feat: Fix grapheme splitting and add automatic UMAP calculation

Critical fixes for core functionality:

1. Fixed grapheme-aware text splitting (app/api/nodes/route.ts)
   - Changed character-based substring to grapheme-ratio calculation
   - Now properly handles emojis and multi-byte characters
   - Prevents posts from exceeding 300 grapheme Bluesky limit
   - Added comprehensive logging for debugging

2. Automatic UMAP coordinate calculation (app/api/nodes/route.ts)
   - Triggers /api/calculate-graph automatically after node creation
   - Only when user has 3+ nodes with embeddings (UMAP minimum)
   - Non-blocking background process
   - Eliminates need for manual "Calculate Graph" button
   - Galaxy visualization ready on first visit

3. Simplified galaxy route (app/api/galaxy/route.ts)
   - Removed auto-trigger logic (now handled on insertion)
   - Simply returns existing coordinates
   - More efficient, no redundant calculations

4. Added idempotency (app/api/calculate-graph/route.ts)
   - Safe to call multiple times
   - Returns early if all nodes already have coordinates
   - Better logging for debugging

Implementation plans documented in /plans directory.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

plans/fix-coords-computation.md

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+# Plan: Fix Coords Computation (Core Functionality)
+
+**Priority:** CRITICAL - This is core functionality of the app
+
+## Current Architecture (Broken)
+
+1. Nodes created with `coords_3d = NONE`
+2. User visits `/galaxy`
+3. Galaxy route checks if unmapped nodes exist
+4. If yes, triggers `/api/calculate-graph` in background
+5. Coordinates may not be ready on first visit
+6. UMAP runs every time someone visits with unmapped nodes
+
+### Problems
+
+- **Inefficient**: Multiple users trigger same calculation
+- **Poor UX**: Galaxy empty on first visit, needs refresh
+- **Wasteful**: UMAP recalculation triggered unnecessarily
+
+## Proposed Architecture (Correct)
+
+**Trigger UMAP automatically on node insertion**
+
+### Implementation
+
+```typescript
+// In POST /api/nodes, after creating node in SurrealDB:
+
+// 1. Check total node count for this user
+const countResult = await db.query(
+  'SELECT count() as total FROM node WHERE user_did = $did AND embedding != NONE',
+  { did: userDid }
+);
+const totalNodes = countResult[0]?.[0]?.total || 0;
+
+// 2. If we now have 3+ nodes, trigger coordinate calculation
+if (totalNodes >= 3) {
+  // Don't await - let it run in background
+  fetch(`${process.env.NEXT_PUBLIC_APP_URL}/api/calculate-graph`, {
+    method: 'POST',
+    headers: {
+      'Cookie': `ponderants-auth=${surrealJwt}`,
+    },
+  }).catch(err => {
+    console.error('[POST /api/nodes] Background coord calculation failed:', err);
+  });
+}
+```
+
+### Why 3 nodes minimum?
+
+- UMAP requires minimum 3 data points for meaningful projection
+- With <3 nodes, coords_3d stays NONE (galaxy shows "create more nodes" message)
+
+## Implementation Steps
+
+1. **Add node count check** after successful SurrealDB insert
+2. **Trigger `/api/calculate-graph`** in background when threshold reached
+3. **Remove auto-trigger logic** from `/api/galaxy` route
+4. **Update `/api/calculate-graph`** to be idempotent (safe to call multiple times)
+5. **Add rate limiting** to prevent spam calculations
+
+## Edge Cases to Handle
+
+### Concurrent inserts
+**Problem**: Two users create nodes simultaneously
+**Solution**: `/api/calculate-graph` checks count again before running UMAP
+
+### Calculation in progress
+**Problem**: Second node created while UMAP running
+**Solution**: Add a lock/flag in DB to prevent concurrent UMAP runs
+
+### Calculation failure
+**Problem**: Network error, UMAP crashes
+**Solution**: Retry logic with exponential backoff
+
+## Files to Modify
+
+- `app/api/nodes/route.ts` - Add trigger logic after node creation
+- `app/api/galaxy/route.ts` - Remove auto-trigger, keep simple fetch
+- `app/api/calculate-graph/route.ts` - Add idempotency check, locking mechanism
+
+## Testing Requirements
+
+1. Create 1st node → verify coords_3d = NONE
+2. Create 2nd node → verify coords_3d = NONE
+3. Create 3rd node → verify `/api/calculate-graph` triggered
+4. Wait for calculation → verify all 3 nodes have coords_3d != NONE
+5. Visit galaxy → verify all nodes visible immediately
+6. Create 4th node → verify UMAP recalculates all 4 nodes