diff --git a/.github/workflows/chatroom-e2e.yml b/.github/workflows/chatroom-e2e.yml
new file mode 100644
index 000000000..85748d82f
--- /dev/null
+++ b/.github/workflows/chatroom-e2e.yml
@@ -0,0 +1,44 @@
+name: Chatroom Browser Tests
+
+# Enable automatic PR coverage after configuring NEXT_PUBLIC_VIRTUOSO_LICENSE.
+# No deployment or database credentials are used by this isolated suite.
+on:
+  workflow_dispatch: {}
+
+permissions:
+  contents: read
+
+concurrency:
+  group: chatroom-e2e-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  chatroom:
+    name: Chatroom E2E
+    runs-on: ubuntu-latest
+    timeout-minutes: 25
+    env:
+      NEXT_PUBLIC_VIRTUOSO_LICENSE: ${{ secrets.NEXT_PUBLIC_VIRTUOSO_LICENSE }}
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/setup-node@249970729cb0ef3589644e2896645e5dc5ba9c38 # v6
+        with:
+          node-version: '26.8.2'
+      - uses: ./.github/actions/setup-bun
+        with:
+          bun-version: '1.4.1'
+      - uses: ./.github/actions/setup-cypress
+      - name: Run the isolated chatroom browser suite
+        run: bash scripts/test-chatroom.sh
+      - name: Retain results and failure screenshots
+        if: always()
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: chatroom-e2e-${{ github.run_id }}
+          include-hidden-files: true
+          path: |
+            Notes/test-results-*.txt
+            Notes/.e2e-logs-*/
+            Notes/chatroom-server.log
+            apps/webapp/cypress/screenshots/
+          retention-days: 7
diff --git a/apps/webapp/cypress/e2e/chatroom/README.md b/apps/webapp/cypress/e2e/chatroom/README.md
new file mode 100644
index 000000000..70882c0b1
--- /dev/null
+++ b/apps/webapp/cypress/e2e/chatroom/README.md
@@ -0,0 +1,49 @@
+# Chatroom browser tests
+
+These nine specs render the real chatroom UI against intercepted Supabase HTTP responses.
+They cover navigation, pagination, message submission and retry, attachments, gallery behavior, and mobile quick reactions.
+
+## Run locally
+
+The workflow uses Bun 1.4.1 and Node 26.8.2, matching the validated local run.
+Install workspace dependencies with `bun install --frozen-lockfile`.
+Provide a valid Virtuoso Message List license through `NEXT_PUBLIC_VIRTUOSO_LICENSE`, then run:
+
+```sh
+bash scripts/test-chatroom.sh
+```
+
+The script builds the extensions and an explicitly opted-in production E2E webapp.
+It starts a temporary standalone server on port 3211 and stops that server after the tests.
+Set `CHATROOM_PORT` to use another free port.
+Keep other Next servers in this checkout stopped while the build runs.
+
+The test environment uses localhost service URLs and dummy authentication.
+The shared fixtures seed the `sb-localhost-auth-token` cookie and intercept the HTTP requests.
+No running Supabase, Redis, or collaboration server is required.
+These tests do not verify database policies, storage persistence, or realtime delivery between clients.
+
+For a prepared E2E server, the shared runner also accepts:
+
+```sh
+BASE_URL=http://127.0.0.1:3211 CYPRESS_PARALLEL=1 CI=true \
+  bash scripts/run-tests.sh --e2e --scope chatroom
+```
+
+Reports and worker logs are written under `Notes/`.
+Scoped runs leave the full-suite timing data unchanged.
+
+## CI and remaining coverage
+
+The `Chatroom Browser Tests` workflow provides a manual run and uploads reports and failure screenshots.
+Configure the repository Actions secret `NEXT_PUBLIC_VIRTUOSO_LICENSE` before running it.
+The job fails clearly when the license is absent.
+Automatic PR coverage remains pending that configuration and a successful hosted run.
+
+The existing media-filter case remains pending because its control is currently unmounted.
+The reaction test verifies the held-touch menu and the submitted emoji payload.
+Realtime reaction-count updates and the first-send server echo need separate integration coverage.
+The production E2E build retains Cypress selectors and disables PWA registration only when `NEXT_PUBLIC_E2E=true`.
+Worker activation otherwise reloads the fixture page during interactions.
+Service-worker lifecycle behavior needs separate PWA coverage.
+Normal production builds retain their existing selector removal and E2E-route exclusion.
diff --git a/apps/webapp/cypress/e2e/chatroom/attachments.cy.ts b/apps/webapp/cypress/e2e/chatroom/attachments.cy.ts
index 61f18b3bd..172c7269d 100644
--- a/apps/webapp/cypress/e2e/chatroom/attachments.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/attachments.cy.ts
@@ -1,9 +1,11 @@
 /// <reference types="cypress" />
 
+import { stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom attachments', () => {
   const storagePath = 'user-1/channel-1/test.png'
-  const imageDataUrl =
-    'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z4EPDwAEhQGAhKmMIQAAAABJRU5ErkJggg=='
 
   const channelAggregateBody = {
     channel_info: {
@@ -64,34 +66,6 @@ describe('chatroom attachments', () => {
     ...overrides
   })
 
-  const seedSupabaseAuthSession = () => {
-    cy.window().then((win) => {
-      win.localStorage.setItem(
-        'sb-docsplus_supabase-auth-token',
-        JSON.stringify({
-          access_token: 'e2e-access-token',
-          refresh_token: 'e2e-refresh-token',
-          expires_in: 3600,
-          expires_at: Math.floor(Date.now() / 1000) + 3600,
-          token_type: 'bearer',
-          user: { id: 'user-1', aud: 'authenticated', role: 'authenticated' }
-        })
-      )
-    })
-  }
-
-  /** Drag-and-drop tests leave IDB attachment drafts that block Send on the next case. */
-  const clearComposerDrafts = () => {
-    cy.window().then((win) => {
-      return new Promise<void>((resolve) => {
-        const request = win.indexedDB.deleteDatabase('chatApp')
-        request.onsuccess = () => resolve()
-        request.onerror = () => resolve()
-        request.onblocked = () => resolve()
-      })
-    })
-  }
-
   const stubStorage = () => {
     cy.intercept({ method: /POST|PUT/, url: '**/storage/v1/object/media/**' }, (req) => {
       req.reply({
@@ -101,17 +75,26 @@ describe('chatroom attachments', () => {
       })
     }).as('storageUpload')
 
+    // Storage returns a relative signed path, which supabase-js prefixes with its URL.
+    // Returning a data URL here creates an invalid prefixed URL and intermittent image failures.
     cy.intercept('POST', '**/storage/v1/object/sign/media/**', (req) => {
-      const body = typeof req.body === 'string' ? JSON.parse(req.body) : req.body
-      const rawPath = body?.paths?.[0] ?? body?.path ?? storagePath
-      const signedUrl = /\.(png|jpe?g|gif|webp)$/i.test(rawPath)
-        ? imageDataUrl
-        : `https://example.test/signed/${rawPath}`
-      req.reply({
-        statusCode: 200,
-        body: { signedURL: signedUrl, signedUrl }
-      })
+      const path = new URL(req.url).pathname.replace('/storage/v1', '')
+      req.reply({ statusCode: 200, body: { signedURL: `${path}?token=test` } })
     }).as('storageSign')
+    cy.intercept('GET', '**/storage/v1/object/sign/media/**', (req) => {
+      if (/\.(png|jpe?g|gif|webp)(\?|$)/i.test(req.url)) {
+        req.reply({
+          fixture: '../../public/icons/favicon-32x32.png',
+          headers: { 'content-type': 'image/png' }
+        })
+      } else {
+        req.reply({
+          statusCode: 200,
+          body: '',
+          headers: { 'content-type': 'application/octet-stream' }
+        })
+      }
+    })
   }
 
   const stubChannelAggregate = () => {
@@ -153,7 +136,6 @@ describe('chatroom attachments', () => {
     stubMessageWindow(rows)
     stubChannelAggregate()
     stubStorage()
-    seedSupabaseAuthSession()
     cy.visit('/c/test-channel')
     cy.wait('@channelAggregate')
     cy.wait('@messageWindow')
@@ -253,25 +235,17 @@ describe('chatroom attachments', () => {
     cy.wait('@messageInsert', { timeout: 15_000 })
   }
 
