internalai-agent/docs/notebook-patterns.md

# Marimo Notebook Patterns

This guide covers how to create [marimo](https://marimo.io) notebooks for data analysis against the InternalAI platform APIs. Marimo notebooks are plain `.py` files with reactive cells — no `.ipynb` format, no Jupyter dependency.

## Marimo Basics

A marimo notebook is a Python file with `@app.cell` decorated functions. Each cell returns values as a tuple, and other cells receive them as function parameters — marimo builds a reactive DAG automatically.

```python
import marimo
app = marimo.App()

@app.cell
def cell_one():
    x = 42
    return (x,)

@app.cell
def cell_two(x):
    # Re-runs automatically when x changes
    result = x * 2
    return (result,)
```

**Key rules:**
- Cells declare dependencies via function parameters
- Cells return values as tuples: `return (var1, var2,)`
- The **last expression at the top level** of a cell is displayed as rich output in the marimo UI (dataframes render as tables, dicts as collapsible trees). Expressions inside `if`/`else`/`for` blocks do **not** count — see [Cell Output Must Be at the Top Level](#cell-output-must-be-at-the-top-level) below
- Use `mo.md("# heading")` for formatted markdown output (import `mo` once in setup — see below)
- No manual execution order; the DAG determines it
- **Variable names must be unique across cells.** Every variable assigned at the top level of a cell is tracked by marimo's DAG. If two cells both define `resp`, marimo raises `MultipleDefinitionError` and refuses to run. Prefix cell-local variables with `_` (e.g., `_resp`, `_rows`, `_data`) to make them **private** to that cell — marimo ignores `_`-prefixed names.
- **All imports must go in the `setup` cell.** Every `import` statement creates a top-level variable (e.g., `import asyncio` defines `asyncio`). If two cells both `import asyncio`, marimo raises `MultipleDefinitionError`. Place **all** imports in a single setup cell and pass them as cell parameters. Do NOT `import marimo as mo` or `import asyncio` in multiple cells — import once in `setup`, then receive via `def my_cell(mo, asyncio):`.

### Cell Variable Scoping — Example

This is the **most common mistake**. Any variable assigned at the top level of a cell (not inside a `def` or comprehension) is tracked by marimo. If two cells assign the same name, the notebook refuses to run.

**BROKEN** — `resp` is defined at top level in both cells:

```python
# Cell A
@app.cell
def search_meetings(client, DATAINDEX):
    resp = client.post(f"{DATAINDEX}/search", json={...})  # defines 'resp'
    resp.raise_for_status()
    results = resp.json()["results"]
    return (results,)

# Cell B
@app.cell
def fetch_details(client, DATAINDEX, results):
    resp = client.get(f"{DATAINDEX}/entities/{results[0]}")  # also defines 'resp' → ERROR
    meeting = resp.json()
    return (meeting,)
```

> **Error:** `MultipleDefinitionError: variable 'resp' is defined in multiple cells`

**FIXED** — prefix cell-local variables with `_`:

```python
# Cell A
@app.cell
def search_meetings(client, DATAINDEX):
    _resp = client.post(f"{DATAINDEX}/search", json={...})  # _resp is cell-private
    _resp.raise_for_status()
    results = _resp.json()["results"]
    return (results,)

# Cell B
@app.cell
def fetch_details(client, DATAINDEX, results):
    _resp = client.get(f"{DATAINDEX}/entities/{results[0]}")  # _resp is cell-private, no conflict
    meeting = _resp.json()
    return (meeting,)
```

**Rule of thumb:** if a variable is only used within the cell to compute a return value, prefix it with `_`. Only leave names unprefixed if another cell needs to receive them.

> **Note:** Variables inside nested `def` functions are naturally local and don't need `_` prefixes — e.g., `resp` inside a `def fetch_all(...)` helper is fine because it's scoped to the function, not the cell.

### Cell Output Must Be at the Top Level

Marimo only renders the **last expression at the top level** of a cell as rich output. An expression buried inside an `if`/`else`, `for`, `try`, or any other block is **not** displayed — it's silently discarded.

