## Why
`CODEX_RS_SSE_FIXTURE` let integration-style CLI, exec, and TUI tests
bypass the normal Responses transport by reading SSE from local files.
That kept test-only behavior wired through production client code. The
affected tests can stay hermetic by using the existing
`core_test_support::responses` mock server and passing `openai_base_url`
instead.
## What Changed
- Removed the `CODEX_RS_SSE_FIXTURE` flag,
`codex_api::stream_from_fixture`, the `env-flags` dependency, and the
checked-in SSE fixture files.
- Repointed the affected core, exec, and TUI tests at `MockServer` with
the existing SSE event constructors.
- Removed the Bazel test data plumbing for the deleted fixtures and
refreshed cargo/Bazel lock state.
## Verification
- `cargo build -p codex-cli`
- `cargo test -p codex-api`
- `cargo test -p codex-core --test all responses_api_stream_cli`
- `cargo test -p codex-core --test all
integration_creates_and_checks_session_file`
- `cargo test -p codex-exec --test all ephemeral`
- `cargo test -p codex-exec --test all resume`
- `cargo test -p codex-tui --test all
resume_startup_does_not_consume_model_availability_nux_count`
- `just bazel-lock-update`
- `just bazel-lock-check`
- `just fix -p codex-api -p codex-core -p codex-exec -p codex-tui`
- `git diff --check`
## Summary
- reduce public module visibility across Rust crates, preferring private
or crate-private modules with explicit crate-root public exports
- update external call sites and tests to use the intended public crate
APIs instead of reaching through module trees
- add the module visibility guideline to AGENTS.md
## Validation
- `cargo check --workspace --all-targets --message-format=short` passed
before the final fix/format pass
- `just fix` completed successfully
- `just fmt` completed successfully
- `git diff --check` passed
pakrym-oai