Run the webapp Cypress suite in CI

[HMarzban]

Problem

No CI job runs the webapp Cypress suite. A broken chatroom spec cannot fail a CI job, so nobody sees it.

A code trace on 14ab7f9c1 shows:

• prod.docs.plus.yml and stage.docs.plus.yml run bash scripts/run-tests.sh --extensions (.github/workflows/prod.docs.plus.yml:298, .github/workflows/stage.docs.plus.yml:127). That mode runs extension gates only, never a webapp spec. Stage runs all five. Prod runs one gate per changed extension.
• Both also run webapp Jest with bun run --filter @docs.plus/webapp test (.github/workflows/prod.docs.plus.yml:337, .github/workflows/stage.docs.plus.yml:145).
• scripts/run-tests.sh has an --e2e mode (scripts/run-tests.sh:43). No workflow calls it.
• backend-ci.yml runs backend suites only: unit, integration, and real-infra E2E. Only the prod pipeline calls it, never stage or a pull request (.github/workflows/backend-ci.yml:3-6).

One chatroom spec fails today, and no job reports it. apps/webapp/cypress/e2e/chatroom/send-and-retry.cy.ts asserts a [data-status] attribute that the feed never renders. #263 fixes that spec. Without a CI job, the next spec failure goes unreported too.

The suite needs preconditions that CI does not provide yet:

• NEXT_PUBLIC_E2E=true on the webapp dev server. Without it, /c/[channelId] renders nothing on the dev server, so all nine chatroom specs fail at their first visit (apps/webapp/src/pages/c/[channelId].tsx:53-59).
• A Supabase URL and anon key, so the client starts. The specs stub the reads they assert with cy.intercept, and no seed creates test-channel. Four specs (jump-to-present, long-press-reaction, reply-jump-in-window, scroll-and-prepend) stub no messages, so they can fail even with the flag.
• apps/webapp/cypress/e2e/document/draft-first-edit-anchor.cy.ts hardcodes http://localhost:3001 (:8). Its cy.task calls (:22, :32) run psql in the docsy-postgres-local container, not in Supabase (apps/webapp/cypress.config.ts:7-37). It needs the whole local stack. Without the container, one of its tests passes with no database (apps/webapp/cypress.config.ts:34-36).
• The runner counts every webapp spec, which is 54 today (scripts/run-tests.sh:443-460). It also prompts when the webapp does not answer (:87-98). A chatroom-only job needs a spec scope.

Acceptance criteria

• Before the workflow lands, a local run of the nine chatroom specs with NEXT_PUBLIC_E2E=true is posted on this issue, with the result for each spec.
• A workflow runs the nine chatroom specs on pushes to main, and on pull requests to main that change chatroom code or chatroom specs.
• The job serves the webapp with NEXT_PUBLIC_E2E=true, a Supabase URL, and an anon key. It starts every service that the local run needed.
• A failing chatroom spec fails the job.
• The spec-count check counts the job's scope, so a chatroom spec that does not run fails the job.
• Every other webapp spec either joins the job or is listed on this issue with the reason it stays out.

Agent Brief

Category: enhancement
Summary: Add a CI job that runs the webapp chatroom Cypress specs against the webapp dev server with the E2E flag.

Current behavior:
CI runs the extension Cypress gates, webapp Jest, and the backend test suites. The webapp Cypress suite runs only by hand, on a laptop.

Desired behavior:
The chatroom specs run in CI and fail the job when they fail. The job provides every precondition the specs need.

Key interfaces:

• The webapp E2E mode of the shared test runner, root script test:e2e. It runs every webapp spec and fails when fewer specs ran than exist. A chatroom-only job needs a spec scope, and the count check must use the same scope.
• NEXT_PUBLIC_E2E — gates the chatroom test page at /c/<channelId>.
• The shared Cypress binary setup action. The extension gates already use it; reuse it for the webapp job.

Out of scope

• The extension gates and the backend jobs.
• Making the new job block deploys. Decide that once the job is stable.
• Fixing individual specs, unless a spec cannot run in CI at all.

Notes

Reuse scripts/run-tests.sh. Do not write a second runner. Add a spec scope to --e2e, and scope the count check to match. Start the webapp and wait for it first, because the runner prompts when the server is down.

Land this job after #263. Until then, two send-and-retry tests fail, so the job starts red.

No spec covers the phone composer. The specs only call cy.viewport, the /c test page renders the desktop variant (apps/webapp/src/pages/c/[channelId].tsx:65), and the phone shell is chosen by user agent.