Add Happy 404, featured/related sidebars, and next-post nav to the post page

Happy 404: an HTML 404 (unmatched route, or an explicit not-found inside a
real route) now renders a random existing post instead of the error page,
using the exact same context builder as a real post view. Toggle is the
happy_404_enabled site setting (default on, /admin/settings); JSON/API
requests and a handful of excluded prefixes are never affected. The pool of
candidate slugs is cached in-process and resampled periodically so it stays
fast and eventually cycles the whole posts table; on any internal failure it
falls straight through to the real 404 page.

Applying this everywhere surfaced ~60 existing tests that asserted a literal
404 for a legitimate resource-not-found flow (deleted post, unknown
container, wrong project slug, etc.) - each now disables the setting for the
duration of that specific check and restores it after, so the underlying
not-found behavior stays covered independently of the new feature.

Post page also gained, all built on the same shared post_page_context() so
they render identically on both a real post and a happy-404 page:
- A left sidebar (three separate cards, matching /feed's sidebar-card
  convention) for "Gists from {author}", "Projects from {author}" (private
  projects filtered through the normal visibility check), and "Related
  Discussions" - each cached per author and invalidated on create/edit/
  delete so new content shows up immediately.
- A right column reusing /feed's exact Daily Topic widget class for up to
  three "Featured" articles (the existing but previously-unused `featured`
  news flag), cached as a pool with per-request random sampling.
- A "Next post -> " link beside "Back to Feed", pointing at the next older
  post site-wide (blocked authors skipped). Wired through the same next_url
  mechanism already used for listing pagination, so it emits a real
  backend-rendered <link rel="next"> tag for SEO, not just a visible link.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BWJy6PrMMt5hwWxQwia2rd

tests/e2e/admin/auditlog.py

@@ -2,7 +2,7 @@
 
 from uuid import uuid4
 from datetime import datetime, timezone
-from tests.conftest import BASE_URL
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
 from devplacepy.database import get_table
 from devplacepy.utils import make_combined_slug
 def seed_admin_news(count=3):
@@ -265,10 +265,16 @@ def test_audit_log_view_detail(alice):
 
 def test_audit_log_detail_unknown_404(alice):
     page, _ = alice
-    resp = page.goto(
-        f"{BASE_URL}/admin/audit-log/nonexistent", wait_until="domcontentloaded"
-    )
-    assert resp.status == 404
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        resp = page.goto(
+            f"{BASE_URL}/admin/audit-log/nonexistent", wait_until="domcontentloaded"
+        )
+        assert resp.status == 404
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 
 
 def test_audit_log_guest_redirects_to_login(page, app_server):

tests/e2e/admin/containers/index.py

@@ -1,9 +1,11 @@
 # retoor <retoor@molodetz.nl>
 
+import time
+
 import requests
 from playwright.sync_api import expect
-from tests.conftest import BASE_URL
-from devplacepy.database import get_table
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
+from devplacepy.database import get_table, set_setting
 
 USER_INPUT = '#cm-admin-create-form input[data-search="user"]'
 USER_OPTIONS = '#cm-admin-create-form [data-suggest="user"] li[data-value]'
@@ -29,8 +31,14 @@ def test_containers_admin_page_loads(alice, app_server):
 
 def test_container_instance_page_404_for_missing(alice, app_server):
     page, _ = alice
-    page.goto(f"{BASE_URL}/admin/containers/nonexistent", wait_until="domcontentloaded")
-    assert page.is_visible("text=Not Found") or page.is_visible("text=404")
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        page.goto(f"{BASE_URL}/admin/containers/nonexistent", wait_until="domcontentloaded")
+        assert page.is_visible("text=Not Found") or page.is_visible("text=404")
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 
 
 def test_user_search_arrow_keys_highlight_and_enter_selects(alice, seeded_db):

tests/e2e/admin/containers/manage.py

@@ -2,12 +2,13 @@
 
 import time
 import requests
-from tests.conftest import BASE_URL, login_user
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS, login_user
 from devplacepy.database import (
     get_table,
     get_primary_admin_uid,
     invalidate_admins_cache,
     refresh_snapshot,
+    set_setting,
 )
 from devplacepy.utils import clear_user_cache
 
@@ -201,11 +202,15 @@ def test_admin_detail_page_404_for_non_viewer_on_private_project(page, app_serve
     other = _make_admin()
     project = _create_project(owner["api_key"], "E2E Manage Detail Private", is_private=True)
     inst_uid = _insert_instance(project["uid"], owner["uid"])
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
     try:
         login_user(page, other)
         page.goto(f"{BASE_URL}/admin/containers/{inst_uid}", wait_until="domcontentloaded")
         assert page.is_visible("text=Not Found") or page.is_visible("text=404")
     finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
         _cleanup(inst_uid)
 
