diff --git a/explorer/package.json b/explorer/package.json
index 0c6f913a..fbd0b202 100644
--- a/explorer/package.json
+++ b/explorer/package.json
@@ -8,10 +8,8 @@
     "build": "tsc -b && vite build",
     "lint": "eslint .",
     "preview": "vite preview",
-    "test": "node --import tsx --test tests/markdownContentViewer.test.ts tests/graphSceneState.display.test.ts tests/temporalLifecycle.test.ts",
     "test:graph-store": "node --test tests/graphStore.multi-edge.test.mjs",
     "test:graph-workspace": "node --import tsx --test tests/markdownContentViewer.test.ts tests/graphSceneState.display.test.ts tests/temporalLifecycle.test.ts",
-    "test:markdown-viewer": "node --import tsx --test tests/markdownContentViewer.test.ts",
     "test:plugin-registry": "node --import tsx --test tests/pluginRegistry.temporal.test.mjs"
   },
   "dependencies": {
diff --git a/explorer/src/workspaces/GraphWorkspace/MarkdownContentViewer.tsx b/explorer/src/workspaces/GraphWorkspace/MarkdownContentViewer.tsx
index 3ac5cd5a..6525c124 100644
--- a/explorer/src/workspaces/GraphWorkspace/MarkdownContentViewer.tsx
+++ b/explorer/src/workspaces/GraphWorkspace/MarkdownContentViewer.tsx
@@ -1,4 +1,4 @@
-import { useState, type CSSProperties } from "react";
+import { useState, useRef, useEffect, type CSSProperties } from "react";
 import ReactMarkdown from "react-markdown";
 import remarkGfm from "remark-gfm";
 import { Check, Copy, Code2, Eye, ExternalLink, Image as ImageIcon } from "lucide-react";
@@ -13,7 +13,9 @@ export interface MarkdownContentViewerProps {
 export function isSafeUrl(url?: string): boolean {
   if (!url) return false;
   const trimmed = url.trim();
-  if (trimmed.startsWith("#") || trimmed.startsWith("/")) return true;
+  if (trimmed.startsWith("//")) return false;
+  if (trimmed.startsWith("#")) return true;
+  if (trimmed.startsWith("/")) return true;
   try {
     const parsed = new URL(trimmed, "http://localhost");
     return ["http:", "https:", "mailto:"].includes(parsed.protocol);
@@ -29,6 +31,15 @@ export function MarkdownContentViewer({
 }: MarkdownContentViewerProps) {
   const [activeMode, setActiveMode] = useState<"preview" | "source">(defaultMode);
   const [copied, setCopied] = useState(false);
+  const copyTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  useEffect(() => {
+    return () => {
+      if (copyTimeoutRef.current) {
+        clearTimeout(copyTimeoutRef.current);
+      }
+    };
+  }, []);
 
   const rawContent = typeof content === "string" ? content : "";
   const hasContent = rawContent.trim().length > 0;
@@ -37,8 +48,11 @@ export function MarkdownContentViewer({
     if (!hasContent) return;
     try {
       await navigator.clipboard.writeText(rawContent);
+      if (copyTimeoutRef.current) {
+        clearTimeout(copyTimeoutRef.current);
+      }
       setCopied(true);
-      setTimeout(() => setCopied(false), 1500);
+      copyTimeoutRef.current = setTimeout(() => setCopied(false), 1500);
     } catch {
       // Clipboard write unavailable
     }
diff --git a/explorer/tests/markdownContentViewer.test.ts b/explorer/tests/markdownContentViewer.test.ts
index d0c608f1..5596d0ab 100644
--- a/explorer/tests/markdownContentViewer.test.ts
+++ b/explorer/tests/markdownContentViewer.test.ts
@@ -1,8 +1,13 @@
 import test from "node:test";
 import assert from "node:assert/strict";
-import { isSafeUrl } from "../src/workspaces/GraphWorkspace/MarkdownContentViewer.tsx";
+import React from "react";
+import { renderToString } from "react-dom/server";
 
