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+# LaTeX Rendering Implementation Plan
+
+> **For Hermes:** Use subagent-driven-development skill to implement this plan task-by-task.
+
+**Goal:** Add reliable LaTeX/math rendering to Hermes Web UI chat Markdown messages so formulas render visually instead of appearing as raw TeX.
+
+**Architecture:** Keep the existing `markdown-it` renderer in `MarkdownRenderer.vue` and add a KaTeX-backed math plugin there. Load KaTeX styles globally once, cover inline and block math in component tests, then verify with a production build and a local Web UI smoke test.
+
+**Tech Stack:** Vue 3, TypeScript, Vite, markdown-it, KaTeX, Vitest, @vue/test-utils.
+
+---
+
+## Acceptance Criteria
+
+- Chat messages render inline math like `$x^2 + y^2 = z^2$` as KaTeX HTML.
+- Chat messages render block math like `$$\n\\int_0^1 x^2 dx = \\frac{1}{3}\n$$` as display KaTeX HTML.
+- Existing Markdown features still work: code fences, Mermaid fences, headings, local file links, mentions.
+- Math inside fenced code blocks stays literal and is not rendered.
+- Invalid/unsupported math syntax does not crash the chat renderer.
+- `npm run test -- tests/client/markdown-rendering.test.ts` passes.
+- `npm run build` passes.
+- Local `hermes-web-ui.service` can be restarted onto the built fork and displays formulas in the real panel.
+
+## Recommended Dependency Choice
+
+Use `markdown-it-katex` + `katex` because the app already uses `markdown-it`, and this is the smallest change surface.
+
+Install as runtime dependencies, not dev-only, because the renderer runs in the browser bundle:
+
+```bash
+npm install katex markdown-it-katex
+npm install -D @types/katex
+```
+
+If TypeScript reports no module declaration for `markdown-it-katex`, add a local declaration file instead of weakening `tsconfig`.
+
+---
+
+## Task 1: Add KaTeX dependencies
+
+**Objective:** Make the required renderer and styles available to the client bundle.
+
+**Files:**
+- Modify: `package.json`
+- Modify: `package-lock.json` or lockfile generated by npm if present
+
+**Step 1: Install packages**
+
+Run from repo root:
+
+```bash
+cd /home/werserk/2-kira/hermes-web-ui
+npm install katex markdown-it-katex
+npm install -D @types/katex
+```
+
+**Expected:** `package.json` includes `katex` and `markdown-it-katex`; lockfile is updated.
+
+**Step 2: Verify dependency tree**
+
+```bash
+npm ls katex markdown-it-katex
+```
+
+**Expected:** both packages resolve without `UNMET DEPENDENCY`.
+
+**Step 3: Commit**
+
+```bash
+git add package.json package-lock.json
+git commit -m "chore: add latex rendering dependencies"
+```
+
+---
+
+## Task 2: Add TypeScript module declaration if needed
+
+**Objective:** Keep TypeScript strict and avoid `any` leaking into the renderer setup.
+
+**Files:**
+- Create if needed: `packages/client/src/types/markdown-it-katex.d.ts`
+
+**Step 1: Run typecheck to discover whether declaration is needed**
+
+```bash
+npm run build
+```
+
+**Expected before implementation:** build may still fail later because code is not changed yet. For this task, only check whether TypeScript knows the `markdown-it-katex` module after it is imported in Task 3.
+
+**Step 2: If TS2307/TS7016 appears, create declaration**
+
+Create `packages/client/src/types/markdown-it-katex.d.ts`:
+
+```ts
+declare module 'markdown-it-katex' {
+  import type MarkdownIt from 'markdown-it'
+
+  interface MarkdownItKatexOptions {
+    throwOnError?: boolean
+    errorColor?: string
+    strict?: boolean | string | ((errorCode: string) => boolean | string)
+    output?: 'html' | 'mathml' | 'htmlAndMathml'
+    trust?: boolean | ((context: unknown) => boolean)
+    macros?: Record<string, string>
+  }
+
+  const markdownItKatex: MarkdownIt.PluginWithOptions<MarkdownItKatexOptions>
+  export default markdownItKatex
+}
+```
+
+**Step 3: Commit only if file was needed**
+
+```bash
+git add packages/client/src/types/markdown-it-katex.d.ts
+git commit -m "chore: add markdown-it-katex types"
+```
+
+---
+
+## Task 3: Wire KaTeX into MarkdownRenderer
+
+**Objective:** Render math in the same path that currently renders Markdown chat messages.
