examples[pdf]: limit context length (#270)

* feat(pdf-server): Interactive PDF viewer example

PDF viewer with PDF.js featuring:
- Chunked binary loading with progress bar
- Text extraction for AI context
- arXiv paper support (fetch by ID)
- Page navigation with keyboard shortcuts
- Zoom controls (including Ctrl+0 reset)
- Fullscreen mode support
- Horizontal swipe for page changes (disabled when zoomed)
- Page persistence in localStorage
- Text selection via PDF.js TextLayer
- Clickable title link to source URL
- Rounded corners and subtle border styling

* chore: Add pdf-server to screenshot generation list

* refactor(pdf-server): Simplify and generalize PDF loading

- Accept any HTTP(s) URLs instead of ArXiv-only
- Use HTTP Range requests for chunked binary loading
- Remove ArXiv-specific code (arxiv.ts, metadata fetching)
- Remove CLAUDE.md index generation
- Flatten hierarchical folder structure to simple entries list
- Remove dead code: getPdfSummary, httpFileSizes
- Simplify base64 encoding using Buffer
- Simplify chunk extraction using slice()
- Consolidate DEFAULT_PDF_URL constant

The server now works with any PDF URL, not just arXiv papers.
HTTP Range requests stream chunks on-demand when supported.

* feat(pdf-server): Include title and selection in model context

- Add pdfTitle to updateModelContext structuredContent
- Include selection position (text, start, end) when text is selected
- Add debounced selectionchange listener to update context on selection

* fix(pdf-server): Restore default URL in view_pdf schema

The UI needs the default value in the schema to show it properly.

* refactor(pdf-server): Further simplifications

- Remove hard-coded test paths from main()
- Remove unused resources: pdfs://metadata/{pdfId}, pdfs://content/{pdfId}
- Remove unused metadata fields: subject, creator, producer, creationDate, modDate
- Remove unused entry fields: relativePath, estimatedTextSize
- Remove filterEntriesByFolder and folder filter from list_pdfs
- Remove redundant output schema validation (trust typed returns)
- Simplify scanDirectory and createLocalEntry signatures

Total: 1836 → 1666 lines (-170 lines, -9%)

* refactor(pdf-server): Major simplification for didactic focus

Simplified the example to focus on key MCP Apps SDK patterns:
- Chunked data through size-limited tool calls
- Model context updates (page text + selection)
- Display modes (fullscreen vs inline)
- External links (openLink)

Changes:
- Remove local file support (HTTP URLs only)
- Restrict dynamic URLs to arxiv.org for security
- Simplify types: url instead of sourcePath/sourceType
- Simplify indexer: 168 → 44 lines
- Simplify loader: 318 → 171 lines
- Simplify server: 337 → 233 lines
- Fix selection text normalization
- Rewrite README with didactic focus

Total: 1836 → 1236 lines (-33%)

* feat(pdf-server): Add file:// URL support for local files

- Local paths are converted to file:// URLs on startup
- file:// URLs must be in the initial list (strict validation)
- Dynamic URLs still restricted to arxiv.org only
- Updated README with local file examples

* fix(pdf-server): Improve selection detection with logging

- Add logging to selectionchange handler to verify it fires
- Add fallback matching without spaces (TextLayer spans may lack spaces)
- Log selection detection success/failure for debugging

The issue: PDF.js TextLayer renders text as positioned spans without
space characters between them. When selecting across spans:
- pageText has spaces (items joined with ' ')
- sel.toString() may not have spaces
- indexOf fails to match

The fix tries exact match first, then falls back to spaceless matching.

* feat(pdf-server): Format model context as markdown with front matter

Model context now looks like:
```markdown
---
url: https://arxiv.org/pdf/...
page: 5/144
---

Page text with <pdf-selection>selected text</pdf-selection> inline.
```

This is cleaner for the model to parse and includes the source URL.

