Feat/english thinking when hidden

crates/tui/src/core/engine.rs

@@ -99,6 +99,10 @@ pub struct EngineConfig {
     /// When true, the model is instructed to respond in the current locale
     /// and a post-hoc translation layer replaces remaining English output.
     pub translation_enabled: bool,
+    /// When false, thinking blocks are hidden in the TUI. Propagated to the
+    /// system prompt builder so `reasoning_content` stays in English (saving
+    /// tokens) while the final reply still matches the user's language.
+    pub show_thinking: bool,
     /// Maximum number of assistant steps before stopping.
     pub max_steps: u32,
     /// Maximum number of concurrently active subagents.
@@ -181,6 +185,7 @@ impl Default for EngineConfig {
             instructions: Vec::new(),
             project_context_pack_enabled: true,
             translation_enabled: false,
+            show_thinking: true,
             max_steps: 100,
             max_subagents: DEFAULT_MAX_SUBAGENTS,
             features: Features::with_defaults(),
@@ -434,6 +439,7 @@ impl Engine {
                     project_context_pack_enabled: config.project_context_pack_enabled,
                     locale_tag: &config.locale_tag,
                     translation_enabled: config.translation_enabled,
+                    show_thinking: config.show_thinking,
                 },
                 session.approval_mode,
             );
@@ -589,6 +595,7 @@ impl Engine {
                     auto_approve,
                     approval_mode,
                     translation_enabled,
+                    show_thinking,
                 } => {
                     self.handle_send_message(
                         content,
@@ -603,6 +610,7 @@ impl Engine {
                         auto_approve,
                         approval_mode,
                         translation_enabled,
+                        show_thinking,
                     )
                     .await;
                 }
@@ -802,6 +810,7 @@ impl Engine {
                         self.session.auto_approve,
                         self.session.approval_mode,
                         self.config.translation_enabled,
+                        self.config.show_thinking,
                     )
                     .await;
                 }
@@ -890,6 +899,7 @@ impl Engine {
         auto_approve: bool,
         approval_mode: crate::tui::approval::ApprovalMode,
         translation_enabled: bool,
+        show_thinking: bool,
     ) {
         // Reset cancel token for fresh turn (in case previous was cancelled)
         self.reset_cancel_token();
@@ -973,6 +983,7 @@ impl Engine {
         self.session.trust_mode = trust_mode;
         self.config.trust_mode = trust_mode;
         self.config.translation_enabled = translation_enabled;
+        self.config.show_thinking = show_thinking;
         self.session.auto_approve = auto_approve;
         self.session.approval_mode = if auto_approve {
             crate::tui::approval::ApprovalMode::Auto
@@ -1792,6 +1803,7 @@ impl Engine {
                 project_context_pack_enabled: self.config.project_context_pack_enabled,
                 locale_tag: &self.config.locale_tag,
                 translation_enabled: self.config.translation_enabled,
+                show_thinking: self.config.show_thinking,
             },
             self.session.approval_mode,
         );

crates/tui/src/core/ops.rs

@@ -31,6 +31,7 @@ pub enum Op {
         auto_approve: bool,
         approval_mode: ApprovalMode,
         translation_enabled: bool,
+        show_thinking: bool,
     },
 
     /// Cancel the current request

crates/tui/src/main.rs

@@ -4636,6 +4636,7 @@ async fn run_exec_agent(
         instructions: config.instructions_paths(),
         project_context_pack_enabled: config.project_context_pack_enabled(),
         translation_enabled: false,
+        show_thinking: true,
         max_steps: 100,
         max_subagents,
         features: config.features(),
@@ -4725,6 +4726,7 @@ async fn run_exec_agent(
             trust_mode,
             auto_approve,
             translation_enabled: false,
+            show_thinking: true,
             approval_mode: if auto_approve {
                 crate::tui::approval::ApprovalMode::Auto
             } else {

crates/tui/src/prompts.rs

@@ -28,6 +28,11 @@ pub struct PromptSessionContext<'a> {
     /// to the system prompt instructing the model to respond in
     /// the resolved session locale.
     pub translation_enabled: bool,
+    /// When false, the user has hidden thinking blocks in the UI.
+    /// The prompt builder injects a language override so
+    /// `reasoning_content` stays in English (saving tokens) while
+    /// the final reply still matches the user's language.
+    pub show_thinking: bool,
 }
 
 /// Conventional location for the structured session relay artifact (#32).
@@ -549,6 +554,7 @@ pub fn system_prompt_for_mode_with_context_and_skills(
             project_context_pack_enabled: true,
             locale_tag: "en",
             translation_enabled: false,
+            show_thinking: true,
         },
     )
 }
@@ -641,6 +647,23 @@ pub fn system_prompt_for_mode_with_context_skills_session_and_approval(
         );
     }
 
