Replace nlohmann/json with native C++20 JSON engine, cut build RAM/time, fix 32-bit build, enable -O2 -march=native

README.md

@@ -34,17 +34,18 @@ The whole philosophy of Bantam rests on two principles:
   `std::map`, `std::span`) instead of raw memory areas.
 - Eliminate hand-rolled allocation/string code; rely on RAII so there is far
   less room for memory-allocation related vulnerabilities.
-- Depend only on **libcurl** (HTTP), **GNU readline** (interactive line
-  editing) and the vendored single-header **nlohmann/json** library (vendored
-  under `nlohmann/json.hpp`); the unsafe json-c C API is no longer used.
+- Depend only on **libcurl** (HTTP) and **GNU readline** (interactive line
+  editing); JSON parsing/serialization and Markdown rendering are implemented
+  natively in C++20 with no external or vendored library bloat, and the unsafe
+  json-c C API is no longer used.
 
 ## Repository layout
 
 ```
-bantam.hpp   all shared declarations (structs, prototypes)
+bantam.hpp   all shared declarations (structs, prototypes, native Json type)
 util.cpp     string building, UTF-8, prompt-injection filter, color, IDs, MD5
 config.cpp   config file parsing, env precedence, /models discovery
-json.cpp     request building + non-stream response parsing (nlohmann/json)
+json.cpp     native RFC 8259 JSON engine, request building + response parsing
 llm.cpp      libcurl HTTP client, OpenCode headers, backoff, SSE streaming
 tools.cpp    bash/read/write tools, oversized-result offloading
 session.cpp  message copy, session save/load, compaction
@@ -52,7 +53,6 @@ render.cpp   terminal markdown renderer (native, box-drawing tables)
 editor.cpp   GNU readline line editor + history (+ term helpers)
 main.cpp     REPL, agentic loop, tool dispatch, commands
 Makefile     POSIX-compatible build
-nlohmann/    vendored nlohmann/json single-header (v3.12.0)
 README.md    this document
 ```
 
@@ -61,8 +61,8 @@ README.md    this document
 - A C++20 compiler (`c++` / `g++` / `clang++`) and a POSIX `make`
   (`bmake`, `gmake`, `smake`, …).
 - **libcurl** development packages, available via the standard include /
-  library search paths. The JSON layer is a vendored single-header
-  (`nlohmann/json.hpp`) and needs no separate dependency.
+  library search paths. The JSON layer is implemented natively in `json.cpp`
+  and needs no separate dependency.
 - **GNU readline** development packages (`libreadline-dev` on Debian/Ubuntu,
   `readline` on Fedora/macOS) for the interactive prompt, history and line
   editing. On common systems:
@@ -99,7 +99,7 @@ make CPPFLAGS="-I/opt/include" LDLIBS="-L/opt/lib -lcurl"
 ## Building
 
 ```bash
-make            # builds ./bantam (c++ -std=c++20 -O2 -s -Wall -Wextra -Wpedantic)
+make            # builds & strips ./bantam (c++ -std=c++20 -O2 -march=native -s -Wall -Wextra -Wpedantic)
 make clean      # remove build artifacts
 make install    # install to $(DESTDIR)/usr/local/bin/bantam
 ```
@@ -391,8 +391,9 @@ collections use `std::vector`, and curl header lists and streaming state are
 wrapped in RAII types (`CurlHeaders`, `StreamCtx`) that free themselves on
 scope exit. There is no hand-rolled allocator and no manual `free` of message
 or tool-call data, so use-after-free and double-free are structurally
-unlikely. The vendored nlohmann/json library is used for all JSON parsing and
-serialization instead of the unsafe json-c C API.
+unlikely. A lightweight, native RFC 8259 JSON engine (`struct Json` in
+`json.cpp`) handles all JSON parsing and serialization using standard C++
+containers instead of an unsafe C API or a heavy header-only template library.
 
 ## Credits