shopdb-flask/docs/wiki-drafts/ADR-019-Plugin-Dynamic-Settings-Routes.md

ADR-019: Plugin Dynamic Settings Routes

Read with the date on it. This is a point-in-time audit, kept as the record of what was found and what it turned out to be, not as current guidance. One thing it says repeatedly is no longer true: it was written when this line carried no ADRs, and the full ADR set now lives beside it in docs/adr. Where this page says a decision record is missing or lives elsewhere, look there first.

Status: Accepted (2026-09-11)
Context: Plugin UI extensions, lean builds
Supersedes: Hardcoded plugin routes in core router
Last checked against code: 2026-09-18, the deployment branch at 35d4fcd41

This draft lives only in docs/wiki-drafts/. There is no docs/adr/ directory on this branch, so this is the sole ADR-shaped record here and nothing enforces it except the tests named below. See ADR-Conformance-2026-09-18.md.

Problem

Plugins that extend core settings pages (like Operating Systems in Model Catalog) required hardcoded imports in frontend/src/router/routes/core.js:

{
  path: 'operatingsystems',
  name: 'model-catalog-os',
  component: () => import('../../.plugins-staged/computers/views/OperatingSystemsList.vue')
}

This broke lean builds (ci-lean profile with only machines,printers plugins) because the import referenced a component that didn't exist in the staged plugins.

The deeper issue: Core code shouldn't know about plugin UI structure. Every plugin that wants a settings tab requires a core code change, violating the plugin architecture principle that plugins are self-contained extensions.

Decision

Plugins declare their settings routes via a get_settings_routes() hook that returns route metadata. The frontend fetches these at runtime from /api/plugins/settings-routes and dynamically registers them via router.addRoute().

Backend: BasePlugin Hook

Added to shopdb/plugins/base.py:

def get_settings_routes(self) -> List[Dict]:
    """Frontend routes this plugin adds to settings pages.
    
    Returns a list of route configurations for the plugin's settings pages.
    Each route is a dict with:
      hub       - settings hub to attach to ('model-catalog', 'asset-config', etc.)
      path      - route path relative to hub (e.g. 'operatingsystems')
      name      - unique route name (e.g. 'model-catalog-os')
      tab       - tab label shown in hub UI (e.g. 'Operating Systems')
      component - path to Vue component relative to frontend/src/
                  (e.g. '.plugins-staged/computers/views/OperatingSystemsList.vue')
    
    Return [] (default) if the plugin adds no settings pages.
    """
    return []

Example: ComputersPlugin

class ComputersPlugin(BasePlugin):
    def get_settings_routes(self) -> List[Dict]:
        """Register Operating Systems management page in Model Catalog."""
        return [{
            'hub': 'model-catalog',
            'path': 'operatingsystems',
            'name': 'model-catalog-os',
            'tab': 'Operating Systems',
            'component': '.plugins-staged/computers/views/OperatingSystemsList.vue'
        }]

Backend: API Endpoint

In shopdb/core/api/plugins.py:46-95, as it stands on the deployment branch at 35d4fcd41:

@plugins_bp.route('/settings-routes', methods=['GET'])
@require_permission('settings.view')
def get_plugin_settings_routes():
    """Return settings routes contributed by all enabled plugins."""
    pm = current_app.extensions.get('plugin_manager')
    if not pm:
        return success_response({'routes': []})

    routes = []
    for plugin_name, plugin in pm.get_all_plugins().items():
        # Only include routes from enabled plugins
        if not pm.registry.is_enabled(plugin_name):
            continue
        if not hasattr(plugin, 'get_settings_routes'):
            continue
        # One broken plugin must not take every settings hub down with it.
        try:
            plugin_routes = plugin.get_settings_routes()
        except Exception:
            current_app.logger.exception(
                'get_settings_routes failed for plugin %s; skipping it',
                plugin_name)
            continue
        routes.extend(renderable_settings_routes(plugin_name, plugin_routes,
                                                 current_app.logger))

    return success_response({'routes': routes})

Earlier revisions of this draft showed a @jwt_required(optional=True) handler iterating pm.get_enabled_plugin_instances(). Neither is in the code: grep -rn get_enabled_plugin_instances shopdb/ plugins/ returns nothing, so that block would not have run. It is replaced above rather than kept, because a copy-paste block that reopens the anonymous read is worse than no block.

