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+# Phase 4: Tags & Organization - Research
+
+**Researched:** 2026-01-31
+**Domain:** Tag management, many-to-many relationships, autocomplete UI
+**Confidence:** HIGH
+
+## Summary
+
+This phase adds tagging capabilities and organizational features (pinning, due dates) to entries. The core challenge is implementing a proper many-to-many relationship between entries and tags using Drizzle ORM with SQLite, while providing a user-friendly tag input with autocomplete.
+
+The schema already has `pinned` (boolean) and `dueDate` (text) columns on the entries table, so ORG-01 and ORG-02 only require UI work. The tag system requires a new `tags` table and `entry_tags` junction table with case-insensitive tag storage.
+
+**Primary recommendation:** Use a normalized three-table schema (entries, tags, entry_tags) with case-insensitive unique index on tag names, and use Svelecte v5 for the tag input component with autocomplete and tag creation.
+
+## Standard Stack
+
+The established libraries/tools for this domain:
+
+### Core
+| Library | Version | Purpose | Why Standard |
+|---------|---------|---------|--------------|
+| drizzle-orm | 0.45.1 | Database ORM | Already in project, handles relations via Query API v1 |
+| svelecte | 5.x | Tag input with autocomplete | Svelte 5 native, supports multi-select, tag creation, filtering |
+
+### Supporting
+| Library | Version | Purpose | When to Use |
+|---------|---------|---------|-------------|
+| nanoid | 5.x | ID generation | Already in project, use for tag IDs |
+| HTML5 date input | native | Due date picker | Native browser support, no extra dependency |
+
+### Alternatives Considered
+| Instead of | Could Use | Tradeoff |
+|------------|-----------|----------|
+| Svelecte | svelte-tags-input | Less certain Svelte 5 compatibility; Svelecte explicitly supports Svelte 5 |
+| Svelecte | Custom component | More control but significant effort for autocomplete, filtering, keyboard nav |
+| Normalized tags table | JSON array on entry | Harder to search, no tag reuse, no autocomplete across entries |
+
+**Installation:**
+```bash
+npm install svelecte
+```
+
+## Architecture Patterns
+
+### Recommended Database Schema
+```
+entries (existing)
+├── id (PK)
+├── pinned (already exists)
+├── dueDate (already exists)
+└── ...
+
+tags (new)
+├── id (PK, nanoid)
+├── name (unique case-insensitive)
+└── createdAt
+
+entry_tags (junction table, new)
+├── entryId (FK -> entries.id, cascade delete)
+├── tagId (FK -> tags.id, cascade delete)
+└── (composite PK on entryId + tagId)
+```
+
+### Pattern 1: Case-Insensitive Tag Storage
+**What:** Store tags with a unique index on lowercased name
+**When to use:** All tag operations to ensure "Work" and "work" are the same tag
+**Example:**
+```typescript
+// Source: https://orm.drizzle.team/docs/guides/unique-case-insensitive-email
+import { sql, SQL } from 'drizzle-orm';
+import { sqliteTable, text, uniqueIndex } from 'drizzle-orm/sqlite-core';
+
+export function lower(column: AnySQLiteColumn): SQL {
+  return sql`lower(${column})`;
+}
+
+export const tags = sqliteTable('tags', {
+  id: text('id').primaryKey(),
+  name: text('name').notNull(),
+  createdAt: text('created_at').notNull().$defaultFn(() => new Date().toISOString()),
+}, (table) => [
+  uniqueIndex('tagNameUniqueIndex').on(lower(table.name)),
+]);
+```
+
+### Pattern 2: Junction Table with Composite Primary Key
+**What:** Link entries to tags through a many-to-many junction table
+**When to use:** All entry-tag associations
+**Example:**
+```typescript
+// Source: https://orm.drizzle.team/docs/relations
+import { sqliteTable, text, primaryKey } from 'drizzle-orm/sqlite-core';
+
