web: honest offline and write-failure messaging across all stores

[rghvgrv]

Parent

#196 — PRD: Angular web client for SubVora (parity minus reminders)

What to build

A consistency pass over every store so network failures tell the truth. The web client has no offline story by design — no service worker, no local mirror, no write queue — which makes the wording load-bearing: a failed save must say the change was not saved, or the user walks away believing it landed. Reads may keep showing what is already on screen; writes may not pretend.

Implementation Steps

1. Audit — go through every store (dashboard, subscriptions list, subscription detail, categories, payment sources, settings) and confirm reads use toDisplayMessage while every create/update/delete/mark-paid path uses toWriteFailureMessage.
2. Disable writes when offline — expose an isOnline signal (from navigator.onLine plus the online/offline events) and disable submit and destructive actions while offline, with a banner explaining why — mirroring the mobile client's behaviour rather than letting the user fill a form that cannot be sent.
3. Keep reads visible — make sure a failed refresh never blanks a populated screen; the previous data stays with an error banner above it.
4. One reporting path — route every store's message through the shared Notifier/banner rather than per-screen ad hoc snackbars, so wording cannot drift.
5. Spec — a spec per store asserting the write path produces the write-failure wording on a status-0 error, and that a failed reload leaves previously loaded data in place.

Agent Routing

agent_routing:
  complexity_hint: medium
  required_capability: balanced
  parallel_safe: false
  cost_preference: balanced
  speed_preference: balanced
  ownership_scope:
    - src/SubVora.Web/src/app/features/**
    - src/SubVora.Web/src/app/core/api/api-error.ts
    - src/SubVora.Web/src/app/layout/shell.component.ts
  verification:
    - cd src/SubVora.Web && npx ng test --no-watch

Technical Context Snapshot

Current stack in scope

• UI: Angular (20+) standalone components with signals and built-in control flow, Angular Material (Material 3) as the only component library, SCSS. Static SPA — no SSR, no service worker.
• State: signal-backed injectable stores, one per domain area, mirroring the MAUI ViewModel split in src/SubVora.Mobile/ViewModels one-to-one. No NgRx.
• API access: hand-written models plus one service per API controller under src/SubVora.Web/src/app/core/api. Enums travel as JSON strings (JsonStringEnumConverter in Program.cs), so TypeScript string-literal unions are exact.
• Backend consumed unchanged: ASP.NET Core net10.0, /api/v1/, JWT bearer in the Authorization header, tokens in JSON bodies (no cookies).
• Tests: Angular CLI unit-test builder (Vitest runner; Karma is deprecated) with HttpTestingController. Stores, interceptors, mappers and utils only — no component-DOM or browser automation.

Dependencies in scope

• Reuse: @angular/*, @angular/material, rxjs, and the utilities already added under src/SubVora.Web/src/app/core. No chart library, no date library, no HTTP wrapper library.
• New dependency additions allowed for this slice: no. If a dependency looks unavoidable, stop and raise it on the issue rather than adding it.

Architecture alignment

• Preserve the repo's load-bearing rules (CLAUDE.md): burn-rate maths is server-side and counts cycles, never days; currency conversion is a read-time projection and stored amounts are never overwritten; nothing advances next_billing_date on a timer; provider matching stays one SQL query; the mobile SQLite cache stays a read-only mirror.
• There is deliberately no shared DTO project. Web models mirror the API's JSON contract by convention — a contract change means editing both sides.
• create-git-issue provides routing hints only and assigns no concrete agent or model.
• run-with-it remains the final runtime routing authority.

Integration touchpoints

• Touches every store built so far; no endpoint or contract changes.
• Architectural rule: there are no offline writes anywhere in SubVora - no outbox, no replay, no conflict resolution (decision Offline writes are discarded — no outbox, no replay on reconnect #144). Do not add one here.
• Wording is ported from the mobile ApiErrorMapper so the two clients say the same thing in the same situation.

Acceptance criteria

• Every write path states that a failed change was not saved; no message implies queuing or later sync.
• Write actions are disabled with an explanation while the browser reports itself offline.
• A failed refresh leaves previously loaded data on screen with an error banner rather than blanking it.

Blocked by

• web: API models, ValidationProblemDetails parser, and error-message mapper #201 (slice 5)
• web: subscriptions list grouped by category with overdue chips #213 (slice 17)