[dasc] Keep form model JSON-only, HTML only at fetch and save boundaries

[kozmaadrian]

Summary

• The form model should not know about HTML, and it should not handle the save mechanism.
• The fetch layer does HTML → JSON and passes only JSON into the form.
• The model holds and mutates only JSON.
• Persistence is the caller’s responsibility: the caller takes the model’s JSON, converts to HTML, and POSTs.
• HTML appears only when fetching and when saving. Converting JSON to HTML on every field update is unnecessary; HTML is needed only for persisting.

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Current behavior

sequenceDiagram
  participant FB as Form block
  participant Load as loadHtml
  participant FM as FormModel
  participant Server

  FB->>Load: fetch doc
  Load-->>FB: html
  FB->>FM: new FormModel(html)
  Note over FM: HTML→JSON, store _html + _json
  FB->>FM: updateProperty(name, value)
  Note over FM: setValueByPath(_json) then updateHtml() → _html
  FB->>FM: saveHtml()
  FM->>Server: POST(_html)

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• FormModel holds both _html and _json, and owns the save mechanism (saveHtml(), building the request, POSTing).
• On every field edit, updateProperty() writes to _json then calls updateHtml() to reconvert _json → _html and keep them in sync—even though _html is only used when saving.
• Conversion and persistence both live inside the model; neither should be the model’s responsibility.

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Proposed change

sequenceDiagram
  participant FB as Form block
  participant Load as loadDocument
  participant FM as FormModel
  participant Server

  FB->>Load: fetch doc
  Note over Load: fetch HTML, HTML→JSON
  Load-->>FB: { json }
  FB->>FM: new FormModel(json)
  Note over FM: store _json only
  FB->>FM: updateProperty(name, value)
  Note over FM: setValueByPath(_json) only
  FB->>FM: formModel.json
  FM-->>FB: json
  Note over FB: JSON→HTML
  FB->>Server: POST(html)

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• FormModel accepts only { path, json, schemas }; single source of truth _json.
• The model does not handle save; the caller (form block or save helper) is responsible for persistence.
• HTML conversion happens only at fetch and at save, outside the model.

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Benefits

• Separation of concerns: format (HTML) at the edges, form logic on JSON only; persistence is the caller’s responsibility, not the model’s.
• Simpler model: one source of truth, no save logic; easier testing; clearer data flow (fetch → JSON → form → JSON → save).
• Easier for new developers to understand the code: model = data only; fetch/save own format and persistence.
• No JSON → HTML conversion on every field update; HTML is produced only when persisting.

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Implementation (minimal)

1. Fetch layer: Convert HTML → JSON and return { json }; form block uses that to construct the model.
2. Form model: Drop html input, _html, converters, updateHtml() / updateJson(), html getter/setter; keep only JSON and updateProperty() on _json.
3. Save: Move serialize-and-POST to form block or helper (caller owns persistence); remove saveHtml() from the model.
4. Call sites: Update form block and any code using formModel.html or clone-with-HTML to use JSON only.