+export const entryTags = sqliteTable('entry_tags', {
+  entryId: text('entry_id').notNull().references(() => entries.id, { onDelete: 'cascade' }),
+  tagId: text('tag_id').notNull().references(() => tags.id, { onDelete: 'cascade' }),
+}, (t) => [
+  primaryKey({ columns: [t.entryId, t.tagId] }),
+]);
+```
+
+### Pattern 3: Drizzle Relations v1 for Many-to-Many
+**What:** Define relations to enable relational queries with the `with` clause
+**When to use:** Fetching entries with their tags in a single query
+**Example:**
+```typescript
+// Source: https://orm.drizzle.team/docs/rqb
+import { relations } from 'drizzle-orm';
+
+export const entriesRelations = relations(entries, ({ many }) => ({
+  entryTags: many(entryTags),
+}));
+
+export const tagsRelations = relations(tags, ({ many }) => ({
+  entryTags: many(entryTags),
+}));
+
+export const entryTagsRelations = relations(entryTags, ({ one }) => ({
+  entry: one(entries, {
+    fields: [entryTags.entryId],
+    references: [entries.id],
+  }),
+  tag: one(tags, {
+    fields: [entryTags.tagId],
+    references: [tags.id],
+  }),
+}));
+```
+
+### Pattern 4: Querying Entries with Tags
+**What:** Use Drizzle's relational queries to fetch entries with nested tags
+**When to use:** Loading entry list with all associated tags
+**Example:**
+```typescript
+// Source: https://orm.drizzle.team/docs/rqb
+const entriesWithTags = await db.query.entries.findMany({
+  with: {
+    entryTags: {
+      with: {
+        tag: true,
+      },
+    },
+  },
+});
+
+// Transform to flat tag array if needed
+const result = entriesWithTags.map(entry => ({
+  ...entry,
+  tags: entry.entryTags.map(et => et.tag),
+}));
+```
+
+### Pattern 5: Svelecte for Tag Input
+**What:** Use Svelecte with creatable mode for tag input with autocomplete
+**When to use:** Tag input UI in entry edit form
+**Example:**
+```svelte
+<!-- Source: https://github.com/mskocik/svelecte -->
+<script lang="ts">
+  import Svelecte from 'svelecte';
+
+  interface Props {
+    availableTags: { id: string; name: string }[];
+    selectedTags: { id: string; name: string }[];
+    onchange: (tags: { id: string; name: string }[]) => void;
+  }
+
+  let { availableTags, selectedTags, onchange }: Props = $props();
+</script>
+
+<Svelecte
+  options={availableTags}
+  value={selectedTags}
+  multiple
+  creatable
+  valueField="id"
+  labelField="name"
+  placeholder="Add tags..."
+  on:change={(e) => onchange(e.detail)}
+/>
+```
+
+### Anti-Patterns to Avoid
+- **Storing tags as JSON array:** Prevents efficient querying, no autocomplete, can't find "all entries with tag X"
+- **Case-sensitive tag matching:** Leads to duplicate tags like "Work", "work", "WORK"
+- **Not using onDelete cascade:** Orphaned junction records when entry or tag deleted
+- **Fetching tags in separate query per entry:** N+1 query problem; use relational queries instead
+
+## Don't Hand-Roll
+
+Problems that look simple but have existing solutions:
+
+| Problem | Don't Build | Use Instead | Why |
+|---------|-------------|-------------|-----|
+| Tag autocomplete | Custom dropdown with keyboard nav | Svelecte | Keyboard navigation, accessibility, fuzzy search, virtual scrolling |
+| Multi-select tag input | Custom chip input | Svelecte with `multiple` | Tag removal UX, paste support, styling |
+| Date picker | Custom calendar component | HTML5 `<input type="date">` | Native browser support, mobile-friendly, accessible |
+| Case-insensitive unique | Runtime deduplication | SQLite unique index with `lower()` | Database-level enforcement, handles concurrent inserts |
+
+**Key insight:** Autocomplete dropdowns have many edge cases (keyboard navigation, accessibility, scroll behavior, mobile touch) that Svelecte handles out of the box.
