fix cell toml and add documentation for tools

docs/c-modules.md

@@ -228,11 +228,105 @@ var d = vector.dot(1, 0, 0, 1) // 0
 C files are automatically compiled when you run:
 
 ```bash
-pit build
-pit update
+cell --dev build
 ```
 
-Each C file is compiled into a per-file dynamic library at `~/.pit/lib/<pkg>/<stem>.dylib`.
+Each C file is compiled into a per-file dynamic library at `.cell/lib/<pkg>/<stem>.dylib`.
+
+## Compilation Flags (cell.toml)
+
+Use the `[compilation]` section in `cell.toml` to pass compiler and linker flags:
+
+```toml
+[compilation]
+CFLAGS = "-Isrc -Ivendor/include"
+LDFLAGS = "-lz -lm"
+```
+
+### Include paths
+
+Relative `-I` paths are resolved from the package root:
+
+```toml
+CFLAGS = "-Isdk/public"
+```
+
+If your package is at `/path/to/mypkg`, this becomes `-I/path/to/mypkg/sdk/public`.
+
+Absolute paths are passed through unchanged.
+
+### Library paths
+
+Relative `-L` paths work the same way:
+
+```toml
+LDFLAGS = "-Lsdk/lib -lmylib"
+```
+
+### Target-specific flags
+
+Add sections named `[compilation.<target>]` for platform-specific flags:
+
+```toml
+[compilation]
+CFLAGS = "-Isdk/public"
+
+[compilation.macos_arm64]
+LDFLAGS = "-Lsdk/lib/osx -lmylib"
+
+[compilation.linux]
+LDFLAGS = "-Lsdk/lib/linux64 -lmylib"
+
+[compilation.windows]
+LDFLAGS = "-Lsdk/lib/win64 -lmylib64"
+```
+
+Available targets: `macos_arm64`, `macos_x86_64`, `linux`, `linux_arm64`, `windows`.
+
+### Sigils
+
+Use `$LOCAL` in flags to refer to the `.cell/local` directory (for prebuilt libraries):
+
+```toml
+LDFLAGS = "-L$LOCAL -lmyprebuilt"
+```
+
+### Example: vendored SDK
+
+A package wrapping an external SDK with platform-specific shared libraries:
+
+```
+mypkg/
+├── cell.toml
+├── wrapper.cpp
+└── sdk/
+    ├── public/
+    │   └── mylib/
+    │       └── api.h
+    └── lib/
+        ├── osx/
+        │   └── libmylib.dylib
+        └── linux64/
+            └── libmylib.so
+```
+
+```toml
+[compilation]
+CFLAGS = "-Isdk/public"
+
+[compilation.macos_arm64]
+LDFLAGS = "-Lsdk/lib/osx -lmylib"
+
+[compilation.linux]
+LDFLAGS = "-Lsdk/lib/linux64 -lmylib"
+```
+
+```cpp
+// wrapper.cpp
+#include "cell.h"
+#include <mylib/api.h>
+// ...
+```
 
 ## Platform-Specific Code