-  const registerUncaughtHandler = () => {
-    cy.on('uncaught:exception', (err) => {
-      if (err.message.includes('ResizeObserver loop')) return false
-    })
-  }
-
   describe('composer', () => {
     beforeEach(() => {
-      registerUncaughtHandler()
       stubStorage()
       stubMessageInsert()
       stubChannelAggregate()
       stubMessageWindow([])
-      seedSupabaseAuthSession()
-      clearComposerDrafts()
       cy.visit('/c/test-channel')
       cy.wait('@channelAggregate')
       cy.wait('@messageWindow')
       cy.waitForMessage('chatroom-feed')
+      cy.get('.message-feed > .absolute').should('not.exist')
       cy.window().its('__chatTestApi').should('exist')
       cy.window().then((win) => {
         win.__chatTestApi?.resetComposerAttachments?.()
@@ -391,13 +365,18 @@ describe('chatroom attachments', () => {
     })
 
     it('accepts pasted files in the composer', () => {
-      attachFixtureFile({
-        contents: Cypress.Buffer.from('89504e470d0a1a0a', 'hex'),
-        fileName: 'pasted.png',
-        mimeType: 'image/png',
-        lastModified: Date.now()
+      cy.get('[data-testid="composer-input"] .ProseMirror').then(($input) => {
+        const win = $input[0].ownerDocument.defaultView!
+        const clipboardData = new win.DataTransfer()
+        clipboardData.items.add(
+          new win.File([Cypress.Buffer.from('89504e470d0a1a0a', 'hex')], 'pasted.png', {
+            type: 'image/png'
+          })
+        )
+        $input[0].dispatchEvent(
+          new win.ClipboardEvent('paste', { bubbles: true, cancelable: true, clipboardData })
+        )
       })
-
       expectAttachmentVisible('pasted.png')
     })
 
@@ -415,10 +394,6 @@ describe('chatroom attachments', () => {
   })
 
   describe('feed gallery', () => {
-    beforeEach(() => {
-      registerUncaughtHandler()
-    })
-
     it('opens the root gallery when clicking a feed image', () => {
       const messageId = 'feed-image-1'
       visitFeed(
@@ -576,7 +551,10 @@ describe('chatroom attachments', () => {
           cy.get('[data-testid="feed-video-poster"]').should('exist')
         })
       cy.get('[data-chat-media] [aria-label="Expand video"]').should('not.exist')
-      cy.get('[data-chat-media] [data-testid="feed-video-poster"]').click()
+      cy.get('[data-chat-media] [data-testid="feed-video-poster"] video').should('have.attr', 'src')
+      cy.get('[data-chat-media] [data-testid="feed-video-poster"]')
+        .should('be.visible')
+        .click({ scrollBehavior: false })
       cy.get('[data-testid="chat-media-gallery"]').contains('2 / 2')
       cy.get('[data-testid="chat-media-gallery"] video').should('exist')
 
@@ -658,13 +636,7 @@ describe('chatroom attachments', () => {
 
       cy.get(`[data-msg-id="${messageId}"] [data-testid="feed-spoiler-reveal"]`).should('exist')
       cy.get(`[data-msg-id="${messageId}"] [data-testid="feed-spoiler-reveal"]`).realClick()
-      cy.get(`[data-msg-id="${messageId}"]`).then(($msg) => {
-        if ($msg.find('[data-testid="feed-image-open"]').length === 0) {
-          cy.window().then((win) => {
-            win.__chatTestApi?.revealFeedSpoiler?.(storagePath)
-          })
-        }
-      })
+      cy.get('[data-testid="chat-media-gallery"]').should('not.exist')
       cy.get(`[data-msg-id="${messageId}"] [data-testid="feed-image-open"]`, {
         timeout: 15_000
       }).should('be.visible')
@@ -691,7 +663,10 @@ describe('chatroom attachments', () => {
       waitForStorageSignIfPending()
       assertVideoPosterReady()
       cy.get('[data-chat-media] [data-media-layout="mosaic"]').should('exist')
-      cy.get('[data-chat-media] [data-testid="feed-video-poster"]').click({ force: true })
+      cy.get('[data-chat-media] [data-testid="feed-video-poster"] video').should('have.attr', 'src')
+      cy.get('[data-chat-media] [data-testid="feed-video-poster"]')
+        .should('be.visible')
+        .click({ scrollBehavior: false })
       cy.get('[data-testid="chat-media-gallery"]').contains('2 / 2')
 
       cy.get('[data-testid="chat-media-gallery"] [aria-label="Previous media"]').click()
diff --git a/apps/webapp/cypress/e2e/chatroom/deep-link.cy.ts b/apps/webapp/cypress/e2e/chatroom/deep-link.cy.ts
index 83557a8ab..39958f0a1 100644
--- a/apps/webapp/cypress/e2e/chatroom/deep-link.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/deep-link.cy.ts
@@ -1,5 +1,9 @@
 /// <reference types="cypress" />
 
+import { stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom deep link', () => {
   it('mounts with the target message visible and flashed', () => {
     const targetId = 'msg-deep-link'
@@ -13,7 +17,10 @@ describe('chatroom deep link', () => {
       }
     }).as('window')
     cy.visit(`/c/test-channel?msg=${targetId}`)
+    cy.wait('@window')
+      .its('request.body')
+      .should('include', { p_anchor_kind: 'message_id', p_anchor_value: targetId })
     cy.waitForMessage(targetId)
-    cy.get('.msg_card--flash').should('be.visible')
+    cy.waitForMessage(targetId).should('have.class', 'msg_card--flash')
   })
 })
diff --git a/apps/webapp/cypress/e2e/chatroom/jump-to-present.cy.ts b/apps/webapp/cypress/e2e/chatroom/jump-to-present.cy.ts
index af511bd6b..1b6e7c9e8 100644
--- a/apps/webapp/cypress/e2e/chatroom/jump-to-present.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/jump-to-present.cy.ts
@@ -1,5 +1,9 @@
 /// <reference types="cypress" />
 
+import { stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom jump to present', () => {
   beforeEach(() => {
     cy.visit('/c/test-channel?msg=msg-deep-link')
@@ -8,8 +12,10 @@ describe('chatroom jump to present', () => {
 
   it('shows the floating button while detached and returns to live tail on tap', () => {
     cy.get('[data-key="jump-to-present"]').should('be.visible')
-    cy.get('[data-key="jump-count"]').should('exist')
+    cy.intercept('POST', '**/rest/v1/rpc/fetch_message_window*').as('presentWindow')
     cy.get('[data-key="jump-to-present"]').click()
+    cy.wait('@presentWindow').its('request.body.p_anchor_kind').should('equal', 'tail')
+    cy.waitForMessage('message-40')
     cy.get('[data-key="jump-to-present"]').should('not.exist')
   })
 })
diff --git a/apps/webapp/cypress/e2e/chatroom/long-press-reaction.cy.ts b/apps/webapp/cypress/e2e/chatroom/long-press-reaction.cy.ts
index 6e349e6bf..2304d9a9d 100644
--- a/apps/webapp/cypress/e2e/chatroom/long-press-reaction.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/long-press-reaction.cy.ts
@@ -1,22 +1,34 @@
 /// <reference types="cypress" />
 