 

tests/e2e/admin/services/data.py

@@ -1,7 +1,9 @@
 # retoor <retoor@molodetz.nl>
 
-from tests.conftest import BASE_URL, login_user
-from devplacepy.database import get_table
+import time
+
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS, login_user
+from devplacepy.database import get_table, set_setting
 def _promote_to_admin(username: str) -> None:
     users = get_table("users")
     user = users.find_one(username=username)
@@ -26,9 +28,15 @@ def test_service_detail_unknown_404(page, seeded_db):
     user = seeded_db["alice"]
     _promote_to_admin(user["username"])
     login_user(page, user)
-    resp = page.request.get(f"{BASE_URL}/admin/services/nope")
-    assert resp.status == 404
-    assert page.request.get(f"{BASE_URL}/admin/services/nope/data").status == 404
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        resp = page.request.get(f"{BASE_URL}/admin/services/nope")
+        assert resp.status == 404
+        assert page.request.get(f"{BASE_URL}/admin/services/nope/data").status == 404
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 
 
 def test_bots_service_registered_and_opt_in(page, seeded_db):

tests/e2e/docs.py

@@ -3,11 +3,22 @@
 import html
 import json
 import re
+import time
+import pytest
 import requests
-from tests.conftest import BASE_URL
-from devplacepy.database import get_table
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
+from devplacepy.database import get_table, set_setting
 from devplacepy.docs_api import API_GROUPS
 from devplacepy.utils import clear_user_cache
+
+
+@pytest.fixture(scope="module", autouse=True)
+def _disable_happy_404(app_server):
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    yield
+    set_setting("happy_404_enabled", "1")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 def _configs_by_id(text):
     configs = re.findall(r"data-config='(.*?)'", text, re.S)
     return {

tests/e2e/feed.py

@@ -1,6 +1,6 @@
 # retoor <retoor@molodetz.nl>
 
-from tests.conftest import BASE_URL, create_post_with_files, paste_image
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS, create_post_with_files, paste_image
 import time
 import requests
 from playwright.sync_api import expect
@@ -11,6 +11,7 @@ from devplacepy.database import (
     list_custom_overrides,
     set_custom_override,
     set_customization_pref,
+    set_setting,
 )
 from devplacepy.utils import clear_user_cache
 def _user_customization_toggle(username):
@@ -851,8 +852,14 @@ def test_delete_own_post(alice):
     page.locator(".post-action-btn:has-text('Delete')").click()
     page.locator(".dialog-overlay.visible .dialog-confirm").click()
     page.wait_for_url(f"{BASE_URL}/feed", wait_until="domcontentloaded")
-    resp = page.goto(post_url, wait_until="domcontentloaded")
-    assert resp.status == 404
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        resp = page.goto(post_url, wait_until="domcontentloaded")
+        assert resp.status == 404
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 
 
 def test_profile_nav_from_topbar(alice):

tests/e2e/forks.py

@@ -1,9 +1,20 @@
 # retoor <retoor@molodetz.nl>
 
 import json
-from tests.conftest import BASE_URL
-from devplacepy.database import get_table
+import time
+import pytest
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
+from devplacepy.database import get_table, set_setting
 from devplacepy.services.jobs import queue
+
+
+@pytest.fixture(scope="module", autouse=True)
+def _disable_happy_404(app_server):
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    yield
+    set_setting("happy_404_enabled", "1")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 def _seed_job(uid="test-fork-uid-001"):
     jobs = get_table("jobs")
     jobs.upsert(

tests/e2e/game/farm.py

@@ -1,11 +1,13 @@
 # retoor <retoor@molodetz.nl>
 
+import time
 from datetime import datetime, timedelta, timezone
 
 from playwright.sync_api import expect
 
-from tests.conftest import BASE_URL
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
 from tests.e2e.game.index import reset_farm, warp_ready
+from devplacepy.database import set_setting
 
 
 def _plant_growing(username, crop="python", slot=0):
@@ -84,10 +86,16 @@ def test_guest_can_view_farm(page):
 
 def test_unknown_farm_is_404(bob):
     page, _ = bob
-    response = page.goto(
-        f"{BASE_URL}/game/farm/nope_nobody", wait_until="domcontentloaded"
-    )
-    assert response is not None and response.status == 404
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        response = page.goto(
+            f"{BASE_URL}/game/farm/nope_nobody", wait_until="domcontentloaded"
+        )
+        assert response is not None and response.status == 404
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 
 
 def test_ready_build_is_protected_during_grace(bob):

tests/e2e/issues/index.py

@@ -1,6 +1,9 @@
 # retoor <retoor@molodetz.nl>
 
-from tests.conftest import BASE_URL
+import time
+
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
+from devplacepy.database import set_setting
 
 
 def test_issues_page_loads(alice):
@@ -61,6 +64,12 @@ def test_issue_button_icon_spacing(alice):
 
 def test_issue_detail_not_configured(alice):
     page, _ = alice
-    page.goto(f"{BASE_URL}/issues/999", wait_until="domcontentloaded")
-    assert page.is_visible("h1.error-code:has-text('404')")
-    assert page.is_visible("text=Page not found")
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        page.goto(f"{BASE_URL}/issues/999", wait_until="domcontentloaded")
+        assert page.is_visible("h1.error-code:has-text('404')")
+        assert page.is_visible("text=Page not found")
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)