+
+## Common Pitfalls
+
+### Pitfall 1: Case Sensitivity in Tag Matching
+**What goes wrong:** User creates "Work" tag, then types "work" and creates duplicate
+**Why it happens:** Default SQLite text comparison is case-sensitive
+**How to avoid:** Create unique index on `lower(name)`, normalize during insert/lookup
+**Warning signs:** Multiple tags that differ only in case appearing in autocomplete
+
+### Pitfall 2: N+1 Queries When Loading Tags
+**What goes wrong:** Fetching entry list, then making separate query for each entry's tags
+**Why it happens:** Not using Drizzle's relational queries with `with` clause
+**How to avoid:** Always use `db.query.entries.findMany({ with: { entryTags: { with: { tag: true }}}})`
+**Warning signs:** Page load slows linearly with entry count
+
+### Pitfall 3: Orphaned Tags
+**What goes wrong:** After removing tag from all entries, tag still appears in autocomplete
+**Why it happens:** Junction records deleted but tag record remains
+**How to avoid:** Either accept orphaned tags (they're useful for autocomplete) OR periodically clean up tags with no associations
+**Warning signs:** Autocomplete shows tags that aren't used anywhere
+
+### Pitfall 4: Race Condition Creating New Tags
+**What goes wrong:** Two users simultaneously create "urgent" tag, one fails with unique constraint error
+**Why it happens:** Check-then-insert pattern without proper handling
+**How to avoid:** Use "INSERT OR IGNORE" or try/catch with lookup on conflict
+**Warning signs:** Intermittent errors when creating new tags
+
+### Pitfall 5: Not Updating Tags Atomically
+**What goes wrong:** Entry has ["work", "urgent"], user saves ["work", "home"], "urgent" not removed
+**Why it happens:** Only inserting new tags, not removing old ones
+**How to avoid:** Replace pattern: delete all entry_tags for entry, then insert new set
+**Warning signs:** Tags accumulate on entries, can't remove tags
+
+## Code Examples
+
+Verified patterns from official sources:
+
+### Tag Repository Operations
+```typescript
+// Find or create tag by name (case-insensitive)
+async findOrCreate(name: string): Tag {
+  const normalizedName = name.trim();
+
+  // Try to find existing (case-insensitive)
+  const existing = db
+    .select()
+    .from(tags)
+    .where(sql`lower(${tags.name}) = lower(${normalizedName})`)
+    .get();
+
+  if (existing) return existing;
+
+  // Create new tag
+  const newTag = {
+    id: nanoid(),
+    name: normalizedName,
+    createdAt: new Date().toISOString(),
+  };
+  db.insert(tags).values(newTag).run();
+  return newTag;
+}
+
+// Get all tags for autocomplete
+getAll(): Tag[] {
+  return db.select().from(tags).orderBy(asc(tags.name)).all();
+}
+```
+
+### Updating Entry Tags
+```typescript
+// Replace all tags for an entry atomically
+async updateEntryTags(entryId: string, tagNames: string[]): void {
+  // Delete existing associations
+  db.delete(entryTags).where(eq(entryTags.entryId, entryId)).run();
+
+  // Find or create each tag and create associations
+  for (const name of tagNames) {
+    const tag = await this.findOrCreate(name);
+    db.insert(entryTags).values({ entryId, tagId: tag.id }).run();
+  }
+}
+```
+
+### Form Action for Tags
+```typescript
+// In +page.server.ts
+updateTags: async ({ request }) => {
+  const formData = await request.formData();
+  const id = formData.get('id')?.toString();
+  const tagsJson = formData.get('tags')?.toString() || '[]';
+
+  if (!id) return fail(400, { error: 'Entry ID required' });