+import { stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom long-press reaction', () => {
-  beforeEach(() => {
+  it('opens quick reactions on a held touch and submits the chosen emoji', () => {
     cy.viewport('iphone-x')
-    cy.visit('/c/test-channel')
-    cy.waitForMessage('chatroom-feed')
-  })
-
-  it('opens the reaction picker on long press and increments the count', () => {
     cy.intercept('POST', '**/rest/v1/rpc/add_reaction*', {
       statusCode: 200,
-      body: { reactions: { '👍': 1 } }
+      body: { '👍': [{ user_id: 'user-1', created_at: '2026-05-13T10:00:00Z' }] }
     }).as('addReaction')
-
-    cy.get('.msg_card').first().realTouch({ position: 'center' }).wait(600)
-    cy.get('[data-key="long-press-menu"]', { timeout: 4000 }).should('be.visible')
-    cy.get('[data-key="reaction-picker"]').first().click()
-    cy.wait('@addReaction')
-    cy.contains('1').should('be.visible')
+    cy.visit('/c/test-channel?variant=mobile')
+    cy.waitForMessage('message-40')
+    // realTouch sends touchEnd immediately; keep this touch down past the 500ms threshold.
+    cy.get('[data-msg-id="message-40"] .chat-bubble').trigger('touchstart', {
+      touches: [{ identifier: 1, clientX: 150, clientY: 400 }],
+      changedTouches: [{ identifier: 1, clientX: 150, clientY: 400 }]
+    })
+    cy.get('[role="toolbar"][aria-label="Quick reactions"]').should('be.visible')
+    cy.get('[data-msg-id="message-40"][data-mode="inline"] .chat-bubble').trigger('touchend', {
+      touches: [],
+      changedTouches: [{ identifier: 1, clientX: 150, clientY: 400 }],
+      force: true
+    })
+    cy.get('[aria-label="React with Like"]').should('be.enabled').realClick()
+    cy.wait('@addReaction').its('request.body').should('deep.equal', {
+      p_message_id: 'message-40',
+      p_emoji: '👍'
+    })
+    cy.get('[role="toolbar"][aria-label="Quick reactions"]').should('not.exist')
   })
 })
diff --git a/apps/webapp/cypress/e2e/chatroom/open-unread.cy.ts b/apps/webapp/cypress/e2e/chatroom/open-unread.cy.ts
index 9e093cb75..2286292cf 100644
--- a/apps/webapp/cypress/e2e/chatroom/open-unread.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/open-unread.cy.ts
@@ -1,5 +1,9 @@
 /// <reference types="cypress" />
 
+import { stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom open with unread', () => {
   it('lands on the unread separator when first_unread anchor exists', () => {
     cy.intercept('POST', '**/rest/v1/rpc/fetch_message_window*', {
@@ -15,6 +19,7 @@ describe('chatroom open with unread', () => {
       }
     }).as('window')
     cy.visit('/c/test-channel')
-    cy.get('[data-key^="unread-"]').should('be.visible')
+    cy.wait('@window').its('request.body.p_anchor_kind').should('equal', 'first_unread')
+    cy.get('[role="separator"][aria-label="New messages"]').should('be.visible')
   })
 })
diff --git a/apps/webapp/cypress/e2e/chatroom/reply-jump-in-window.cy.ts b/apps/webapp/cypress/e2e/chatroom/reply-jump-in-window.cy.ts
index b24e35716..04f659ae7 100644
--- a/apps/webapp/cypress/e2e/chatroom/reply-jump-in-window.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/reply-jump-in-window.cy.ts
@@ -1,5 +1,9 @@
 /// <reference types="cypress" />
 
+import { stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom reply jump in-window', () => {
   beforeEach(() => {
     cy.visit('/c/test-channel')
@@ -7,7 +11,7 @@ describe('chatroom reply jump in-window', () => {
   })
 
   it('smooth-scrolls and flashes the target on reply-ref tap', () => {
-    cy.get('[data-key^="reply-ref-"]').first().click()
-    cy.get('.msg_card--flash').should('be.visible')
+    cy.get('[data-key="reply-ref-message-35"]').click()
+    cy.waitForMessage('message-35').should('have.class', 'msg_card--flash')
   })
 })
diff --git a/apps/webapp/cypress/e2e/chatroom/reply-jump-out-of-window.cy.ts b/apps/webapp/cypress/e2e/chatroom/reply-jump-out-of-window.cy.ts
index 49324c011..06a689371 100644
--- a/apps/webapp/cypress/e2e/chatroom/reply-jump-out-of-window.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/reply-jump-out-of-window.cy.ts
@@ -1,23 +1,37 @@
 /// <reference types="cypress" />
 
+import { chatroomRows, stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom reply jump out-of-window', () => {
-  beforeEach(() => {
+  it('fetches the off-window reply target and flashes it', () => {
+    const target = { ...chatroomRows[0], id: 'msg-off-window', content: 'Earlier reply target' }
+    cy.intercept('POST', '**/rest/v1/rpc/fetch_message_window*', (req) => {
+      const jumping = req.body.p_anchor_kind === 'message_id'
+      if (jumping) req.alias = 'targetWindow'
+      req.reply({
+        body: {
+          rows: jumping
+            ? [target]
+            : chatroomRows.map((row, index) =>
+                index === 39
+                  ? {
+                      ...row,
+                      reply_to_message_id: target.id,
+                      replied_message_preview: target.content
+                    }
+                  : row
+              ),
+          anchor_seq: jumping ? target.seq : null,
+          has_more_before: false,
+          has_more_after: jumping
+        }
+      })
+    })
     cy.visit('/c/test-channel')
-    cy.waitForMessage('chatroom-feed')
-  })
-
-  it('replaces data and lands on the off-window target', () => {
-    const offWindowId = 'msg-off-window'
-    cy.intercept('POST', '**/rest/v1/rpc/fetch_message_window*', {
-      statusCode: 200,
-      body: {
-        rows: [{ id: offWindowId, seq: 42, created_at: '2026-05-13T10:00:00Z', content: 'off' }],
-        anchor_seq: 42,
-        has_more_before: false,
-        has_more_after: true
-      }
-    }).as('window')
-    cy.scrollToMessageViaApi(offWindowId)
-    cy.get(`[data-key="${offWindowId}"]`).should('be.visible')
+    cy.get(`[data-key="reply-ref-${target.id}"]`).click()
+    cy.wait('@targetWindow').its('request.body.p_anchor_value').should('equal', target.id)
+    cy.waitForMessage(target.id).should('have.class', 'msg_card--flash')
   })
 })
diff --git a/apps/webapp/cypress/e2e/chatroom/scroll-and-prepend.cy.ts b/apps/webapp/cypress/e2e/chatroom/scroll-and-prepend.cy.ts
index c2d3d582a..a3671fabb 100644
--- a/apps/webapp/cypress/e2e/chatroom/scroll-and-prepend.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/scroll-and-prepend.cy.ts
@@ -1,23 +1,54 @@
 /// <reference types="cypress" />
 