Auth: the endpoint is gated on settings.view. It was written anonymous, on the reasoning that unauthenticated pages (kiosks, TV displays) register plugin tabs before login. Nothing does: its only caller is ModelCatalogHub.vue, which sits behind requiresAuth and requiresAdmin. Open, it handed an anonymous caller the enabled plugin list, the settings hub layout and the internal Vue component paths, so it was closed.

Frontend: Dynamic Route Registration

Settings hub pages (e.g., ModelCatalogHub.vue) fetch plugin routes at mount and register them dynamically:

<script setup>
import { ref, onMounted } from 'vue'
import { useRoute, useRouter } from 'vue-router'
import axios from 'axios'

const route = useRoute()
const router = useRouter()
const pluginTabs = ref([])

onMounted(async () => {
  // Fetch plugin-contributed settings routes
  try {
    const response = await axios.get('/api/plugins/settings-routes')
    if (response.data && response.data.data) {
      // Filter for this hub's routes
      pluginTabs.value = response.data.data.routes.filter(r => r.hub === 'model-catalog')
      
      // Dynamically register routes
      pluginTabs.value.forEach(tab => {
        if (!router.hasRoute(tab.name)) {
          router.addRoute('model-catalog', {
            path: tab.path,
            name: tab.name,
            component: () => import(`../../${tab.component}`)
          })
        }
      })
    }
  } catch (error) {
    console.error('Failed to load plugin settings routes:', error)
  }
  
  // Default redirect
  if (route.name === 'model-catalog') {
    router.replace({ name: 'model-catalog-vendors' })
  }
})
</script>

<template>
  <div class="tabs">
    <!-- Core tabs -->
    <router-link :to="{ name: 'model-catalog-vendors' }" class="tab">
      Vendors
    </router-link>
    <router-link :to="{ name: 'model-catalog-types' }" class="tab">
      Model Types
    </router-link>
    <router-link :to="{ name: 'model-catalog-models' }" class="tab">
      Models
    </router-link>
    
    <!-- Plugin tabs loaded dynamically -->
    <router-link
      v-for="tab in pluginTabs"
      :key="tab.name"
      :to="{ name: tab.name }"
      class="tab"
    >
      {{ tab.tab }}
    </router-link>
  </div>
  
  <router-view />
</template>

Key behavior:

• Routes registered via router.addRoute() persist for the session
• Components lazy-load when the tab is clicked (code-splitting preserved)
• Tabs only appear if the plugin is enabled and staged

Constraints as implemented

What the sections above describe is the mechanism as designed. What ships is narrower, and a plugin author reading only the hook signature would not find this out until a tab failed to appear in front of a user. The three constraints below are the ones the contract does not express.

One hub draws plugin tabs: Model Catalog. router.addRoute appears exactly once in the frontend, in frontend/src/views/settings/ModelCatalogHub.vue. AssetConfigHub, SiteConfigHub, NetworkHub, SecurityHub, LocationsHub, IntegrationsHub and AssetTypeHub render their own tabs and nothing else, so a route declaring any of their ids is accepted by the hook, returned by the API and drawn by nobody. Adding a hub to the supported set means writing the fetch-and-register code into that hub's .vue file, not editing a list. The supported set is named once, in SETTINGS_HUBS_WITH_PLUGIN_TABS (shopdb/plugins/base.py); /api/plugins/settings-routes drops a route outside it and logs an error naming the plugin and the hub, the plugin manager logs the same finding at startup, and tests/test_core/test_plugin_settings_hubs.py fails if a bundled plugin declares an unsupported hub or if the list and the frontend drift apart.

