# mesh-delivery-gate

The `mesh-delivery-gate` module of the mesh catalogue: the gate of design 47. It claims the seat `mesh-delivery`, whose
name stays (ADR 0437 §11), and takes over from the module `mesh-delivery` (ADR 0437 §3, ADR 0450 §6). Its buckets are
`mesh-delivery-gate_*`.

## Files it does not know

Each directory or archive this module declares says how it treats a file it did not write (ADR 0422, ADR 0416).

- `${dir:state}`: everything in it is the program's; the mesh moves nothing out (ADR 0422 §2).

## A backup that failed before the send

The controller backs up the data of the modules a delivery moves before it asks or sends anything (ADR 0404). When its
walk's record, in `plan-moved`, names a backup that failed or stayed silent and nothing of the plan was sent, the
delivery goes from delivering to held (the observed row `backup failed`); the held reason names the machine, the
module and the backup's words, and the pull request's comment shows it. The hold does not lift by itself. `release`
of such a delivery asks the controller (`delivery-backups-again`) to take the backups again and the delivery goes on
delivering; a record from before the controller cleared the failure does not hold it again. A held delivery already
ends as covered or delivered when a later merge covers it.

## Taking the seat over from today's module

The gate claims the seat `mesh-delivery` and took it over from the module `mesh-delivery`, which the catalogue no longer holds.
The controller refuses a merge that removes a module that is assigned, so today's module stayed in the catalogue until it was
unassigned, and went by a handover of verbs after the merge, never by hand on a machine (novox/hq ADR 0449 §4, ADR 0450 §6, ADR 0454):

1. assign `mesh-delivery-gate` to the machine that holds the seat (`mesh-controller.assign`);
2. check that `mesh-controller.seats` still names `mesh-delivery`, held by the running module;
3. unassign `mesh-delivery` from that machine (`mesh-controller.unassign`) and push it (`mesh-controller.push`);
4. the seat passes: the gate reads the controller's assignments and the node-engine's have keys, finds the module on no machine,
   carries its deliveries, groups and pull keys over once (the key `carried` in its `deliveries` says it did), reads the controller's
   walks and the forge's open pull requests, and acts.

Until then the gate is silent: it takes no event, writes no key, asks nothing and answers no verb but `delivery_status`, which
says why (`holds-the-seat`, `seat-waits`).

The removal of `modules/mesh-delivery` followed the handover as a pull request of its own, merged by the gate (ADR 0454); the
catalogue has one claimant of the seat, and no manifest but the gate's and the issue tracker's names the old module but the names
the handover needed: the three buckets the gate carries over, and the event the issue tracker and the tool runner hear
(`catalogue_test.go`).