+import { chatroomRows, stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom scroll and prepend', () => {
   beforeEach(() => {
+    cy.intercept('POST', '**/rest/v1/rpc/fetch_message_window*', (req) => {
+      const older = req.body.p_anchor_kind === 'before_seq'
+      if (older) req.alias = 'olderWindow'
+      req.reply({
+        delay: older ? 300 : 0,
+        body: {
+          rows: older
+            ? [{ ...chatroomRows[0], id: 'older-message', seq: 0, content: 'Earlier message' }]
+            : chatroomRows,
+          anchor_seq: null,
+          has_more_before: !older,
+          has_more_after: false
+        }
+      })
+    })
     cy.visit('/c/test-channel')
-    cy.waitForMessage('chatroom-feed')
+    cy.waitForMessage('message-40')
+    cy.get('[data-testid="virtuoso-scroller"]').scrollTo('top', { duration: 200 })
+    cy.get('[data-key="pagination-loader"]').should('be.visible')
+    cy.wait('@olderWindow').its('request.body.p_anchor_value').should('equal', '1')
+    cy.get('[data-key="pagination-loader"]').should('not.exist')
+    // Virtuoso measures the prepended rows, then compensates the scroll on two frames.
+    cy.window().then(
+      (win) =>
+        new Promise<void>((resolve) =>
+          win.requestAnimationFrame(() => win.requestAnimationFrame(() => resolve()))
+        )
+    )
   })
 
-  it('loads older messages when scrolled to top', () => {
-    cy.get('.message-feed').scrollTo('top', { duration: 200 })
-    cy.get('[data-key="pagination-loader"]').should('exist')
+  it('prepends the older page without losing the loaded page', () => {
+    cy.scrollToMessageViaApi('older-message')
+    cy.waitForMessage('older-message')
+    cy.waitForMessage('message-1')
+    cy.get('[data-key="pagination-loader"]').should('not.exist')
   })
 
-  it('does not emit duplicate day separators across the join', () => {
-    cy.get('.message-feed').scrollTo('top', { duration: 200 })
-    cy.get('.date_chip').then(($chips) => {
-      const dates = [...$chips].map((el) => el.textContent?.trim() ?? '')
-      const unique = new Set(dates)
-      // Allow re-use across natural day boundaries, just no immediate dupes.
-      expect(dates.length).to.be.at.most(unique.size + 1)
-    })
+  it('keeps exactly one day separator across a same-day page join', () => {
+    cy.scrollToMessageViaApi('older-message')
+    cy.waitForMessage('older-message')
+    cy.get('[data-testid="virtuoso-list"] .date_chip[data-msg-date="2026-05-13"]').should(
+      'have.length',
+      1
+    )
   })
 })
diff --git a/apps/webapp/cypress/e2e/chatroom/send-and-retry.cy.ts b/apps/webapp/cypress/e2e/chatroom/send-and-retry.cy.ts
index 11ddd79d3..72b67073c 100644
--- a/apps/webapp/cypress/e2e/chatroom/send-and-retry.cy.ts
+++ b/apps/webapp/cypress/e2e/chatroom/send-and-retry.cy.ts
@@ -1,27 +1,99 @@
 /// <reference types="cypress" />
 
+import { clearChatroomDrafts, stubChatroom } from '../../support/chatroomFixtures'
+
+beforeEach(stubChatroom)
+
 describe('chatroom send and retry', () => {
   beforeEach(() => {
     cy.visit('/c/test-channel')
-    cy.waitForMessage('chatroom-feed')
+    cy.waitForMessage('message-40')
+  })
+
+  it('clears persisted drafts from the app origin before the next visit', () => {
+    cy.get('[data-testid="composer-input"] .ProseMirror').should('be.visible')
+    cy.window().then(
+      (win) =>
+        new Promise<void>((resolve, reject) => {
+          const request = win.indexedDB.open('chatApp')
+          request.onerror = () => reject(request.error)
+          request.onsuccess = () => {
+            const db = request.result
+            const transaction = db.transaction('composer', 'readwrite')
+            transaction.objectStore('composer').put({
+              workspaceId: 'e2e-workspace',
+              roomId: 'test-channel',
+              state: { text: 'Draft left by the previous case' },
+              updatedAt: Date.now()
+            })
+            transaction.oncomplete = () => {
+              db.close()
+              resolve()
+            }
+            transaction.onerror = () => {
+              db.close()
+              reject(transaction.error)
+            }
+          }
+        })
+    )
+    clearChatroomDrafts()
+    cy.window().then(async (win) => {
+      expect(win.location.origin).to.equal(new URL(Cypress.config('baseUrl')!).origin)
+      const databases = await win.indexedDB.databases()
+      expect(databases.map((database) => database.name)).not.to.include('chatApp')
+    })
+    cy.visit('/c/test-channel')
+    cy.waitForMessage('message-40')
+    cy.get('[data-testid="composer-input"]').should('have.text', '')
   })
 
-  it('sends a message and renders it', () => {
+  it('posts a message and renders the optimistic row', () => {
+    cy.intercept('POST', '**/rest/v1/messages*').as('send')
     cy.get('[data-testid="composer-input"]').type('hello from cypress')
-    cy.get('[data-testid="composer-primary-action"]').click()
-    cy.contains('hello from cypress').should('be.visible')
+    cy.get('[data-testid="composer-primary-action"]')
+      .should('have.attr', 'aria-label', 'Send message')
+      .click()
+    cy.wait('@send').its('request.body.content').should('equal', 'hello from cypress')
+    cy.contains('.msg_card', 'hello from cypress').should('be.visible')
+    cy.get('[data-testid="composer-input"]').should('have.text', '')
   })
 
-  it('shows failed state on RLS error', () => {
+  it('retries an RLS failure with the original message id', () => {
     cy.intercept('POST', '**/rest/v1/messages*', {
       statusCode: 401,
       body: { code: '42501' }
     }).as('failedSend')
     cy.get('[data-testid="composer-input"]').type('this will fail')
-    cy.get('[data-testid="composer-primary-action"]').click()
+    cy.get('[data-testid="composer-primary-action"]')
+      .should('have.attr', 'aria-label', 'Send message')
+      .click()
     cy.wait('@failedSend')
-    cy.get('[data-status="failed"]').should('be.visible')
-    cy.get('[data-testid="composer-input"]').should('contain.text', 'this will fail')
+    cy.contains('.msg_card', 'this will fail').within(() => {
+      cy.contains('Failed to send').should('be.visible')
+      cy.get('[aria-label="Retry sending message"]').should('be.visible')
+    })
+    cy.get('[data-testid="composer-input"]').should('have.text', '')
+    cy.get('@failedSend').then((failed) => {
+      const originalId = (failed as unknown as { request: { body: { id: string } } }).request.body
+        .id
+      cy.intercept('POST', '**/rest/v1/messages*', (req) => {
+        expect(req.body.id).to.equal(originalId)
+        expect(req.body.content).to.equal('this will fail')
+        req.reply({ statusCode: 201, body: [{ ...req.body, seq: 41 }] })
+      }).as('retrySend')
+    })
+    cy.get('[aria-label="Retry sending message"]')
+      .should('be.visible')
+      .click({ scrollBehavior: false })
+    cy.wait('@retrySend')
+    cy.contains('.msg_card', 'this will fail')
+      .should('be.visible')
+      .within(() => {
+        cy.contains('Failed to send').should('not.exist')
+        cy.get('[aria-label="Sending"]').should('not.exist')
+        cy.get('time').should('exist')
+      })
   })
 
   it('treats 23505 duplicate-key as success', () => {
@@ -30,8 +102,17 @@ describe('chatroom send and retry', () => {
       body: { code: '23505', message: 'duplicate key value violates unique constraint' }
     }).as('dupSend')
     cy.get('[data-testid="composer-input"]').type('idempotent send')
-    cy.get('[data-testid="composer-primary-action"]').click()
+    cy.get('[data-testid="composer-primary-action"]')
+      .should('have.attr', 'aria-label', 'Send message')
+      .click()
     cy.wait('@dupSend')
-    cy.get('[data-status="sent"]').should('exist')
+    cy.contains('.msg_card', 'idempotent send')
+      .should('be.visible')
+      .within(() => {
+        cy.contains('Failed to send').should('not.exist')
+        cy.get('[aria-label="Sending"]').should('not.exist')
+        cy.get('time').should('exist')
+        cy.get('[aria-label="Retry sending message"]').should('not.exist')
+      })
   })
 })
diff --git a/apps/webapp/cypress/support/chatroom.ts b/apps/webapp/cypress/support/chatroom.ts
index 6d62f092a..8fcbcd942 100644
--- a/apps/webapp/cypress/support/chatroom.ts
+++ b/apps/webapp/cypress/support/chatroom.ts
@@ -28,7 +28,7 @@ declare global {
 }
 
