Restore the green release matrix: stale cohort_year route kwargs and flat cohort literals break the widened Playwright tier and module page tests

[alexeygrigorev]

Goal

Keep the release matrix moving: main run 34189651084 (4e7d218) failed both the django and playwright jobs. The django failure decomposes into the already-claimed classes (#345 NOT NULL archive_commit_sha; #347/#348 catalogue card routes) plus stragglers, and the playwright job failed for the first time because the change-selective plan widened the browser tier to 281 of 284 tests after #343 and exposed stale #320 route expectations in playwright_tests/ that the 30-test smoke selection never touches. This issue claims the remaining URL-shape stragglers: the Playwright cohort_year reverse kwargs and the flat cohort literals in courses/tests/test_module_pages.py.

Deliberately out of scope here (owned elsewhere): #345 (NOT NULL on course creation), #347/#348 (catalogue card tests and course_list_base.py helpers). Also out of scope, different failure classes: courses.tests.test_curriculum_models.test_cohort_curriculum_format_defaults_to_legacy (expects choices {legacy, modules}, model now also has shared) and courses.tests.test_local_cmp_content_import.test_every_required_column_is_written_by_the_copy (copy does not write the three archive_* columns) - both need their own triage.

Evidence

Playwright job, run 34189651084, 281 selected, 267 passed, 2 failed, 12 errors in 3032.77s:

• 12 errors in playwright_tests/test_accessibility.py (core smoke, visual evidence, registry, keyboard focus, breadcrumb spacing, javascript-off, reflow, named blink tree): NoReverseMatch: Reverse for 'dashboard' with keyword arguments '{'course_slug': ..., 'cohort_year': '2026'}' not found.
• 2 failures in playwright_tests/test_course_design_parity.py::test_database_course_catalog_renders_the_design_system_index (desktop + mobile): NoReverseMatch: Reverse for 'course' with keyword arguments '{'course_slug': ..., 'cohort_year': '2026'}' not found.

Django job, same run, 3764 tests, failures=5, errors=45; the URL-shape straggler beyond #347/#348's scope:

• courses.tests.test_module_pages.ModulePageTests.test_module_and_unit_links_keep_numeric_source_slugs: reverses with the post-Share current Zoomcamp curriculum across live and self-paced cohorts with GitHub archives #320 route names and cohort_identifier kwargs, but then asserts the legacy flat literals; reverse returns /courses/llm-zoomcamp/cohorts/2026/modules/01-agentic-rag, the test expects /courses/llm-zoomcamp/2026/modules/01-agentic-rag (and the /01-intro unit literal).

Root cause: #320 renamed the cohort route kwargs from cohort_year to cohort_identifier and moved cohort paths under /cohorts/. The catalogue template and courses/urls.py were migrated; four reverse kwarg dicts in playwright_tests/ and two literals in test_module_pages.py were not.

Deciding spec

_docs/compatibility/shared-curriculum-route-aliases.json (decided 2026-09-07, owner website PM #320/W0; spec authority _docs/specs/02-url-link-seo-compatibility.md and open-decisions.md #5):

• /courses/<family>/cohorts/<identifier> (route cohort) is canonical.
• /courses/<family>/cohorts/<identifier>/dashboard (route cohort_dashboard) is canonical.
• /courses/<family>/cohorts/<identifier>/modules/<module-slug> (route cohort_module) is redirect-only for shared-format cohorts and resolves against the cohort's own module-format rows for cohorts that still use them. The test fixture creates curriculum_format=CurriculumFormat.MODULES, so the cohorts-shaped URL serves content directly; only the literals are stale.

The product is aligned with the spec; the tests are not. Test-only change.

Scope

• playwright_tests/test_accessibility.py: rename the two "cohort_year" keys to "cohort_identifier" in the course_route/empty_course_route kwargs dicts (they feed reverse for dashboard, enrollment, homework, projects, leaderboard surfaces).
• playwright_tests/test_course_design_parity.py: rename the two "cohort_year" keys to "cohort_identifier" in the reverse("course", ...) calls.
• courses/tests/test_module_pages.py::test_module_and_unit_links_keep_numeric_source_slugs: update the two expected literals to the cohorts shape.

courses/tests/test_wrapped_statistics.py also contains the string cohort_year, but only as a data-dict key of calculate_wrapped_statistics output, not a route kwarg; it passes and stays untouched.

Non-goals

• No product, template, urlconf, or spec change.
• No change to Restore the green release matrix: Course creation hits NOT NULL on courses_course.archive_commit_sha #345 or Align the catalogue tests with the canonical cohort routes #347/Align the catalogue tests with the canonical cohort routes #348 scope.
• No triage of the curriculum-format choices or CMP copy-column failures named above.
• No workflow or quality-contract edits.

Acceptance criteria

• DJANGO_SETTINGS_MODULE=website.settings.test uv run --frozen python manage.py test courses.tests.test_module_pages --noinput --parallel 1 passes.
• The two playwright files pass under pytest (with --ignore=e2e).
• make lint, make format-check, make typecheck stay green.
• The next main CI run's playwright and django jobs show no cohort_year/flat-cohort failures from the files in scope.