Module host_env 

Issue 1763 — the same env rung for a #![no_std] image inside a host process (threadx-linux, freertos-posix), read with the C library’s getenv. target_os = "linux" is “a C library is linked” on this tree. Compiled on every Linux build, not only not(feature = "env") ones: feature unification can turn nros/env on under a caller whose own env is off, and the caller must still find this. Where a caller has env, it uses the std::env reader instead (nros-c/nros-cpp resolve_boot). Issue 1763 — the boot-config ENV rung for a #![no_std] image that still runs inside a host process, read through the C library’s getenv.

crate::env reads the same variables through std::env, so it needs std. Until issue 1763 every image that had an environment also had std, so that was one fact. It stopped being one when the host simulators dropped libstd: threadx-linux’s C/C++ runtime staticlib (issue 1763) and freertos-posix’s (issue 1778) are alloc, but they are still Linux processes with a C library and an environment. Without this module those images silently stopped honouring $ROS_DOMAIN_ID and $NROS_LOCATOR. That was measured on freertos-posix: the C and C++ cells, run in parallel with distinct domains, both fell back to the baked domain and heard each other, so the C++ listener printed a Received: before its own talker published.

The variables, their precedence and their errors are the SAME as crate::env’s. Only the reader differs. Issue 0687’s rule still holds: the edge that has an environment reads it, and the core takes values. The edge is “a C library is linked”, which on this tree is target_os = "linux". A cross target has no getenv to call, and this module does not exist there.

Strings are borrowed from the process environment, which outlives the boot. Nothing in nano-ros calls setenv after boot, and the std reader made the same assumption by caching its first read.

Functions

try_resolve_hosted

ExecutorConfig::try_resolve_with with the getenv rung — the #![no_std] hosted twin of crate::env::try_resolve_hosted.