gatewayd: secrets from a credential, the environment or a file; runbook entries

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 |
 |---|---|---|---|---|---|---|---|
+| M4a/04-gatewayd-secrets | 2026-09-23 | done | 1 | pass | none | Filled the copied `crates/gatewayd/src/secrets.rs` skeleton. `value`: `from_utf8` else "the value is not UTF-8", one trailing `\n` stripped with `strip_suffix`, empty refused, raw bytes kept in `Zeroizing` until inside the `Secret`. `check_file` in the given order: not absolute, `symlink_metadata` else "cannot read <path>", symlink via `file_type().is_symlink()`, not a regular file via inherent `is_file()`, owner uid compared to `/proc/self`'s uid (`MetadataExt`), then `mode & 0o077 != 0` reporting the mode as `{:03o}`. `load` matches the three `SecretSource` forms, reading `CREDENTIALS_DIRECTORY` and the variable through the passed `env` closure (never `std::env`), every failure wrapped in `SecretError` naming the secret and never the value, file secrets setting the exact plaintext warning. Replaced the skeleton's `PermissionsExt` import with `MetadataExt` and used inherent `FileType::is_file`/`is_symlink` (Rust 1.98) so no `FileTypeExt`, `unsafe` or `libc`. All 8 tests in `tests/secrets.rs` pass; `docs/runbook.md` gained the seven gatewayd fail-closed entries (14→21 `## ` lines) and `scripts/check-runbook.sh` exits 0. | ? |
 | M4a/03-gatewayd-config | 2026-09-23 | done | 2 | fail | none | Filled the copied `crates/gatewayd/src/config.rs` skeleton. `ConfigError::fmt`: `"<path>: <why>"` with `path.display()`. `load`: read (else `Read`), `toml::from_str` (else `Parse`), then `problem()` (Some is `Invalid`). `parse_url`: strip `https://`/`http://`, `rsplit_once(':')` for an optional port, `valid_host` (1..=253 bytes of a-z 0-9 . -, not starting/ending with . or -) and `parse_port` (digits, 1..=65535, equal to its own `to_string()`, via `u16::try_from`); every failure returns one `[mattermost] url "<url>" must be...` message. `SecretSpec::source`: count the set fields (else "needs exactly one"), then validate credential (a-z0-9 _ . -), env (A-Z0-9 _) and file (absolute) in turn. `problem` checks url, ca_file, missing token, each secret's `source()`, empty users, ids in users then channels, then limits queue/typing/ping/dead. `valid_id` is 26 bytes of a-z0-9; `loop_socket` falls back to `<home>/run/loop/loop.sock`; `state_path` is `<home>/gateway/state.json`. All 7 config tests pass; `make gate` prints `gate: ok`. | ? |
 | M4a/02-gatewayd-deps | 2026-09-23 | done | 1 | pass | none | Added the dependencies gatewayd needs for TLS to Mattermost and nothing that uses them yet. Added `rustls` (0.23.45, `default-features = false` with `ring`/`std`/`tls12`), `rustls-native-certs` (0.8.4) and `zeroize` (1.9.0) to `[workspace.dependencies]` in the root `Cargo.toml`, the three plus `serde`/`serde_json`/`toml` to `crates/gatewayd/Cargo.toml`, copied `deny.toml` and the whole `crates/gatewayd/tests/fixtures/tls/` directory (9 files), replaced the one-line doc comment in `lib.rs` with the M4a spec doc, and in `docs/dependencies.md` added `gatewayd` to the `serde`/`serde_json`/`toml` rows and appended the `rustls`/`rustls-native-certs`/`zeroize` rows. `cargo build -p gatewayd` succeeded offline (all crates already in the local cache). cargo-deny reported `bans ok, licenses ok, sources ok`. `make gate` printed `gate: ok` on the first run. | ? |
 | M4a/01-proto-sha1 | 2026-09-23 | done | 2 | fail | none | Wrote `crates/proto/src/sha1.rs`: `sha1` (new/update/finish), `Sha1 { state, block, filled, length }` with `length` counting bits. `compress`: `w: [u32; 80]` via `as_chunks::<4>()` + `from_be_bytes`, `w[i] = (w[i-3]^w[i-8]^w[i-14]^w[i-16]).rotate_left(1)`, eighty wrapping rounds with f/k by range, state added with `wrapping_add`. `update`: `wrapping_add(8u64.wrapping_mul(data.len() as u64))`, `split_at`/`get_mut(..).copy_from_slice`, copy the block out (`let block = self.block`) before `compress` so the mutable receiver and shared slice do not clash. `finish`: builds a 128-byte pad (`0x80`, zeros, 8 big-endian length bytes) sized `56-filled` or `120-filled` plus the 8 length bytes, feeds it through `update`, restores `length`, then the five words big-endian. One logic bug caught by the empty-string vector: the `w[i]` expansion rotated only `w[i-16]` instead of the whole XOR, fixed with parentheses. First gate failed on clippy `needless_range_loop` for the 0..80 round loop; switched to `w.iter().enumerate()` with a bound `&ww`. All 4 sha1 tests pass; `make gate` prints `gate: ok`. | ? |