+
+**Files:**
+- Modify: `packages/client/src/components/hermes/chat/MarkdownRenderer.vue`
+
+**Step 1: Import the plugin**
+
+Near existing Markdown imports:
+
+```ts
+import markdownItKatex from 'markdown-it-katex'
+```
+
+**Step 2: Register the plugin after creating `md`**
+
+After the `new MarkdownItConstructor(...)` block and before custom fence renderer setup:
+
+```ts
+md.use(markdownItKatex, {
+  throwOnError: false,
+  errorColor: '#cc3344',
+  output: 'htmlAndMathml',
+})
+```
+
+**Step 3: Preserve existing Mermaid fence behavior**
+
+Do not move or remove this existing code:
+
+```ts
+const defaultFenceRenderer = md.renderer.rules.fence?.bind(md.renderer.rules)
+
+md.renderer.rules.fence = (tokens, idx, options, env, self) => {
+  const token = tokens[idx]
+  if (isMermaidFence(token.info)) {
+    return renderMermaidPlaceholder(token.content)
+  }
+
+  if (defaultFenceRenderer) {
+    return defaultFenceRenderer(tokens, idx, options, env, self)
+  }
+
+  return self.renderToken(tokens, idx, options)
+}
+```
+
+**Step 4: Run focused test suite**
+
+```bash
+npm run test -- tests/client/markdown-rendering.test.ts
+```
+
+**Expected:** existing tests still pass or only fail because new math tests are not yet added.
+
+**Step 5: Commit**
+
+```bash
+git add packages/client/src/components/hermes/chat/MarkdownRenderer.vue
+git commit -m "feat: enable latex rendering in chat markdown"
+```
+
+---
+
+## Task 4: Load and tune KaTeX CSS
+
+**Objective:** Ensure rendered math is visually correct in the Web UI.
+
+**Files:**
+- Modify: `packages/client/src/main.ts`
+- Optionally modify: `packages/client/src/styles/global.scss`
+
+**Step 1: Import KaTeX CSS once globally**
+
+In `packages/client/src/main.ts`, add after global styles import:
+
+```ts
+import 'katex/dist/katex.min.css'
+```
+
+Current import area should become:
+
+```ts
+import App from './App.vue'
+import './styles/global.scss'
+import 'katex/dist/katex.min.css'
+```
+
+**Step 2: Add Hermes-specific layout tweaks only if needed**
+
+If visual smoke test shows cramped block equations, append to `packages/client/src/styles/global.scss`:
+
+```scss
+.markdown-body {
+  .katex-display {
+    overflow-x: auto;
+    overflow-y: hidden;
+    padding: 0.25rem 0;
+  }
+}
+```
+
+Do not restyle KaTeX itself unless there is a concrete visual bug.
+
+**Step 3: Commit**
+
+```bash
+git add packages/client/src/main.ts packages/client/src/styles/global.scss
+git commit -m "style: load katex styles for markdown math"
+```
+
+---
+
+## Task 5: Add regression tests for math rendering
+
+**Objective:** Prove formulas render, code fences stay literal, and malformed math is safe.
+
+**Files:**
+- Modify: `tests/client/markdown-rendering.test.ts`
+
+**Step 1: Add inline math test**
+
+Inside `describe('MarkdownRenderer', () => { ... })`:
+
+```ts
+it('renders inline latex math with katex', () => {
+  const wrapper = mount(MarkdownRenderer, {
+    props: {
+      content: 'Pythagoras: $x^2 + y^2 = z^2$.',
+    },
+  })
+
+  const body = wrapper.find('.markdown-body')
+  expect(body.find('.katex').exists()).toBe(true)
+  expect(body.html()).toContain('x')
+  expect(body.html()).toContain('z')
+  expect(body.text()).not.toContain('$x^2 + y^2 = z^2$')
+})
+```
+
+**Step 2: Add block math test**
+
+```ts
+it('renders display latex math with katex', () => {
+  const wrapper = mount(MarkdownRenderer, {
+    props: {
+      content: '$$\n\\int_0^1 x^2 dx = \\frac{1}{3}\n$$',
+    },
+  })
+
+  const body = wrapper.find('.markdown-body')
+  expect(body.find('.katex-display').exists()).toBe(true)
+  expect(body.find('.katex').exists()).toBe(true)
+  expect(body.text()).not.toContain('$$')
+})
+```
+
+**Step 3: Add fenced-code non-rendering test**
+
+```ts
+it('does not render latex inside fenced code blocks', () => {
+  const wrapper = mount(MarkdownRenderer, {
+    props: {
+      content: '```md\n$x^2 + y^2 = z^2$\n```',
+    },
+  })
+
+  expect(wrapper.find('.markdown-body').find('.katex').exists()).toBe(false)
+  expect(wrapper.find('code.hljs').text()).toContain('$x^2 + y^2 = z^2$')
+})
+```
+
+**Step 4: Add invalid math safety test**
+
+```ts
+it('keeps rendering when latex syntax is invalid', () => {
+  const wrapper = mount(MarkdownRenderer, {
+    props: {
+      content: 'Before $\\notacommand{ after',
+    },
+  })
+
+  expect(wrapper.find('.markdown-body').text()).toContain('Before')
+})
+```
+
+**Step 5: Run focused tests**
+
+```bash
+npm run test -- tests/client/markdown-rendering.test.ts
+```
+
+**Expected:** all tests in the file pass.
+
+**Step 6: Commit**
+
+```bash
+git add tests/client/markdown-rendering.test.ts
+git commit -m "test: cover latex rendering in markdown"
+```
+
+---
+
+## Task 6: Run build and broader regression checks
+
+**Objective:** Catch TypeScript, Vite, and existing client regressions before deploying locally.
+
+**Files:**
+- No source changes expected unless checks fail.
