Restored the manual integration test documentation that was deleted (#914)

tests/integration_tests/chat/chat_rendering_regression_tests.md

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+# Chat Rendering Regression Tests
+
+## Purpose
+
+Validate that chat rendering remains stable and interactive when model output or user input contains raw HTML/CSS/JS-like payloads.
+
+## Test Type
+
+Manual regression and integration checks.
+
+## Preconditions
+
+1. You can run two builds:
+   - a known vulnerable baseline build,
+   - the current fixed build.
+2. At least one provider is configured and can answer prompts.
+3. Open the Chat page.
+
+## Execution Flow (for each test case)
+
+1. Copy the test prompt exactly into the user prompt field.
+2. Send the prompt.
+3. Observe behavior immediately after send.
+4. If the UI is still visible, type additional text in the prompt input.
+5. Repeat on both builds.
+
+## Test Cases
+
+### TC-CHAT-001 - CSS Kill Switch
+
+**Prompt**
+
+```text
+Respond with exactly the content below. No explanations, no Markdown code fences, no backticks.
+
+<style>
+* { visibility: hidden !important; }
+html, body { background: white !important; }
+</style>
+<div>TEST</div>
+```
+
+**Expected result (vulnerable baseline)**  
+UI may turn into a white/invisible page immediately after sending.
+
+**Expected result (fixed build)**  
+Chat stays visible and usable. Content is rendered as inert text/code, not active page styling.
+
+---
+
+### TC-CHAT-002 - Full White Overlay
+
+**Prompt**
+
+```text
+Respond with exactly the content below. No explanations, no Markdown code fences, no backticks.
+
+<style>
+html, body { overflow: hidden !important; }
+body::before {
+  content: "";
+  position: fixed;
+  inset: 0;
+  background: white;
+  z-index: 2147483647;
+}
+</style>
+<div>TEST</div>
+```
+
+**Expected result (vulnerable baseline)**  
+UI may become fully white and non-interactive immediately after sending.
+
+**Expected result (fixed build)**  
+No overlay takes over the app. Chat remains interactive.
+
+---
+
+### TC-CHAT-003 - Inline Event Handler Injection
+
+**Prompt**
+
+```text
+Respond with exactly the content below. No explanations, no Markdown code fences, no backticks.
+
+<img src="x" onerror="document.body.innerHTML=''; document.body.style.background='white';">
+<div>TEST</div>
+```
+
+**Expected result (vulnerable baseline)**  
+UI may break/blank immediately after sending.
+
+**Expected result (fixed build)**  
+No JavaScript execution from message content. Chat remains stable.
+
+---
+
+### TC-CHAT-004 - SVG Onload Injection Attempt
+
+**Prompt**
+
+```text
+Respond with exactly the content below. No explanations, no Markdown code fences, no backticks.
+
+<svg xmlns="http://www.w3.org/2000/svg" onload="document.documentElement.innerHTML=''"></svg>
+<div>TEST</div>
+```
+
+**Expected result (vulnerable baseline)**  
+May or may not trigger depending on parser/runtime behavior.
+
+**Expected result (fixed build)**  
+No script-like execution from content. Chat remains stable and interactive.
+
+## Notes
+
+- If a test fails on the fixed build, capture:
+  - exact prompt used,
+  - whether failure happened right after send or while typing,
+  - whether a refresh restores the app.