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X4 — Update Gate · Session Card

Per-module session list for X4 Update Gate. Read alongside docs/plan/13-execution-modules-and-sessions.md (the framework), 04-backend-togo.md (resource/migration/REST conventions), 12-legacy-reference-map.md §5.7 (the proven legacy precedent), and the per-surface PRDs (05 web, 07 apple, 08 android, 09 desktop). A future build session opens this card to know exactly what to build for its cell.

Purpose

The Update Gate makes release management server-owned, not store-owned. A single app_releases resource plus a public, unauthenticated GET /api/app/version?platform=&build= endpoint lets the ToGO backend tell any client whether its installed build is up_to_date, update_available, or update_required — the verdict is computed server-side by comparing the client's reported build against the release manifest, never by the client. Admin CRUD plus a Releases admin page mean a new version is published without a code deploy or a psql session. Each client acts on the server verdict in the way its platform allows: Android drives Play In-App Updates (the download mechanism only), Apple deep-links to the App Store (no equivalent API exists), Electron uses electron-updater against the same manifest, and web shows an update banner. This is the module that gates the first store submission (doc 13 §4).

Engine / feature parameters (exact — do not invent)

This module has no protocol-engine constants (it is a backend resource + version-verdict service, not one of the 8 protocol engines). Its fixed contract, carried from the proven legacy pattern (GitHub issue #4, brain memory healthdebug-update-gate-contract):

Resource app_release fields: platform, version, build, min_supported_build, store_url, release_notes_en, release_notes_ar, is_mandatory, released_at.
Public endpoint: GET /api/app/version?platform=<>&build=<> → returns one of up_to_date | update_available | update_required, plus store_url, release_notes_en/ar, and is_mandatory.
Verdict rule (server-computed SSOT): reported build < min_supported_build ⇒ update_required; reported build < latest published build for the platform ⇒ update_available; otherwise up_to_date. is_mandatory on the target release also forces update_required.
Unauthenticated by necessity: the endpoint must answer for a client whose token was invalidated by the very change that requires the update — so it is on the deny-by-default guard's allowlist as public (no Authorization required).
Android uses Play In-App Updates (AppUpdateManager) — IMMEDIATE flow for mandatory, FLEXIBLE otherwise — for the download only. Play's own updateAvailability is a fallback, not the source of truth (it cannot express "this build is protocol-incompatible"); the server manifest verdict decides.
Apple has no equivalent API — the update sheet deep-links to the App Store via store_url.
Desktop uses electron-updater sharing the same manifest.
Web shows an update banner.

Sessions

Surface order is backend → web → mcp → chrome → apple → android → desktop (doc 13 §4); backend must land before any client session. mcp and chrome get no session in this module: Chrome extensions auto-update through the Web Store and the MCP server/CLI updates through its package manager, so neither needs an in-app update gate (mirrors how M6/M7 skip chrome). Session-ID <date> and NN are placeholders filled at session start.

