Companion App Patterns

Canvas Provider Companion Application Patterns

This skill captures conventions for building Canvas provider companion plugins — mobile-oriented modals launched from the provider companion harness. They read as small single-page apps rendered inside an iframe, served by a SimpleAPI handler.

When to Use This Skill

Invoke this skill when you are:

• Creating a new plugin that declares provider_companion_global, provider_companion_patient_specific, or provider_companion_note_specific in its manifest.
• Reviewing or modifying a plugin whose Application subclass emits a LaunchModalEffect that points at a SimpleAPI endpoint served by the same plugin.
• Deciding where a piece of logic should live between the Application, the SimpleAPI, and the client-side main.js.
• Choosing between client-side render and server-round-trip for a new interaction.

It complements plugin-patterns (generic Canvas plugin patterns) and testing (mock-based test discipline) rather than replacing them.

Quick Reference

Reference companion_app_patterns_context.txt in this skill directory for the full rule set with rationale and examples. High-level rules:

1. Scope awareness. Only read the event context keys your scope actually provides. Global apps get no patient or note; patient-specific gets patient.id; note-specific gets both.
2. Mutations via effects, never .save(). Writes flow through SDK effects (UpdateTask, AddTaskComment, etc.). The plugin sandbox disallows direct ORM writes.
3. Auth with StaffSessionAuthMixin, never bare SessionCredentials. Provider companion handlers MUST inherit from StaffSessionAuthMixin so non-staff sessions are rejected at the auth layer. A custom authenticate that only checks logged_in_user is not None lets any logged-in patient reach the endpoint; "mine"-style filters are not a substitute for auth.
4. Server enforces permissions; client renders. The task serializer sets can_complete / can_assign_to_me; the client gates button visibility on those flags, and the mutating endpoint re-verifies before emitting the effect.
5. FK lookups by public UUID use fk__id=<uuid>. assignee_id / provider_id target the integer dbid PK and will raise ValueError: Field 'dbid' expected a number if passed a UUID string.
6. Timezone: client sends ISO, server parses ISO. Client builds date-range boundaries from local Date objects and calls .toISOString(). Server parses with datetime.fromisoformat (supporting Z). Display uses toLocaleTimeString / toLocaleDateString.
7. One HTML shell + main.js + styles.css per plugin. Vanilla JS, no framework, no bundler. The shell is served by @api.get("/"); JS and CSS are served by sibling routes.
8. Material-style card language. 4px radius, layered box-shadow for elevation, consistent neutral/accent palette. Tap-to-expand cards get a visible, rotating chevron. Carrying the launcher icon's accent color through the UI (blue icon → blue primary buttons and links) is a nice polish touch that makes the modal feel like the same thing the user tapped.
9. Mobile-first scroll isolation. body is a full-height flex column with overflow: hidden; only the content region scrolls so header/filter chrome stays pinned.
10. Deep links break out of the iframe via target="_top". Navigating to another part of Canvas (e.g., a patient page) must replace the top frame; don't try to reproduce host chrome inside the modal.
11. One plugin = one surface, one purpose. Ship them self-contained: own README.md leading with end-user usage, own LICENSE, own 256×256 icon (SVG source + PNG), own tests at 100% coverage. Don't cross-reference sibling companion plugins — fork, don't import.
12. Realtime push via WebSocket uses a deterministic channel name. The URL path segment is the channel name — /plugin-io/ws/<plugin_name>/<channel_name>/ (trailing slash required). Use a scheme like staff-<uuid> derived from the logged-in user so the browser can compute it and a separate BaseHandler subscribed to a model event (e.g. MESSAGE_CREATED) can emit Broadcast(channel=f"staff-{uuid}", message={...}) without any registry. Unwrap the broadcast envelope client-side (the wire format is {"message": {...}}).
13. Originate commands on the launching note (note-scope only). Note-scope companion apps receive note.id in self.event.context and should pass it through the launcher URL to the handler. The handler uses it as note_uuid when constructing an SDK command (e.g. VitalsCommand(note_uuid=…, …)) and calling command.originate(). Return the resulting effect alongside the JSON response — the platform materializes the command in the note.
14. Self-dismiss via the INIT_CHANNEL / CLOSE_MODAL contract. The host transfers a MessagePort to the modal iframe via a {type:'INIT_CHANNEL'} postMessage with event.ports[0]. Store the port and, when done (e.g. after a successful submit), call port.postMessage({type:'CLOSE_MODAL'}). Fall back to window.close() if the port wasn't delivered. Don't invent alternate message shapes (window.parent.postMessage, lowercase close, etc.); stick to the documented contract.

Reference Implementations

Five companion-scope plugins demonstrate this skill end-to-end in Medical-Software-Foundation/canvas:

• extensions/provider_schedule_companion/ — the logged-in provider's schedule with day/week/month views (provider_companion_global).
• extensions/provider_task_dashboard_companion/ — filterable task list with inline comment thread, assign-to-me, and mark-complete actions (provider_companion_global).
• extensions/provider_my_panel_companion/ — the logged-in provider's patient panel with last/next visit and open-task counts (provider_companion_global).
• extensions/provider_patient_messages_companion/ — live SMS-style messaging surface with WebSocket push on MESSAGE_CREATED (provider_companion_global).
• extensions/provider_note_vitals_companion/ — mobile vitals entry form that originates a Vitals command on the current note (provider_companion_note_specific).

All ship with detailed READMEs, 100% pytest coverage, and MIT licensing. The messaging plugin is the canonical reference for realtime push (rule 12); the vitals plugin is the canonical reference for note-scope command origination and the INIT_CHANNEL / CLOSE_MODAL dismiss contract (rules 13–14).