W1: Land Thread C — "Create from…" (G16) and GitHub label/assignee pickers (G18) #45

Part of #44 · Lane W1 — ship work already written · Size S (review + verify + land)

What this is

G16 ("Create from…" / materialize) and G18 (GitHub metadata depth) are already implemented
on the branch feat/create-from-and-github-depth (f2320ee, worktree ~/Codez/il-ios-threadC) —
22 files, +2,704 / −45 — but the branch has no PR and is not in main. Until it lands,
two documented parity features are invisible to users, and the branch rots against main
(which has moved on: #41 server limits, #42 docs, #43 AI).

Landing this is the highest value-per-hour item in the whole parity effort.

What's on the branch

Tasks

• Rebase feat/create-from-and-github-depth onto current main (625a19b or later). Expect
  conflicts in project.pbxproj (both feat(ai): AI writing assistance across composer, lists and documents (G15) #43 and this branch add file references) and possibly
  in FeedView/DocumentsView toolbars where AI buttons landed.
• Full unit suite green on a pinned UDID with its own -derivedDataPath.
• Self-review against the repo gotchas before opening the PR:
  • Materialize sends id-only references — the server re-fetches and authorizes every id
    and ignores client-supplied cell values.
  • GitHub row writes still go through the full-row updateItem path
    (ListDetailView.setGitHubState). A partial PUT renames the issue to "Untitled".
  • POST /api/materialize is subscriber-gated — the entry points must be absent for
    free accounts, not disabled-with-a-pitch (Guideline 3.1.1).
  • Every new file is registered in project.pbxproj.
• Open the PR, get it reviewed, merge.
• Update work-consolidation.md: mark G15 ✅ (feat(ai): AI writing assistance across composer, lists and documents (G15) #43), G16/G18 ✅ (this PR), and fix the three
  errors listed in [Epic] Feature parity with interlinedlist.com — evaluation and tracking #44 §5.
• Delete the il-ios-threadC worktree once merged; verify by content, not by GitHub state
  (this repo has already lost PRs that showed MERGED but never reached main — see fix: restore PRs #31/#32 that never rolled up into main #35).

Acceptance criteria

• main contains the materialize sheet reachable from a message, a multi-message selection, a
  list, list rows, and a document; destination List / Document / Both with a live preview.
• GitHub-backed list rows offer label and assignee pickers sourced from
  /api/github/repos/{owner}/{repo}/{labels,assignees}.
• Suite green on main after merge; no unregistered files.

Contract: https://interlinedlist.com/help/api/create-from (source kinds, listConfig.fields +
sourceKey, docConfig).