diff --git a/CHANGELOG.md b/CHANGELOG.md
index 25aefd9c..f21fc532 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@
 - Added a keyboard skip link to jump directly from the workbench shell to active workspace content.
 - Added an explicit primary workspace navigation label and main focus target.
 - Made narrow-view context chips, sidebar navigation and workspace shortcuts more compact and scroll-safe.
+- Locked the smallest mobile breakpoint so the topbar context remains a horizontal rail instead of expanding into a tall preamble.
 - Added static regression coverage for shell density, skip-link and mobile navigation contracts.
 - No API contracts, migrations, backend behavior, provider fetching or AI model behavior changed.
 
diff --git a/backend/tests/test_sprint82_shell_density_polish.py b/backend/tests/test_sprint82_shell_density_polish.py
index edb17e33..1ea17115 100644
--- a/backend/tests/test_sprint82_shell_density_polish.py
+++ b/backend/tests/test_sprint82_shell_density_polish.py
@@ -26,6 +26,7 @@ def test_mobile_shell_density_contracts_are_defined() -> None:
     assert "overflow-x: auto;" in css
     assert "scroll-snap-type: x proximity;" in css
     assert "white-space: nowrap;" in css
+    assert ".context-bar,\n  .quick-action-grid,\n  .workspace-nav-cluster" not in css
 
 
 def test_small_screen_navigation_keeps_labels_readable() -> None:
diff --git a/docs/CODEX_EXECUTION_LOG.md b/docs/CODEX_EXECUTION_LOG.md
index 94050bfa..b8874705 100644
--- a/docs/CODEX_EXECUTION_LOG.md
+++ b/docs/CODEX_EXECUTION_LOG.md
@@ -3002,6 +3002,8 @@ Tested:
 - `cd frontend && npm run typecheck`
 - `cd frontend && npm run build`
 - `bash scripts/run_readiness_check.sh` (`279 passed`; frontend typecheck/build passed; Alembic single head `202606120900`)
+- Live post-deploy browser check found a narrow-screen cascade override that made `.context-bar` one-column again; tightened the regression test and kept the context rail scrollable through the smallest breakpoint.
+- Re-ran `python -m pytest backend/tests/test_sprint82_shell_density_polish.py -q`, `cd frontend && npm run typecheck`, `cd frontend && npm run build` and `bash scripts/run_readiness_check.sh` (`279 passed`) after that fix.
 
 Open:
 - Deployment and live browser verification still need to run for this pass.
diff --git a/frontend/src/styles/app.css b/frontend/src/styles/app.css
index fbd6082a..9ded4a59 100644
--- a/frontend/src/styles/app.css
+++ b/frontend/src/styles/app.css
@@ -2435,7 +2435,6 @@ button.entity-card {
     overflow-x: hidden;
   }
 
-  .context-bar,
   .quick-action-grid,
   .workspace-nav-cluster {
     grid-template-columns: 1fr;