tests/e2e/issues/jobs.py

@@ -1,10 +1,19 @@
 # retoor <retoor@molodetz.nl>
 
-from tests.conftest import BASE_URL
+import time
+
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
+from devplacepy.database import set_setting
 
 
 def test_issue_job_status_not_found(alice):
     page, _ = alice
-    page.goto(f"{BASE_URL}/issues/jobs/nonexistent-job", wait_until="domcontentloaded")
-    assert page.is_visible("h1.error-code:has-text('404')")
-    assert page.is_visible("text=Page not found")
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        page.goto(f"{BASE_URL}/issues/jobs/nonexistent-job", wait_until="domcontentloaded")
+        assert page.is_visible("h1.error-code:has-text('404')")
+        assert page.is_visible("text=Page not found")
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)

tests/e2e/news.py

@@ -1,10 +1,12 @@
 # retoor <retoor@molodetz.nl>
 
+import time
+
 import pytest
 from uuid import uuid4
 from datetime import datetime, timedelta, timezone
-from tests.conftest import BASE_URL, assert_share_copies
-from devplacepy.database import get_table
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS, assert_share_copies
+from devplacepy.database import get_table, set_setting
 from devplacepy.utils import make_combined_slug
 def _seed_news_paginated(count):
     news_table = get_table("news")
@@ -258,8 +260,14 @@ def test_news_detail_loads(page, news_article):
 
 
 def test_news_detail_404(page, app_server):
-    page.goto(f"{BASE_URL}/news/nonexistent-article", wait_until="domcontentloaded")
-    assert page.is_visible("text=not found", timeout=5000)
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        page.goto(f"{BASE_URL}/news/nonexistent-article", wait_until="domcontentloaded")
+        assert page.is_visible("text=not found", timeout=5000)
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 
 
 def test_news_comment(alice, news_article):

tests/e2e/projects/index.py

@@ -4,9 +4,20 @@ import re
 from uuid import uuid4
 from datetime import datetime, timedelta, timezone
 from playwright.sync_api import expect
-from tests.conftest import BASE_URL, assert_share_copies
-from devplacepy.database import get_table
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS, assert_share_copies
+from devplacepy.database import get_table, set_setting
 from devplacepy.utils import make_combined_slug
+
+
+def _goto_expect_404(page, url):
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        resp = page.goto(url, wait_until="domcontentloaded")
+        assert resp.status == 404
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 def _seed_posts(count):
     suite = uuid4().hex[:8]
     topic = f"pag{suite}"
@@ -496,8 +507,7 @@ def test_delete_own_project(alice):
     page.locator(".context-menu-item:has-text('Delete')").click()
     page.locator(".dialog-overlay.visible .dialog-confirm").click()
     page.wait_for_url(f"{BASE_URL}/projects", wait_until="domcontentloaded")
-    resp = page.goto(proj_url, wait_until="domcontentloaded")
-    assert resp.status == 404
+    _goto_expect_404(page, proj_url)
 
 
 def test_project_edit_button(alice):
@@ -850,8 +860,7 @@ def test_data_confirm_accept_proceeds(alice):
     _click_delete(page)
     page.locator(".dialog-overlay.visible .dialog-confirm").click()
     page.wait_for_url(f"{BASE_URL}/projects", wait_until="domcontentloaded")
-    resp = page.goto(proj_url, wait_until="domcontentloaded")
-    assert resp.status == 404
+    _goto_expect_404(page, proj_url)
 
 
 def test_detail_download_button_downloads(app_server, page):

tests/e2e/reports/ui.py

@@ -1,9 +1,11 @@
 # retoor <retoor@molodetz.nl>
 
+import time
+
 from playwright.sync_api import expect
 
-from devplacepy.database import get_table, refresh_snapshot
-from tests.conftest import BASE_URL
+from devplacepy.database import get_table, refresh_snapshot, set_setting
+from tests.conftest import BASE_URL, CACHE_VERSION_PROPAGATION_SECONDS
 
 
 def _create_post(page, content):
@@ -124,10 +126,16 @@ def test_the_legal_pages_render_for_a_guest(page, app_server):
 
 
 def test_the_admin_operations_page_is_hidden_from_a_guest(page, app_server):
-    page.goto(
-        f"{BASE_URL}/docs/moderation-operations.html", wait_until="domcontentloaded"
-    )
-    assert "not found" in page.content().lower()
+    set_setting("happy_404_enabled", "0")
+    time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
+    try:
+        page.goto(
+            f"{BASE_URL}/docs/moderation-operations.html", wait_until="domcontentloaded"
+        )
+        assert "not found" in page.content().lower()
+    finally:
+        set_setting("happy_404_enabled", "1")
+        time.sleep(CACHE_VERSION_PROPAGATION_SECONDS)
 
 
 def test_the_admin_operations_page_renders_for_an_admin(alice):