refactor(ollama): replace handcrafted HTTP logic with ollama‑rs client and simplify request handling

- Switch to `ollama-rs` crate for chat, model listing, and streaming.
- Remove custom request building, authentication handling, and debug logging.
- Drop unsupported tool conversion; now ignore tool descriptors with a warning.
- Refactor model fetching to use local model info and optional cloud details.
- Consolidate error mapping via `map_ollama_error`.
- Update health check to use the new HTTP client.
- Delete obsolete `provider_interface.rs` test as the provider interface has changed.

crates/owlen-core/src/config.rs

@@ -134,10 +134,13 @@ impl Config {
             config.ensure_defaults();
             config.mcp.apply_backward_compat();
             config.apply_schema_migrations(&previous_version);
+            config.expand_provider_env_vars()?;
             config.validate()?;
             Ok(config)
         } else {
-            Ok(Config::default())
+            let mut config = Config::default();
+            config.expand_provider_env_vars()?;
+            Ok(config)
         }
     }
 
@@ -201,6 +204,13 @@ impl Config {
         }
     }
 
+    fn expand_provider_env_vars(&mut self) -> Result<()> {
+        for (provider_name, provider) in self.providers.iter_mut() {
+            expand_provider_entry(provider_name, provider)?;
+        }
+        Ok(())
+    }
+
     /// Validate configuration invariants and surface actionable error messages.
     pub fn validate(&self) -> Result<()> {
         self.validate_default_provider()?;
@@ -336,6 +346,56 @@ fn default_ollama_provider_config() -> ProviderConfig {
     }
 }
 
+fn expand_provider_entry(provider_name: &str, provider: &mut ProviderConfig) -> Result<()> {
+    if let Some(ref mut base_url) = provider.base_url {
+        let expanded = expand_env_string(
+            base_url.as_str(),
+            &format!("providers.{provider_name}.base_url"),
+        )?;
+        *base_url = expanded;
+    }
+
+    if let Some(ref mut api_key) = provider.api_key {
+        let expanded = expand_env_string(
+            api_key.as_str(),
+            &format!("providers.{provider_name}.api_key"),
+        )?;
+        *api_key = expanded;
+    }
+
+    for (extra_key, extra_value) in provider.extra.iter_mut() {
+        if let serde_json::Value::String(current) = extra_value {
+            let expanded = expand_env_string(
+                current.as_str(),
+                &format!("providers.{provider_name}.{}", extra_key),
+            )?;
+            *current = expanded;
+        }
+    }
+
+    Ok(())
+}
+
+fn expand_env_string(input: &str, field_path: &str) -> Result<String> {
+    if !input.contains('$') {
+        return Ok(input.to_string());
+    }
+
+    match shellexpand::env(input) {
+        Ok(expanded) => Ok(expanded.into_owned()),
+        Err(err) => match err.cause {
+            std::env::VarError::NotPresent => Err(crate::Error::Config(format!(
+                "Environment variable {} referenced in {field_path} is not set",
+                err.var_name
+            ))),
+            std::env::VarError::NotUnicode(_) => Err(crate::Error::Config(format!(
+                "Environment variable {} referenced in {field_path} contains invalid Unicode",
+                err.var_name
+            ))),
+        },
+    }
+}
+
 /// Default configuration path with user home expansion
 pub fn default_config_path() -> PathBuf {
     if let Some(config_dir) = dirs::config_dir() {
@@ -836,6 +896,48 @@ pub fn session_timeout(config: &Config) -> Duration {
 mod tests {
     use super::*;
 
+    #[test]
+    fn expand_provider_env_vars_resolves_api_key() {
+        std::env::set_var("OWLEN_TEST_API_KEY", "super-secret");
+
+        let mut config = Config::default();
+        if let Some(ollama) = config.providers.get_mut("ollama") {
+            ollama.api_key = Some("${OWLEN_TEST_API_KEY}".to_string());
+        }
+
+        config
+            .expand_provider_env_vars()
+            .expect("environment expansion succeeded");
+
+        assert_eq!(
+            config.providers["ollama"].api_key.as_deref(),
+            Some("super-secret")
+        );
+
+        std::env::remove_var("OWLEN_TEST_API_KEY");
+    }
+
+    #[test]
+    fn expand_provider_env_vars_errors_for_missing_variable() {
+        std::env::remove_var("OWLEN_TEST_MISSING");
+
+        let mut config = Config::default();
+        if let Some(ollama) = config.providers.get_mut("ollama") {
+            ollama.api_key = Some("${OWLEN_TEST_MISSING}".to_string());
+        }
+
+        let error = config
+            .expand_provider_env_vars()
+            .expect_err("missing variables should error");
+
+        match error {
+            crate::Error::Config(message) => {
+                assert!(message.contains("OWLEN_TEST_MISSING"));
+            }
+            other => panic!("expected config error, got {other:?}"),
+        }
+    }
+
     #[test]
     fn test_storage_platform_specific_paths() {
         let config = Config::default();