Summary

• When a client sends Accept: text/markdown, the exception handler returns the same rich markdown payload used by the error page's copy button (text/markdown; charset=UTF-8)
• Precedence follows the existing pattern: JSON → Markdown → HTML, using a new shouldReturnMarkdown() / shouldRenderMarkdownWhen() API that mirrors the JSON equivalent
• Debug-off and custom ExceptionRenderer scenarios fall back to a minimal # Server Error document to avoid leaking internals

Changes

• Renderer: Extracted resolveException() and added renderMarkdown() so HTML and markdown responses share one code path
• Handler: Added shouldReturnMarkdown, shouldRenderMarkdownWhen, prepareMarkdownResponse, renderExceptionAsMarkdown; updated renderExceptionResponse to branch markdown after JSON
• RendererTest: 7 new integration tests covering happy path, charset parameter, all precedence combos, debug-off, and custom renderer fallback

Test plan

• Happy path: Accept: text/markdown returns 500 with markdown content type and rich stack trace
• Charset parameter: text/markdown; charset=utf-8 works identically
• JSON > markdown: Accept: application/json, text/markdown returns JSON
• Markdown > JSON: Accept: text/markdown, application/json returns markdown
• HTML > markdown: Accept: text/html, text/markdown returns HTML
• Debug off: no stack trace or message leakage, returns generic "Server Error"
• Custom ExceptionRenderer: falls back to minimal markdown