+    // 2.3b. Thinking language override — when the user has hidden
+    // thinking blocks in the UI, redirect reasoning_content to
+    // English regardless of user language. This saves tokens
+    // (English is the most token-efficient language) while keeping
+    // the final reply in the user's language as described above.
+    if !session_context.show_thinking {
+        full_prompt.push_str(
+            "\n\n## Thinking Language\n\n\
+             The user has disabled thinking display in settings — they will \
+             never see your `reasoning_content`. Therefore, your internal \
+             thinking MUST be in English regardless of the user's language. \
+             This directive overrides the `## Language` section above for \
+             reasoning_content only. Your final reply must STILL match the \
+             user's language.",
+        );
+    }
+
     // 3. Skills block. #432: walks every candidate workspace
     // skills directory (`.agents/skills`, `skills`,
     // `.opencode/skills`, `.claude/skills`, `.cursor/skills`) plus global
@@ -881,6 +904,7 @@ mod tests {
                 project_context_pack_enabled: false,
                 locale_tag: "zh-Hans",
                 translation_enabled: false,
+                show_thinking: true,
             },
             ApprovalMode::Suggest,
         ) {
@@ -950,6 +974,7 @@ mod tests {
                 project_context_pack_enabled: false,
                 locale_tag: "zh-Hans",
                 translation_enabled: false,
+                show_thinking: true,
             },
             ApprovalMode::Suggest,
         ) {
@@ -994,6 +1019,7 @@ mod tests {
                 project_context_pack_enabled: false,
                 locale_tag: "en",
                 translation_enabled: false,
+                show_thinking: true,
             },
             ApprovalMode::Suggest,
         ) {
@@ -1083,6 +1109,7 @@ mod tests {
                 project_context_pack_enabled: true,
                 locale_tag: "ja",
                 translation_enabled: false,
+                show_thinking: true,
             },
         ) {
             SystemPrompt::Text(text) => text,
@@ -1118,6 +1145,7 @@ mod tests {
                 project_context_pack_enabled: false,
                 locale_tag: "en",
                 translation_enabled: false,
+                show_thinking: true,
             },
         ) {
             SystemPrompt::Text(text) => text,
@@ -1145,6 +1173,7 @@ mod tests {
                 project_context_pack_enabled: false,
                 locale_tag: "en",
                 translation_enabled: false,
+                show_thinking: true,
             },
         ) {
             SystemPrompt::Text(text) => text,
@@ -1174,6 +1203,7 @@ mod tests {
                 project_context_pack_enabled: false,
                 locale_tag: "en",
                 translation_enabled: false,
+                show_thinking: true,
             },
         ) {
             SystemPrompt::Text(text) => text,
@@ -1201,6 +1231,7 @@ mod tests {
                 project_context_pack_enabled: true,
                 locale_tag: "en",
                 translation_enabled: false,
+                show_thinking: true,
             },
         ) {
             SystemPrompt::Text(text) => text,
@@ -1395,6 +1426,7 @@ mod tests {
                 project_context_pack_enabled: true,
                 locale_tag: "en",
                 translation_enabled: false,
+                show_thinking: true,
             },
         ) {
             SystemPrompt::Text(text) => text,
@@ -1428,6 +1460,7 @@ mod tests {
                 project_context_pack_enabled: true,
                 locale_tag: "en",
                 translation_enabled: false,
+                show_thinking: true,
             },
         ) {
             SystemPrompt::Text(text) => text,

crates/tui/src/runtime_threads.rs

@@ -1616,6 +1616,7 @@ impl RuntimeThreadManager {
                 trust_mode,
                 auto_approve,
                 translation_enabled: false,
+                show_thinking: false,
                 approval_mode: if auto_approve {
                     crate::tui::approval::ApprovalMode::Auto
                 } else {
@@ -1933,6 +1934,7 @@ impl RuntimeThreadManager {
             instructions: self.config.instructions_paths(),
             project_context_pack_enabled: self.config.project_context_pack_enabled(),
             translation_enabled: false,
+            show_thinking: false,
             max_steps: 100,
             max_subagents: self.config.max_subagents().clamp(1, MAX_SUBAGENTS),
             features: self.config.features(),

crates/tui/src/tui/ui.rs

@@ -676,6 +676,7 @@ fn build_engine_config(app: &App, config: &Config) -> EngineConfig {
         instructions: config.instructions_paths(),
         project_context_pack_enabled: config.project_context_pack_enabled(),
         translation_enabled: app.translation_enabled,
+        show_thinking: app.show_thinking,
         // Effectively unlimited. V4 has a 1M context window and the user
         // wants the model running until it's actually done. The previous cap
         // of 100 hit the ceiling on long multi-step plans (wide refactors,
@@ -3882,6 +3883,7 @@ async fn dispatch_user_message(
                 project_context_pack_enabled: config.project_context_pack_enabled(),
                 locale_tag: app.ui_locale.tag(),
                 translation_enabled: app.translation_enabled,
+                show_thinking: app.show_thinking,
             },
         ),
     );
@@ -3978,6 +3980,7 @@ async fn dispatch_user_message(
             auto_approve: app.mode == AppMode::Yolo,
             approval_mode: app.approval_mode,
             translation_enabled: app.translation_enabled,
+            show_thinking: app.show_thinking,
         })
         .await
     {