feat(context): render STRUCTURED CHANGES section in LLM prompt

Formats SymbolDiff entries as concise one-line descriptions showing
parent scope, parameter changes, return type changes, and body
modification magnitude. Section omitted when no structural diffs exist.

Author: Sephyi

src/domain/context.rs

@@ -44,8 +44,7 @@ pub struct PromptContext {
     /// e.g., "src/services/context.rs <-> tests/context.rs (test file)"
     pub test_correlations: Vec<String>,
     /// Structured semantic changes for modified symbols (from AstDiffer).
-    /// Used by the prompt formatter in T1-4 to show semantic diffs to the LLM.
-    #[allow(dead_code)]
+    /// Formatted as a `STRUCTURED CHANGES:` section in the prompt.
     pub structured_changes: Vec<SymbolDiff>,
 }
 
@@ -69,6 +68,17 @@ impl PromptContext {
             )
         };
 
+        let structured_section = if self.structured_changes.is_empty() {
+            String::new()
+        } else {
+            let lines: Vec<String> = self
+                .structured_changes
+                .iter()
+                .map(|d| d.format_oneline())
+                .collect();
+            format!("\nSTRUCTURED CHANGES:\n{}\n", lines.join("\n"))
+        };
+
         let imports_section = if self.import_changes.is_empty() {
             String::new()
         } else {
@@ -160,7 +170,7 @@ impl PromptContext {
 SUMMARY: {summary}
 FILES: {files}
 SUGGESTED TYPE: {commit_type}{scope}
-{group_rationale}{evidence}{primary_change}{symbols}{connections}{imports}{related}
+{group_rationale}{evidence}{primary_change}{symbols}{structured}{connections}{imports}{related}
 DIFF:
 {diff}
 {constraints}{breaking}{metadata_breaking}{locale}{focus}{history}
@@ -179,6 +189,7 @@ Respond with ONLY this JSON:
                 .unwrap_or_default(),
             evidence = evidence_section,
             symbols = symbols_section,
+            structured = structured_section,
             connections = connections_section,
             imports = imports_section,
             related = related_section,

tests/context.rs

@@ -1746,6 +1746,69 @@ fn test_correlations_capped_at_5() {
     assert!(ctx.test_correlations.len() <= 5);
 }
 
+// ─── Structured changes in prompt ─────────────────────────────────────────────
+
+#[test]
+fn structured_changes_shown_in_prompt() {
+    use commitbee::domain::diff::{ChangeDetail, SymbolDiff};
+
+    let changes = make_staged_changes(vec![make_file_change(
+        "src/lib.rs",
+        ChangeStatus::Modified,
+        "+pub fn validate(input: &str, strict: bool) -> Result<()> { Ok(()) }",
+        1,
+        0,
+    )]);
+    let diffs = vec![SymbolDiff {
+        name: "validate".into(),
+        file: "src/lib.rs".into(),
+        line: 1,
+        parent_scope: Some("Validator".into()),
+        changes: vec![
+            ChangeDetail::ParamAdded("strict: bool".into()),
+            ChangeDetail::ReturnTypeChanged {
+                old: "bool".into(),
+                new: "Result<()>".into(),
+            },
+        ],
+    }];
+    let ctx = ContextBuilder::build(&changes, &[], &diffs, &default_config());
+    let prompt = ctx.to_prompt();
+    assert!(
+        prompt.contains("STRUCTURED CHANGES:"),
+        "prompt should contain structured changes section"
+    );
+    assert!(
+        prompt.contains("Validator::validate()"),
+        "should show parent scope"
+    );
+    assert!(
+        prompt.contains("+param strict: bool"),
+        "should show added param"
+    );
+    assert!(
+        prompt.contains("return bool"),
+        "should show return type change"
+    );
+}
+
+#[test]
+fn empty_structured_changes_not_shown() {
+    let changes = make_staged_changes(vec![make_file_change(
+        "src/lib.rs",
+        ChangeStatus::Modified,
+        "+code\n",
+        1,
+        0,
+    )]);
+    let ctx = ContextBuilder::build(&changes, &[], &[], &default_config());
+    let prompt = ctx.to_prompt();
+    assert!(
+        !prompt.contains("STRUCTURED CHANGES:"),
+        "empty structured changes should not appear"
+    );
+}
+
 #[test]
 fn python_comment_only_change_classified_as_docs() {
     let changes = make_staged_changes(vec![make_file_change(