feat(properties): underscore relationship keys + Has Many row (TS parity)

Context: completes the underscore-canonical relationship rework on the
frontend. The Rust index now reads _belongs_to/_related_to/_has_many and
exposes a first-class has_many field; the TS layer mirrors that.

Solution:
- vault-v2.types.ts: add `hasMany: string[]` to NoteEntryV2 (mirrors the
  Rust `has_many` field); doc the underscore frontmatter keys; mention
  has_many in RelationshipBacklinkV2.
- PropertiesView.svelte: FIXED_RELATIONSHIPS keys become the canonical
  underscore form (_belongs_to/_related_to/_has_many); rename the `has`
  row to `_has_many` labelled "Has Many". The bare label keeps the row
  human-readable; the property key matches the on-disk frontmatter key.
- backlinks.service.ts: doc comment lists the underscore keys + has_many.

Behavior: the Properties panel renders Belongs To / Related To / Has Many
rows keyed on the underscore frontmatter fields. Collection/portent
filters key on _belongs_to/_related_to/_has_many (verified: the query
expression parser accepts the leading underscore).

Files:
- src/lib/types/vault-v2.types.ts: hasMany field + docs (L125-131, L144).
- src/lib/features/properties/PropertiesView.svelte: FIXED_RELATIONSHIPS
  (L49-53).
- src/lib/features/backlinks/backlinks.service.ts: doc (L142-143).
- src/tests/.../portent-filters.test.ts: _belongs_to/_related_to filters
  + new _has_many.contains case (L71-100).
- src/tests/.../properties.logic.test.ts: formatRelationshipLabel
  has_many; drop relationship space-alias, add no-alias case (L577-595,
  L711-722).
- src/tests/.../properties.service.test.ts: upsert _belongs_to (L74-80).
- src/tests/.../vault-v2.types.test.ts: pin hasMany key (L111-131).
- six NoteEntryV2 fixtures: add `hasMany: []`.
- tasks/todo/relationship-aliases-has-many.md: Task 3 done.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: diegorv

src/lib/features/backlinks/backlinks.service.ts

@@ -140,7 +140,7 @@ export const fetchBacklinksV2 = dedupeInflight(fetchBacklinksV2Inner, (path: str
 /**
  * Fetches relationship backlinks for a file from the Rust `VaultIndex`.
  * These are notes that reference the target via frontmatter fields
- * (`belongs_to`, `related_to`, or custom wikilink-bearing fields).
+ * (`_belongs_to`, `_related_to`, `_has_many`, or custom wikilink-bearing fields).
  */
 async function fetchRelationshipBacklinksInner(path: string): Promise<void> {
 	try {

src/lib/features/properties/PropertiesView.svelte

@@ -47,9 +47,9 @@
 
 	const LIFECYCLE_KEYS = new Set(['_favorite', '_organized', '_archived']);
 	const FIXED_RELATIONSHIPS: { key: string; label: string }[] = [
-		{ key: 'belongs_to', label: 'Belongs To' },
-		{ key: 'related_to', label: 'Related To' },
-		{ key: 'has', label: 'Has' },
+		{ key: '_belongs_to', label: 'Belongs To' },
+		{ key: '_related_to', label: 'Related To' },
+		{ key: '_has_many', label: 'Has Many' },
 	];
 	const RELATIONSHIP_KEYS = new Set(FIXED_RELATIONSHIPS.map((r) => r.key));
 

src/lib/types/vault-v2.types.ts

@@ -122,10 +122,12 @@ export interface NoteEntryV2 {
 	archived: boolean;
 	/** Lifecycle flag: note is pinned as a favorite. */
 	favorite: boolean;
-	/** Hierarchical ownership targets from `belongs_to` frontmatter (wikilink targets). */
+	/** Hierarchical ownership targets from `_belongs_to` frontmatter (wikilink targets). */
 	belongsTo: string[];
-	/** Lateral relationship targets from `related_to` frontmatter (wikilink targets). */
+	/** Lateral relationship targets from `_related_to` frontmatter (wikilink targets). */
 	relatedTo: string[];
+	/** Inverse-ownership targets from `_has_many` frontmatter (wikilink targets). */
+	hasMany: string[];
 	/** Generic relationships: field name -> wikilink targets for fields containing `[[...]]`. */
 	relationships: Record<string, string[]>;
 }
@@ -141,7 +143,7 @@ export interface RelationshipBacklinkV2 {
 	sourcePath: string;
 	/** Title of the source note. */
 	sourceName: string;
-	/** Relationship type (e.g. "belongs_to", "related_to", or custom field name). */
+	/** Relationship type (e.g. "belongs_to", "related_to", "has_many", or custom field name). */
 	relationshipType: string;
 }
 

src/tests/fixtures/vault-entries.fixture.ts

@@ -35,6 +35,7 @@ export function entryV2(
 		favorite: false,
 		belongsTo: [],
 		relatedTo: [],
+		hasMany: [],
 		relationships: {},
 		...overrides,
 	};

src/tests/lib/core/filesystem/link-updater.service.test.ts

@@ -41,6 +41,7 @@ function entry(path: string, title?: string): NoteEntryV2 {
 		favorite: false,
 		belongsTo: [],
 		relatedTo: [],
+		hasMany: [],
 		relationships: {},
 	};
 }

src/tests/lib/features/backlinks/backlinks.logic.test.ts

@@ -195,6 +195,7 @@ describe('noteEntryV2ToBacklinkEntry', () => {
 			favorite: false,
 			belongsTo: [],
 			relatedTo: [],
+			hasMany: [],
 			relationships: {},
 			...overrides,
 		};

src/tests/lib/features/collection/portent-filters.test.ts

@@ -68,23 +68,33 @@ describe('Portent collection filters', () => {
 		expect(result.records.map((r) => r.path)).toEqual(['/a.md']);
 	});
 