A plugin tab is not deep-linkable. The hub registers its plugin routes in onMounted. Before the hub has mounted, the router has no such route, so navigating straight to a plugin tab URL - from a link, a bookmark, or a refresh while sitting on one - resolves against a router that does not know the path. Only arriving through the parent hub works. This is a real limit on what a plugin settings page can be: it cannot be somewhere you send a person.

The component does not load in a production build at all. The component field is a server-supplied string interpolated into a dynamic import, () => import(`../../${tab.component}`). Vite refuses that template - it has no static file extension - and says so during every build:

[plugin vite:dynamic-import-vars] src/views/settings/ModelCatalogHub.vue:
invalid import "../../${tab.component}". A file extension must be included
in the static part of the import.

The build still succeeds, and the emitted chunk carries the expression verbatim (import(../../${e.component})), rewritten to nothing. At runtime the browser resolves it against the chunk's own URL under /assets/ and asks the server for a .vue file; dist/ contains no .vue files, so the request 404s and the tab throws when it is clicked. Under npm run dev the same import works, because the dev server serves sources by path. So the mechanism as it stands is a development-only path: a tab that appears in production and fails on the click.

Nothing visibly broke because the one plugin using it does not depend on it. plugins/computers/frontend/routes.js also registers the same page statically at /settings/operatingsystems, and that route - a normal static import, a real URL - is what production actually uses. The dynamic tab is a duplicate way in.

Two ways out, and this ADR does not pick one: give the template a static extension (declare component without .vue and import ${component}.vue), which makes Vite glob every .vue under frontend/src at build time and makes the tab real for staged plugins while staying build-time bound; or accept that plugin settings pages are ordinary plugin routes and drop the hub-tab mechanism. Deciding that is the open question the architectural review raised.

What a plugin author must therefore do:

1. Declare hub: 'model-catalog' or declare nothing. For a settings page that belongs anywhere else, own a full page under the plugin's own routes (plugins/<name>/frontend/routes.js), which is statically registered, deep- linkable and not subject to any of this.
2. Register the page in plugins/<name>/frontend/routes.js even when you do declare a tab, and treat that route as the real one. A tab whose component is reachable no other way is a page nobody can open in production. tests/test_core/test_plugin_settings_hubs.py enforces this.
3. Point component at the staged path - .plugins-staged/<name>/views/X.vue, relative to frontend/src - and keep the source at plugins/<name>/frontend/views/X.vue so staging finds it.
4. Expect the frontend to be rebuilt when the plugin is added to a site. Enabling the plugin alone does not put its component in the bundle.
5. Do not publish, link to or bookmark the tab's URL. Send people to the hub.

Consequences

Benefits

Lean builds work: A build with SITE_PLUGINS=machines,printers doesn't stage the computers plugin, so its component doesn't exist. The frontend fetches zero routes from /api/plugins/settings-routes, no tabs appear, and no imports fail.

Plugins self-contain their UI: Adding a settings page to a plugin no longer requires touching core code. The plugin declares the route; the framework discovers it.

Runtime flexibility: Enabling/disabling a plugin (via /api/plugins/{name} PUT) changes what routes are returned. After an app restart, the tabs appear or disappear automatically - for a plugin whose frontend is in the running bundle. Enabling one that was never staged adds a tab whose component cannot be resolved (see "Constraints as implemented").

Composability: Multiple plugins can contribute to the same hub. Model Catalog could have tabs from computers (Operating Systems), printers (Printer Models), machines (Machine Types), etc., with no conflicts.

Trade-offs

Route registration is async: The tabs appear after mount, not at router initialization. In practice this is <100ms and visually seamless, but the router doesn't know about plugin routes at build time.

Component paths are strings: The component field is a string path that gets interpolated into import(). This prevents static analysis tools from tracing the dependency, and as written Vite will not rewrite the import at all, so it resolves in the dev server and 404s in a build (see "Constraints as implemented").

