Integration: Every Module, One Program

The capstone exercises every module. Where each one shows up:

| Module | Shows up as | |---|---| | M2-M4 classes | Book, Library with encapsulation, const correctness | | M5 STL | std::vector<Book> storage, std::map for counts | | M6 algorithms | std::sort the listing, std::find_if the search | | M7 modern | std::optional for lookups, enum class Status | | M8 RAII | ownership discipline if you hold resources | | M9 templates | a generic format_table helper if you generalize | | M10 errors | ValidationError carrying field data | | M11 DSA | complexity awareness for search choices |

The integration lesson: each seam is a place you already practiced. When the compiler complains, you now know which module's lesson to reread.

A worked skeleton to extend — search with optional + find_if:

#include <algorithm>
#include <optional>
#include <vector>

class Library {
public:
    std::optional<const Book*> find(std::string_view title) const {
        auto it = std::find_if(books_.begin(), books_.end(),
                               [&](const Book& b) { return b.title() == title; });
        if (it == books_.end()) return std::nullopt;
        return &*it;
    }
private:
    std::vector<Book> books_;
};

Every piece is review; the composition is the new skill.