+
+  const tagNames = JSON.parse(tagsJson) as string[];
+  await tagRepository.updateEntryTags(id, tagNames);
+
+  return { success: true };
+}
+```
+
+### Native Date Input for Due Date
+```svelte
+<!-- HTML5 native date picker - mobile-friendly -->
+<input
+  type="date"
+  bind:value={dueDate}
+  onchange={handleDueDateChange}
+  class="px-3 py-2 border rounded-lg"
+/>
+```
+
+## State of the Art
+
+| Old Approach | Current Approach | When Changed | Impact |
+|--------------|------------------|--------------|--------|
+| Drizzle Relations v1 | Relations v2 with `through` | 1.0.0-beta.1 | Simpler many-to-many queries (not available in 0.45.x) |
+| Manual joins for M:M | `with` clause in relational queries | 0.17.0+ | Single query, automatic aggregation |
+| Svelte stores for reactivity | Svelte 5 runes ($state, $props) | Svelte 5 | More explicit reactivity |
+
+**Note on Drizzle version:** Project uses Drizzle 0.45.1 which uses Relations v1 API. Relations v2 with `through` syntax requires 1.0.0-beta.1+. The patterns documented here use v1 API which is stable and well-supported.
+
+**Deprecated/outdated:**
+- Svelecte v4.x for Svelte 4 projects (use v5.x for Svelte 5)
+- svelte-tags-input may have Svelte 5 compatibility issues (not verified)
+
+## Open Questions
+
+Things that couldn't be fully resolved:
+
+1. **Orphaned tag cleanup strategy**
+   - What we know: When tag removed from all entries, tag record remains
+   - What's unclear: Should orphaned tags be kept (useful for autocomplete history) or cleaned up?
+   - Recommendation: Keep orphaned tags for now, they provide autocomplete suggestions. Add cleanup later if tag list grows too large.
+
+2. **Tag rename cascading**
+   - What we know: Tags have unique IDs, name stored in tags table
+   - What's unclear: If user renames a tag, should it propagate to all entries?
+   - Recommendation: Not in scope for this phase. Tags are simple strings; if users want to "rename", they add new tag and remove old one.
+
+## Sources
+
+### Primary (HIGH confidence)
+- [Drizzle ORM Relations](https://orm.drizzle.team/docs/relations) - Junction table pattern
+- [Drizzle Query API v1](https://orm.drizzle.team/docs/rqb) - Relational queries with `with` clause
+- [Drizzle Case-Insensitive Guide](https://orm.drizzle.team/docs/guides/unique-case-insensitive-email) - `lower()` helper function
+- [Drizzle SQLite Column Types](https://orm.drizzle.team/docs/column-types/sqlite) - Schema definition
+- [Svelecte GitHub](https://github.com/mskocik/svelecte) - Svelte 5 support confirmed (v5.x)
+
+### Secondary (MEDIUM confidence)
+- [SQLite COLLATE NOCASE](https://www.designcise.com/web/tutorial/how-to-do-case-insensitive-comparisons-in-sqlite) - Case-insensitive patterns
+- [Tagging System Database Design](https://www.geeksforgeeks.org/dbms/how-to-design-a-database-for-tagging-service/) - Normalized schema patterns
+
+### Tertiary (LOW confidence)
+- svelte-tags-input Svelte 5 compatibility status - Unclear from docs, Svelecte is safer choice
+
+## Metadata
+
+**Confidence breakdown:**
+- Standard stack: HIGH - Drizzle patterns verified via official docs, Svelecte explicitly supports Svelte 5
+- Architecture: HIGH - Many-to-many junction table is standard pattern, verified with Drizzle docs
+- Pitfalls: MEDIUM - Based on general database design principles and common issues with tagging systems
+
+**Research date:** 2026-01-31
+**Valid until:** 60 days (stable patterns, no fast-moving dependencies)