+
+**Step 1: Run focused tests**
+
+```bash
+npm run test -- tests/client/markdown-rendering.test.ts tests/client/markdown-rendering-mermaid-import-timeout.test.ts
+```
+
+**Expected:** pass.
+
+**Step 2: Run all tests if practical**
+
+```bash
+npm run test
+```
+
+**Expected:** pass. If unrelated pre-existing failures appear, record them in the PR body with evidence.
+
+**Step 3: Run production build**
+
+```bash
+npm run build
+```
+
+**Expected:** pass and update `dist/` only as build output. Do not commit `dist/` unless the package/release workflow requires it.
+
+**Step 4: Commit fixes only if needed**
+
+```bash
+git add <fixed-files>
+git commit -m "fix: stabilize latex markdown rendering"
+```
+
+---
+
+## Task 7: Deploy to Maxim's local Hermes Web UI instance
+
+**Objective:** Start using the feature on `https://hermes.kiraproject.ru/` before upstream PR review completes.
+
+**Files:**
+- Local runtime install under npm/global prefix may change outside the repo.
+- Do not commit generated deployment artifacts unless intentionally part of the repo.
+
+**Step 1: Build from the fork checkout**
+
+```bash
+cd /home/werserk/2-kira/hermes-web-ui
+npm run build
+```
+
+**Step 2: Replace currently installed package using npm link or local global install**
+
+Preferred reversible approach:
+
+```bash
+cd /home/werserk/2-kira/hermes-web-ui
+npm install -g --prefix /home/werserk/.npm-global .
+```
+
+**Step 3: Restart the Web UI service**
+
+```bash
+systemctl --user restart hermes-web-ui.service
+systemctl --user status hermes-web-ui.service --no-pager --lines=20
+```
+
+**Step 4: Smoke test HTTP response**
+
+```bash
+curl -sS -I --max-time 5 http://127.0.0.1:8648/ | head -20
+```
+
+**Expected:** HTTP 200/304 or another successful static response, not connection refused.
+
+**Step 5: Browser smoke test**
+
+Open the chat panel and send/render a message containing:
+
+```md
+Inline: $x^2 + y^2 = z^2$
+
+Block:
+$$
+\\int_0^1 x^2 dx = \\frac{1}{3}
+$$
+
+Code fence should stay literal:
+```md
+$x^2 + y^2 = z^2$
+```
+```
+
+**Expected:** first two formulas render visually; fenced formula stays literal.
+
+---
+
+## Task 8: Prepare upstream PR
+
+**Objective:** Make the contribution easy for upstream maintainers to review.
+
+**Files:**
+- No code changes required unless PR polish finds an issue.
+
+**Step 1: Push branch**
+
+```bash
+git push origin feat/latex-rendering
+```
+
+**Step 2: Create PR draft**
+
+```bash
+gh pr create \
+  --repo EKKOLearnAI/hermes-web-ui \
+  --head kira-project-lab:feat/latex-rendering \
+  --base main \
+  --title "feat(chat): render LaTeX math in Markdown messages" \
+  --body "$(cat <<'EOF'
+## Summary
+- Adds KaTeX-backed LaTeX rendering to chat Markdown messages.
+- Supports inline `$...$` and display `$$...$$` math.
+- Keeps math inside fenced code blocks literal.
+
+## Test Plan
+- [ ] npm run test -- tests/client/markdown-rendering.test.ts
+- [ ] npm run test -- tests/client/markdown-rendering-mermaid-import-timeout.test.ts
+- [ ] npm run build
+- [ ] Manual browser smoke test with inline, block, and fenced math
+
+## Notes
+This uses the existing markdown-it rendering path and keeps HTML disabled.
+EOF
+)" \
+  --draft
+```
+
+**Step 3: Attach visual proof**
+
+Add before/after screenshots in the PR body or a PR comment:
+
+- Before: raw `$...$` / `$$...$$` text.
+- After: rendered KaTeX inline and display equations.
+
+---
+
+## Risks and Guardrails
+
+- **Delimiter ambiguity:** `$` is common in shell snippets and prices. The fenced-code test protects code blocks, but inline text like `cost is $5 and $6` may be parsed depending on plugin behavior. If this is noisy, switch to `markdown-it-texmath` with explicit delimiter options or configure delimiters to prioritize `\(...\)` / `\[...\]`.
+- **Security:** keep `html: false` in `markdown-it`; do not enable arbitrary HTML. KaTeX should run with `trust: false` unless a clear need appears.
+- **Bundle size:** KaTeX adds client bundle weight. Acceptable for this feature, but mention it in PR if maintainers ask.
+- **CSS scope:** KaTeX CSS is global. Import once in `main.ts`; avoid duplicating it inside component styles.
+- **Invalid math:** `throwOnError: false` should prevent chat crashes. Regression test required.
+
+## Definition of Done
+
+- Branch `feat/latex-rendering` contains committed implementation.
+- Local Web UI renders inline and block formulas.
+- Focused Markdown tests pass.
+- Production build passes.
+- PR draft exists against `EKKOLearnAI/hermes-web-ui:main` or is ready to create.