How connections to packages are read

This is the detail behind Connecting in app.jadpo: which keys a connection to a package takes and needs, and what jadpo check writes about the hosts it reaches.

• Naming the package. package: names a provider package the app holds, installed or its own, by its name and version (AcmeCouriers.v1), as the lock does; app.jadpo needs no use line for it. A version the app doesn't hold names the ones it does; a library package is refused, since it needs no connection (connection.package_unknown).
• The keys. A connection to a package takes package:, domains:, credential:, environment:, host:, timeout:, retry:, max_concurrent:, webhooks:, erasure:, development:, polls: and outbound:, and each setting its package declares; anything else is connection.key_invalid, with the nearest key. Each is read where it connection.key_invalid, with the nearest key. Each is read where it is used. Driver connections keep their own keys.
• What a package needs. domains: always, a list of the app's domains by name, each once and at least one. credential: exactly when provider.jadpo names a credential: scheme, read from a secret: true setting. environment: exactly when the package has hosts:, read from a ProviderEnvironment setting, the new built-in enum (.sandbox, .live); a value written in source is refused, so each deployment says which it calls. host: exactly when the package has neither hosts: nor runs:, read from a Url setting (or a type built on it); beside runs: it may be given, and beside hosts: it is refused. A missing one is connection.key_missing, a value of the wrong kind connection.value_invalid, a key the package doesn't take connection.key_invalid. That a host is HTTPS is checked when calls go out, since a Url setting may hold http://.
• A package's settings. provider.jadpo's settings: names each setting and its type, one of Text, Int, Decimal, Bool and Duration (package.provider_invalid otherwise), and every connection gives each, written out or read from a setting whose type is built on it. A setting has no default: every connection gives each one.
• The network report. build/report/network.md and .json, written by jadpo check once the connections and their addresses read cleanly, designed with the CLI design language's calm, plain rules: a title, one sentence, and one table row per host in order of connection and host, with no times or totals, so a change is a one-line diff. A package's live and sandbox hosts each get a row, when its environment setting says so; a package with no fixed host is listed at the address in its host: setting; a package Jadpo runs, as the service it runs from its image. Database and cache connections are listed at their url: setting, for the domains whose entities they store; the disk driver reaches no host and isn't listed. The JSON gives each host's connection, address, setting or service, when, for and domains. The manifest has a host node for each row, under its connection, and the graph's diff says which changes to them need a person (Package upgrades).
• How the seam finds a connection's driver. The capability seam asks the host for capability(connection); a host gives a driver only for a connection whose declared driver it carries. Natively and in jadpo dev that is the disk driver for the stores of files the running program's plan lists (re-read after every reload); in jadpo test the in-memory store for the same list, which the executor gives the test's host. A package's connection is given the package driver ("How provider calls are made"), or in jadpo dev and jadpo test the package's fake ("Fakes and the development call log").

outbound: waits for services, which aren't built yet. Package settings have no defaults yet. The approval report that shows host changes isn't built yet.