proto: gateway, the four messages between brokerd and gatewayd

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

docs/implementer-log.md

@@ -6,6 +6,7 @@ reviewer adds findings under "Reviews" once per milestone.
 
 | Task | Date | Status | Gate runs | First gate | Deviations | Notes | Model |
 |---|---|---|---|---|---|---|---|
+| M4b/02-proto-gateway-wire | 2026-09-24 | done | 2 | fail | none | Copied `gateway.rs`, `gateway_wire.rs` and the eight `gateway_*.json` fixtures into place; added `pub mod gateway;` after `pub mod frame;` and the re-export to `lib.rs`, the four `Message` variants plus the `use` to `wire.rs`, and the four `kind` arms (changing "fourteen" to "eighteen") in `broker.rs`. Filled `is_mattermost_id` (`id.len() == 26 && every byte a-z0-9`) and `ApprovalReply::check` in the given order: `by`, `post`, then a reason over `MAX_REASON` chars by `chars().count()`. All 3 `gateway_wire` tests pass; the first `make gate` failed on clippy `collapsible_if`, fixed by collapsing the nested `if let` into a let-chain guard, and the second prints `gate: ok`. | ? |
 | M4b/01-proto-escape | 2026-09-24 | done | 1 | pass | none | Copied `docs/plans/M4b/files/crates/proto/src/escape.rs`, `bxctl/src/escape.rs` and `proto/tests/escape.rs` into place, and added `pub mod escape;` to `proto/src/lib.rs` after `pub mod class;`. The bxctl file is now the one-line re-export `pub use proto::escape::{escape_json_text, escape_model_text};`, so no bxctl source or test changed and behaviour is identical. `cargo test -p proto --test escape` reports 8 passed; every bxctl suite passes unchanged (the moved escape test now runs against `proto::escape`); `cargo fmt --all` then `make gate` prints `gate: ok` on the first run. | ? |
 | M4a/16-gatewayd-secret-file-race | 2026-09-24 | done | 2 | pass | Reworded the template comment in `read_checked` to drop the literal `check_file` token, so step 5's grep prints only the credential branch's `std::fs::read(&path)` | Replaced `check_file` with `pub fn read_checked(path, between) -> Result<Zeroizing<Vec<u8>>, String>`: check the path (absolute; `symlink_metadata` as `named`; not a symlink; a regular file), call `between()`, open the path, take `opened` metadata, refuse if `(opened.dev(), opened.ino()) != (named.dev(), named.ino())`, then the owner-uid and mode checks on `opened` (not `named`), then read the whole file into a `Zeroizing<Vec<u8>>` from that same handle. Added `use std::io::Read;`. In `load`, the File branch now calls `read_checked(path, &|| {})` and `value(std::mem::take(&mut *bytes))` so nothing unwiped remains. The three suites pass (5, 8, 5); the only remaining `std::fs::read(` is the credential branch and `check_file` is gone. `make gate` prints `gate: ok`. | ? |
 | M4a/15-gatewayd-main | 2026-09-24 | done | 1 | pass | none | Replaced the placeholder `src/main.rs` with the skeleton and copied `tests/main.rs`. `main` parses `args_os` like `loopd`'s; `serve` runs the five start checks in order — `Config::load` (`gatewayd: {e}\n{START_FAILED}`), `token_source` (`gatewayd: {}: {why}\n{START_FAILED}` with the path), `secrets::load` (`gatewayd: {e}`, its own `#secret-unavailable` pointer, then the file warning if any), then the state dir via `DirBuilder` recursive + `mode(0o700)` (`gatewayd: cannot prepare {}: {e}\n{START_FAILED}`), each returning exit 1 before anything is written. Then `run` with a `Log` that echoes to stderr and the returned `Stop` printed, exit 1. The todo comment matches the function and every test; the token never reaches output (it is only ever `expose`d inside `serve`, never here). `cargo test -p gatewayd` every suite passes; `make gate` prints `gate: ok` first run. | ? |