gatewayd: gateway, the gateway.sock listener and one thread per connection

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/13-gatewayd-gateway-sock | 2026-09-24 | done | 1 | pass | none | Copied `docs/plans/M4b/files/crates/gatewayd/src/gateway.rs` to `crates/gatewayd/src/` and `docs/plans/M4b/files/crates/gatewayd/tests/gateway_sock.rs` to `crates/gatewayd/tests/`, then added `pub mod gateway;` to `lib.rs` after `pub mod deliver;`. Filled the four `todo!()`s the skeleton left in `gateway.rs`: `end` (send `ToLoop::Ended { approval, ending }` to the loop, the only thing that touches the loop); `frames` (`try_clone` the stream, spawn a reader thread that hands whole frames over an mpsc channel so the connection waits with a timeout without losing half a frame, `Ok(rx)` — the same as brokerd's courier); `listen` (the parent dir made 0700 via a recursive `DirBuilder` then `set_permissions`, a stale socket removed, anything else left in place as "cannot listen on <socket>: something else is there", bind, then the socket made 0600, with the spec's error strings and paths via `.display()`); and `serve` (spawn an accept loop that skips `incoming()` errors and starts a `connection` thread per stream, logging a spawn failure as "gatewayd: cannot start a thread for an approval: <e>", keeping a separate `log` clone for that message). The skeleton's `ToLoop` was already complete with `Ended`, so it needed no change. All six `gateway_sock` tests pass three times running in ~1 s; `make gate` prints `gate: ok` on the first run. | ? |
 | M4b/12-gatewayd-state-approvals | 2026-09-24 | done | 1 | pass | none | Copied `docs/plans/M4b/files/crates/gatewayd/tests/state_approvals.rs` into `crates/gatewayd/tests/`. In `state.rs`: added the `#[serde(default)] approvals: Vec<ApprovalPosts>` field after `in_flight` (optional so an M4a state file loads unchanged) and the `ApprovalPosts { approval, channel, posts }` struct (`#[serde(deny_unknown_fields)`) after `struct StateFile`; in `problem` the `in_flight` loop now has a loop over `approvals` requiring a `valid_id` channel and at least one `valid_id` post, else "approval {}'s posts are not valid"; added `turn_of` (find the `in_flight` entry of a session, cloned), `add_approval` (replace any entry of the same approval, push, save), `remove_approval` (retain by approval, save only when one was removed) and `take_approvals` (`std::mem::take`, save only when there were some, return them) at the end of `impl State`. `cargo fmt --all` then `cargo test -p gatewayd --test state_approvals --test state --test serve_restart` green (4, 4 and 7 passed); `make gate` prints `gate: ok` on the first run. | ? |
 | M4b/11-gatewayd-approvals-registry | 2026-09-24 | done | 1 | pass | none | Copied `docs/plans/M4b/files/crates/gatewayd/src/approvals/mod.rs` (the structs `Posted`/`Judged`/`Registry`, the `pub mod text;` still there, and the five `todo!()`s) to `crates/gatewayd/src/approvals/`, and `docs/plans/M4b/files/crates/gatewayd/tests/approvals_judge.rs` to `crates/gatewayd/tests/`. Filled `add` (insert by `approval`), `remove` (remove by id), `holds` (contains_key), `waiting_sessions` (the `session` of every entry), and `judge` (the six spec-section-7 checks in order: `user` in `approvers` else `NOT_APPROVER`, the command to `(id, approved, reason)` — `Approve` true/None, `Deny` false/`reason.clone()`, `Malformed` `USAGE`, then `get(&id)` present else "not pending here", `answerable` else "bxctl approvals", `root` matches else "its own thread", `at <= shown_at` else "answered before shown in full", then `remove` and `send` the `ApprovalReply`, a gone connection → "not pending here"). Brought `Approve`/`Deny`/`Malformed` into scope with the `ApprovalCommand` type, and cloned the `answer` `Sender` out of the entry before the early-return refusals so the held lock's `remove` does not conflict. All six `approvals_judge` and six `approvals_text` tests pass; `make gate` prints `gate: ok` on the first run. | ? |
 | M4b/10-gatewayd-approval-text | 2026-09-24 | done | 1 | pass | none | Copied `docs/plans/M4b/files/crates/gatewayd/src/approvals/mod.rs-task10` to `crates/gatewayd/src/approvals/mod.rs` (the module comment and `pub mod text;`), the `text.rs` skeleton, and `docs/plans/M4b/files/crates/gatewayd/tests/approvals_text.rs` to `crates/gatewayd/tests/`, then added `pub mod approvals;` to `lib.rs` first, before `pub mod config;`. Filled the eight functions the skeleton left as `todo!()`: `code` (a backtick run one longer than `longest_run`, with a padding space on both sides when the text starts or ends with a backtick so CommonMark keeps it literal), `fence` (same, at least three backticks, wrapped `fence\n`), `longest_run` (a char scan keeping the longest run of consecutive backticks), `minute` (the rfc3339 date and `HH:MM` plus ` UTC`), `name` (the serde string form when there is one, else `{value:?}`), `reply_line` (the `!approve`/`!deny` line), `ended_line` (the six-arm match on `Ended`, the `Denied` reason and any `Refused` reason run through `name`/`code`), and `with_ending` (the last post, a blank line, then `ended_line`). `render` was already written in the skeleton. All six `approvals_text` tests pass; `make gate` prints `gate: ok` on the first run. | ? |