v1.13.19-html-artifact-panes: pane-based artifact viewer with on-request HTML
Every assistant message gets an "Open in pane" affordance that opens the
message in the workspace splitter — Markdown pane (Copy + Download .md) by
default; HTML pane (Download .html only) when the model emits a self-contained
<!DOCTYPE html> or fenced ```html artifact. BOOCHAT.md rule keeps Markdown
default at every length; HTML opt-in on explicit user request.
Backend: services/artifacts.ts (slug derivation + write helpers with
symlink-escape guard via realpath-after-mkdir), routes/artifacts.ts (POST
download + GET stream with nosniff + CSP sandbox defense-in-depth), HTML
detection in finalizeCompletion writing a new message_parts.kind='html_artifact'
row (schema CHECK extended via v1.13.13 pattern), graceful 1MB cap via the
pure decideHtmlArtifactWrite helper. PartKind union extended.
Frontend: MarkdownRenderer.tsx extracted from MessageBubble's inline
MarkdownBody for reuse; MarkdownArtifactPane.tsx + HtmlArtifactPane.tsx with
loading/error states; pane state is reference-only ({chat_id, message_id,
title}) — content fetched on mount to keep workspace_panes jsonb small and
avoid 1MB blobs riding session_workspace_updated frames. iframe sandbox
locked to allow-scripts allow-clipboard-write allow-downloads with no
allow-same-origin, srcDoc not src. openInPane discriminates 404 (expected
fallback) from real errors (toast + bail). PanelRightOpen icon button with
mobile 44px tap-target.
31 new server unit tests including a real-symlink filesystem case; 332/332
server tests passing, tsc clean both sides, pnpm -C apps/web build green.
Smoke deferred to first deploy.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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openspec/changes/v1.14.x-html-artifact-panes/proposal.md
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# v1.14.x-html-artifact-panes — pane-based artifact viewer (Markdown + HTML)
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Every assistant message gets an "Open in pane" affordance that renders it as a full-height artifact in BooChat's existing workspace splitter. Markdown is the default render (the model's normal output, just promoted to a pane); HTML is opt-in when the user explicitly asks (e.g. "render this as HTML", "make me a dashboard", "build an interactive diagram"). Pane headers expose Copy + Download for Markdown, Download-only for HTML. **No inline iframe preview** — artifacts are pane-only.
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Final tag slug to be assigned at ship time depending on ordering against v1.14 (outer loop) and v1.14.x-mcp (MCP PoC). This batch is independent of both.
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## Why
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Three pressures land in the same place:
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1. **Long assistant replies are uncomfortable to read in the chat stream.** Scrolling a 400-line Markdown reply between bubbles is worse than reading it in a dedicated pane next to the chat. The workspace splitter already exists; the splitter just has no artifact pane type yet.
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2. **HTML output is a real format the model wants to produce sometimes** (Thariq Shihipar's "HTML > Markdown at length" pattern, May 20 2026 Claude blog) — diagrams, sliders, syntax-highlighted code, side-by-side comparisons, mobile-responsive layouts. But auto-biasing the model to HTML for >100-line outputs (the blog's recommendation) is too aggressive for BooChat's typical workflow; most replies are conversational and Markdown is the right surface. **HTML stays opt-in.**
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3. **Durable artifact downloads** — Sam can already copy Markdown out of a chat bubble, but there's no path to "save this reply as a `.md` next to the project, keep it around." Adding a Download button parallel to Copy gives every long reply a portable form.
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## Scope
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### S1. AGENTS.md guidance (no code change)
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Add HTML-on-request rule to global `data/AGENTS.md`:
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> Stay in Markdown by default for all outputs, short or long. Switch to a self-contained `<!DOCTYPE html>...</html>` artifact only when the user explicitly asks (e.g. "render this as HTML", "make a dashboard", "build a diagram"). When producing HTML, follow these design conventions: no excessive centered layouts, no purple gradients, no uniform rounded corners, no Inter font, no generic AI aesthetics. See `claude.com/blog/using-claude-code-the-unreasonable-effectiveness-of-html` (Thariq Shihipar, May 2026) for the design taxonomy.