-	it('filters by belongs_to contains', () => {
+	it('filters by _belongs_to contains', () => {
 		const index = makeIndex([
-			makeRecord('/a.md', { belongs_to: ['project', 'area'] }),
-			makeRecord('/b.md', { belongs_to: ['other'] }),
+			makeRecord('/a.md', { _belongs_to: ['project', 'area'] }),
+			makeRecord('/b.md', { _belongs_to: ['other'] }),
 			makeRecord('/c.md', {}),
 		]);
-		const def = baseDef("belongs_to.contains('project')");
+		const def = baseDef("_belongs_to.contains('project')");
 		const result = executeQuery(def, baseView(), index);
 		expect(result.records.map((r) => r.path)).toEqual(['/a.md']);
 	});
 
-	it('filters by related_to contains', () => {
+	it('filters by _related_to contains', () => {
 		const index = makeIndex([
-			makeRecord('/a.md', { related_to: ['maps'] }),
+			makeRecord('/a.md', { _related_to: ['maps'] }),
 			makeRecord('/b.md', {}),
 		]);
-		const def = baseDef("related_to.contains('maps')");
+		const def = baseDef("_related_to.contains('maps')");
+		const result = executeQuery(def, baseView(), index);
+		expect(result.records.map((r) => r.path)).toEqual(['/a.md']);
+	});
+
+	it('filters by _has_many contains', () => {
+		const index = makeIndex([
+			makeRecord('/a.md', { _has_many: ['task-a', 'task-b'] }),
+			makeRecord('/b.md', {}),
+		]);
+		const def = baseDef("_has_many.contains('task-a')");
 		const result = executeQuery(def, baseView(), index);
 		expect(result.records.map((r) => r.path)).toEqual(['/a.md']);
 	});

src/tests/lib/features/file-icons/icon-resolver.test.ts

@@ -39,6 +39,7 @@ const makeEntry = (overrides: Partial<NoteEntryV2>): NoteEntryV2 => ({
 	favorite: false,
 	belongsTo: [],
 	relatedTo: [],
+	hasMany: [],
 	relationships: {},
 	...overrides,
 });

src/tests/lib/features/properties/lifecycle-filter.logic.test.ts

@@ -26,6 +26,7 @@ function entry(path: string, archived: boolean): NoteEntryV2 {
 		favorite: false,
 		belongsTo: [],
 		relatedTo: [],
+		hasMany: [],
 		relationships: {},
 	};
 }

src/tests/lib/features/properties/properties.logic.test.ts

@@ -575,10 +575,21 @@ describe('frontmatter alias normalization', () => {
 	});
 
 	it('normalizes space-separated aliases', () => {
-		const content = '---\nis a: place\nbelongs to: geography\n---\n';
+		const content = '---\nis a: place\nsidebar label: Places\n---\n';
 		const props = parseFrontmatterProperties(content);
 		expect(props.find((p) => p.key === 'type')?.value).toBe('place');
-		expect(props.find((p) => p.key === 'belongs_to')?.value).toBe('geography');
+		expect(props.find((p) => p.key === '_sidebar_label')?.value).toBe('Places');
+	});
+
+	it('does not alias relationship keys', () => {
+		// Relationship fields are underscore-canonical and take no alias:
+		// the bare/space spellings stay verbatim.
+		const content = '---\nbelongs to: geography\nrelated_to: maps\n---\n';
+		const props = parseFrontmatterProperties(content);
+		expect(props.find((p) => p.key === 'belongs_to')).toBeUndefined();
+		expect(props.find((p) => p.key === '_belongs_to')).toBeUndefined();
+		expect(props.find((p) => p.key === 'belongs to')?.value).toBe('geography');
+		expect(props.find((p) => p.key === 'related_to')?.value).toBe('maps');
 	});
 
 	it('normalizes underscore-prefixed system keys', () => {
@@ -711,10 +722,11 @@ describe('computeRemoveRelationshipValue', () => {
 describe('formatRelationshipLabel', () => {
 	it('converts snake_case to Title Case', () => {
 		expect(formatRelationshipLabel('belongs_to')).toBe('Belongs To');
+		expect(formatRelationshipLabel('has_many')).toBe('Has Many');
 	});
 
 	it('handles single word', () => {
-		expect(formatRelationshipLabel('has')).toBe('Has');
+		expect(formatRelationshipLabel('mentor')).toBe('Mentor');
 	});
 
 	it('handles triple underscore segments', () => {