feat(s072): the Mattermost gateway

.env.example

@@ -52,3 +52,15 @@ TELEGRAM_BOT_TOKEN=
 # SECRET_KEY_BASE=
 # PHX_HOST=
 # TRINITY_AUTHORITY=local
+
+# ---- Mattermost gateway, optional (slice 072) -----------------------------------------
+# A server the operator names. Unset MATTERMOST_URL and no adapter starts. The callback URL
+# is where that server reaches this node, for the approval dialog and the /trinity slash
+# command; without it approvals are answered by command only. Under
+# TRINITY_PROFILE=regulated the adapter must also be named on TRINITY_REGULATED_GATEWAYS
+# (Trinity.Gateways.Mattermost) or the node refuses to boot.
+MATTERMOST_URL=
+MATTERMOST_CALLBACK_URL=
+# The bot account's access token, and the token the server issued for the /trinity command.
+MATTERMOST_BOT_TOKEN=
+MATTERMOST_COMMAND_TOKEN=

CHANGELOG.md

@@ -22,6 +22,32 @@ evidence for each increment is retained by the maintainers and summarised here.
   tree, engineering rules consolidated into `docs/03-conventions.md`, and this changelog added as
   the public record of delivered work.
 
+## 2026-10-08
+
+### `slice/072`: Trinity answers in Mattermost
+
+The second messaging platform, after Telegram. A Mattermost adapter for a server the operator names: direct
+messages and channel mentions are answered, each thread its own conversation, and the reply
+streams into one post that is edited as the words arrive. An approval raised during the turn is
+posted with a button that opens an interactive dialog; the answer goes back through the same
+router, pairing check, rate limit and channel cap as a typed command, so a request above what a
+channel may approve is refused there and receipted. A `/trinity` slash command carries the
+commands, and the scheduler can deliver a task's result to a channel. Posts are cut to the size
+the server says it accepts, counted the way the server counts.
+
+Trinity opens the connection; the server is not assumed to be reachable from anywhere, and it only
+calls back for the dialog and the slash command, when the operator gives it an address to call.
+Every callback carries proof of where it came from or is refused unread. The bot token is read
+when it is used and appears in no log line, checked on every failure path including a crash.
+A node under the regulated profile refuses to start with the adapter configured unless it is named
+on the gateway allow-list. Choosing Mattermost makes the channel authorizable; whether a given
+deployment is authorized remains the operator's statement.
+
+Along the way: a scheduled delivery the platform refused is no longer recorded as delivered, and
+the session origin vocabulary names Mattermost in place of the dropped Discord slot.
+
+Verified: gate green at exit 0; 1,065 tests passing (24 properties); coverage 80.49%.
+
 ### `slice/071`: Trinity answers on Telegram
 
 A Telegram bot is now a channel Trinity can be reached from, alongside the console. It answers in

README.md

@@ -136,6 +136,10 @@ enforces it.
   a bot that answers in private chats and in groups where it is mentioned, streams its reply by
   editing one message, offers approvals as buttons (within the same cap), and passes a photo to a
   model that can see. Set `TELEGRAM_BOT_TOKEN` and `TRINITY_GATEWAYS=telegram` to turn it on.
+  A Mattermost adapter ships too, for a server the operator names: direct messages and channel
+  mentions, replies streamed by editing one post, approvals answered in an interactive dialog
+  (within the same cap), a `/trinity` slash command, and scheduled results delivered to a channel.
+  Set `MATTERMOST_URL`, `MATTERMOST_BOT_TOKEN` and `TRINITY_GATEWAYS=mattermost` to turn it on.
 - **Delegates.** The assistant can hand a bounded piece of work to a child session with a
   `delegate` tool: its own context, its own history, and a result handed back as text. The
   parent's conversation never contains the child's messages, which is the point:
@@ -174,9 +178,9 @@ enforces it.
   curator that marks old memories stale and archives the untouched ones (never deleting)
   run on the same queues; `/oban` shows the jobs.
 
-Not there yet: the second messaging platform (072), the native desktop shell and signed releases
-(the rest of M6), store-and-forward receipts for disconnected operation (026, waiting on an answer
-from the external authority plane). The [Milestones](#milestones) section below sets out the order the remaining work
+Not there yet: the native desktop shell and signed releases (the rest of M6),
+store-and-forward receipts for disconnected operation (026, waiting on an answer from the external
+authority plane). The [Milestones](#milestones) section below sets out the order the remaining work
 is being built in.
 
 The interface is a local web page; the desktop shell exists as a packaging spike, not a product.
@@ -191,7 +195,7 @@ Those are failures of the substrate, not of the product. The BEAM was built to r
 of failure, so on it these properties can be structural rather than aspirational:
 
 - A crash in one session, tool or gateway never affects another and never loses persisted state.
-- One agent, seen on the desktop, in Telegram and in Discord at the same time, in real time.
+- One agent, seen on the desktop, in Telegram and in Mattermost at the same time, in real time.
 - Memory in tiers: a small always-on set of facts plus unlimited retrievable history.
 - Every side-effecting action passes a permission gate, and dangerous ones need explicit approval.
 - Any model or provider, cloud or local, switched by configuration.