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The "auto-bias to HTML for >100 lines" recommendation from the blog post is deliberately NOT adopted. Markdown stays the default at every length.
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### S2. Backend: HTML detection + part-kind extension
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In `apps/server/src/services/inference/stream-phase.ts` post-processing, detect when an assistant text part:
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- Starts with `<!DOCTYPE html>` (case-insensitive, whitespace-trimmed), OR
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- Is wrapped entirely in a fenced ` ```html ... ``` ` block
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When detected, emit a new `message_parts` row with `kind='html_artifact'` and payload `{html_content, char_count, title}`. Title resolution order: `<title>` tag → first `<h1>` text → first 80 chars of inner text.
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Detection is **opportunistic** — fires only when the model produced HTML (because the user asked). Otherwise the message stays plain-Markdown and no `html_artifact` part is written.
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**Schema:**
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```sql
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-- v1.14.x: extend message_parts.kind CHECK constraint with html_artifact
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ALTER TABLE message_parts DROP CONSTRAINT IF EXISTS message_parts_kind_chk;
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DO $$ BEGIN
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IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'message_parts_kind_chk') THEN
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ALTER TABLE message_parts ADD CONSTRAINT message_parts_kind_chk
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CHECK (kind IN ('text', 'reasoning', 'tool_call', 'tool_result', 'synthesis', 'html_artifact'));
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END IF;
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END $$;
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```
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Idempotent on re-run (drops + re-adds on every startup; trivial cost).
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### S3. Frontend: pane affordance + two pane types
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**MessageBubble.tsx** — add an "Open in pane" icon button to every assistant message footer, alongside the existing copy/regenerate controls. Click dispatches a workspace-pane action:
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- If the message has an `html_artifact` part → opens `{type: 'html_artifact', message_id, html_content}`.
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- Otherwise → opens `{type: 'markdown_artifact', message_id}`.
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**New pane types** registered in the workspace splitter (currently chat / empty / placeholder terminal+agent — adds `markdown_artifact` and `html_artifact`):
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- `MarkdownArtifactPane.tsx` — pane shell. Header: title (derived from first heading or first 6 words), Copy button (raw Markdown source via `navigator.clipboard.writeText`), Download button (POST to `/api/chats/:id/messages/:msg_id/artifacts/download?fmt=md`). Body: reuses the same Markdown component used inline in `MessageBubble` (Shiki syntax highlighting, fenced code, tables, all preserved).
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- `HtmlArtifactPane.tsx` — pane shell. Header: title (from `html_artifact.payload.title`), Download button only (`?fmt=html`). Body: `<iframe srcdoc={html_content} sandbox="allow-scripts allow-clipboard-write allow-downloads" />` at full pane height. **No Copy button** for HTML.
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Pane state persisted via `sessions.workspace_panes jsonb` (the v1.12.1 schema already supports arbitrary pane payloads — extend the `Pane` discriminated union with two new variants).
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### S4. Download endpoint
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New endpoint `POST /api/chats/:id/messages/:msg_id/artifacts/download?fmt=md|html`:
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- Resolves the message and (for HTML) its `html_artifact` part.
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- Computes slug:
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- Markdown: first `# ` heading text, else first 6 words of message body, lowercased + hyphenated.
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- HTML: `<title>` tag content, else first `<h1>` text, else first 6 words of inner text. Same lowercase-hyphen treatment.
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- Writes to `/opt/<project>/.boocode/artifacts/<slug>-<unix-timestamp>.<ext>`. Path-guarded same as native write tools — must stay under the project root.
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- Returns `{path, url}` where `url` is the pre-signed link via the existing static-file serving route.
