feat: show intent summary before file approval prompt (#2381)

When the model invokes write/modify/delete tools, extract its preceding
text content as an 'intent summary' and pass it to the approval view.
This gives users context about why a change is being made before they
review what will change.

Changes:
- Add intent_summary field to ApprovalRequired event (events.rs)
- Extract model text from current_text_visible when write tools
  are detected in the turn loop (turn_loop.rs)
- Add ApprovalRequest::new_with_intent constructor with
  intent_summary parameter (approval.rs)
- Pass intent_summary through TUI event handler to approval view
  (ui.rs)
- Render intent summary in approval widget: up to 3 lines of the
  model explanation, truncated to available card width, with
  i18n labels for zh-Hans locale (widgets/mod.rs)
- Adapt existing tests to new event field (runtime_threads.rs,
  ui/tests.rs)

Design decisions:
- Non-blocking: if the model provides no explanation, the approval
  still proceeds normally (no extra round-trip or token cost)
- Backward compatible: YOLO mode and approval cache unaffected
- The new() constructor is gated behind #[cfg(test)] since
  production code now uses new_with_intent()

crates/tui/src/core/engine/turn_loop.rs

@@ -1344,6 +1344,27 @@ impl Engine {
             }
             active_tool_names.extend(deferred_tools_hydrated_this_batch);
 
+            // --- Intent summary for write tools (#2381) ---
+            // When the model invokes write tools, extract its preceding text
+            // as an "intent summary" so the approval view can show *why* the
+            // change is being made, not just *what* will change.
+            let has_write_tools = plans.iter().any(|p| {
+                !p.read_only
+                    && p.approval_required
+                    && p.blocked_error.is_none()
+                    && p.guard_result.is_none()
+            });
+            let intent_summary: Option<String> = if has_write_tools {
+                let text = current_text_visible.trim();
+                if text.is_empty() {
+                    None
+                } else {
+                    Some(text.to_string())
+                }
+            } else {
+                None
+            };
+
             let plan_count = plans.len();
             let batches = plan_tool_execution_batches(plans);
             let parallel_chunks = batches
@@ -1702,6 +1723,7 @@ impl Engine {
                                     description: plan.approval_description.clone(),
                                     approval_key,
                                     approval_grouping_key,
+                                    intent_summary: intent_summary.clone(),
                                 })
                                 .await;
 

crates/tui/src/core/events.rs

@@ -234,6 +234,10 @@ pub enum Event {
         /// Lossy / arity-aware fingerprint, used to scope *approvals* so an
         /// "approve for session" covers later flag variants (v0.8.37).
         approval_grouping_key: String,
+        /// The model's explanation of intent before invoking write tools (#2381).
+        /// Displayed in the approval view so users understand *why* the change
+        /// is being made before reviewing *what* will change.
+        intent_summary: Option<String>,
     },
 
     /// Request user input for a tool call

crates/tui/src/runtime_threads.rs

@@ -4217,6 +4217,7 @@ mod tests {
                 tool_name: "exec_command".to_string(),
                 description: "stale approval".to_string(),
                 input: serde_json::json!({}),
+                intent_summary: None,
             })
             .await?;
 
@@ -4291,6 +4292,7 @@ mod tests {
                 tool_name: "exec_command".to_string(),
                 description: "external allow".to_string(),
                 input: serde_json::json!({}),
+                intent_summary: None,
             })
             .await?;
 
@@ -4369,6 +4371,7 @@ mod tests {
                 tool_name: "exec_command".to_string(),
                 description: "external deny".to_string(),
                 input: serde_json::json!({}),
+                intent_summary: None,
             })
             .await?;
 
@@ -4556,6 +4559,7 @@ mod tests {
                 tool_name: "exec_command".to_string(),
                 description: "remember=true".to_string(),
                 input: serde_json::json!({}),
+                intent_summary: None,
             })
             .await?;
 

crates/tui/src/tui/approval.rs

@@ -134,15 +134,31 @@ pub struct ApprovalRequest {
     /// Lossy / arity-aware fingerprint, used to scope *approvals* so an
     /// "approve for session" covers later flag variants (v0.8.37).
     pub approval_grouping_key: String,
+    /// The model's explanation of intent before invoking write tools (#2381).
+    /// Displayed in the approval view so users understand *why* the change
+    /// is being made before reviewing *what* will change.
+    pub intent_summary: Option<String>,
 }
 