VERSIONS.md

@@ -140,7 +140,8 @@ never pin a version hex marks as retired or vulnerable.
 | `luerl (+ sandbox)` | latest | 🔍 not a single package | Slice 110 only. Two packages, so no single lock key. |
 | `burrito` | ~> 1.6 | ✅ in `mix.lock` | ⚠️ ERTS availability drives the OTP pin, and Slice 000 measured it: only the OTP 28 line is fetchable for macOS and Linux. Corrected 2026-09-05: this row previously read `~> 1.5 / 1.5.0 ✅`; that mark was not measured. Added at Slice 001. |
 | `ex_tauri` | ~> 0.2 | ✅ in `mix.lock` | ⚠️ Declares `otp_release: "~> 27.0"`, and Slice 000's probe refutes the reason it gives: OTP 28 macOS universal returns 200 and OTP 27 returns 404. Whether it runs on the pinned OTP is Slice 001's first measurement. ⚠️ 439 downloads all-time, so the ADR-0004 fallback matrix carries real weight. |
-| `nostrum` | ~> 0.10 | 🔍 not yet a dependency | Discord. ⚠️ No release in roughly 18 months. R11's trigger already fires. Check intents and components against the current gateway before Slice 072. |
+| `nostrum` | not used (Slice 072 retargeted to Mattermost, 2026-10-07) | 🔍 not a single package | Discord. Was the planned library for Slice 072, which the owner retargeted to Mattermost on 2026-10-07: Discord has no authorization path for a regulated deployment, and the work is dropped rather than deferred. The row stays so the decision is visible where a reader would look for the package. |
+| `websockex` | ~> 0.5.1 | ✅ in `mix.lock` | The Mattermost gateway's connection to its server's WebSocket (`Trinity.Gateways.Mattermost.Socket`, Slice 072). Was transitive through req_llm and already in every release; direct since Slice 072 because a module of ours calls it. ⚠️ Its own default is `insecure: true` (`verify: :verify_none`); the socket always passes verifying `ssl_options` and never relies on the default. |
 | `telegex` | not used (measured at Slice 071, 2026-10-08) | 🔍 not a single package | Telegram. Measured at Slice 071: the latest release on hex is `1.9.0-rc.0` (2024-09-18) and the last stable `1.8.0` (2024-05-28); this file's own rule forbids pinning an `-rc`. Not used: `Trinity.Gateways.Telegram` speaks the Bot API with `req` (slice 071 NOTES, "The library, measured"). The row stays so the decision is visible where a reader would look for the package. |
 | `ex_gram` | not used (measured at Slice 071, 2026-10-08) | 🔍 not a single package | Telegram. Measured at Slice 071 on `0.71.0` (2026-10-01): its poller keeps the `getUpdates` offset in process state and starts at `-1`, so a restarted poller reprocesses or skips unconfirmed updates (Slice 071's AC5 is that property); its file download host is a module attribute that cannot be pointed at a test server; Beerware licence; 18,054 lines for what is here a handful of JSON calls. Not used: `Trinity.Gateways.Telegram` speaks the Bot API with `req` and owns its poller. |
 | `phoenix_streamdown` | not used (measured at Slice 013, 2026-09-20) | 🔍 not a single package | Streaming markdown renderer for LiveView. Measured at Slice 013: 1.0.0-beta.4 (2026-05-03) was still the latest release with no stable behind it, and this file's own rule forbids a pre-release. It is 801 lines over `mdex`, whose own `streaming: true` option completes fragments; the rest is a rendering rule Slice 013 keeps anyway. The row stays so the decision is visible where a reader would look for the package. |

config/config.exs

@@ -234,6 +234,12 @@ config :logger, :default_formatter,
 # Use Jason for JSON parsing in Phoenix
 config :phoenix, :json_library, Jason
 
+# Slice 072: request parameters whose names contain these are logged as [FILTERED]. Phoenix's
+# default is "password" alone, and a Mattermost slash command arrives with its verification token
+# in a parameter called `token` (and an action's signed context under `context.token`), and with a
+# `response_url` that lets whoever holds it post into the channel for a time after the command.
+config :phoenix, :filter_parameters, ["password", "token", "secret", "response_url"]
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{config_env()}.exs"
@@ -246,4 +252,5 @@ config :trinity, :deliveries, %{"gateway" => Trinity.Scheduler.Delivery.Gateway}
 # `config :trinity, :gateways, adapters: [...]` names modules, and `TRINITY_GATEWAYS`
 # (config/runtime.exs) names adapters from this list by their name ("telegram", "console"), so an
 # environment variable never mints an atom. A new platform is a module and a line here.
-config :trinity, :gateways, available: [Trinity.Gateways.Console, Trinity.Gateways.Telegram]
+config :trinity, :gateways,
+  available: [Trinity.Gateways.Console, Trinity.Gateways.Telegram, Trinity.Gateways.Mattermost]

config/runtime.exs

@@ -52,6 +52,24 @@ if roots = System.get_env("TRINITY_FS_ROOTS") do
   config :trinity, :fs, roots: String.split(roots, ":", trim: true)
 end
 
+# Slice 072: the Mattermost gateway's server, when the operator names one. It runs when it is
+# named on TRINITY_GATEWAYS ("mattermost"); named without MATTERMOST_URL it starts idle and says
+# why on /gateways. MATTERMOST_CALLBACK_URL, if set, is the base URL the server reaches this node at,
+# for the approval dialog and the /trinity slash command. The bot token is MATTERMOST_BOT_TOKEN and
+# the command's token MATTERMOST_COMMAND_TOKEN, both read when used (`Trinity.Config.secret/1`)
+# and never here. Under TRINITY_PROFILE=regulated the adapter must also be named on
+# TRINITY_REGULATED_GATEWAYS or the node refuses to boot.
+if config_env() != :test do
+  mattermost =
+    [
+      url: System.get_env("MATTERMOST_URL"),
+      callback_url: System.get_env("MATTERMOST_CALLBACK_URL")
+    ]
+    |> Enum.reject(fn {_key, value} -> value in [nil, ""] end)
+
+  if mattermost != [], do: config(:trinity, :mattermost, mattermost)
+end
+
 # Slice 022: the search provider's key is read at call time from BRAVE_SEARCH_API_KEY; the
 # provider module is configuration so a fake can stand in.
 if config_env() != :test do