-test("isSafeUrl permits safe http, https, and mailto URLs", () => {
+(globalThis as any).React = React;
+
+import { isSafeUrl, MarkdownContentViewer } from "../src/workspaces/GraphWorkspace/MarkdownContentViewer.tsx";
+
+test("isSafeUrl permits safe http, https, and mailto URLs and relative paths", () => {
   assert.equal(isSafeUrl("https://example.com"), true);
   assert.equal(isSafeUrl("http://localhost:8000"), true);
   assert.equal(isSafeUrl("mailto:user@example.com"), true);
@@ -10,7 +15,13 @@ test("isSafeUrl permits safe http, https, and mailto URLs", () => {
   assert.equal(isSafeUrl("/relative/path"), true);
 });
 
-test("isSafeUrl rejects dangerous schemes like javascript:, data:, and vbscript:", () => {
+test("isSafeUrl rejects protocol-relative URLs and dangerous schemes", () => {
+  // Protocol-relative URLs (must be blocked)
+  assert.equal(isSafeUrl("//evil.com"), false);
+  assert.equal(isSafeUrl("//localhost:8000"), false);
+  assert.equal(isSafeUrl("//"), false);
+
+  // Dangerous schemes
   assert.equal(isSafeUrl("javascript:alert('xss')"), false);
   assert.equal(isSafeUrl("JAVASCRIPT:alert(1)"), false);
   assert.equal(isSafeUrl("data:text/html;base64,PHNjcmlwdD4="), false);
@@ -19,52 +30,91 @@ test("isSafeUrl rejects dangerous schemes like javascript:, data:, and vbscript:
   assert.equal(isSafeUrl(undefined), false);
 });
 
-test("preserves exact unmodified content, whitespace, and Unicode in source format", () => {
-  const sampleMarkdown = `# Title with Unicode 🚀\n\n  * Indented item 1\n  * Indented item 2\n\n\`\`\`python\ndef test():\n    return "α + β = γ"\n\`\`\``;
-  
-  // Exact characters, newlines, and whitespace must remain unmodified
-  assert.equal(sampleMarkdown.includes("  * Indented item 1"), true);
-  assert.equal(sampleMarkdown.includes("🚀"), true);
-  assert.equal(sampleMarkdown.includes("α + β = γ"), true);
-  assert.equal(sampleMarkdown.includes("    return"), true);
+test("renders Preview mode with formatted Markdown elements and tabs", () => {
+  const markdown = `# Main Title\n\n**Bold Statement**\n\n* Item A\n* Item B`;
+  const html = renderToString(React.createElement(MarkdownContentViewer, { content: markdown, defaultMode: "preview" }));
+
+  // Tab buttons are present
+  assert.equal(html.includes("Preview"), true);
+  assert.equal(html.includes("Source"), true);
+  assert.equal(html.includes("Copy"), true);
+
+  // Formatted preview elements
+  assert.equal(html.includes("Main Title"), true);
+  assert.equal(html.includes("Bold Statement"), true);
+  assert.equal(html.includes("<strong>Bold Statement</strong>"), true);
+  assert.equal(html.includes("Item A"), true);
+  assert.equal(html.includes("Item B"), true);
 });
 
-test("handles empty, null, and whitespace content gracefully without errors", () => {
-  const emptyValues = ["", "   \n\t  ", null, undefined];
-  for (const val of emptyValues) {
-    const raw = typeof val === "string" ? val : "";
-    const hasContent = raw.trim().length > 0;
-    assert.equal(hasContent, false);
-  }
+test("renders Source mode with exact unmodified text inside pre/code", () => {
+  const markdown = `# Title 🚀\n\n  * Indented item\n\n\`\`\`python\ndef test():\n    return "α + β"\n\`\`\``;
+  const html = renderToString(React.createElement(MarkdownContentViewer, { content: markdown, defaultMode: "source" }));
+
+  assert.equal(html.includes("<pre"), true);
+  assert.equal(html.includes("<code"), true);
+  assert.equal(html.includes("# Title 🚀"), true);
+  assert.equal(html.includes("  * Indented item"), true);
+  assert.equal(html.includes('return &quot;α + β&quot;'), true);
 });
 
-test("handles plain text without requiring Markdown syntax", () => {
-  const plainText = "Simple plain text summary of graph entity without any formatting.";
-  const raw = typeof plainText === "string" ? plainText : "";
-  const hasContent = raw.trim().length > 0;
-  assert.equal(hasContent, true);
-  assert.equal(raw, plainText);
+test("renders raw HTML safely as escaped text without executing elements", () => {
+  const dangerousHtml = `<script>alert("XSS")</script><iframe src="https://evil.com"></iframe>`;
+  const html = renderToString(React.createElement(MarkdownContentViewer, { content: dangerousHtml, defaultMode: "preview" }));
+
+  // Script and iframe tags must NOT be rendered as active DOM tags
+  assert.equal(html.includes("<script>"), false);
+  assert.equal(html.includes("<iframe"), false);
+  // Content is escaped as text
+  assert.equal(html.includes("&lt;script&gt;"), true);
 });
 
