Add OpenAI/LiteLLM provider support with settings UI

- Add openai/ provider module with translator, client, convert, request/response translators
- Add shared provider/ types (ConversationMessage, MessageRole, ProviderConfig enum)
- Wire OpenAI-compatible provider dispatch alongside Bedrock in response_stream.rs
- Add ai.openai.* settings (enabled, base_url, api_key, model, models)
- Add OpenAI/LiteLLM settings page with model fetch, picker, and config UI
- Extend model menu items and llms.rs to surface LiteLLM models
- Update WARP.md with OpenAI provider architecture docs

app/src/ai/bedrock/convert.rs

@@ -11,6 +11,11 @@ use serde_json::Value as JsonValue;
 
 use super::external_config::ExternalBedrockConfig;
 
+// Re-export shared provider types so existing imports from bedrock::convert continue to work.
+pub use crate::ai::provider::types::{
+    ContentPart, ConversationMessage, MessageContent, MessageRole, ToolDefinition,
+};
+
 #[derive(Clone, Debug)]
 pub struct CachingConfig {
     pub enabled: bool,
@@ -42,56 +47,6 @@ pub struct ConvertedRequest {
     pub tool_config: Option<ToolConfiguration>,
 }
 
-#[derive(Clone, Debug)]
-pub struct ConversationMessage {
-    pub role: MessageRole,
-    pub content: MessageContent,
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub enum MessageRole {
-    User,
-    Assistant,
-}
-
-#[derive(Clone, Debug)]
-pub enum MessageContent {
-    Text(String),
-    ToolUse {
-        tool_use_id: String,
-        name: String,
-        input: JsonValue,
-    },
-    ToolResult {
-        tool_use_id: String,
-        content: String,
-        is_error: bool,
-    },
-    MultiPart(Vec<ContentPart>),
-}
-
-#[derive(Clone, Debug)]
-pub enum ContentPart {
-    Text(String),
-    ToolUse {
-        tool_use_id: String,
-        name: String,
-        input: JsonValue,
-    },
-    ToolResult {
-        tool_use_id: String,
-        content: String,
-        is_error: bool,
-    },
-}
-
-#[derive(Clone, Debug)]
-pub struct ToolDefinition {
-    pub name: String,
-    pub description: String,
-    pub input_schema: JsonValue,
-}
-
 pub fn build_converse_request(
     messages: Vec<ConversationMessage>,
     system_prompt: Option<String>,

app/src/ai/bedrock/models_tests.rs

@@ -92,6 +92,7 @@ fn test_get_effective_models_custom_overrides() {
         model_id: "custom.model-v1:0".to_string(),
         display_name: "Custom Model".to_string(),
         vision_supported: false,
+        context_size: 200_000,
     }];
     let models = get_effective_models(&custom);
     assert_eq!(models.len(), 1);

app/src/ai/bedrock/request_translator.rs

@@ -992,7 +992,12 @@ pub fn extract_tools(request: &api::Request) -> Vec<ToolDefinition> {
     // Filter out suggest_next_prompt — its action executor waits on a oneshot
     // channel for UI interaction that never fires in the Bedrock path, causing
     // the conversation to stay InProgress forever.
-    tools.retain(|t| t.name != "suggest_next_prompt");
+    // Filter out start_agent/send_message_to_agent — sub-agents are disabled.
+    tools.retain(|t| {
+        t.name != "suggest_next_prompt"
+            && t.name != "start_agent"
+            && t.name != "send_message_to_agent"
+    });
 
     tools
 }

app/src/ai/bedrock/response_translator.rs

@@ -560,7 +560,7 @@ pub fn bedrock_stream_to_response_events(
     Box::pin(stream)
 }
 
-pub(crate) fn build_create_task(task_id: &str) -> ResponseEvent {
+pub fn build_create_task(task_id: &str) -> ResponseEvent {
     let task = api::Task {
         id: task_id.to_string(),
         description: String::new(),
@@ -617,7 +617,7 @@ fn build_user_query_message(task_id: &str, query_text: &str) -> ResponseEvent {
     }
 }
 
-pub(super) fn build_stream_init(request_id: &str, conversation_id: &str) -> ResponseEvent {
+pub fn build_stream_init(request_id: &str, conversation_id: &str) -> ResponseEvent {
     ResponseEvent {
         r#type: Some(api::response_event::Type::Init(
             api::response_event::StreamInit {
@@ -629,7 +629,7 @@ pub(super) fn build_stream_init(request_id: &str, conversation_id: &str) -> Resp
     }
 }
 
-pub(super) fn build_stream_finished(
+pub fn build_stream_finished(
     reason: stream_finished::Reason,
     input_tokens: i32,
     output_tokens: i32,
@@ -820,7 +820,7 @@ fn build_append_text(task_id: &str, message_id: &str, text_delta: &str) -> Respo
     }
 }
 
-fn build_tool_call_message(
+pub fn build_tool_call_message(
     task_id: &str,
     tool_use_id: &str,
     tool_name: &str,

app/src/ai/bedrock/response_translator_tests.rs

@@ -19,7 +19,15 @@ fn test_build_stream_init_has_valid_ids() {
 #[test]
 fn test_build_stream_finished_done_reason() {
     let reason = stream_finished::Reason::Done(stream_finished::Done {});
-    let event = build_stream_finished(reason, 100, 50, 20, 10, "anthropic.claude-sonnet-4-6", false);
+    let event = build_stream_finished(
+        reason,
+        100,
+        50,
+        20,
+        10,
+        "anthropic.claude-sonnet-4-6",
+        false,
+    );
 
     match event.r#type {
         Some(api::response_event::Type::Finished(finished)) => {