fix: chunk large note reads to prevent output-too-large errors (fixes #5)

Add offset and max_chars parameters to obsidian_read_note:
- max_chars (default 50000, max 500000): caps characters returned per call
- offset (default 0): start position for reading, enabling pagination

When content is truncated a trailer message is appended telling the
caller the total size and the exact offset to pass on the next call.

This prevents the 26MB+ responses that caused Claude to reject output
when reading large PDFs stored in an Obsidian vault.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/tools/file-operations.ts

@@ -130,7 +130,7 @@ export async function registerFileOperationTools(server: ObsidianMCPServer): Pro
   // T031: Read note tool
   server.registerTool(
     'obsidian_read_note',
-    'Read the content of a note from the Obsidian vault. Specify either the note name (file) or full path (path).',
+    'Read the content of a note from the Obsidian vault. Specify either the note name (file) or full path (path). For large files (e.g. PDFs), use max_chars and offset to read in chunks and avoid exceeding context limits.',
     {
       type: 'object',
       properties: {
@@ -142,6 +142,14 @@ export async function registerFileOperationTools(server: ObsidianMCPServer): Pro
           type: 'string',
           description: 'Exact file path (folder/note.md)',
         },
+        max_chars: {
+          type: 'number',
+          description: 'Maximum characters to return (default: 50000, max: 500000). Use to avoid output-too-large errors on big files.',
+        },
+        offset: {
+          type: 'number',
+          description: 'Character offset to start reading from (default: 0). Use with max_chars to page through large files.',
+        },
       },
     },
     createToolHandler(
@@ -157,6 +165,14 @@ export async function registerFileOperationTools(server: ObsidianMCPServer): Pro
             type: 'string',
             description: 'Exact file path (folder/note.md)',
           },
+          max_chars: {
+            type: 'number',
+            description: 'Maximum characters to return (default: 50000, max: 500000)',
+          },
+          offset: {
+            type: 'number',
+            description: 'Character offset to start reading from (default: 0)',
+          },
         },
       },
       async (args) => {
@@ -170,11 +186,24 @@ export async function registerFileOperationTools(server: ObsidianMCPServer): Pro
         const result = await executeObsidianCommand('read', cmdArgs);
         handleCLIResult(result, { operation: 'read_note', identifier: sanitized.file || sanitized.path });
 
+        const offset: number = validated.offset ?? 0;
+        const maxChars: number = validated.max_chars ?? 50000;
+        const fullContent = result.stdout;
+        const totalChars = fullContent.length;
+        const chunk = fullContent.slice(offset, offset + maxChars);
+        const isTruncated = offset + maxChars < totalChars;
+
+        let text = chunk;
+        if (isTruncated) {
+          const nextOffset = offset + maxChars;
+          text += `\n\n[Content truncated: showing characters ${offset}–${offset + chunk.length} of ${totalChars} total. To read the next chunk, call obsidian_read_note again with offset=${nextOffset}.]`;
+        }
+
         return {
           content: [
             {
               type: 'text',
-              text: formatForMCP(result.stdout, 'text'),
+              text,
             },
           ],
         };

src/validation/schemas.ts

@@ -104,11 +104,13 @@ export const createNoteSchema = z.object({
 });
 
 // Read note parameters
-export const readNoteSchema = z.union([
-  z.object({ file: noteNameSchema }),
-  z.object({ path: filePathSchema }),
-]).refine(
-  (data) => ('file' in data && data.file) || ('path' in data && data.path),
+export const readNoteSchema = z.object({
+  file: noteNameSchema.optional(),
+  path: filePathSchema.optional(),
+  offset: z.number().int().nonnegative().optional().default(0),
+  max_chars: z.number().int().positive().max(500000).optional().default(50000),
+}).refine(
+  (data) => data.file || data.path,
   { message: 'Either file or path must be provided' }
 );