fix(sdc-assemble): preserve regular items mixed with subQuestionnaire placeholders

[oliveregger]

Problem

$assemble assumed every child of a form group (item[0].item) is a sdc-questionnaire-subQuestionnaire placeholder. getItems() returns a compact list (one entry per subquestionnaire, in document order) while propagateProperties() indexes it by parent item position. Those only align when the group is all placeholders.

When a regular item is mixed in with placeholders, the child items are applied at the wrong positions — regular items are silently dropped and the placeholder is left in the output with its subQuestionnaire extension unresolved.

Reproduction

Form group mixing a regular question with a placeholder:

// item[0].item
[
  { "linkId": "manifestation", "type": "choice" },           // regular item (index 0)
  { "linkId": "begin-ref", "type": "display", "extension": [ // placeholder  (index 1)
      { "url": ".../sdc-questionnaire-subQuestionnaire",
        "valueCanonical": ".../ManifestationBegin|1.0.0" } ] }
]

child ManifestationBegin → [ beginUnknown (boolean), beginDate (date) ]

Expected	Actual (before fix)
manifestation, beginUnknown, beginDate	beginUnknown, beginDate, begin-ref (unresolved) — manifestation dropped

Fix

Add alignItemsWithParentForm() (utils/canonical.ts) that re-expands the compact per-subquestionnaire item list into an array aligned to the parent form's item positions — child items at each placeholder position, null for every regular item. assembleQuestionnaire() aligns the list before calling propagateProperties().

propagateProperties() is unchanged: its existing contract (positional array, null where the parent item is not a placeholder — as its own unit tests already encode) is exactly what it now receives. Also extracts the extension URL into a SUB_QUESTIONNAIRE_EXTENSION_URL constant and an itemIsSubQuestionnaire() predicate, reused by getCanonicalUrls().

Behaviour change

• Pure-modular forms (all placeholders): identical output — the aligned array equals the compact array index-for-index.
• Mixed forms: now correct — regular items keep their position, placeholders are replaced in place, no leftover unresolved placeholders.

Tests

• assemble.test.ts: end-to-end should preserve regular items mixed alongside a subquestionnaire placeholder — verified it fails on main (manifestation dropped) and passes with this change.
• canonical.test.ts: unit tests for alignItemsWithParentForm (regular-before-placeholder, interleaved, all-placeholder no-op, empty-form passthrough).
• Full suite: 128 passed (was 123). npm run build (tsup CJS/ESM/DTS) succeeds.

🤖 Generated with Claude Code