V2 §2: Path identity — drop dot-joined strings

[CarlosNZ]

Closes #246. Part of the V2.0 roadmap, §2.

Summary

• Internal node identity is now CollectionKey[] everywhere instead of a dot-joined string.
• areChildrenBeingEdited, the drag-onto-self guard, and the editing-state comparisons all use array predicates (pathsEqual, isDescendantOf) — no more string .includes() / .startsWith() substring checks.
• toPathString survives as a public utility but its encoding changes to / + encodeURIComponent (injective by construction). The key?: 'key_' second arg is removed — mode is now a field on the editing-state object, not a string prefix.

Bugs fixed

This kills three related bugs that were all rooted in the same string-encoding shortcut. Paste this into the demo to see them on v2.0-dev (and watch them vanish here):

```json
{
"foo": { "name": "A" },
"foobar": { "name": "B" },
"with.dot": "I collide with 'with > dot'",
"with": { "dot": "I collide with 'with.dot'" }
}
```

1. Dotted-key collision. Editing the root `"with.dot"` value used to put both it and the nested `with > dot` value into edit mode simultaneously — they serialised to the same path string.
2. Substring match in `areChildrenBeingEdited`. Editing `foobar > name` would force the unrelated `foo` collection to open (because `"foobar.name".includes("foo")`).
3. Substring match in drag-onto-self guard. Dragging `foo` over `foobar` would hide the drop indicator (`"foobar".startsWith("foo")`).

Also fixes a related latent bug in `handleDrop` (useDragNDrop.tsx:122–123) where `sourceBase` was joined with `.` but `thisBase` was joined with `''` — so `KEY_EXISTS` fired spuriously on legitimate same-parent drags at depth ≥ 3.

Implementation shape

• Editing state is now `{ path: CollectionKey[]; mode: 'value' | 'key' } | null`, bundled so transitions are atomic (the §4 reducer work in V2 §4: TreeStateProvider refactor #247 can grow this into a discriminated union naturally).
• `previouslyEditedElement` stays path-only (tab nav only ever targets value-mode).
• `dragSource` drops the mirrored `pathString` field.
• New helpers in `src/helpers.ts`: `pathsEqual`, `isDescendantOf` (reflexive — a path is a trivial descendant of itself; both callers want that), `editingStatesEqual`.

Bundle size impact

Essentially a wash — adding new symbol names slightly reduces gzip efficiency:

	Raw	Gzipped
ESM	53,421 → 53,418 (−3 bytes)	18,054 → 18,072 (+18 bytes, +0.10%)
CJS	54,589 → 54,587 (−2 bytes)	18,104 → 18,115 (+11 bytes, +0.06%)

Test plan

• New unit tests in `test/pathHelpers.test.ts` cover `pathsEqual`, `isDescendantOf` (including reflexive case + substring-lookalike regression), and `toPathString` (encoding injectivity, slashes, percents, empties, unicode).
• `pnpm lint && pnpm compile && pnpm test` — all green (126 tests).
• `pnpm -r build` — core + themes + components all build cleanly.
• Demo verification: paste the JSON above, confirm all three bugs are gone.
• Tab navigation through the tree (exercises `previouslyEditedElement`).
• External `edit` trigger fires correctly on the matching path.

🤖 Generated with Claude Code

[github-actions]

Bundle size impact

json-edit-react

Format	Base raw	PR raw	Δ raw	Base gzip	PR gzip	Δ gzip
esm	52.17 KB	52.20 KB	🔺 +29 B (+0.05%)	17.69 KB	17.72 KB	🔺 +34 B (+0.19%)
cjs	53.31 KB	53.34 KB	🔺 +30 B (+0.05%)	17.74 KB	17.77 KB	🔺 +31 B (+0.17%)

_{Measured from build/index.{cjs,esm}.js. Gzip at level 9.}

[Copilot]

Pull request overview

Replaces dot-joined string path identity with CollectionKey[] arrays throughout the editing/drag/match flow, eliminating ambiguity and substring-matching bugs in areChildrenBeingEdited and drag guards. Editing state becomes a structured { path, mode } object instead of a key_-prefixed string. The exported toPathString survives but switches to a /-joined encodeURIComponent encoding (breaking change, documented in migration guide).

Changes:

• Introduce array path helpers (pathsEqual, isDescendantOf, editingStatesEqual) and the EditingState type; refactor TreeStateProvider, useCommon, useDragNDrop, useTriggers, CollectionNode, and ValueNodeWrapper to use them.
• Re-encode toPathString to /+encodeURIComponent, drop the 'key_' second arg, and update README/migration guide/changeset accordingly.
• Add test/pathHelpers.test.ts covering the new helpers and encoding semantics.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/types.ts	Adds EditingState interface.
src/helpers.ts	New array path helpers; rewrites toPathString encoding.
src/contexts/TreeStateProvider.tsx	Editing state stored as EditingState, drag source loses pathString, areChildrenBeingEdited uses isDescendantOf.
src/CollectionNode.tsx	Stops reading currentlyEditingElement; uses areChildrenBeingEdited(path).
src/hooks/useCommon.ts	Computes isEditing/isEditingKey via pathsEqual + mode.
src/hooks/useDragNDrop.tsx	Drag source becomes {path}; reflexive descendant guard; parent comparison via pathsEqual; fixes the join('.')/join('') mismatch in handleDrop.
src/hooks/useTriggers.ts	External edit-trigger path matching via pathsEqual.
src/ValueNodeWrapper.tsx	Stores path array (not string) into previouslyEditedElement.
test/pathHelpers.test.ts	New unit coverage for path helpers and encoding.
README.md / migration-guide.md / .changeset	Document the encoding change and removal of the 'key_' arg.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[CarlosNZ]

Good catch — the injectivity claim was overstated. Fixed in f25c49b:

• [''] now maps to '\0' via a single-case short-circuit before the join-based encoding runs. Safe because encodeURIComponent never emits a literal null char (it produces '%00' for the null byte).
• All other empty-key positions already disambiguate via separator structure, so they're unchanged: ['a', ''] → 'a/', ['', 'a'] → '/a', ['', ''] → '/', ['', '', ''] → '//', ['a', '', 'b'] → 'a//b'.
• Added explicit tests for each empty-key position plus a covering injectivity check over the edge-case paths (including ['\0'] to verify the sentinel doesn't collide with a literal null-byte key).

Docstring updated to document the sentinel rather than overstate the guarantee.

[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated no new comments.