feat(provider): add dedicated AWS Bedrock Converse API provider

Replace the non-functional OpenAI-compatible stub with a purpose-built
Bedrock provider that implements AWS SigV4 signing from first principles
using hmac/sha2/hex crates — no AWS SDK dependency.

Key capabilities:
- SigV4 authentication (AKSK + optional session token)
- Converse API with native tool calling support
- Prompt caching via cachePoint heuristics
- Proper URI encoding for model IDs containing colons
- Resilient response parsing with unknown block type fallback

Also updates:
- Factory wiring and credential resolution bypass for AKSK auth
- Onboard wizard with Bedrock-specific model selection and guidance
- Provider reference docs with auth, region, and model ID details

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/onboard/wizard.rs

@@ -547,6 +547,7 @@ fn default_model_for_provider(provider: &str) -> String {
         "ollama" => "llama3.2".into(),
         "gemini" => "gemini-2.5-pro".into(),
         "kimi-code" => "kimi-for-coding".into(),
+        "bedrock" | "aws-bedrock" => "anthropic.claude-sonnet-4-5-20250929-v1:0".into(),
         "nvidia" => "meta/llama-3.3-70b-instruct".into(),
         "astrai" => "anthropic/claude-sonnet-4.6".into(),
         _ => "anthropic/claude-sonnet-4.6".into(),
@@ -864,6 +865,24 @@ fn curated_models_for_provider(provider_name: &str) -> Vec<(String, String)> {
             ("codellama".to_string(), "Code Llama".to_string()),
             ("phi3".to_string(), "Phi-3 (small, fast)".to_string()),
         ],
+        "bedrock" => vec![
+            (
+                "anthropic.claude-sonnet-4-6".to_string(),
+                "Claude Sonnet 4.6 (latest, recommended)".to_string(),
+            ),
+            (
+                "anthropic.claude-opus-4-6-v1".to_string(),
+                "Claude Opus 4.6 (strongest)".to_string(),
+            ),
+            (
+                "anthropic.claude-haiku-4-5-20251001-v1:0".to_string(),
+                "Claude Haiku 4.5 (fastest, cheapest)".to_string(),
+            ),
+            (
+                "anthropic.claude-sonnet-4-5-20250929-v1:0".to_string(),
+                "Claude Sonnet 4.5".to_string(),
+            ),
+        ],
         "gemini" => vec![
             (
                 "gemini-3-pro-preview".to_string(),
@@ -1826,29 +1845,51 @@ fn setup_provider(workspace_dir: &Path) -> Result<(String, String, String, Optio
         };
 
         println!();
-        if !key_url.is_empty() {
+        if matches!(provider_name, "bedrock" | "aws-bedrock") {
+            // Bedrock uses AWS AKSK, not a single API key.
+            print_bullet("Bedrock uses AWS credentials (not a single API key).");
             print_bullet(&format!(
-                "Get your API key at: {}",
-                style(key_url).cyan().underlined()
+                "Set {} and {} environment variables.",
+                style("AWS_ACCESS_KEY_ID").yellow(),
+                style("AWS_SECRET_ACCESS_KEY").yellow(),
             ));
-        }
-        print_bullet("You can also set it later via env var or config file.");
-        println!();
-
-        let key: String = Input::new()
-            .with_prompt("  Paste your API key (or press Enter to skip)")
-            .allow_empty(true)
-            .interact_text()?;
-
-        if key.is_empty() {
-            let env_var = provider_env_var(provider_name);
             print_bullet(&format!(
-                "Skipped. Set {} or edit config.toml later.",
-                style(env_var).yellow()
+                "Optionally set {} for the region (default: us-east-1).",
+                style("AWS_REGION").yellow(),
             ));
-        }
+            if !key_url.is_empty() {
+                print_bullet(&format!(
+                    "Manage IAM credentials at: {}",
+                    style(key_url).cyan().underlined()
+                ));
+            }
+            println!();
+            String::new()
+        } else {
+            if !key_url.is_empty() {
+                print_bullet(&format!(
+                    "Get your API key at: {}",
+                    style(key_url).cyan().underlined()
+                ));
+            }
+            print_bullet("You can also set it later via env var or config file.");
+            println!();
 
-        key
+            let key: String = Input::new()
+                .with_prompt("  Paste your API key (or press Enter to skip)")
+                .allow_empty(true)
+                .interact_text()?;
+
+            if key.is_empty() {
+                let env_var = provider_env_var(provider_name);
+                print_bullet(&format!(
+                    "Skipped. Set {} or edit config.toml later.",
+                    style(env_var).yellow()
+                ));
+            }
+
+            key
+        }
     };
 
     // ── Model selection ──

src/providers/mod.rs

@@ -1,4 +1,5 @@
 pub mod anthropic;
+pub mod bedrock;
 pub mod compatible;
 pub mod copilot;
 pub mod gemini;
@@ -502,6 +503,9 @@ fn resolve_provider_credential(name: &str, credential_override: Option<&str>) ->
         }
         name if is_glm_alias(name) => vec!["GLM_API_KEY"],
         name if is_minimax_alias(name) => vec![MINIMAX_OAUTH_TOKEN_ENV, MINIMAX_API_KEY_ENV],
+        // Bedrock uses AWS AKSK from env vars (AWS_ACCESS_KEY_ID + AWS_SECRET_ACCESS_KEY),
+        // not a single API key. Credential resolution happens inside BedrockProvider.
+        "bedrock" | "aws-bedrock" => return None,
         name if is_qianfan_alias(name) => vec!["QIANFAN_API_KEY"],
         name if is_qwen_alias(name) => vec!["DASHSCOPE_API_KEY"],
         name if is_zai_alias(name) => vec!["ZAI_API_KEY"],
@@ -669,12 +673,7 @@ pub fn create_provider_with_url(
                 AuthStyle::Bearer,
             )
         )),
-        "bedrock" | "aws-bedrock" => Ok(Box::new(OpenAiCompatibleProvider::new(
-            "Amazon Bedrock",
-            "https://bedrock-runtime.us-east-1.amazonaws.com",
-            key,
-            AuthStyle::Bearer,
-        ))),
+        "bedrock" | "aws-bedrock" => Ok(Box::new(bedrock::BedrockProvider::new())),
         name if is_qianfan_alias(name) => Ok(Box::new(OpenAiCompatibleProvider::new(
             "Qianfan", "https://aip.baidubce.com", key, AuthStyle::Bearer,
         ))),
@@ -1417,8 +1416,11 @@ mod tests {
 
     #[test]
     fn factory_bedrock() {
-        assert!(create_provider("bedrock", Some("key")).is_ok());
-        assert!(create_provider("aws-bedrock", Some("key")).is_ok());
+        // Bedrock uses AWS env vars for credentials, not API key.
+        assert!(create_provider("bedrock", None).is_ok());
+        assert!(create_provider("aws-bedrock", None).is_ok());
+        // Passing an api_key is harmless (ignored).
+        assert!(create_provider("bedrock", Some("ignored")).is_ok());
     }
 
     #[test]