-test("handles very long content without truncation or performance failure", () => {
-  const longParagraph = "Semantica knowledge graph node content with structured facts. ".repeat(500);
-  const longMarkdown = `# Big Document\n\n${longParagraph}\n\n## Section 2\n\n${longParagraph}`;
-  assert.equal(longMarkdown.length > 50000, true);
-  const raw = typeof longMarkdown === "string" ? longMarkdown : "";
-  assert.equal(raw.length, longMarkdown.length);
+test("renders safe links as <a> with target blank and unclickable span for unsafe links", () => {
+  const content = `[Safe Link](https://getsemantica.ai)\n\n[Unsafe Scheme](javascript:alert(1))\n\n[Protocol Relative](//evil.com)`;
+  const html = renderToString(React.createElement(MarkdownContentViewer, { content, defaultMode: "preview" }));
+
+  // Safe link renders as <a> with security attributes
+  assert.equal(html.includes('href="https://getsemantica.ai"'), true);
+  assert.equal(html.includes('target="_blank"'), true);
+  assert.equal(html.includes('rel="noopener noreferrer"'), true);
+
+  // Unsafe links do NOT render as <a> tags
+  assert.equal(html.includes('href="javascript:alert(1)"'), false);
+  assert.equal(html.includes('href="//evil.com"'), false);
+  assert.equal(html.includes("Unsafe Scheme"), true);
+  assert.equal(html.includes("Protocol Relative"), true);
 });
 
-test("handles raw HTML content safely as text", () => {
-  const dangerousHtml = `<script>alert("XSS")</script><img src="x" onerror="steal()"/><iframe src="evil.com"></iframe>`;
-  // In source mode, content is preserved literally without execution
-  assert.equal(dangerousHtml.includes("<script>"), true);
-  assert.equal(dangerousHtml.includes("onerror="), true);
+test("renders remote images as safe placeholder badges instead of <img> tags", () => {
+  const content = `![System Diagram](https://example.com/diagram.png)`;
+  const html = renderToString(React.createElement(MarkdownContentViewer, { content, defaultMode: "preview" }));
+
+  // No <img> tag rendered
+  assert.equal(html.includes("<img"), false);
+  // Image placeholder badge rendered
+  assert.equal(html.includes("Image:"), true);
+  assert.equal(html.includes("System Diagram"), true);
 });
 
-test("preserves fenced code blocks with language identifiers and indentation", () => {
-  const codeBlockMarkdown = "```typescript\nfunction processGraph(id: string): boolean {\n  return id.length > 0;\n}\n```";
-  assert.equal(codeBlockMarkdown.startsWith("```typescript"), true);
-  assert.equal(codeBlockMarkdown.includes("  return id.length > 0;"), true);
-  assert.equal(codeBlockMarkdown.endsWith("```"), true);
+test("renders clear empty-state message when content is empty or null", () => {
+  const emptyHtml = renderToString(React.createElement(MarkdownContentViewer, { content: "" }));
+  assert.equal(emptyHtml.includes("No content available for this node."), true);
+
+  const nullHtml = renderToString(React.createElement(MarkdownContentViewer, { content: null }));
+  assert.equal(nullHtml.includes("No content available for this node."), true);
 });
 
+test("renders plain text cleanly without requiring Markdown formatting", () => {
+  const plainText = "Plain entity summary text without markdown formatting.";
+  const html = renderToString(React.createElement(MarkdownContentViewer, { content: plainText, defaultMode: "preview" }));
+
+  assert.equal(html.includes(plainText), true);
+});
+
+test("handles very large Markdown content without failure", () => {
+  const largeContent = `# Large Knowledge Node\n\n` + "Structured observation paragraph. ".repeat(400);
+  assert.equal(largeContent.length > 10000, true);
+
+  const html = renderToString(React.createElement(MarkdownContentViewer, { content: largeContent, defaultMode: "preview" }));
+  assert.equal(html.includes("Large Knowledge Node"), true);
+});