 impl ApprovalRequest {
+    #[cfg(test)]
     pub fn new(
         id: &str,
         tool_name: &str,
         description: &str,
         params: &Value,
         approval_key: &str,
+    ) -> Self {
+        Self::new_with_intent(id, tool_name, description, params, approval_key, None)
+    }
+
+    pub fn new_with_intent(
+        id: &str,
+        tool_name: &str,
+        description: &str,
+        params: &Value,
+        approval_key: &str,
+        intent_summary: Option<&str>,
     ) -> Self {
         let category = get_tool_category(tool_name);
         let risk = classify_risk(tool_name, category, params);
@@ -159,6 +175,7 @@ impl ApprovalRequest {
             params: params.clone(),
             approval_key: approval_key.to_string(),
             approval_grouping_key,
+            intent_summary: intent_summary.map(std::string::ToString::to_string),
         }
     }
 

crates/tui/src/tui/ui.rs

@@ -1929,6 +1929,7 @@ async fn run_event_loop(
                         input,
                         approval_key,
                         approval_grouping_key,
+                        intent_summary,
                     } => {
                         let session_approved =
                             is_session_approved_for_tool(app, &tool_name, &approval_grouping_key);
@@ -1980,6 +1981,7 @@ async fn run_event_loop(
                                 &description,
                                 &tool_input,
                                 &approval_key,
+                                intent_summary.as_deref(),
                             );
                             log_sensitive_event(
                                 "tool.approval.prompted",
@@ -6609,12 +6611,20 @@ fn push_approval_request_view(
     description: &str,
     tool_input: &serde_json::Value,
     approval_key: &str,
+    intent_summary: Option<&str>,
 ) {
     if tool_name == "apply_patch" {
         maybe_add_patch_preview(app, tool_input);
     }
 
-    let request = ApprovalRequest::new(id, tool_name, description, tool_input, approval_key);
+    let request = ApprovalRequest::new_with_intent(
+        id,
+        tool_name,
+        description,
+        tool_input,
+        approval_key,
+        intent_summary,
+    );
     app.view_stack
         .push(ApprovalView::new_for_locale(request, app.ui_locale));
 }

crates/tui/src/tui/ui/tests.rs

@@ -5529,6 +5529,7 @@ fn approval_prompt_uses_event_input_after_message_complete_drain() {
         "Run cargo tests",
         &event_input,
         "approval-key",
+        None,
     );
 
     let mut view = app.view_stack.pop().expect("approval view");

crates/tui/src/tui/widgets/mod.rs

@@ -1166,6 +1166,50 @@ impl Renderable for ApprovalWidget<'_> {
             ]));
         }
 
+        // Intent summary — the model's explanation of why this change is needed (#2381).
+        if let Some(ref summary) = self.request.intent_summary {
+            if !summary.is_empty() {
+                let max_width = card_area.width.saturating_sub(14) as usize;
+                if max_width > 0 {
+                    lines.push(Line::from(""));
+                    let intent_label = match locale {
+                        Locale::ZhHans => "意图：",
+                        _ => "Intent: ",
+                    };
+                    let summary_lines: Vec<&str> = summary.lines().collect();
+                    for (i, sline) in summary_lines.iter().take(3).enumerate() {
+                        let prefix = if i == 0 { intent_label } else { "  " };
+                        let truncated =
+                            crate::utils::truncate_with_ellipsis(sline, max_width, "...");
+                        lines.push(Line::from(vec![
+                            Span::raw("  "),
+                            Span::styled(
+                                prefix,
+                                if i == 0 {
+                                    Style::default().fg(palette::TEXT_HINT)
+                                } else {
+                                    Style::default()
+                                },
+                            ),
+                            Span::styled(truncated, Style::default().fg(palette::TEXT_SECONDARY)),
+                        ]));
+                    }
+                    if summary_lines.len() > 3 {
+                        let more = match locale {
+                            Locale::ZhHans => {
+                                format!("  … (还有 {} 行)", summary_lines.len() - 3)
+                            }
+                            _ => format!("  … (+{} lines)", summary_lines.len() - 3),
+                        };
+                        lines.push(Line::from(vec![
+                            Span::raw("  "),
+                            Span::styled(more, Style::default().fg(palette::TEXT_HINT)),
+                        ]));
+                    }
+                }
+            }
+        }
+
         lines.push(Line::from(""));
         let params_str = self.request.params_display();
         let params_width = card_area.width.saturating_sub(14) as usize;