* refactor(pdf-server): Extract smart truncation helpers

Added two well-designed helpers:

formatPageContent(text, maxLength, selection?)
- Centers truncation window around selection if present
- Adds <truncated-content/> markers at elision points
- Wraps selection in <pdf-selection> tags
- Allocates 60% context before, 40% after for readability

findSelectionInText(pageText, selectedText)
- Tries exact match first
- Falls back to spaceless match for TextLayer quirks
- Returns { start, end } or undefined

Example output with selection:
```
<truncated-content/>
...context before... <pdf-selection>selected text</pdf-selection> ...context after...
<truncated-content/>
```

* fix(pdf-server): Truncate inside selection tags when selection too long

When selection is too large for the budget:
<truncated-content/><pdf-selection><truncated-content/>start...end<truncated-content/></pdf-selection><truncated-content/>

This keeps the selection structure intact while showing beginning and end.

* refactor(pdf-server): Remove unused read_pdf_text, use Attention paper as default

- Remove read_pdf_text tool (viewer extracts text client-side with pdfjs)
- Remove PdfTextChunk and ReadPdfTextInput types
- Remove loadPdfTextChunk from pdf-loader
- Change default PDF to 'Attention Is All You Need' (1706.03762)
- Update README with modest language

* refactor(pdf-server): Simplify to use URL as ID, rename view_pdf to display_pdf

Major simplifications:
- Use URL directly as identifier (no hashing)
- Remove displayName - show elided URL with full URL as tooltip
- Rename view_pdf to display_pdf with better description
- Update all references from pdfId to url
- Simplify storage key and model context

The tool description now explains it displays an interactive viewer in the chat.

* feat(pdf-server): Normalize arxiv URLs to PDF format

arxiv.org/abs/... -> arxiv.org/pdf/...

Applied both at startup and when loading dynamic URLs.

* docs(pdf-server): Add prompt engineering to display_pdf description

* fix(pdf-server): Sharp rendering on retina displays

Account for devicePixelRatio when rendering canvas:
- Scale canvas dimensions by dpr
- Scale context by dpr
- Keep CSS size at logical pixels

* fix(pdf-server): Normalize arxiv URLs in read_pdf_bytes too

* add to e2e spec

* add to e2e spec

* add to e2e spec

* add to e2e spec

* regen

* chore: regenerate package-lock.json and fix hono vulnerability

* docs: add pdf-server screenshot to READMEs

* regen

* ci: add missing examples to pkg-pr-new publish

* ci: add pdf-server to npm publish examples

* Update README.md

* pdf-server: improve tool response text for better model context

* revert unrelated screenshot changes

* pdf-server: dynamically add arxiv URLs in read_pdf_bytes

Fixes 'PDF not found' error when server restarts between display_pdf
(which adds the entry) and read_pdf_bytes (which previously only looked
up existing entries). Now read_pdf_bytes mirrors display_pdf's logic
and dynamically adds arxiv URLs to the index.

* cap length of context update in pdf-server

* format

Author: ochafik

examples/pdf-server/src/mcp-app.ts

@@ -13,6 +13,9 @@ import { TextLayer } from "pdfjs-dist";
 import "./global.css";
 import "./mcp-app.css";
 
+// const MAX_MODEL_CONTEXT_LENGTH = 5000;
+const MAX_MODEL_CONTEXT_LENGTH = 1500;
+
 // Configure PDF.js worker
 pdfjsLib.GlobalWorkerOptions.workerSrc = new URL(
   "pdfjs-dist/build/pdf.worker.mjs",
@@ -273,7 +276,11 @@ async function updatePageContext() {
     }
 
     // Format content with selection and truncation
-    const content = formatPageContent(pageText, 5000, selection);
+    const content = formatPageContent(
+      pageText,
+      MAX_MODEL_CONTEXT_LENGTH,
+      selection,
+    );
 
     const markdown = `---
 title: ${pdfTitle || ""}