# M5a task 16: the gate passes on macOS as well as on Linux

**Branch:** `m5a` (run `git switch m5a`; `git status --short` must be empty, otherwise stop)
**Commit subject:** `gate: pass on macOS: tests use /tmp, gatewayd finds its uid without /proc`

## Goal

Work moved to titan, a Mac, on 2026-09-24. There `make gate` fails although the code is right,
because three places assume Linux. The harness itself still runs on straylight (Linux); this
task only makes the gate pass on both. No behaviour change on Linux, and no new test.

1. **Unix socket paths are too long.** Tests put sockets under `std::env::temp_dir()`. On macOS
   that is `/var/folders/…/T/`, about 50 bytes, and a socket's whole path may be at most 104
   bytes there, so some tests' daemons cannot bind (for example brokerd's
   `serve_runner.rs` and gatewayd's `serve_restart.rs`). A new `.cargo/config.toml` sets
   `TMPDIR=/tmp` for every process Cargo runs, tests included.
2. **`gatewayd` reads `/proc/self`** for the user id it runs as, when it checks a secret file's
   owner. macOS has no `/proc`. `std` has no call for the user id, and `unsafe` (for `libc`) is
   not allowed, so a new function `user_id` takes the owner of a pipe the process has just made,
   which is the user the process runs as on Linux and on macOS (checked on both: 1000 on talos,
   501 on titan, the same as `id -u`).
3. **`toolkit`'s `shell.rs` test** expects `pwd` to print `/tmp`; on macOS `/tmp` is a link to
   `/private/tmp`, and `pwd` prints the resolved path. A new version of that given test compares
   with the resolved path.

## Files

- Create: `.cargo/config.toml` (at the repository root, next to `Cargo.toml`)
- Copy: a **new version** of the given `crates/toolkit/tests/shell.rs`, from
  `docs/plans/M5a/files/crates/toolkit/tests/shell.rs`
- Modify: `crates/gatewayd/src/secrets.rs`, `docs/implementer-log.md`

## The changes, exactly

**1. Create `.cargo/config.toml`** with exactly this content:

```toml
# Tests put Unix sockets under `std::env::temp_dir()`. macOS's is long (/var/folders/…/T/), and a
# socket's path there can pass the 104 bytes macOS allows, so every process Cargo runs, tests
# included, uses /tmp.
[env]
TMPDIR = { value = "/tmp", force = true }
```

**2. `crates/gatewayd/src/secrets.rs`**, in `read_checked`. Nothing else in the file changes.

**a.** In the comment, the line

```rust
    //    on `named`): the uid of "/proc/self"; "<path> is not owned by the user gatewayd runs as";
```

becomes

```rust
    //    on `named`): the uid of `user_id()`; "<path> is not owned by the user gatewayd runs as";
```

**b.** The three lines

```rust
    let owner = std::fs::metadata("/proc/self")
        .map_err(|e| format!("cannot read /proc/self: {}", e))?
        .uid();
```

become the one line

```rust
    let owner = user_id()?;
```

**c.** Insert this function immediately above the line
`/// The text without one trailing newline; not empty; UTF-8.` (the doc comment of `value`), with
one blank line between them:

```rust
/// The user id this process runs as: the owner of a pipe it has just made. `std` has no call for
/// it, and `/proc/self` is Linux only.
fn user_id() -> Result<u32, String> {
    let (reader, _writer) = std::io::pipe().map_err(|e| format!("cannot make a pipe: {e}"))?;
    let pipe = std::fs::File::from(std::os::fd::OwnedFd::from(reader));
    let meta = pipe
        .metadata()
        .map_err(|e| format!("cannot read a pipe: {e}"))?;
    Ok(meta.uid())
}
```

No `use` line changes: `MetadataExt` (for `.uid()`) is already imported, and the rest is named in
full.

## Steps

- [ ] **1. Create `.cargo/config.toml`**, then copy the test:
  `cp docs/plans/M5a/files/crates/toolkit/tests/shell.rs crates/toolkit/tests/`
- [ ] **2. Make the three edits to `secrets.rs`.** Run `cargo fmt --all`.
- [ ] **3. Run the tests.** `cargo test -p gatewayd -p toolkit -p brokerd`: every suite passes.
- [ ] **4. Run the gate.** `make gate`. Expected last line: `gate: ok`, with 936 tests, the same
  as before this task. On macOS it failed before this task, with 8 tests failing; now it passes.
- [ ] **5. Log and commit.**
  `git add .cargo/config.toml crates/gatewayd crates/toolkit docs/implementer-log.md && git commit`

## Done when

- `make gate` prints `gate: ok` with 936 tests.

## Stop and report if

- Any line quoted above is not in the file exactly as shown.
- `cargo-deny` is missing (`error: no such command: deny`): report it, do not install anything.
- Any test fails after the changes. Do not change a test.