Session ID	Surface	Scope (what this one session builds)	Entry deps	Done criteria (doc 13 §5)	Plan docs to read
`S-<date>-X4-backend-NN`	backend	`app_releases` table (migration; every column NOT NULL with a default; strictly expand-contract) + sqlc queries. Server-side version-verdict service implementing the `up_to_date/update_available/update_required` rule. Public unauthenticated `GET /api/app/version?platform=&build=` on the guard allowlist, returning verdict + `store_url` + `release_notes_en/ar` + `is_mandatory`. Admin CRUD endpoints (authenticated, admin-scoped) so releases are published without a deploy.	M0.1–M0.4 (microkernel, TOGO auth for the admin endpoints, migration harness, error envelope)	Adapted Backend-engine template: migration is expand-contract and every column NOT NULL + default; the public endpoint returns server-computed verdicts; the verdict logic lives server-side and is covered by unit tests that encode all three outcomes + the `min_supported_build` / `is_mandatory` edges literally; integration test against real Postgres (unknown/lower/equal/higher build; admin-created release flips a client from `up_to_date`→`update_required`); admin endpoints reject non-admin (404-not-403 isolation); the version endpoint answers with no token. (`plugin/core` clause is N/A — this is a resource+service, not one of the 8 engines — but the verdict comparison is the SSOT and never leaves the server.)	04, 13, 10 (admin auth), 12 §5.7
`S-<date>-X4-web-NN`	web	End-user update banner that renders the server verdict (dismissible for `update_available`, blocking for `update_required`) using `release_notes_en/ar` + `store_url` from the API. Plus the Releases admin page: a CRUD form over the admin API so a version is published from the browser (no deploy, no psql).	M0.5–M0.7 (app shell, theme engine, i18n), `S-<date>-X4-backend-NN`	Client-engine template: renders `/api/app/version` state and the admin API only; thin-client/SSOT audit passes — grep finds no `min_supported_build`/`build` comparison or mandatory logic in client code; both dark-glow and light-flat themes per the strict color spec; Arabic RTL mirrors correctly; banner + admin copy are ICU messages, release notes rendered as server strings (never concatenated).	05, 13, 01 (colors/i18n), 12
`S-<date>-X4-apple-NN`	apple	Update sheet shown on the server verdict; for `update_required` it blocks and deep-links to the App Store via `store_url`, for `update_available` it offers an optional prompt. No local version math.	`S-<date>-X4-backend-NN`, Apple app shell (M1 apple)	Client-engine template: renders the server verdict and deep-links only; thin-client audit passes (no build comparison, no client-decided "mandatory"); both themes; Arabic RTL; ICU strings; release notes from `release_notes_en/ar`.	07, 13, 02 (divergences), 12
`S-<date>-X4-android-NN`	android	Wire Play In-App Updates (`AppUpdateManager`): IMMEDIATE flow when the server verdict is `update_required`/`is_mandatory`, FLEXIBLE otherwise. Server manifest is the source of truth; Play `updateAvailability` is only a download fallback.	`S-<date>-X4-backend-NN`, Android app shell (M1 android)	Client-engine template: the decision to prompt/force comes from the server verdict, not from Play or client math; thin-client audit passes (grep finds no `min_supported_build` comparison); both themes; Arabic RTL; ICU strings; release notes from the API.	08, 13, 02, 12
`S-<date>-X4-desktop-NN`	desktop	Configure electron-updater to consult the shared manifest / `store_url` feed and surface the server verdict (reuses the web banner components where possible); blocking behavior for `update_required`.	`S-<date>-X4-backend-NN`, Desktop Electron shell (M0.5 web + Electron scaffold)	Client-engine template: acts on the server verdict, no local version logic; thin-client audit passes; both themes; Arabic RTL; ICU strings.	09, 13, 12

Notes & gotchas

Legacy precedents worth reusing. The whole pattern is proven in the legacy tree (GitHub issue #4; brain memory healthdebug-update-gate-contract, 9d7ee1e2): legacy Android already shipped an update gate, and legacy desktop/ already carried electron-updater in its scaffold (doc 12 §3). Mine those for the wiring; carry no code forward (doc 12 header rule) — reference only what matches this plan.
Liability: never let the client decide "mandatory." The is_mandatory / update_required verdict is server-owned. Android must treat Play updateAvailability as a fallback, not the truth, because Play cannot express "this build is protocol-incompatible." A client that computes its own mandatory state re-introduces the duplicated-logic liability the thin-client rule exists to prevent (doc 12 §6).
Liability: keep the version endpoint unauthenticated. It is deliberately on the deny-by-default allowlist. If it ever required a token it could not answer the exact clients (token invalidated by the update) it exists to serve. Do not add auth "for consistency."
Do not hardcode store URLs in clients. store_url comes from the manifest so a store move needs no client release.
PENDING DESIGN.
- Exact banner/sheet copy and layout and the Releases admin page UI (colors follow the strict spec; composition is a UI-phase decision).
- FLEXIBLE-update UX: snooze cadence / re-prompt interval for non-mandatory updates.
- Theme override behavior for the banner/sheet (tracks the M0.6 system-vs-manual override decision, still PENDING DESIGN).
- Build/version comparison edge policy to confirm at implementation: build is treated as a per-platform monotonic integer; the tie-break and cross-platform semantics of version vs build should be recorded as an architecture-decision memory when fixed.

Handoff reminder

At session end, write one session-handoff memory to the healthdebug brain — retain the content in the doc 13 §6 structure, then memory/edit to attach metadata {category:"session-handoff", module:"X4", surface:"<surface>", status:"...", next:"<module+surface>", ...}, with a unique source_ref: handoff/X4-update-gate/<surface>/<n> (never reuse — a repeated source_ref supersedes the prior handoff). Then update the single build-ledger memory (source_ref: build-ledger, edited in place) so one recall shows the whole frontier and the recommended next session. Any architectural decision (e.g. the build-comparison policy above) also gets its own classified memory and, if it changes the plan, an edit to the relevant plan doc. See doc 13 §6 and docs/brain/BRAIN-INDEX.md.