Thinking Path

• Hermes WebUI's markdown renderer should preserve code-block text exactly, especially for structured formats like YAML and diff output.
• Issue Bug: YAML rendering still flattened in v0.50.291 #1618 showed that YAML blocks were still visually flattened even though the CSS token whitespace rule existed.
• The root cause is earlier in the renderer pipeline: JSON/YAML tree-view and diff blocks render <pre> elements with classes, but the paragraph-protection stash only matched literal <pre>.
• Because <pre class="tree-raw-view"> and <pre class="diff-block"> were not stashed, paragraph wrapping converted their internal newlines into <br> before Prism/rendering could preserve them.
• This PR expands the existing stash regex to protect attributed <pre> blocks too, keeping the fix to the smallest affected renderer primitive.

Fixes #1618

What Changed

• Updated the rendered-pre stash in static/ui.js from <pre> to <pre[^>]*> so attributed code blocks are protected before paragraph wrapping.
• Added behavioral Node-backed regression tests that execute the real renderMd() implementation and assert YAML tree raw views and diff blocks keep newline characters inside <code>.
• Added before/after UI media showing the collapsed YAML block and the corrected multi-line rendering.

Why It Matters

YAML, diff, JSON, and similar code blocks are only useful if their structure survives rendering. Flattening YAML into one line changes the meaning and makes copied examples harder to read or use. Protecting attributed <pre> blocks fixes the current YAML bug and prevents the same paragraph wrapping path from mangling other classed code blocks.

Verification

/home/michael/.hermes/hermes-agent/venv/bin/python -m pytest tests/test_issue1618_yaml_rendering.py -q
/home/michael/.hermes/hermes-agent/venv/bin/python -m pytest tests/test_issue1618_yaml_rendering.py tests/test_renderer_comprehensive.py tests/test_issue1438_fence_anchoring.py tests/test_streaming_markdown.py -q
node --check static/ui.js
git diff --check
env -u HERMES_CONFIG_PATH /home/michael/.hermes/hermes-agent/venv/bin/python -m pytest tests/ -q

Result:

2 passed in 1.39s
128 passed in 1.88s
Full suite: 4247 passed, 2 skipped, 3 xpassed, 1 warning, 8 subtests passed in 406.14s (0:06:46)

Manual verification:

• Started isolated before/after WebUI instances.
• Before: YAML textContent was flattened and innerHTML contained <br> inside code.language-yaml.
• After: YAML textContent contains real newlines, innerHTML does not contain <br>, and the rendered block is multi-line with indentation preserved.
• Verified temporary local servers were killed after QA.

UI media:

Before — YAML block flattened into one line:

After — YAML line breaks and indentation preserved:

Risks / Follow-ups

• This intentionally broadens the existing pre-stash to all attributed <pre> blocks, which matches the behavior already used by the autolink stash and keeps code-block internals out of paragraph wrapping.
• The generated code-tree-wrap HTML can still be wrapped by an outer paragraph in the string output; this PR fixes the newline-loss bug without widening scope into renderer markup normalization.
• The full suite warning is existing pytest marker noise: PytestUnknownMarkWarning: Unknown pytest.mark.integration.

Model Used

AI assisted.

• Provider: openai-codex
• Model: gpt-5.5
• Notable tool use: terminal/git/gh, pytest, Node syntax checks, isolated browser QA, before/after screenshot capture