fix: review fixes + feat: imports, assertions, merge engine, per-package overrides

Review fixes (8 blocking issues):
- Extract ParseError to shared error.hpp (ODR fix)
- Remove dead package.cpp/package.hpp + tomlplusplus dep
- Safe parse_int() helper replacing crash-prone std::stoi
- consume_string() now accepts bare numbers and idents
- line_at() fixed for post-EOF line numbers
- Subcommand validation before file read in CLI
- KwService/KwAssert/KwImport added to consume_ident()
- root partition promoted to first-class BootBlock field

New features:
- Imports: imports = [...] with recursive merge resolution
- Assertions: assert { "msg" : field op value } in both parsers
- Merge engine: resolve_package() with features/config merge + force support
- Per-package overrides: /kappa/system/builds/<name>.kap
- .gitignore: added vcpkg_installed/ and kappa binary

include/kappa/config/merge.hpp

@@ -0,0 +1,28 @@
+#pragma once
+
+#include "kappa/dsl/ast.hpp"
+#include "kappa/dsl/system.hpp"
+
+#include <optional>
+#include <unordered_map>
+#include <string>
+
+namespace kappa::config {
+
+struct ResolvedPackage {
+    dsl::PackageDef original;
+    std::unordered_map<std::string, dsl::FeatureDef> features;
+    std::unordered_map<std::string, std::string> config;
+};
+
+ResolvedPackage resolve_package(
+    const dsl::PackageDef& pkg,
+    const dsl::SystemBlock& system,
+    const std::optional<dsl::PackageRef>& overrides);
+
+std::unordered_map<std::string, std::string> resolve_config(
+    const dsl::PackageDef& pkg,
+    const dsl::SystemBlock& system,
+    const std::optional<dsl::PackageRef>& overrides);
+
+} // namespace kappa::config

include/kappa/dsl/ast.hpp

@@ -52,6 +52,13 @@ struct ServiceInit {
     std::unordered_map<std::string, std::string> env;
 };
 
+struct Assertion {
+    std::string message;
+    std::string field;
+    std::string op;     // "==" or "!="
+    std::string value;
+};
+
 struct PackageDef {
     std::string name;
     std::string version;
@@ -65,6 +72,7 @@ struct PackageDef {
     std::vector<Patch> patches;
     std::vector<EnvEntry> env_entries;
     std::unordered_map<std::string, ServiceInit> service;
+    std::vector<Assertion> assertions;
     std::unordered_set<std::string> const_keys;
     Phase prepare;
     Phase build;

include/kappa/dsl/error.hpp

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <format>
+#include <stdexcept>
+#include <string>
+
+namespace kappa::dsl {
+
+class ParseError : public std::runtime_error {
+public:
+    ParseError(int line, int col, const std::string& msg)
+        : std::runtime_error(std::format("{}:{}: {}", line, col, msg)) {}
+};
+
+inline int parse_int(int line, int col, const std::string& lexeme) {
+    try {
+        std::size_t pos = 0;
+        int val = std::stoi(lexeme, &pos);
+        if (pos != lexeme.size()) {
+            throw ParseError(line, col,
+                           std::format("expected integer, got '{}'", lexeme));
+        }
+        return val;
+    } catch (const std::invalid_argument&) {
+        throw ParseError(line, col,
+                        std::format("expected integer, got '{}'", lexeme));
+    } catch (const std::out_of_range&) {
+        throw ParseError(line, col,
+                        std::format("integer out of range: '{}'", lexeme));
+    }
+}
+
+} // namespace kappa::dsl

include/kappa/dsl/system.hpp

@@ -34,6 +34,7 @@ struct BootBlock {
     std::string init;
     std::string efi;
     std::string swap;
+    std::string root;
     std::string bootloader;
     std::unordered_map<std::string, std::string> params;
 };
@@ -52,13 +53,16 @@ struct ServiceRef {
 };
 
 struct SystemConfig {
+    std::vector<std::string> imports;
     SystemBlock system;
     std::vector<PackageRef> packages;
     std::vector<ServiceRef> services;
     BootBlock boot;
     std::vector<UserRef> users;
+    std::vector<Assertion> assertions;
 };
 
 SystemConfig parse_system_config(std::string_view source);
+SystemConfig resolve_imports(const SystemConfig& cfg, const std::string& base_dir);
 
 } // namespace kappa::dsl

include/kappa/dsl/token.hpp

@@ -35,6 +35,8 @@ enum class TokenType {
     KwPatches,
     KwEnv,
     KwService,
+    KwAssert,
+    KwImport,
     KwPrepare,
     KwBuild,
     KwCheck,

include/kappa/package.hpp

@@ -1,23 +0,0 @@
-#pragma once
-
-#include <iosfwd>
-#include <string>
-#include <vector>
-
-namespace kappa {
-
-struct PackageConfig {
-    std::string name;
-    std::string version;
-    std::string description;
-    std::string source_url;
-    std::string source_extension;
-    std::string source_hash;
-    std::vector<std::string> dependencies;
-    std::string build_system;
-};
-
-PackageConfig parse_package(const std::string& toml_path);
-void print_package(std::ostream& os, const PackageConfig& pkg);
-
-} // namespace kappa