examples: add PDF viewer w/ chunked data loading, full-screen, model context updates, private tool (#267)

* 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.

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

@@ -0,0 +1,292 @@
+body {
+  overscroll-behavior-x: none;
+}
+
+.main {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+  width: 100%;
+  background: var(--bg100, #f5f5f5);
+  color: var(--text000, #1a1a1a);
+  overflow: hidden; /* Prevent scrollbars in inline mode - we request exact size */
+  border-radius: 0.75rem;
+  border: 1px solid var(--bg200, rgba(0, 0, 0, 0.08));
+}
+
+/* Loading State */
+.loading {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  flex: 1;
+  gap: 0.75rem;
+  padding: 2rem;
+}
+
+.spinner {
+  width: 24px;
+  height: 24px;
+  border: 2px solid var(--bg200, #e0e0e0);
+  border-top-color: var(--text100, #888);
+  border-radius: 50%;
+  animation: spin 0.8s linear infinite;
+}
+
+@keyframes spin {
+  to {
+    transform: rotate(360deg);
+  }
+}
+
+#loading-text {
+  font-size: 0.8rem;
+  color: var(--text100, #888);
+}
+
+/* Progress Bar */
+.progress-container {
+  width: 100%;
+  max-width: 200px;
+  height: 3px;
+  background: var(--bg200, #e0e0e0);
+  border-radius: 2px;
+  overflow: hidden;
+}
+
+.progress-bar {
+  height: 100%;
+  background: var(--text100, #888);
+  width: 0%;
+  transition: width 0.15s ease-out;
+}
+
+.progress-text {
+  font-size: 0.7rem;
+  color: var(--text200, #aaa);
+}
+
+/* Error State */
+.error {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  height: 100%;
+  gap: 1rem;
+  padding: 2rem;
+  text-align: center;
+}
+
+.error-icon {
+  font-size: 3rem;
+}
+
+#error-message {
+  color: var(--text200, #999);
+  max-width: 400px;
+}
+
+/* Viewer Container */
+.viewer {
+  display: flex;
+  flex-direction: column;
+  flex: 1;
+  overflow: visible;
+}
+
+/* Toolbar */
+.toolbar {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 0.5rem 1rem;
+  background: var(--bg000, #ffffff);
+  border-bottom: 1px solid var(--bg200, #e0e0e0);
+  flex-shrink: 0;
+  gap: 0.5rem;
+  height: 48px;
+  box-sizing: border-box;
+}
+
+.toolbar-left {
+  flex: 1;
+  min-width: 0;
+  overflow: hidden;
+}
+
+.pdf-title {
+  font-weight: 500;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  font-size: 0.9rem;
+  display: block;
+  max-width: 100%;
+}
+
+.toolbar-center {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  flex-shrink: 0;
+}
+
+.toolbar-right {
+  display: flex;
+  align-items: center;
+  gap: 0.25rem;
+  flex-shrink: 0;
+}
+
+/* Page Navigation */
+.page-nav {
+  display: flex;
+  align-items: center;
+  gap: 0.25rem;
+}
+
+.page-input {
+  width: 50px;
+  padding: 0.25rem 0.5rem;
+  border: 1px solid var(--bg200, #e0e0e0);
+  border-radius: 4px;
+  font-size: 0.85rem;
+  text-align: center;
+  background: var(--bg000, #ffffff);
+  color: var(--text000, #1a1a1a);
+}
+
+.page-input:focus {
+  outline: none;
+  border-color: var(--text100, #666);
+}
+
+.page-input::-webkit-outer-spin-button,
+.page-input::-webkit-inner-spin-button {
+  -webkit-appearance: none;
+  margin: 0;
+}
+.page-input[type="number"] {
+  -moz-appearance: textfield;
+}
+
+.total-pages {
+  font-size: 0.85rem;
+  color: var(--text100, #666);
+  white-space: nowrap;
+}
+
+.nav-btn,
+.zoom-btn,
+.fullscreen-btn {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 32px;
+  height: 32px;
+  border: 1px solid var(--bg200, #e0e0e0);
+  border-radius: 4px;
+  background: var(--bg000, #ffffff);
+  color: var(--text000, #1a1a1a);
+  cursor: pointer;
+  font-size: 1rem;
+  transition: all 0.15s ease;
+}
+
+.nav-btn:hover:not(:disabled),
+.zoom-btn:hover:not(:disabled),
+.fullscreen-btn:hover {
+  background: var(--bg100, #f5f5f5);
+  border-color: var(--bg300, #ccc);
+}
+
+.nav-btn:disabled,
+.zoom-btn:disabled {
+  opacity: 0.4;
+  cursor: not-allowed;
+}
+
+.zoom-level {
+  font-size: 0.8rem;
+  color: var(--text100, #666);
+  min-width: 50px;
+  text-align: center;
+}
+
+/* Single Page Canvas Container */
+.canvas-container {
+  flex: 1;
+  overflow: visible;
+  display: flex;
+  justify-content: center;
+  align-items: flex-start;
+  padding: 1rem;
+  background: var(--bg200, #e0e0e0);
+}
+
+.page-wrapper {
+  position: relative;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
+  background: white;
+}
+
+#pdf-canvas {
+  display: block;
+}
+
+/* Text Layer for Selection */
+.text-layer {
+  position: absolute;
+  left: 0;
+  top: 0;
+  right: 0;
+  bottom: 0;
+  overflow: hidden;
+  opacity: 0.2;
+  line-height: 1;
+  text-size-adjust: none;
+  forced-color-adjust: none;
+  transform-origin: 0 0;
+  z-index: 2;
+}
+
+.text-layer span,
+.text-layer br {
+  color: transparent;
+  position: absolute;
+  white-space: pre;
+  cursor: text;
+  transform-origin: 0% 0%;
+}
+
+.text-layer ::selection {
+  background: rgba(0, 0, 255, 0.3);
+}
+
+.text-layer > span {
+  pointer-events: all;
+}
+
+/* Fullscreen mode */
+.main.fullscreen {
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  z-index: 1000;
+  overflow: hidden; /* No scrolling on main - only canvas-container scrolls */
+  border-radius: 0;
+  border: none;
+}
+
+.main.fullscreen .viewer {
+  min-height: 0; /* Allow flex item to shrink below content size */
+}
+
+.main.fullscreen .canvas-container {
+  min-height: 0; /* Allow flex item to shrink below content size */
+  overflow: auto; /* Scroll within the document area only */
+}