLASCLOUD_BASE_URL").ok())
             .unwrap_or_else(|| "https://api.atlascloud.ai/v1".into());
-        let model = model.unwrap_or_else(|| "qwen/qwen3.5-flash".into());
+        let model = model
+            .or_else(|| std::env::var("ATLASCLOUD_MODEL").ok())
+            .unwrap_or_else(|| "qwen/qwen3.5-flash".into());
         let inner = OpenAiProvider::new(Some(key), Some(base_url), Some(model))?;
         Some(Self { inner })
     }