refactor: migrate Xblock callers to standardized v1 REST endpoint (FC-0118)

[taimoor-ahmed-1]

⛔ Draft — depends on a backend PR (do not merge yet)

Item #1 (Xblock) of the FC-0118 Studio-API caller migration tracked in
#3127.

Blocked by / merge after: openedx/openedx-platform#38908 — the v1 XblockViewSet
validates writes with a strict serializer that 400s on unlisted fields, and the
real Studio create payload sends library_content_key (v2-library import). That
backend PR declares the field on the serializer. This PR must not merge until
#38908 is merged and deployed, or block creation/import will 400.

Independent of the Course Home (#3140) / Home Courses (#3139) drafts.

Description

Migrates Studio's xblock CRUD callers from the legacy /xblock/ Studio route to
the standardized /api/contentstore/v1/xblock/ REST endpoint (FC-0118,
ADR 0028/0037). The v1 XblockViewSet uses strict REST routing, so the verbs and
URLs change per operation:

Operation	Legacy	v1 REST
create / duplicate / paste	POST /xblock/	POST /api/contentstore/v1/xblock/ (unchanged verb)
retrieve	GET /xblock/{id}	GET …/xblock/{id}/
update (metadata / publish / children / grader / access …)	POST /xblock/{id}	PATCH …/xblock/{id}/
move	PATCH /xblock/ (collection)	PATCH …/xblock/{sourceId}/ (detail)
delete	DELETE /xblock/{id}	DELETE …/xblock/{id}/
custom-pages "add page"	PUT /xblock/	POST …/xblock/ (create)

Trailing slashes are required by the DRF DefaultRouter. For "move",
update_xblock_response still routes off move_source_locator in the body — the
URL key only scopes the permission check, so we PATCH the source block's detail URL.

Request-body changes (strict serializer)

The v1 serializer rejects unlisted top-level fields. Two fields the legacy route
ignored are dropped from request bodies:

• type on create — redundant with category (category: category || type), which
  the backend actually reads.
• courseKey on the editor save — not read by the update handler.

library_content_key (functional, library import) is kept and accepted by the
v1 serializer via #38908.

Left on the legacy route (NOT part of the v1 REST viewset)

These are handler/view sub-routes the v1 viewset does not serve, so they stay on
/xblock/…:

• /xblock/outline/{id} (course-outline getXBlockApiUrl, content-tags-drawer)
• /xblock/{id}/studio_view (editors blockStudioView)
• /xblock/{id}/handler/… (editors transcripts, PdfEditor handler)

The editors block() URL helper is kept for those sub-routes; a new blockV1()
helper serves the CRUD callers (fetchBlockById, saveBlock, blockAncestor).

Files

Source

• src/course-unit/data/api.ts — helpers → v1; editUnitDisplayName POST→PATCH; patchUnitItem (move) → PATCH source detail URL.
• src/course-outline/data/api.ts — helpers → v1 (split out the legacy /xblock/outline/ builder); update calls POST→PATCH; drop type from create.
• src/custom-pages/data/api.ts — delete/update → v1 detail; addCustomPage PUT→POST.
• src/course-updates/data/api.js — handouts helper → v1 detail (GET + PUT).
• src/editors/data/services/cms/{urls,api,utils}.ts — add blockV1() + patch() helper; fetchBlockById/saveBlock → blockV1; saveBlock POST→PATCH; drop courseKey from normalizeContent.

Tests — mocks/verbs/assertions updated to match (course-unit, course-outline, custom-pages, editors).

Testing

• npx jest src/course-unit → 210 pass
• npx jest src/course-outline → 524 pass (1 pre-existing PageAlerts flake, unrelated: deprecated toBeCalled matcher, fails on master too)
• npx jest src/custom-pages → pass (1 pre-existing date flake in UpdateForm, fails on master)
• npx jest src/editors/data/services/cms → 75 pass; PdfEditor → 4 pass
• dprint check + oxlint --deny-warnings on changed files → clean

Remaining failures in a full src/editors run are pre-existing (identical set on master: GalleryCard date, ImageUploadModal, SocialShareWidget, VideoEditorHandout) plus known parallel-run flakes.

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