fix: extract PKGBUILD build()/package() bodies for Custom templates

- extract_bash_function() extracts bash function bodies by brace-matching
- Custom template now populates build_script from build() body
- Custom template now populates install_script from package() body
- Fixes 'custom builds require prepare/build/install instructions' error

local/recipes/system/cub/source/cub-lib/src/pkgbuild.rs

@@ -58,6 +58,22 @@ pub fn convert_pkgbuild(content: &str) -> Result<ConversionResult, CubError> {
     let mut warnings = detect_linuxisms(content);
     let mut actions_required = Vec::new();
 
+    let build_body = if matches!(template, BuildTemplate::Custom) {
+        extract_bash_function(content, "build")
+    } else {
+        None
+    };
+    let package_body = if matches!(template, BuildTemplate::Custom) {
+        extract_bash_function(content, "package")
+    } else {
+        None
+    };
+
+    if template == BuildTemplate::Custom && build_body.is_none() && package_body.is_none() {
+        warnings.push("Custom build detected but could not extract build() or package() function body".to_string());
+        actions_required.push("review the PKGBUILD build() and package() functions manually".to_string());
+    }
+
     let mapped_runtime = map_dep_list(&depends, &mut warnings, &mut actions_required);
     let mapped_build = map_dep_list(&makedepends, &mut warnings, &mut actions_required);
     let mapped_check = map_dep_list(&checkdepends, &mut warnings, &mut actions_required);
@@ -117,6 +133,8 @@ pub fn convert_pkgbuild(content: &str) -> Result<ConversionResult, CubError> {
         },
         build: BuildSection {
             template,
+            build_script: build_body.into_iter().collect(),
+            install_script: package_body.into_iter().collect(),
             ..BuildSection::default()
         },
         install: InstallSection::default(),
@@ -326,6 +344,37 @@ pub fn detect_build_template(content: &str) -> BuildTemplate {
     }
 }
 
+pub fn extract_bash_function(content: &str, name: &str) -> Option<String> {
+    for pattern in &[format!("{name}() {{"), format!("function {name} () {{"), format!("{name} () {{")] {
+        if let Some(pos) = content.find(pattern) {
+            let start = pos + pattern.len();
+            let rest = &content[start..];
+            let mut depth = 1u32;
+            let mut end = 0usize;
+            for (i, ch) in rest.char_indices() {
+                match ch {
+                    '{' => depth += 1,
+                    '}' => {
+                        depth -= 1;
+                        if depth == 0 {
+                            end = i;
+                            break;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+            if end > 0 {
+                let body = rest[..end].trim().to_string();
+                if !body.is_empty() {
+                    return Some(body);
+                }
+            }
+        }
+    }
+    None
+}
+
 pub fn detect_linuxisms(content: &str) -> Vec<String> {
     let lowered = content.to_ascii_lowercase();
     let checks = [