 Cypress.Commands.add('waitForMessage', (key: string) =>
-  cy.get(`[data-key="${key}"]`, { timeout: 10_000 }).should('be.visible')
+  cy.get(`[data-msg-id="${key}"], [data-key="${key}"]`, { timeout: 10_000 }).should('be.visible')
 )
 
 Cypress.Commands.add('scrollToMessageViaApi', (id: string) =>
diff --git a/apps/webapp/cypress/support/chatroomFixtures.ts b/apps/webapp/cypress/support/chatroomFixtures.ts
new file mode 100644
index 000000000..a250efb13
--- /dev/null
+++ b/apps/webapp/cypress/support/chatroomFixtures.ts
@@ -0,0 +1,121 @@
+/// <reference types="cypress" />
+
+const user = {
+  id: 'user-1',
+  aud: 'authenticated',
+  role: 'authenticated',
+  email: 'tester@example.test'
+}
+const profile = {
+  ...user,
+  username: 'tester',
+  full_name: 'Tester',
+  display_name: 'Tester',
+  status: 'ONLINE'
+}
+
+export const chatroomRows = Array.from({ length: 40 }, (_, i) => ({
+  id: i === 19 ? 'msg-deep-link' : `message-${i + 1}`,
+  seq: i + 1,
+  created_at: new Date(Date.UTC(2026, 4, 13, 9, i)).toISOString(),
+  channel_id: 'test-channel',
+  user_id: 'user-2',
+  user_details: { id: 'user-2', username: 'teammate', fullname: 'Teammate' },
+  content: `Message ${i + 1}`,
+  type: 'text',
+  reply_to_message_id: i === 39 ? 'message-35' : null,
+  replied_message_preview: i === 39 ? 'Message 35' : null,
+  reactions: {}
+}))
+
+export function clearChatroomDrafts() {
+  // Visit an inert document on the app origin: about:blank has no explicit origin,
+  // and visiting the real chatroom would reopen its database before deletion.
+  const resetPath = '/__chatroom_fixture_reset__'
+  cy.intercept('GET', resetPath, {
+    headers: { 'content-type': 'text/html' },
+    body: '<!doctype html><html><body></body></html>'
+  })
+  cy.visit(resetPath)
+  return cy.window().then(
+    (win) =>
+      new Promise<void>((resolve, reject) => {
+        const request = win.indexedDB.deleteDatabase('chatApp')
+        request.onsuccess = () => resolve()
+        request.onerror = () => reject(request.error)
+        request.onblocked = () =>
+          reject(new Error('The previous chat draft database is still open'))
+      })
+  )
+}
+
+export function stubChatroom() {
+  // Cypress clears cookies/localStorage between cases, but IndexedDB drafts persist.
+  clearChatroomDrafts()
+  // Virtuoso measures items synchronously; these browser notifications are benign.
+  // https://virtuoso.dev/message-list/resize-observer-errors/
+  cy.on('uncaught:exception', (error) => {
+    if (
+      error.message.includes('ResizeObserver loop completed with undelivered notifications.') ||
+      error.message.includes('ResizeObserver loop limit exceeded')
+    ) {
+      return false
+    }
+  })
+  const encode = (value: unknown) =>
+    btoa(JSON.stringify(value)).replace(/=/g, '').replace(/\+/g, '-').replace(/\//g, '_')
+  const expires = Math.floor(Date.now() / 1000) + 3600
+  const session = {
+    access_token: `${encode({ alg: 'HS256', typ: 'JWT' })}.${encode({ sub: user.id, exp: expires, aud: 'authenticated', role: 'authenticated' })}.test-signature`,
+    refresh_token: 'test-refresh-token',
+    expires_at: expires,
+    expires_in: 3600,
+    token_type: 'bearer',
+    user
+  }
+  const base = new URL(Cypress.config('baseUrl')!)
+  cy.setCookie('sb-localhost-auth-token', `base64-${encode(session)}`, { domain: base.hostname })
+  cy.intercept('GET', '**/auth/v1/user*', { body: user })
+  cy.intercept('POST', '**/auth/v1/token*', { body: session })
+  cy.intercept({ method: /GET|PATCH/, url: '**/rest/v1/users*' }, { body: profile })
+  cy.intercept('POST', '**/rest/v1/rpc/get_channel_aggregate_data*', {
+    body: {
+      channel_info: {
+        id: 'test-channel',
+        type: 'PUBLIC',
+        name: 'test-channel',
+        slug: 'test-channel'
+      },
+      is_user_channel_member: true,
+      is_user_channel_owner: true,
+      is_user_channel_admin: true,
+      channel_member_info: { member_id: user.id, channel_id: 'test-channel', last_read_seq: 0 },
+      pinned_messages: [],
+      peer_max_read_seq: null,
+      last_read_seq: 0,
+      last_messages: [],
+      has_more_older: false,
+      has_more_newer: false
+    }
+  })
+  cy.intercept('POST', '**/rest/v1/rpc/fetch_message_window*', (req) => {
+    const before = req.body.p_anchor_kind === 'before_seq'
+    req.reply({
+      body: {
+        rows: before ? [] : chatroomRows,
+        anchor_seq: req.body.p_anchor_kind === 'message_id' ? 20 : null,
+        has_more_before: !before,
+        has_more_after: req.body.p_anchor_kind === 'message_id'
+      }
+    })
+  })
+  cy.intercept('POST', '**/rest/v1/rpc/get_channel_notif_state*', {
+    body: JSON.stringify('ALL'),
+    headers: { 'content-type': 'application/json' }
+  })
+  cy.intercept('POST', '**/rest/v1/rpc/fetch_messages_since*', { body: [] })
+  cy.intercept('POST', '**/rest/v1/rpc/advance_read_cursor*', { body: null })
+  cy.intercept('POST', '**/rest/v1/messages*', (req) => {
+    req.reply({ statusCode: 201, body: [{ ...req.body, seq: 41 }] })
+  })
+}
diff --git a/apps/webapp/next.config.js b/apps/webapp/next.config.js
index 527ff4207..84d70f552 100644
--- a/apps/webapp/next.config.js
+++ b/apps/webapp/next.config.js
@@ -12,13 +12,15 @@ const {
   GLITCHTIP_CONNECT_HOSTS
 } = require('./config/security/third-party-hosts')
 const isProduction = process.env.NODE_ENV === 'production'
+const isE2E = process.env.NEXT_PUBLIC_E2E === 'true'
 const isCoverageInstrumentation =
   process.env.COVERAGE === 'true' || process.env.CYPRESS_COVERAGE === 'true'
 const path = require('path')
 const { createSecureHeaders } = require('next-secure-headers')
 const withPWA = require('next-pwa')({
   dest: 'public',
-  disable: !isProduction,
+  // Fixture suites need a stable page; worker activation otherwise reloads mid-test.
+  disable: !isProduction || isE2E,
   register: true,
   skipWaiting: false,
   // next-pwa defaults this on, and reloads the page the moment the network returns.
@@ -172,7 +174,8 @@ module.exports = withPWA({
     //     }
     //   : false,
     // Enable React optimizations
-    reactRemoveProperties: isProduction
+    // Keep Cypress selectors in the explicitly opted-in local/CI test build.
+    reactRemoveProperties: isProduction && !isE2E
   },
 
