[devin-ai-integration]

Rewrites the C++ backend on top of cpp_architecture, using C++20 coroutines. The C++17 state machine is gone.

Backend (src/engine/internal/codegen/cpp)

• CppCodeBuilder outputs one class per script. The class derives from CppExecutableCode and overrides runScript / runReporter / runPredicate / runProcedure. It registers itself (CppCompilerContext::registerCode) under the FNV-1a hash of its source.
• build() hashes the source and creates the registered class. If there is none, it reports the source through CppCompilerContext::setSourceCallback and returns a no-op code.
• Pointers (constants, variables, lists) are passed in at runtime as a pointer table, so the source is the same in every process.
• Scripts and procedures that can suspend are C++20 coroutines (CppCoroutine). A yield is co_await std::suspend_always{}, and the end-thread flag is the coroutine's return value. Warp code never suspends. kill() keeps the coroutine alive until reset().
• Function calls follow the LLVM convention: strings are returned through a StringPtr * first parameter. Externs are declared type-erased and cast at the call site, because the tests call one function with different signatures.

Tests

• The shared codebuilder_test and operator tests now also run for cpp. codegen_test_generator runs them once to collect the generated code. It maps ASSERT to EXPECT and restarts the test process after a crash, so every builder in a test is reached. It writes 16 shards, which are compiled into codegen_test.
• cpp_test mock updated for CppCoroutine.

Codebase generation

• scratchcpp-transpiler <project.sb3> <output dir> [name] (cpp backend only) writes project.cpp, project_data.cpp (the embedded .sb3), main.cpp and a C++20 CMakeLists.txt.

Also adds a missing <bit> include in string_functions.cpp, which GCC 11 needs for std::bit_ceil.

Still not done: #682 (inlining) and type analysis. Variables stay ValueData.

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring