Add proof-backed parser byte reads and preserve retryable source failures

src/lib/canvas-runtime/import-json-array.ts

@@ -1,9 +1,10 @@
+import {readImportRange,type ImportByteReader} from './import-byte-reader.ts';
 import {createImportBudget,type ImportScheduling} from './import-budget.ts';
 import type {ImportSource,ImportLine} from './imports.ts';
 import {fault,validJson} from '../canvas-core/values.ts';
 /** Seekable JSON array reader. Cursors are byte offsets after '[' or a record comma.
  * Structure errors end the source; previously published records remain explicit. */
-export function createJsonArrayImportSource(options:{bytes:Blob;fingerprint:string;maxRecordBytes?:number;chunkBytes?:number}&ImportScheduling):ImportSource{
+export function createJsonArrayImportSource(options:{bytes:Blob;fingerprint:string;readBytes?:ImportByteReader;maxRecordBytes?:number;chunkBytes?:number}&ImportScheduling):ImportSource{
  const bytes=options.bytes,max=options.maxRecordBytes??256*1024,chunk=options.chunkBytes??16384;
  if(!(bytes instanceof Blob)||!options.fingerprint||!Number.isSafeInteger(max)||max<1||!Number.isSafeInteger(chunk)||chunk<1||chunk>max)throw fault('invalid_import_source');
  let cache={offset:-1,value:new Uint8Array()};const whitespace=(b:number)=>[9,10,13,32].includes(b);
@@ -12,7 +13,7 @@ export function createJsonArrayImportSource(options:{bytes:Blob;fingerprint:stri
   if(start>0&&start===bytes.size){if(signal.aborted)throw fault('import_aborted');return null;}
   if(bytes.size===0)throw fault('invalid_json_array');
   let cursor=start;const budget=createImportBudget(signal,options);
-  async function peek(){if(signal.aborted)throw fault('import_aborted');if(cursor>=bytes.size)return -1;if(cursor<cache.offset||cursor>=cache.offset+cache.value.length){cache={offset:cursor,value:new Uint8Array(await bytes.slice(cursor,cursor+chunk).arrayBuffer())};if(signal.aborted)throw fault('import_aborted');}return cache.value[cursor-cache.offset];}
+  async function peek(){if(signal.aborted)throw fault('import_aborted');if(cursor>=bytes.size)return -1;if(cursor<cache.offset||cursor>=cache.offset+cache.value.length){cache={offset:cursor,value:await readImportRange(bytes,options.readBytes,cursor,cursor+chunk,signal)};if(signal.aborted)throw fault('import_aborted');}return cache.value[cursor-cache.offset];}
   function advance(){cursor++;return budget.step();}
   async function spaces(){while(whitespace(await peek()))await advance();}
   const failure=(error:string):ImportLine=>({cursor:start,nextCursor:bytes.size,key:`byte:${start}`,error});