Composability is one hub wide: "Multiple plugins contribute to the same hub" is true of Model Catalog and of no other hub, because no other hub page registers plugin routes. See "Constraints as implemented".

A plugin tab has no URL worth sharing: routes register at hub mount, so the tab is not reachable by link, bookmark or refresh.

No SSR for plugin tabs: Server-side rendering can't evaluate router.addRoute() at build time. ShopDB doesn't use SSR, so this is not a concern, but it would block SSR adoption without refactoring.

Hub pages need updates: Every settings hub that wants to support plugin tabs must fetch /api/plugins/settings-routes and register them. The pattern is copy-paste (see ModelCatalogHub), but it's not automatic.

Alternatives Considered

1. Conditional imports at build time

Use Vite's conditional imports based on SITE_PLUGINS:

const routes = [
  { path: 'vendors', component: () => import('../../views/settings/VendorsList.vue') },
  { path: 'types', component: () => import('../../views/settings/ModelTypesList.vue') },
]

if (import.meta.env.VITE_SITE_PLUGINS.includes('computers')) {
  routes.push({
    path: 'operatingsystems',
    component: () => import('../../.plugins-staged/computers/views/OperatingSystemsList.vue')
  })
}

Rejected: Still requires core code to know about every plugin's routes. Not composable - adding a new plugin means editing core.

2. Plugin manifests drive build-time codegen

Each plugin has a manifest.json with routes. The build reads all manifests and generates a plugin-routes.js that imports components and exports merged routes.

Rejected: Build-time coupling is tighter than runtime. Changing a plugin's routes requires rebuilding the entire frontend. Dynamic enable/disable doesn't work without a rebuild.

3. Frontend plugin discovery via import.meta.glob

Use Vite's glob imports to discover all plugin components:

const pluginComponents = import.meta.glob('../.plugins-staged/*/views/*.vue')

Rejected: Discovery is too broad. Not every Vue file in a plugin is a settings page, and the hub doesn't know what tab label to show or where to mount it without metadata. You'd still need a manifest or a naming convention, which is equivalent to declaring the routes explicitly.

Implementation

Commits:

• fe09d2745e - Plugin dynamic settings routes architecture (backend hook + frontend registration)
• d59d0c3194 - Add /api/plugins/settings-routes to OpenAPI spec

Files changed:

• shopdb/plugins/base.py - Added get_settings_routes() hook
• plugins/computers/plugin.py - Implemented hook for Operating Systems tab
• shopdb/core/api/plugins.py - Added /api/plugins/settings-routes endpoint
• frontend/src/views/settings/ModelCatalogHub.vue - Fetch and register plugin routes
• frontend/src/router/routes/core.js - Removed hardcoded computers plugin import
• docs/openapi.json - Documented new endpoint

Tests: Gate tests pass (test_openapi_spec.py, test_public_read_surface.py).

Future Extensions

Other settings hubs: AssetConfigHub, SecurityHub, NetworkHub, etc. can adopt the same pattern. The fetch/register logic is hub-specific (filter by hub field), so each hub only sees its own tabs.

Nested routes: A plugin could return routes with children: [...] for nested settings pages. Router supports this via addRoute(parentName, childRoute).

Permissions: The tab could include a permission field (e.g., "computers.manage_os"), and the frontend would filter out tabs the user cannot reach. This would be UI gating only, and the page behind the tab must still enforce its own permission; the settings.view gate on /api/plugins/settings-routes says who may read the tab list, not who may use a given tab.

Icons: Add an icon field to the route metadata (e.g., "mdi-microsoft-windows"), and the tab renders the icon next to the label.

Plugin-specific hubs: A plugin could declare hub: "my-plugin-hub" and render its own hub page, not just tabs within core hubs. The router would need to discover and register hub pages too.

References

• ADR-001: Asset as platform contract (plugin architecture principles)
• ADR-013: Plugin catalog and lean builds (problem context)
• PR #XXX: Plugin dynamic settings routes (implementation)
• Issue #XXX: Lean builds fail with hardcoded plugin imports