   // Production logging and monitoring
diff --git a/apps/webapp/src/pages/c/[channelId].tsx b/apps/webapp/src/pages/c/[channelId].tsx
index 4bcbff8e2..37f5926e5 100644
--- a/apps/webapp/src/pages/c/[channelId].tsx
+++ b/apps/webapp/src/pages/c/[channelId].tsx
@@ -1,6 +1,5 @@
 import Chatroom from '@components/chatroom/Chatroom'
 import { useAuthStore, useChatStore, useStore } from '@stores'
-import { supabaseClient } from '@utils/supabase'
 import { GetServerSideProps } from 'next'
 import { useRouter } from 'next/router'
 import { useEffect } from 'react'
@@ -14,10 +13,7 @@ function bootstrapE2EChannel(channelId: string, fetchMsgsFromId?: string | null)
   useAuthStore.getState().setProfile(e2eProfile)
   useAuthStore.getState().setSession({ user: { id: 'user-1' } })
 
-  void supabaseClient.auth.setSession({
-    access_token: 'e2e-access-token',
-    refresh_token: 'e2e-refresh-token'
-  })
+  // Cypress seeds the browser session; do not replace it with an invalid JWT.
 
   useChatStore
     .getState()
@@ -62,7 +58,9 @@ export default function E2EChatroomPage() {
 
   return (
     <div className="bg-base-100 flex h-dvh flex-col">
-      <Chatroom variant="desktop" className="flex min-h-0 flex-1 flex-col">
+      <Chatroom
+        variant={router.query.variant === 'mobile' ? 'mobile' : 'desktop'}
+        className="flex min-h-0 flex-1 flex-col">
         <Chatroom.Toolbar>
           <span className="text-sm font-medium">E2E Chat</span>
           <div className="ml-auto flex items-center gap-1" />
diff --git a/scripts/check-ci.ts b/scripts/check-ci.ts
index ab06b8336..b9dc91648 100644
--- a/scripts/check-ci.ts
+++ b/scripts/check-ci.ts
@@ -11,6 +11,7 @@ import { existsSync, lstatSync, rmSync, unlinkSync } from 'fs'
 import { tmpdir } from 'os'
 import { resolve } from 'path'
 
+import { nextServerConflict } from './check-next-server.ts'
 import { PUBLISHABLE_EXTENSION_DIRS } from './publishable-extensions.ts'
 
 const ROOT = resolve(import.meta.dir, '..')
@@ -99,14 +100,6 @@ function extensionsFor(changed: string[]): string[] {
   )
 }
 
-async function nextDevLive(): Promise<string | null> {
-  const result = await $`ps -ax -o command=`.quiet().nothrow()
-  const text = result.stdout.toString()
-  if (/\bnext\s+(dev|start)\b/.test(text))
-    return 'Next dest is live; a production build would corrupt that .next'
-  return null
-}
-
 function discardNextBuild(appDir: string): void {
   const dest = resolve(ROOT, appDir, '.next')
   if (!existsSync(dest)) return
@@ -141,7 +134,7 @@ const subject = (await gitLines(['log', '-1', '--format=%s']))[0] ?? ''
 const appDeploy = /^\(build\):\s/.test(subject) && /\b(back|front)\b/.test(subject)
 const changed = await changedPaths()
 const extMatrix = extensionsFor(changed)
-const destBlock = await nextDevLive()
+const destBlock = await nextServerConflict(ROOT)
 
 console.log('check:ci — local replica of the prod quality gates')
 console.log(`HEAD  ${subject || '(no commits)'}`)
@@ -155,6 +148,9 @@ console.log('')
 
 let failed = false
 
+if (!(await runGate('Next server guard', ['bun', 'test', 'scripts/check-next-server.test.ts']))) {
+  failed = true
+}
 if (!(await runGate('lint', ['bun', 'run', 'lint']))) failed = true
 if (!(await runGate('lint:styles', ['bun', 'run', 'lint:styles']))) failed = true
 
