feat: extract page tree logic into testable utility (#113)

[zacharias-ona]

Closes #113

What

Extracts pure tree-manipulation logic from src/components/sidebar/page-tree.tsx (836 lines) into src/lib/page-tree.ts — a side-effect-free utility module with no React or Supabase dependencies.

How

New file: src/lib/page-tree.ts — 10 exported functions:

• buildTree — flat pages → nested TreeNode[] hierarchy
• getDescendantIds — collect all descendant IDs recursively
• findNode — locate a node by ID in the tree
• getNextSiblingPosition — next available position among siblings
• getSortedSiblings — siblings sorted by position
• computeSwapPositions — position swaps for move up/down
• computeNest — new parent_id and position for nesting under preceding sibling
• computeUnnest — parent_id, position, and sibling shifts for unnesting
• computeDrop — full update set for drag-and-drop (inside/before/after)
• TreeNode type export

Updated: src/components/sidebar/page-tree.tsx — imports and uses the extracted functions. All Supabase mutation calls remain in the component. Also improved the fetchPages effect to use an inline async function with cancellation cleanup (fixes a lint warning from react-hooks/set-state-in-effect).

New file: src/lib/page-tree.test.ts — 35 unit tests covering:

• Tree building: flat list → hierarchy, orphan handling, position sorting, empty input
• Descendant collection: recursive traversal, leaf nodes
• Node finding: root, nested, missing
• Position calculation: empty siblings, max+1, parent scoping
• Reorder: swap up/down, boundary cases, missing page
• Nest: under preceding sibling, after existing children, first sibling (impossible), missing page
• Unnest: to parent level with sibling shifts, root page (impossible), deep nesting
• Drop: self-drop, descendant prevention, inside/before/after, cross-parent moves

Testing

• pnpm lint ✅
• pnpm typecheck ✅
• pnpm test — 93 tests pass (35 new)
• pnpm test:e2e — 40 tests pass (including page-crud.spec.ts and sidebar-drag.spec.ts)

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Project	Deployment	Actions	Updated (UTC)
memo	Ready	Preview, Comment	Apr 16, 2026 10:20pm

[zacharias-ona]

✅ UI verification passed — design spec compliance confirmed.

This PR extracts pure logic functions from page-tree.tsx into src/lib/page-tree.ts without modifying any JSX, styling, or visual output. No color tokens, typography, spacing, component usage, accessibility attributes, or layout were changed. Visual screenshot verification was skipped as the rendered UI is identical.

[zacharias-ona]

✅ Post-merge verification passed.

E2E suite: 35/42 passed, 4 did not run (dependent on a failed test).

3 pre-existing failures (unrelated to this PR's page-tree changes):

• members.spec.ts — "owner can revoke a pending invite" (invite row doesn't disappear after revocation)
• search.spec.ts — "typing in search input shows matching results" (search results not rendering)
• search.spec.ts — "search with no matches shows empty state" (empty state not rendering)

These tests exercise member management and search — code paths not touched by this PR.

Ad-hoc smoke tests: All passed.

• ✅ Landing page — loads, has title
• ✅ /sign-in — renders email input
• ✅ /api/health — returns healthy status
• ✅ Authenticated login flow — redirects to workspace
• ✅ Workspace page — fully loaded
• ✅ Page navigation via sidebar — editor route loads with contenteditable element
• ✅ No console errors (unauthenticated or authenticated)