Ensure build configuration explicitly sets (1) include paths and (2) required language/toolchain modes to prevent environment-dependent header resolution and compiler-mode breakages. - Include paths: Add third-party include directories explicitly and in a way that selects the intended headers. If a dependency’s headers conflict by name, adjust `-I` order/paths to avoid accidental inclusion of the wrong header. Example: ```make # Prefer the dependency’s local includes to avoid header-name collisions CFLAGS += -I../deps/tre/local_includes ``` - Language standard/toolchain mode: Do not rely on compiler defaults. Set the language standard required by the code (especially for C/C++ standard library features and syntax supported only in newer modes). If the code uses C99-only syntax (e.g., loop variable declarations), configure `-std=c99` so older toolchains can compile successfully. Example: ```make # Required because the code uses C99 syntax (e.g., for (size_t i = ...)) STD ?= -std=c99 CFLAGS += $(STD) ``` Apply this rule whenever you change a Makefile/feature flag/build script that depends on external headers or compiler behavior—treat build flags and include paths as configuration that must be deterministic across environments.