fix: accept all valid tldraw fractional indices (b1, c10, etc.)

The index validation was incorrectly rejecting valid tldraw fractional
indices like "b1", "c10", etc. tldraw's fractional indexing uses:
- First letter (a-z) indicates integer part length (a=1 digit, b=2 digits)
- Followed by alphanumeric characters for value and jitter

This was causing ValidationError on production for Embed shapes with
index "b1". Fixed regex in all validation functions to accept any
lowercase letter prefix, not just 'a'.

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

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

src/automerge/AutomergeToTLStore.ts

@@ -11,39 +11,23 @@ function isValidIndexKey(index: string): boolean {
     return false
   }
 
-  // The first character indicates the integer part length:
+  // tldraw uses fractional indexing where:
-  // 'a' = 1 digit, 'b' = 2 digits, etc. for positive integers
+  // - First character is a lowercase letter indicating integer part length (a=1, b=2, c=3, etc.)
-  // 'Z' = 1 digit, 'Y' = 2 digits, etc. for negative integers
+  // - Followed by alphanumeric characters for the value and optional jitter
-  // But for normal shapes, 'a' followed by a digit is the most common pattern
+  // Examples: "a0", "a1", "b10", "b99", "c100", "a1V4rr", "b10Lz"
+  //
+  // Also uppercase letters for negative indices (Z=1, Y=2, etc.)
 
-  // Simple invalid patterns that are definitely wrong:
+  // Valid fractional index: lowercase letter followed by alphanumeric characters
-  // - Just a number like "1", "2"
+  if (/^[a-z][a-zA-Z0-9]+$/.test(index)) {
-  // - Old format like "b1", "c1" (letter + single digit that's not a valid fractional index)
-  // - Empty or whitespace
-
-  // Valid fractional indices from tldraw start with 'a' for small positive numbers
-  // and follow with digits + optional alphanumeric jitter
-  // Pattern: starts with 'a', followed by at least one digit, then optional alphanumeric chars
-
-  // Simple patterns that are DEFINITELY invalid for tldraw:
-  // "b1", "c1", "d1" etc - these are old non-fractional indices
-  if (/^[b-z]\d$/i.test(index)) {
-    return false
-  }
-
-  // Valid tldraw indices should start with lowercase 'a' followed by digits
-  // and optionally more alphanumeric characters for the fractional part
-  // Examples from actual tldraw: "a0", "a1", "a24sT", "a1V4rr"
-  if (/^a\d/.test(index)) {
     return true
   }
 
-  // Also allow 'Z' prefix for very high indices (though rare)
+  // Also allow uppercase prefix for negative/very high indices
-  if (/^Z[a-z]/i.test(index)) {
+  if (/^[A-Z][a-zA-Z0-9]+$/.test(index)) {
     return true
   }
 
-  // If none of the above, it's likely invalid
   return false
 }
 

src/automerge/MinimalSanitization.ts

@@ -23,13 +23,15 @@ function minimalSanitizeRecord(record: any): any {
     // NOTE: Index assignment is handled by assignSequentialIndices() during format conversion
     // Here we only ensure index exists with a valid format, not strictly validate
     // This preserves layer order that was established during conversion
-    // Valid formats: a1, a2, a10, a1V, a1Lz, etc. (fractional indexing)
+    // tldraw uses fractional indexing: a0, a1, b10, c100, a1V4rr, etc.
+    // - First letter (a-z) indicates integer part length (a=1 digit, b=2 digits, etc.)
+    // - Uppercase (A-Z) for negative/special indices
     if (!sanitized.index || typeof sanitized.index !== 'string' || sanitized.index.length === 0) {
       // Only assign default if truly missing
       sanitized.index = 'a1'
-    } else if (!/^a\d/.test(sanitized.index) && !/^Z[a-z]/i.test(sanitized.index)) {
+    } else if (!/^[a-zA-Z][a-zA-Z0-9]+$/.test(sanitized.index)) {
-      // Accept any index starting with 'a' + digit, or 'Z' prefix
+      // Accept any letter followed by alphanumeric characters
-      // Only reset clearly invalid formats
+      // Only reset clearly invalid formats (e.g., numbers, empty, single char)
       console.warn(`⚠️ MinimalSanitization: Invalid index format "${sanitized.index}" for shape ${sanitized.id}`)
       sanitized.index = 'a1'
     }

src/automerge/useAutomergeSyncRepo.ts

@@ -20,31 +20,23 @@ import { getDocumentId, saveDocumentId } from "./documentIdMapping"
 function isValidTldrawIndex(index: string): boolean {
   if (!index || typeof index !== 'string' || index.length === 0) return false
 