diff --git a/scripts/check-next-server.test.ts b/scripts/check-next-server.test.ts
new file mode 100644
index 000000000..33c347f52
--- /dev/null
+++ b/scripts/check-next-server.test.ts
@@ -0,0 +1,137 @@
+import { afterAll, expect, test } from 'bun:test'
+import { mkdtempSync, mkdirSync, rmSync, symlinkSync, writeFileSync } from 'fs'
+import { tmpdir } from 'os'
+import { join } from 'path'
+
+import { nextServerConflict } from './check-next-server'
+
+const fixture = mkdtempSync(join(tmpdir(), 'next-checkout-guard-'))
+const checkout = join(fixture, 'repo')
+const otherCheckout = join(fixture, 'repo-other')
+mkdirSync(checkout)
+mkdirSync(otherCheckout)
+const probe = join(fixture, 'server-probe.ts')
+writeFileSync(probe, 'setInterval(() => {}, 1000)\n')
+afterAll(() => rmSync(fixture, { recursive: true, force: true }))
+
+// Real process discovery, without starting Next, binding ports or touching .next.
+// Trailing arguments reproduce the command signature inspected by the guard.
+async function withServer(
+  directory: string,
+  check: () => Promise<void>,
+  args: string[] = [],
+  command: 'dev' | 'start' = 'dev'
+) {
+  const child = Bun.spawn([process.execPath, probe, 'next', command, ...args], {
+    cwd: directory,
+    stdout: 'ignore',
+    stderr: 'ignore'
+  })
+  try {
+    await check()
+  } finally {
+    child.kill()
+    await child.exited
+  }
+}
+
+test('blocks a server using this checkout before its output can be rebuilt', async () => {
+  await withServer(checkout, async () => {
+    expect(await nextServerConflict(checkout)).toContain('using this checkout')
+  })
+})
+
+test('allows a running server in another clone with a shared path prefix', async () => {
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toBeNull()
+  })
+})
+
+test('allows an unrelated production server with a keep-alive timeout', async () => {
+  await withServer(
+    otherCheckout,
+    async () => {
+      expect(await nextServerConflict(checkout)).toBeNull()
+    },
+    ['--keepAliveTimeout', '60000'],
+    'start'
+  )
+})
+
+test('blocks a relative checkout target after a keep-alive timeout', async () => {
+  await withServer(
+    otherCheckout,
+    async () => {
+      expect(await nextServerConflict(checkout)).toContain('targets this checkout')
+    },
+    ['--keepAliveTimeout', '60000', '../repo'],
+    'start'
+  )
+})
+
+test.each([
+  ['--inspect', '127.0.0.1:9229'],
+  ['--internal-trace', 'overview']
+])('allows an unrelated server with the optional %s value', async (option, value) => {
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toBeNull()
+  }, [option, value])
+})
+
+test.each(['--inspect', '--internal-trace'])(
+  'keeps resolving checkout targets when %s has no value',
+  async (option) => {
+    await withServer(otherCheckout, async () => {
+      expect(await nextServerConflict(checkout)).toContain('targets this checkout')
+    }, [option, '--', '../repo'])
+  }
+)
+
+test('blocks a server launched from an app subdirectory', async () => {
+  const app = join(checkout, 'apps', 'webapp')
+  mkdirSync(app, { recursive: true })
+  await withServer(app, async () => {
+    expect(await nextServerConflict(checkout)).toContain('using this checkout')
+  })
+})
+
+test('blocks an explicit app path launched from a different checkout', async () => {
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toContain('references this checkout')
+  }, [checkout])
+})
+
+test('blocks a relative app path launched from another checkout', async () => {
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toContain('targets this checkout')
+  }, ['-p', '3211', '../repo/apps/webapp'])
+})
+
+test('fails closed when the observed app path cannot be resolved', async () => {
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toContain('Cannot resolve the app directory')
+  }, ['../missing-app'])
+})
+
+test('blocks an app reached through an absolute symlink alias', async () => {
+  const alias = join(fixture, 'alias')
+  symlinkSync(checkout, alias)
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toContain('targets this checkout')
+  }, [alias])
+})
+
+test('resolves dash-prefixed app directories after the option delimiter', async () => {
+  symlinkSync(checkout, join(otherCheckout, '-app'))
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toContain('targets this checkout')
+  }, ['--', '-app'])
+})
+
+test('fails closed on multiple positional app paths in the process listing', async () => {
+  mkdirSync(join(otherCheckout, 'first'))
+  mkdirSync(join(otherCheckout, 'second'))
+  await withServer(otherCheckout, async () => {
+    expect(await nextServerConflict(checkout)).toContain('Cannot resolve ambiguous app arguments')
+  }, ['first', 'second'])
+})
diff --git a/scripts/check-next-server.ts b/scripts/check-next-server.ts
new file mode 100644
index 000000000..5f90ffd0e
--- /dev/null
+++ b/scripts/check-next-server.ts
@@ -0,0 +1,110 @@
+#!/usr/bin/env bun
+/** Protect this checkout's .next output while allowing servers in other clones. */
+import { $ } from 'bun'
+import { realpathSync } from 'fs'
+import { resolve, sep } from 'path'
+
+async function processDirectory(pid: number): Promise<string | null> {
+  try {
+    if (process.platform === 'linux') return realpathSync(`/proc/${pid}/cwd`)
+    const result = await $`lsof -a -p ${pid} -d cwd -Fn`.quiet().nothrow()
+    const directory = result.stdout
+      .toString()
+      .split('\n')
+      .find((line) => line.startsWith('n'))
+    return directory ? realpathSync(directory.slice(1)) : null
+  } catch {
+    // The process may exit between ps and this lookup. The caller verifies that case.
+    return null
+  }
+}
+
+export async function nextServerConflict(
+  root = resolve(import.meta.dir, '..')
+): Promise<string | null> {
+  const canonicalRoot = realpathSync(root)
+  const processes = await $`ps -ax -o pid=,command=`.quiet().nothrow()
+  if (processes.exitCode !== 0) return 'Cannot inspect running Next servers safely'
+
+  for (const line of processes.stdout.toString().split('\n')) {
+    const match = line.trim().match(/^(\d+)\s+(.+)$/)
+    if (!match) continue
+    const launch = match[2].match(/\bnext\s+(dev|start)\b(.*)$/)
+    if (!launch) continue
+    const pid = Number(match[1])
+    const directory = await processDirectory(pid)
+    if (directory === canonicalRoot || directory?.startsWith(`${canonicalRoot}${sep}`)) {
+      return `Next server ${pid} is using this checkout; stop it before building its .next output`
+    }
+    // Also cover `next dev /absolute/app/path` launched from another directory.
+    if (
+      [root, canonicalRoot].some((path) => {
+        const escaped = path.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+        return new RegExp(`${escaped}(?:[/\\s"']|$)`).test(match[2])
+      })
+    ) {
+      return `Next server ${pid} references this checkout; stop it before building its .next output`
+    }
+    if (!directory) {
+      const alive = await $`ps -p ${pid} -o pid=`.quiet().nothrow()
+      if (alive.exitCode === 0) return `Cannot determine the checkout used by Next server ${pid}`
+      continue
+    }
+    // Next accepts a positional app directory relative to the launcher's cwd.
+    // ps renders argv as text; unknown/ambiguous positional paths fail closed.
+    const args = launch[2].match(/"[^"]*"|'[^']*'|\S+/g) ?? []
+    const optionsWithValue = new Set([
+      '-p',
+      '--port',
+      '-H',
+      '--hostname',
+      '--keepAliveTimeout',
+      '--experimental-https-key',
+      '--experimental-https-cert',
+      '--experimental-https-ca',
+      '--experimental-upload-trace'
+    ])
+    const optionsWithOptionalValue = new Set(['--inspect', '--internal-trace'])
+    let positionalOnly = false
+    const directories: string[] = []
+    for (let index = 0; index < args.length; index++) {
+      const argument = args[index].replace(/^(["'])(.*)\1$/, '$2')
+      if (!positionalOnly && argument === '--') {
+        positionalOnly = true
+        continue
+      }
+      if (!positionalOnly && optionsWithValue.has(argument)) {
+        index++
+        continue
+      }
+      if (!positionalOnly && optionsWithOptionalValue.has(argument)) {
+        if (args[index + 1] && !args[index + 1].startsWith('-')) index++
+        continue
+      }
+      if (!positionalOnly && argument.startsWith('-')) continue
+      directories.push(argument)
+    }
+    if (directories.length > 1)
+      return `Cannot resolve ambiguous app arguments for Next server ${pid}`
+    for (const argument of directories) {
+      let appDirectory: string
+      try {
+        appDirectory = realpathSync(resolve(directory, argument))
+      } catch {
+        return `Cannot resolve the app directory used by Next server ${pid}`
+      }
+      if (appDirectory === canonicalRoot || appDirectory.startsWith(`${canonicalRoot}${sep}`)) {
+        return `Next server ${pid} targets this checkout; stop it before building its .next output`
+      }
+    }
+  }
+  return null
+}
+
+if (import.meta.main) {
+  const conflict = await nextServerConflict()
+  if (conflict) {
+    console.error(conflict)
+    process.exit(1)
+  }
+}
diff --git a/scripts/hooks/pre-push.sh b/scripts/hooks/pre-push.sh
index 05a14934f..820d69600 100755
--- a/scripts/hooks/pre-push.sh
+++ b/scripts/hooks/pre-push.sh
@@ -11,9 +11,9 @@ fi
 
 # check:ci skips webapp build:ci when a Next development server is live.
 # A green skip is not the GitHub job. A live server plus a production
-# build also corrupts .next.
-if ps -ax -o command= | grep -E '[n]ext (dev|start)' >/dev/null; then
-    echo "❌ A Next development server is running."
+# build in the same checkout also corrupts .next. Other clones have separate output.
+if ! bun "$REPO_ROOT/scripts/check-next-server.ts"; then
+    echo "❌ Cannot safely build this checkout while its Next server is running."
     echo "   Stop the webapp development server, then push again."
     echo "   After the push: restart the development server."
     echo "   check:ci already removes the production .next after build:ci."
diff --git a/scripts/run-tests.sh b/scripts/run-tests.sh
index 06048ac14..7eb73f165 100755
--- a/scripts/run-tests.sh
+++ b/scripts/run-tests.sh
@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 # Unit + clean-room + webapp E2E. Gate order: scripts/publishable-extensions.ts.
-# Usage: bash scripts/run-tests.sh [--unit | --extensions | --e2e | all]
+# Usage: bash scripts/run-tests.sh [--unit | --extensions | --e2e | all] [--scope <directory>]
 # Needs bash (process substitution). E2E needs make dev-local. Report → Notes/.
 
 set -o pipefail
@@ -44,11 +44,21 @@ case "${1:-all}" in
   all|"")  RUN_EXTENSION_GATES=true; RUN_WEBAPP_UNIT=true; RUN_E2E=true ;;
   *)
     echo -e "${RED}Unknown option: $1${NC}"
-    echo "Usage: $0 [--unit | --extensions | --e2e | all]"
+    echo "Usage: $0 [--unit | --extensions | --e2e | all] [--scope <directory>]"
     exit 1
     ;;
 esac
 
