kandev/docs/decisions/2026-08-20-settings-prompt-editor-provider-ownership.md

ADR-2026-08-20-settings-prompt-editor-provider-ownership: Settings Prompt Editors Own Monaco Completion Providers

Status: accepted Date: 2026-08-20 Area: frontend

Context

Monaco registers completion providers by language, but Settings can mount more than one prompt editor with different placeholder and saved-prompt catalogs. The previous language-wide singleton allowed the last mounted editor to replace the provider used by another open editor. Saved-prompt catalogs also load asynchronously, so registration must handle data arriving before or after Monaco mounts.

Decision

Each ScriptEditor instance owns its primary and saved-prompt completion registrations. The registrations wrap their providers with a model-identity check and return no suggestions for another model. Provider disposables are updated and cleaned up per instance. The shared SettingsPromptEditor enables saved-prompt registration only for fields whose runtime expands @name references, and its completion widget is layered above the mobile Settings Save bar.

Consequences

Open editors no longer share mutable provider state, so placeholder and saved- prompt suggestions remain local to the editor that requested them. Each editor performs its own registration and disposal work, and provider changes replace only that editor's registration. The shared prompt editor must retain the latest registration callback because prompt data may load before Monaco's one-shot mount callback.

Alternatives Considered

• Keep one language-wide provider per slot. This is simpler, but it reintroduces cross-editor catalog leakage and makes unmount order observable.
• Keep a global provider and route requests through the active editor. This requires focus and model bookkeeping outside Monaco and is fragile when several editors are mounted or a completion request races a focus change.
• Give every editor a distinct Monaco language identifier. This avoids some collisions, but multiplies language registrations and does not improve the provider lifecycle or async catalog handling.