-  // The first character indicates the integer part length:
+  // tldraw uses fractional indexing where:
-  // 'a' = 1 digit, 'b' = 2 digits, etc. for positive integers
+  // - First character is a lowercase letter indicating integer part length (a=1, b=2, c=3, etc.)
-  // 'Z' = 1 digit, 'Y' = 2 digits, etc. for negative integers
+  // - Followed by alphanumeric characters for the value and optional jitter
-  // But for normal shapes, 'a' followed by a digit is the most common pattern
+  // Examples: "a0", "a1", "b10", "b99", "c100", "a1V4rr", "b10Lz"
+  //
+  // Also uppercase letters for negative indices (Z=1, Y=2, etc.)
 
-  // Simple patterns that are DEFINITELY invalid for tldraw:
+  // Valid fractional index: lowercase letter followed by alphanumeric characters
-  // "b1", "c1", "d1" etc - these are old non-fractional indices (single letter + single digit)
+  if (/^[a-z][a-zA-Z0-9]+$/.test(index)) {
-  // These were used before tldraw switched to fractional indexing
-  if (/^[b-z]\d$/i.test(index)) {
-    return false
-  }
-
-  // Valid tldraw indices should start with lowercase 'a' followed by digits
-  // and optionally more alphanumeric characters for the fractional/jitter part
-  // Examples from actual tldraw: "a0", "a1", "a24sT", "a1V4rr"
-  if (/^a\d/.test(index)) {
     return true
   }
 
-  // Also allow 'Z' prefix for very high indices (though rare)
+  // Also allow uppercase prefix for negative/very high indices
-  if (/^Z[a-z]/i.test(index)) {
+  if (/^[A-Z][a-zA-Z0-9]+$/.test(index)) {
     return true
   }
 
-  // If none of the above, it's likely invalid
   return false
 }
 

src/routes/Board.tsx

@@ -68,20 +68,18 @@ import "@/css/style.css"
 import "@/css/obsidian-browser.css"
 
 // Helper to validate and fix tldraw IndexKey format
-// Valid: "a0", "a1", "a24sT", "a1V4rr" - Invalid: "b1", "c1" (old format)
+// tldraw uses fractional indexing: a0, a1, b10, c100, a1V4rr, etc.
+// - First letter (a-z) indicates integer part length (a=1 digit, b=2 digits, etc.)
+// - Uppercase (A-Z) for negative/special indices
 function sanitizeIndex(index: any): IndexKey {
   if (!index || typeof index !== 'string' || index.length === 0) {
     return 'a1' as IndexKey
   }
-  // Old format "b1", "c1" etc are invalid (single letter + single digit)
+  // Valid: letter followed by alphanumeric characters
-  if (/^[b-z]\d$/i.test(index)) {
+  if (/^[a-zA-Z][a-zA-Z0-9]+$/.test(index)) {
-    return 'a1' as IndexKey
-  }
-  // Valid: starts with 'a' followed by at least one digit
-  if (/^a\d/.test(index)) {
     return index as IndexKey
   }
-  // Fallback
+  // Fallback for invalid formats
   return 'a1' as IndexKey
 }
 

worker/AutomergeDurableObject.ts

@@ -747,11 +747,12 @@ export class AutomergeDurableObject {
     shapesNeedingIndex.sort((a, b) => a.originalIndex - b.originalIndex)
 
     // Check if shapes already have valid indices we should preserve
-    // Valid index: starts with 'a' followed by digits, optionally followed by alphanumeric jitter
+    // Valid tldraw fractional index: starts with a lowercase letter followed by alphanumeric characters
+    // Examples: a1, a2, b1, c10, a1V, a1Lz, etc. (the letter increments as indices grow)
     const isValidIndex = (idx: any): boolean => {
       if (!idx || typeof idx !== 'string' || idx.length === 0) return false
-      // Valid fractional index format: a1, a2, a1V, a10, a1Lz, etc.
+      // Valid fractional index format: lowercase letter followed by alphanumeric (a1, b1, c10, a1V, etc.)
-      if (/^a\d/.test(idx)) return true
+      if (/^[a-z][a-zA-Z0-9]+$/.test(idx)) return true
       // Also allow 'Z' prefix for very high indices
       if (/^Z[a-z]/i.test(idx)) return true
       return false