+E2E_SPEC_ROOT="$WEBAPP_DIR/cypress/e2e"
+if [ "$#" -gt 1 ]; then
+  if [ "$1" != "--e2e" ] || [ "$#" -ne 3 ] || [ "$2" != "--scope" ] || \
+    [[ ! "$3" =~ ^[a-zA-Z0-9_-]+$ ]] || [ ! -d "$E2E_SPEC_ROOT/$3" ]; then
+    echo "Usage: $0 --e2e [--scope <directory under cypress/e2e>]"
+    exit 1
+  fi
+  E2E_SPEC_ROOT="$E2E_SPEC_ROOT/$3"
+fi
+
 # One extension's gate command. The caller owns cwd, logging and exit handling,
 # so the serial and parallel paths cannot drift apart.
 extension_gate_cmd() {
@@ -89,6 +99,10 @@ if $RUN_E2E; then
     echo -e "${YELLOW}  Start it with: make dev-local${NC}"
     echo -e "${YELLOW}  Or set BASE_URL env var if running elsewhere.${NC}"
     echo ""
+    if [ "${CI:-}" = "true" ] || [ ! -t 0 ]; then
+      echo "Start the webapp before running E2E tests."
+      exit 1
+    fi
     echo -n "Continue anyway? [y/N] "
     read -r answer
     if [[ ! "$answer" =~ ^[Yy]$ ]]; then
@@ -262,6 +276,7 @@ if $RUN_E2E; then
     echo " E2E TESTS (Cypress)"
     echo " Started: $(date)"
     echo " Base URL: ${BASE_URL}"
+    echo " Spec root: ${E2E_SPEC_ROOT}"
     echo " Parallel workers: ${CYPRESS_PARALLEL}"
     echo "============================================================================="
     echo ""
@@ -291,11 +306,12 @@ if $RUN_E2E; then
     # the `cypress/e2e/...` keys the write-back below stores.
     ( cd "$WEBAPP_DIR" && \
       SPLIT="$CYPRESS_PARALLEL" SPLIT_INDEX="$i" SPLIT_FILE="cypress/timings.json" \
+      SPLIT_OUTPUT_FILE="$WORKER_LOGS_DIR/worker-${i}-timings.json" \
       bunx cypress run \
         --project "$WEBAPP_DIR" \
         --browser electron \
         --config "baseUrl=${BASE_URL}" \
-        --spec "$WEBAPP_DIR/cypress/e2e/**/*.cy.{js,ts}" \
+        --spec "$E2E_SPEC_ROOT/**/*.cy.{js,ts}" \
     ) > "$WORKER_LOGS_DIR/worker-${i}.log" 2>&1 &
     WORKER_PIDS+=($!)
     WORKER_EXITS+=(-)
@@ -443,12 +459,12 @@ if $RUN_E2E; then
   # A narrower spec glob drops files silently; totals then hide the shortfall.
   # Editor-only globbing hid 10 specs for two months — compare against the tree.
   # Skip `manual-browser-test` to match excludeSpecPattern in cypress.config.ts.
-  DISCOVERED_SPECS=$(find "$WEBAPP_DIR/cypress/e2e" \
+  DISCOVERED_SPECS=$(find "$E2E_SPEC_ROOT" \
     \( -name '*.cy.js' -o -name '*.cy.ts' \) -type f \
     -not -path '*manual-browser-test*' 2>/dev/null | wc -l | tr -d ' ')
   if [ "$DISCOVERED_SPECS" -eq 0 ]; then
-    echo -e "  ${RED}✗ Found no spec files under ${WEBAPP_DIR}/cypress/e2e${NC}"
-    echo "  E2E found no spec files under ${WEBAPP_DIR}/cypress/e2e" >> "$REPORT"
+    echo -e "  ${RED}✗ Found no spec files under ${E2E_SPEC_ROOT}${NC}"
+    echo "  E2E found no spec files under ${E2E_SPEC_ROOT}" >> "$REPORT"
     E2E_EXIT=1
     echo ""
   elif [ "$TOTAL_SPECS" -lt "$DISCOVERED_SPECS" ]; then
@@ -546,7 +562,8 @@ if $RUN_E2E; then
   done
   echo '' >> "$TIMINGS_TMP"
   echo ']}' >> "$TIMINGS_TMP"
-  if [ "$(wc -l < "$TIMINGS_TMP")" -gt 3 ]; then
+  # A scoped run must not replace timings for the rest of the webapp suite.
+  if [ "$E2E_SPEC_ROOT" = "$WEBAPP_DIR/cypress/e2e" ] && [ "$(wc -l < "$TIMINGS_TMP")" -gt 3 ]; then
     mv "$TIMINGS_TMP" "$TIMINGS_FILE"
     echo -e "  ${DIM}Updated timings: ${TIMINGS_FILE}${NC}"
   else
diff --git a/scripts/test-chatroom.sh b/scripts/test-chatroom.sh
new file mode 100644
index 000000000..eca19c472
--- /dev/null
+++ b/scripts/test-chatroom.sh
@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+# Isolated browser contract tests. The Cypress fixtures own all Supabase HTTP data.
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT_DIR"
+
+if [ -z "${NEXT_PUBLIC_VIRTUOSO_LICENSE:-}" ]; then
+  echo "Set NEXT_PUBLIC_VIRTUOSO_LICENSE to a valid Virtuoso Message List license."
+  exit 1
+fi
+
+export TZ=UTC
+export NODE_ENV=production
+export NEXT_PUBLIC_E2E=true
+export NEXT_PUBLIC_SUPABASE_URL=http://localhost:54321
+export NEXT_PUBLIC_SUPABASE_ANON_KEY=dummy-key
+export NEXT_PUBLIC_RESTAPI_URL=http://localhost:4000
+export NEXT_PUBLIC_PROVIDER_URL=ws://localhost:1234
+export CHATROOM_PORT="${CHATROOM_PORT:-3211}"
+export BASE_URL="http://127.0.0.1:${CHATROOM_PORT}"
+export CYPRESS_PARALLEL=1
+export CI=true
+
+# Never accidentally run against a developer's existing server.
+node -e '
+  const net = require("node:net")
+  const port = Number(process.env.CHATROOM_PORT)
+  if (!Number.isInteger(port) || port < 1 || port > 65535) process.exit(1)
+  const server = net.createServer()
+  server.on("error", (error) => { console.error(error.message); process.exit(1) })
+  server.listen(port, "127.0.0.1", () => server.close())
+'
+
+mkdir -p Notes
+bash scripts/build-extensions.sh
+bun run --filter @docs.plus/webapp build:ci
+
+# Next's standalone output does not copy public or static assets automatically.
+STANDALONE_DIR="$ROOT_DIR/apps/webapp/.next/standalone/apps/webapp"
+mkdir -p "$STANDALONE_DIR/public" "$STANDALONE_DIR/.next/static"
+cp -R "$ROOT_DIR/apps/webapp/public/." "$STANDALONE_DIR/public/"
+cp -R "$ROOT_DIR/apps/webapp/.next/static/." "$STANDALONE_DIR/.next/static/"
+(
+  cd "$STANDALONE_DIR"
+  exec env PORT="$CHATROOM_PORT" HOSTNAME=127.0.0.1 node server.js
+) > "$ROOT_DIR/Notes/chatroom-server.log" 2>&1 &
+SERVER_PID=$!
+trap 'kill "$SERVER_PID" 2>/dev/null || true; wait "$SERVER_PID" 2>/dev/null || true' EXIT
+
+READY=false
+for attempt in $(seq 1 60); do
+  if ! kill -0 "$SERVER_PID" 2>/dev/null; then
+    cat Notes/chatroom-server.log
+    exit 1
+  fi
+  if curl -fsS --connect-timeout 2 --max-time 3 "$BASE_URL/api/health" > /dev/null; then
+    READY=true
+    break
+  fi
+  sleep 1
+done
+if [ "$READY" != true ]; then
+  cat Notes/chatroom-server.log
+  echo "The chatroom test server did not become ready."
+  exit 1
+fi
+
+bash scripts/run-tests.sh --e2e --scope chatroom