Set up Cursor Cloud dev environment for 3FS

[rchalamala]

Summary

Sets up and documents the development environment for 3FS (Fire-Flyer File System) on the Cursor Cloud VM (Ubuntu 24.04, x86_64), and adds an AGENTS.md with durable, non-obvious setup/run guidance for future agents.

No product code was modified. The only file added is AGENTS.md.

What was installed / configured

• Build toolchain: clang-14 + lld-14 (from noble/universe), gcc-12/g++-12, CMake, Boost, glog/gflags/gtest, libuv, lz4, double-conversion, libunwind, gperftools, OpenSSL.
• FoundationDB client + server 7.3.63; libfuse 3.16.2 built from source; gettext-base + iproute2 (needed by the local harness).
• Rust pinned to 1.85.0 (newer stable defaults to rust-lld and breaks C++ linking).
• Git submodules initialized + patches/apply.sh applied.
• Set cc/c++ alternatives to gcc (matching CI) and pinned clang-14 to the gcc-12 libstdc++ (the VM's newest gcc-14 dir is incomplete). Exact build command is documented in AGENTS.md.

Verification (build / lint / test)

Capability	Command	Result
Rust build	cargo build --release	Success
C++ build	cmake --build build -j8 -- -k (clang-14, gcc-12 pin)	All 10 service/client binaries + 17 test executables built
Lint	make check-format (clang-format-14)	Runs; flags pre-existing violations
Tests	./build/tests/test_kv	3 passed
Tests	./build/tests/test_mgmtd	26 passed (CRAQ chain replication)
Tests	./build/tests/test_meta	110 passed (mkdir/stat/symlink/truncate/perm/sync)
Tests	./build/tests/test_client	43/44 passed (RPC over TCP)

Known limitations (documented in AGENTS.md)

• No RDMA in this VM (no /sys/class/infiniband, ibv_get_device_list = ENOSYS). All service/client binaries FATAL at IBManager::start, so the full cluster + FUSE harness (tests/fuse/run.sh) cannot run here. Functional verification is done via the TCP/LOCAL gtest suites above.
• tests/common/utils/TestShuffle.cc has a latent missing #include <fstream> and fails to compile under clang-14 (both libstdc++-12 and -13); build the rest with -- -k.

Build and test evidence

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