`group_vars/matrix_servers` selects postgres whenever postgres is enabled, which
is the default, so postgres is what essentially every deployment runs. The
scenarios were testing sqlite - a path almost nobody is on.

How little that path is used is not a guess: the mautrix-meta bridges could not
start at all under sqlite, and nobody reported it. Testing the engine users are
actually on is worth more than keeping coverage of the one they are not, so no
scenario is left behind on sqlite.

Four of the eight scenarios have a database and are converted; the other four
have none and are untouched.

molecule-shared/tasks/postgres.yml stands Postgres up on the scenario's network,
with the data directory on a tmpfs since it is thrown away with the container.
The image is pinned at the major the postgres role deploys to new installations
and left to Renovate: when a new major lands, the PR bumping that pin runs every
scenario against it, which is the earliest warning we get that a component does
not cope.

Each scenario gives its database and user names that differ from the role's
defaults, so the component reaching the database proves the role built its
connection string out of them. The assertions moved from "a file appeared at the
path we configured" to "these tables exist", which is strictly stronger: tables
can only appear once the component has resolved the hostname, authenticated with
the credentials the role rendered, and run its migrations to completion.

Costs about 10 seconds per affected scenario (115s to 125s locally for
mautrix-whatsapp), on jobs that run in parallel.

Gotcha worth recording: since Postgres 18 the image puts PGDATA in a versioned
subdirectory and refuses to start if it finds a mount at the old
/var/lib/postgresql/data, so the tmpfs is mounted at /var/lib/postgresql.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SEH3vxYSQ5SV4N5z61eyGT

They were hard-wrapped at 80 characters, broke mid-parenthesis, and spent lines
restating what the code below them does.

Rewrapped at natural boundaries instead, with the narration dropped and only the
reasons, gotchas and surprises kept. Section dividers stay - they delineate long
plays rather than narrate them.

Comments only; no scenario behaviour changes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SEH3vxYSQ5SV4N5z61eyGT

The second scenario, chosen to be a bridge rather than another HTTP
component: bridges are roughly 40 of the 70 roles here, and validating the
shape on role two is cheaper than discovering it on role forty. It found
two things the first role could not.

Bridges read a whole family of variables from outside themselves -
matrix_bridges_relay_enabled, _encryption_enabled, _encryption_default,
_msc4190_enabled, _self_sign_enabled, plus matrix_admin - all defined in
matrix-base. Since every bridge reads them, they belong in shared context
rather than in each bridge's scenario: molecule-shared/playbook-context.yml
now carries them along with the identity and path variables the first
scenario had inline. Note it is loaded through vars_files, which outranks
inventory group_vars, so it is authoritative; a scenario that wants to prove
one of these reaches the rendered configuration should say so explicitly.

Appservices call /whoami while starting and refuse to run if the id returned
is not the bot user they were configured as - mautrix-whatsapp exits 17 with
"Unexpected user ID in whoami call". The shared stub now takes the id it
should claim to be. Expect every bridge and bot to need this.

What the scenario proves: the bridge starts and stays up, opens its
appservice port, its rendered config and appservice registration carry the
scenario's tokens and bot user, it created its sqlite database under the
role's data path as the role's uid, and it runs the version the role pins.
It does not bridge anything and never will.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Components here contact a homeserver while starting up and exit if it is
unreachable, so nearly every scenario will need one. Standing up a real
Synapse per role would dominate the run and drag in Postgres, and these
scenarios are not testing Synapse.

The stub answers the handful of endpoints components touch during startup
with the blandest plausible response, and is deliberately permissive: an
unrecognised path returns {} rather than 404, because the goal is to get the
component past its startup checks. It is not an authentication check or a
room state machine, and a scenario should not assert *about* it - if one
starts needing it to behave like a real homeserver, that scenario has
outgrown what these tests are for.

matrix-alertmanager-receiver now includes it instead of carrying its own
inline copy. Verified green afterwards.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Three things that would not have scaled to 70 roles:

- The Python and Ansible dependency pins were about to be copied into every
  role. They now live once in molecule-shared/, which scenarios reference
  relatively, so they cannot drift apart.
- The helper container images used for probing were hardcoded inline. They
  are pinned once in molecule-shared/vars.yml, carry `# renovate:`
  annotations, and a custom manager in .github/renovate.json keeps them
  current - verified with a local Renovate dry run, which offers
  curl 8.11.1 -> 8.21.0 and python 3.13 -> 3.14-alpine. Seventy invisible
  hardcodes is the blindness class we have been removing elsewhere.
- Running a scenario meant knowing the venv and cd incantation. `just
  molecule <role>` does it, and with no argument lists the roles that have
  a scenario.

Molecule is deliberately not wired into prek: a run takes minutes, pulls
images and needs Docker, which is fine on request and not fine per commit.

docs/molecule-testing.md covers how to run and write these, including the
four things a role here needs that a standalone role does not. AGENTS.md
points at it rather than carrying the detail.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Not for merging as-is. One role's scenario plus the workflow that would
make per-role testing affordable here, so we can see how it behaves before
deciding whether to do the other 69.

Unlike the MASH repositories, one repository holds every role, so running
everything on every push is not an option. The workflow's first job works
out which roles a push touched and builds the matrix from that; a change to
docs, or to a role with no scenario yet, runs nothing.

Three things this role needed that a MASH role does not:

- The variables matrix-base would supply (matrix_base_data_path,
  matrix_domain, matrix_user_name, matrix_group_name and the uid/gid) have
  to be provided by the scenario, and the user and group have to exist
  before the role's file tasks run.
- The service contacts the homeserver while starting up - it fetches
  /_matrix/client/v3/joined_rooms to resolve its room mapping and exits 1
  if that fails - so prepare.yml stands up a stub homeserver. Most roles
  here are bridges and bots, so this is likely the rule rather than the
  exception.
- verify.yml runs as its own play, where role defaults are out of scope, so
  the paths it reads are pinned in molecule.yml. The version is deliberately
  NOT pinned: it is read from defaults/main.yml so the assertion compares
  the running image against what the role ships.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>