feat: sift parquet integration — interactive DataFrame rendering

[rgbkrk]

Problem

DataFrames displayed in nteract notebooks currently render as text/html tables (pandas) or text/plain (fallback). We want them to render as interactive, filterable, sortable tables using sift (@nteract/sift) — a fast dataframe viewer built on pretext + WASM (100k+ rows at 120fps).

Architecture

Data flow: Kernel → RuntimeAgent → Daemon → Frontend

Kernel (Python)                  RuntimeAgent              Daemon            Frontend
  |                                  |                       |                  |
  | df.to_parquet(buf)               |                       |                  |
  | blob_upload(parquet) ----------->| blob_store.put()      |                  |
  |                                  | → hash                |                  |
  | display_data on IOPub:           |                       |                  |
  |   {blob_hash, text/plain}        |                       |                  |
  |                                  |                       |                  |
  |   [agent IOPub task picks up] -->|                       |                  |
  |                                  | create_manifest()     |                  |
  |                                  | store in blob store   |                  |
  |                                  | write hash to CRDT    |                  |
  |                                  |--- RuntimeStateSync ->|                  |
  |                                  |                       |--- sync frame -->|
  |                                  |                       |                  |
  |                                  |                       |  resolve manifest|
  |                                  |                       |  GET /blob/{hash}|
  |                                  |                       |  SiftTable render|

Key insight: Parquet bytes bypass IOPub entirely. The kernel writes directly to the blob store (same filesystem as agent), then emits a lightweight JSON reference on IOPub. The agent's normal manifest pipeline picks up the reference. The frontend resolves the blob URL and sift's WASM decodes the parquet client-side.

Why out-of-band (not IOPub)

• IOPub base64-encodes binary → 33% inflation (100MB parquet → 133MB on wire → decoded back)
• The agent's blob store is the same filesystem directory — direct writes have no protocol overhead
• Display data on IOPub is just {"blob_hash": "..."} — a few bytes

MIME type

application/vnd.nteract.dataframe+parquet

The data field is a JSON string with the blob hash. All schema metadata (columns, types, row count) lives inside the parquet file itself — parquet is self-describing. No separate metadata needed.

---

Components

1. Repo structure: monorepo package at packages/sift/

Add sift as a pnpm workspace package. pnpm-workspace.yaml already has packages/*. The nteract-predicate WASM crate joins the Cargo workspace. Sift's standalone dev workflow (cd packages/sift && pnpm dev) is preserved for fast iteration.

2. Frontend: DataFrameOutput component

• Register custom MIME type in MediaProvider (same pattern as widget-view in App.tsx)
• Add to MAIN_DOM_SAFE_TYPES (sift is pure DOM, no script execution risk)
• Add to DEFAULT_PRIORITY above text/html
• DataFrameOutput resolves blob URL via blob port, renders <SiftTable url={blobUrl} />
• Sift's WASM decodes parquet → virtual scrolled table with filter/sort/crossfilter

3. Python: IPython display formatter + blob upload

Follow the pattern pandas uses for application/vnd.dataresource+json (pandas/io/formats/printing.py:302):

• Register a custom IPython formatter for our MIME type
• Handles both pandas.DataFrame and polars.DataFrame (by type, not method)
• On display: df.to_parquet(buf) → write to blob store → return {blob_hash} + text/plain fallback
• Non-invasive: adds alongside existing text/html, other frontends fall back gracefully

Research findings:

• pandas: has _repr_html_(), no _repr_mimebundle_(). Has precedent for custom MIME formatters via IPython's display_formatter.formatters
• polars: has _repr_html_() only, no _repr_mimebundle_(). Our formatter registers by type so it works

4. Output widget / iframe handling

DataFrames inside ipywidgets.Output render in iframes. Start with a hybrid: sift in main DOM, fall back to text/html in iframe contexts (the isInIframe() check already exists in MediaRouter). Revisit iframe sift rendering later if needed.

5. Daemon: no changes needed

Blob store is content-addressed and media-type-agnostic. The custom MIME type's data is JSON text → normal manifest pipeline.

---

Phasing

Phase 1: Sift in monorepo + frontend renderer

• Copy sift source into packages/sift/
• Add nteract-predicate to Cargo workspace, wire up WASM build
• Create DataFrameOutput component + MIME registration
• Manual test with parquet in blob store
• Verify sift standalone dev still works

Phase 2: Python formatter + blob upload (end-to-end)

• blob.upload() in runtimed (direct filesystem write)
• IPython display formatter for pandas + polars
• Auto-registration on kernel start
• Test: pd.DataFrame({"x": range(100_000)}) → sift table

Phase 3: Polish

• Output widget iframe fallback
• Truncation UX for large DataFrames
• Theme integration (dark/light mode)
• .ipynb save with text/plain + text/html fallbacks
• Streaming by row group for very large DataFrames

---

Open questions

1. WASM in Tauri bundle — nteract-predicate.wasm needs to be in the app assets. Copy pipeline TBD.
2. Formatter auto-registration — agent-injected startup code vs IPython extension vs kernel spec hook?
3. Max DataFrame size — UX for exceeding 100MB blob limit? Truncate? Warn?
4. Remote kernels — blob upload API is abstract (blob_store.upload()) so transport can change for SSH agents (feat(runtimed): SSH remote runtimes #1334). Not solving now.

Related

• feat(runtimed): SSH remote runtimes #1334 (SSH runtime agents — informs blob upload API design)

[rgbkrk]

Done, other than the streaming bits and max dataframe size. Tracked in other issues.