## What changed
- `codex-stdio-to-uds` now tolerates `NotConnected` when
`shutdown(Write)` happens after the peer has already closed.
- The socket test was rewritten to send stdin from a fixture file and to
read an exact request payload length instead of waiting on EOF timing.
## Why this fixes the flake
- This one exposed a real cross-platform runtime edge case: on macOS,
the peer can close first after a successful exchange, and
`shutdown(Write)` can report `NotConnected` even though the interaction
already succeeded.
- Treating that specific ordering as a harmless shutdown condition
removes the production-level false failure.
- The old test compounded the problem by depending on EOF timing, which
varies by platform and scheduler. Exact-length IO makes the test
deterministic and focused on the actual data exchange.
## Scope
- Production logic change with matching test rewrite.
This PR introduces a `codex-utils-cargo-bin` utility crate that
wraps/replaces our use of `assert_cmd::Command` and
`escargot::CargoBuild`.
As you can infer from the introduction of `buck_project_root()` in this
PR, I am attempting to make it possible to build Codex under
[Buck2](https://buck2.build) as well as `cargo`. With Buck2, I hope to
achieve faster incremental local builds (largely due to Buck2's
[dice](https://buck2.build/docs/insights_and_knowledge/modern_dice/)
build strategy, as well as benefits from its local build daemon) as well
as faster CI builds if we invest in remote execution and caching.
See
https://buck2.build/docs/getting_started/what_is_buck2/#why-use-buck2-key-advantages
for more details about the performance advantages of Buck2.
Buck2 enforces stronger requirements in terms of build and test
isolation. It discourages assumptions about absolute paths (which is key
to enabling remote execution). Because the `CARGO_BIN_EXE_*` environment
variables that Cargo provides are absolute paths (which
`assert_cmd::Command` reads), this is a problem for Buck2, which is why
we need this `codex-utils-cargo-bin` utility.
My WIP-Buck2 setup sets the `CARGO_BIN_EXE_*` environment variables
passed to a `rust_test()` build rule as relative paths.
`codex-utils-cargo-bin` will resolve these values to absolute paths,
when necessary.
---
[//]: # (BEGIN SAPLING FOOTER)
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* #8498
* __->__ #8496