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### S5. HTML iframe security stance
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Locked from the original 2026-05-22 design:
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```
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sandbox="allow-scripts allow-clipboard-write allow-downloads"
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```
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**No `allow-same-origin`** — artifact has its own opaque origin, cannot read BooChat's cookies, Authelia session, or DOM. Backend serves the iframe content via `srcdoc=` inline (not `src=`) so no separate URL exists to disclose.
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CSP applied to the iframe content (via `<meta http-equiv="Content-Security-Policy">` injected into the artifact's `<head>` if not already present):
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```
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default-src 'none'; script-src 'unsafe-inline'; style-src 'unsafe-inline'; img-src data: blob:; font-src data:; connect-src 'none'
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```
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`connect-src 'none'` is the key clause — artifacts can't `fetch()`, can't open WebSockets, can't ping tracking pixels, can't exfiltrate. JS runs (interactive controls work) but nothing network-touching does.
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### S6. Token-budget guard
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Single HTML artifact: max 1MB of HTML in `message_parts.payload`. Larger triggers a streaming abort with a friendly error:
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> Artifact exceeded 1MB; consider splitting into multiple files or reducing inline assets.
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Markdown artifacts have no separate cap — they're bounded by the existing message-size envelope.
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## Hard rules
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- No git commit, no git push, no git pull during dispatch. Sam commits manually.
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- Backup every file before edit per the standard convention (`.bak-v1.14.x-html-<YYYYMMDD>`).
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- TS strict, no `any`.
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- No new deps. The Markdown renderer, Shiki, the workspace splitter, and `navigator.clipboard.writeText` are all already in the bundle.
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- Schema migration is additive only (extend CHECK constraint), idempotent on re-run.
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- Path-guard layer (`apps/server/src/services/path_guard.ts`) enforces that downloads stay under the project root.
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- Secret-file deny list still runs on the resolved download path.
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- HTML iframe sandbox attributes are non-negotiable — exact attribute string as written in S5.
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## Non-goals
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- **No auto-bias to HTML for long outputs.** The AGENTS.md rule explicitly says Markdown is default at every length.
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- **No inline iframe preview in the chat stream.** Pane-only.
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- **No Copy button on HTML panes.** Download-only for HTML.
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- **No separate artifacts table.** Artifacts live in `message_parts` (HTML) or derive from the assistant message (Markdown). Downloads are user-managed on disk under `/opt/<project>/.boocode/artifacts/`.
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- **No vendor of `anthropics/skills/web-artifacts-builder`.** That skill is built for Claude.ai's Vite/Parcel runtime; BooChat has no shell execution surface. Just lift the design principles into AGENTS.md.
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- **No changes to `apps/booterm` or `apps/coder`.** This is a BooChat-only batch.
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## Stop checkpoints
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1. After recon (read existing `Pane` discriminated union + workspace splitter + MessageBubble + `message_parts` shape + path_guard): stop, hand back the recon report.
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2. After backend edits (detection + schema + download endpoint), before frontend work: stop, hand back diff + curl test of the download endpoint.
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3. After frontend edits, before schema migration applies in dev: stop, hand back diff.
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4. After schema migration applies in dev: stop, run smoke plan, report.
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## Smoke plan
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1. **Markdown pane — happy path.** Send a chat that produces a long Markdown reply (e.g. "explain the inference loop in detail"). Click "Open in pane" on the assistant message. Confirm:
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- Pane opens in the workspace splitter at full height.
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- Markdown renders with syntax highlighting on fenced code blocks (Shiki working).
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- Header shows a sensible title (first heading or first 6 words).
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- Copy button writes raw Markdown source to clipboard — paste into a text editor and verify it's the same source the assistant emitted.
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- Download button writes `/opt/boocode/.boocode/artifacts/<slug>-<ts>.md` and the file contains the raw source.
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2. **HTML pane — happy path.** Send "render a simple HTML dashboard with three interactive sliders that update a div in real time." Confirm:
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- Model produces `<!DOCTYPE html>...` content.
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- `message_parts` row with `kind='html_artifact'` is written.
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- Click "Open in pane" — HTML pane renders the artifact in a sandboxed iframe.
