[HackTuah]

Slice 072, the Mattermost gateway. Stacked on #120 (slice 071): this PR's base is 071's branch, so the diff shows 072 alone. Merge #120 first; GitHub then retargets this PR to main. It builds on 071's gateway core rather than adding a second one.

The slice stays in_progress until the owner's live run against their own server. The live criterion already ran here, against a throwaway Mattermost Team Edition 11.11.1 server pinned by digest.

What lands

• WebSocket inbound:
  • the server never has to reach Trinity except for the controls;
  • authenticated in the upgrade header so it can resume, with the server's connection id and sequence number;
  • TLS verified explicitly (the library's default is verify_none);
  • posts handled at most once.
• Approvals:
  • buttons and a dialog with HMAC-signed context, the dialog state bound to the user, single-use and 10 minutes long;
  • the slash command's token compared in constant time;
  • a dialog decides nothing: its answer reaches the router as the typed command, so the channel cap applies. An exec request was refused by the cap and receipted.
• POST /gateways/callback/:adapter/:kind: the adapter verifies each callback; an unconfigured adapter answers 404.
• Posts fit the server's MaxPostSize in code points, checked by a property.
• An adapter census: it reads compiled imports and refuses calls into LLM, Sessions, Permissions, Effects or Tools. A planted direct Permissions call passed both the compiler and the boundary check; only the census caught it.
• Delivery: a cron delivery the server refuses is no longer marked delivered.
• :regulated: Mattermost boots only when named in TRINITY_REGULATED_GATEWAYS.
• Token handling: redaction, the secret scan and the request-log filter learn the token.

Criteria

AC1 to AC7 are proven, AC7 on the throwaway server. AC8 is the gate, below.

Evidence

• Reviewer's full mix gate on the final tree (071 plus 072), before commit: exit 0, 1065 passed (24 properties, 1041 tests), 18 excluded, prod_check: PASS, credo found no issues.
  • The author's four runs on that tree each failed only SandboxTest's 1 s Lua timeout, at load average 20 to 40. My run was green at load average about 20.
• Reviewer checks: the callback route verifies before acting; Trinity attaches telemetry only to its own event catalogue.
  • F-7 (websockex telemetry metadata carries the bearer header) is therefore latent, not live, and is a follow-up.

Owner decision needed (F-6)

Gateway sessions have no project root, so a shell request from a channel always comes out :ask. Decide whether a gateway session should get one.