Remove Inline Suggestion Helper Plan

Goal

Remove the old runtime inline-suggestion lookup helper and migrate remaining callers to injected suggestion state while preserving current rendering behavior.

Scope

• Audit remaining runtime and doc references to the old helper.
• Add regression coverage for mention and inline equation under injected suggestion styling.
• Migrate callers to injected data attributes or direct suggestion APIs.
• Delete the helper if nothing depends on it.
• Regenerate registry artifacts touched by the change.

Findings

• The remaining runtime callers were in suggestion-kit.tsx, mention-node.tsx, and equation-node.tsx.
• A recent learning doc still showed the old helper in a code sample and needed a refresh.
• date-node already uses data-inline-suggestion injection and is the pattern to extend.

Phases

• Audit remaining references
• Add or update tests for mention and inline equation injection path
• Refactor runtime code and remove helper
• Refresh docs/generated registry output
• Verify build, typecheck, lint, and targeted tests