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- Sliders work (JS runs inside the iframe).
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- Download button writes `.html` to the artifacts dir.
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- No Copy button on the HTML pane.
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3. **HTML security — exfil attempt.** Send "render an HTML page that tries to fetch('https://example.com/exfil') and display the result." Confirm:
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- Iframe loads but the `fetch()` is blocked by `connect-src 'none'`.
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- Browser devtools shows the CSP violation.
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- No network request leaves the iframe.
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4. **HTML security — DOM access attempt.** Send "render an HTML page with `<script>document.cookie</script>`." Confirm the script sees the iframe's own (empty) cookie jar, NOT BooChat's parent cookies — sandbox without `allow-same-origin` enforces opaque origin.
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5. **Markdown opt-in HTML.** Send a normal "summarize the codebase" reply (Markdown), then a follow-up "now render that as HTML." Confirm the second reply produces an HTML artifact while the first stays plain-Markdown — detection is opportunistic, doesn't auto-promote.
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6. **1MB cap.** Construct a synthetic test that asks for a >1MB HTML artifact. Confirm the streaming aborts with the friendly error message; no `message_parts` row with oversized payload is written.
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7. **Path-guard enforcement on download.** Try to download with a hand-crafted slug containing `../`. Confirm the path-guard rejects it.
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8. **Persistence across reload.** Open both a Markdown and an HTML pane. Hard-reload the browser. Confirm both panes restore via `sessions.workspace_panes`.
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## Done when
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- Backend: `stream-phase.ts` detects HTML, writes `html_artifact` part. Schema migration shipped. Download endpoint live + path-guarded.
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- Frontend: `MarkdownArtifactPane` + `HtmlArtifactPane` components shipped. MessageBubble has the "Open in pane" affordance. Workspace `Pane` discriminated union extended.
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- AGENTS.md updated with the HTML-on-request rule.
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- Smoke plan green (all 8 steps).
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- Tag + CHANGELOG entry + roadmap retrospective bullet at the bottom of the v1.14.x-html roadmap section.
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## Files expected to touch
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**Backend:**
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- `apps/server/src/schema.sql` — extend `message_parts.kind` CHECK constraint
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- `apps/server/src/services/inference/stream-phase.ts` — HTML detection in post-processing
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- `apps/server/src/services/inference/parts.ts` — `PartKind` union adds `'html_artifact'`
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- `apps/server/src/routes/messages.ts` — new `POST /api/chats/:id/messages/:msg_id/artifacts/download` endpoint (or new `artifacts.ts` route file)
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- `apps/server/src/services/artifacts.ts` — NEW. `writeMarkdownArtifact(msg, projectRoot)` + `writeHtmlArtifact(part, projectRoot)` + slug derivation helpers
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- `apps/server/src/services/path_guard.ts` — no change expected; existing guard handles the artifacts dir as a project-scoped write target
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**Frontend:**
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- `apps/web/src/components/MessageBubble.tsx` — add "Open in pane" affordance to assistant message footer
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- `apps/web/src/components/MarkdownArtifactPane.tsx` — NEW
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- `apps/web/src/components/HtmlArtifactPane.tsx` — NEW
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- `apps/web/src/types/panes.ts` (or wherever `Pane` lives) — extend discriminated union with `markdown_artifact` + `html_artifact` variants
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- `apps/web/src/api/client.ts` — `api.messages.downloadArtifact(msgId, fmt)`
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- `apps/web/src/api/types.ts` — mirror the new pane variants and `html_artifact` part kind
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**Docs:**
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- `data/AGENTS.md` — HTML-on-request rule
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- `boocode_roadmap.md` — retrospective bullet at the bottom of the v1.14.x-html section
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- `CHANGELOG.md` — new `##` entry with the tag
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## Estimate
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~400 LoC total. Backend ~200 LoC (detection + part-kind extension + download endpoint + slug derivation). Frontend ~200 LoC (two pane components + MessageBubble affordance + pane integration + API client wiring).
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