**BROKEN** — `_df` inside the `if` branch is never rendered:

```python
@app.cell
def show_results(results, mo):
    if results:
        _df = pl.DataFrame(results)
        mo.md(f"**Found {len(results)} results**")
        _df  # Inside an if block — marimo does NOT display this
    else:
        mo.md("**No results found**")
    return
```

**FIXED** — assign inside the branches, display at the top level:

```python
@app.cell
def show_results(results, mo):
    _output = None
    if results:
        _output = pl.DataFrame(results)
        mo.md(f"**Found {len(results)} results**")
    else:
        mo.md("**No results found**")
    _output  # Top-level last expression — marimo renders this
    return
```

**Rule of thumb:** initialize a `_output = None` variable before any conditional, assign the displayable value inside the branches, then put `_output` as the last top-level expression. When it's `None` (e.g., the `else` path), marimo shows nothing — which is fine since the `mo.md()` already provides feedback.

### Async Cells

When a cell uses `await` (e.g., for `llm_call` or `asyncio.gather`), you **must** declare it as `async def`:

```python
@app.cell
async def analyze(meetings, llm_call, ResponseModel, asyncio):
    async def _score(meeting):
        return await llm_call(prompt=..., response_model=ResponseModel)

    results = await asyncio.gather(*[_score(_m) for _m in meetings])
    return (results,)
```

Note that `asyncio` is imported in the `setup` cell and received here as a parameter — never `import asyncio` inside individual cells.

If you write `await` in a non-async cell, marimo cannot parse the cell and saves it as an `_unparsable_cell` string literal — the cell won't run, and you'll see `SyntaxError: 'return' outside function` or similar errors. See [Fixing `_unparsable_cell`](#fixing-_unparsable_cell) below.

### Cells That Define Classes Must Return Them

If a cell defines Pydantic models (or any class) that other cells need, it **must** return them:

```python
@app.cell
def models():
    from pydantic import BaseModel

    class MeetingSentiment(BaseModel):
        overall_sentiment: str
        sentiment_score: int

    class FrustrationExtraction(BaseModel):
        has_frustrations: bool
        frustrations: list[dict]

    return MeetingSentiment, FrustrationExtraction  # Other cells receive these as parameters
```

A bare `return` (or no return) means those classes are invisible to the rest of the notebook.

### Fixing `_unparsable_cell`

When marimo can't parse a cell into a proper `@app.cell` function, it saves the raw code as `app._unparsable_cell("...", name="cell_name")`. These cells **won't run** and show errors like `SyntaxError: 'return' outside function`.

**Common causes:**
1. Using `await` without making the cell `async def`
2. Using `return` in code that marimo failed to wrap into a function (usually a side effect of cause 1)

**How to fix:** Convert the `_unparsable_cell` string back into a proper `@app.cell` decorated function:

```python
# BROKEN — saved as _unparsable_cell because of top-level await
app._unparsable_cell("""
results = await asyncio.gather(...)
return results
""", name="my_cell")

# FIXED — proper async cell function (asyncio imported in setup, received as parameter)
@app.cell
async def my_cell(some_dependency, asyncio):
    results = await asyncio.gather(...)
    return (results,)
```

**Key differences to note when converting:**
- Wrap the code in an `async def` function (if it uses `await`)
- Add cell dependencies as function parameters (including imports like `asyncio`)
- Return values as tuples: `return (var,)` not `return var`
- Prefix cell-local variables with `_`
- Never add `import` statements inside the cell — all imports belong in `setup`

### Inline Dependencies with PEP 723

Use PEP 723 `/// script` metadata so `uv run` auto-installs dependencies:

```python
# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "marimo",
#     "httpx",
#     "polars",
#     "mirascope[openai]",
#     "pydantic",
#     "python-dotenv",
# ]
# ///
```

### Checking Notebooks Before Running

Always run `marimo check` before opening or running a notebook. It catches common issues — duplicate variable definitions, `_unparsable_cell` blocks, branch expressions that won't display, and more — without needing to start the full editor:

```bash
uvx marimo check notebook.py           # Check a single notebook
uvx marimo check workflows/            # Check all notebooks in a directory
uvx marimo check --fix notebook.py     # Auto-fix fixable issues
```

**Run this after every edit.** A clean `marimo check` (no output, exit code 0) means the notebook is structurally valid. Any errors must be fixed before running.

### Running Notebooks

```bash
uvx marimo edit notebook.py   # Interactive editor (best for development)
uvx marimo run notebook.py    # Read-only web app
uv run notebook.py            # Script mode (terminal output)
```

### Inspecting Cell Outputs

In `marimo edit`, every cell's return value is displayed as rich output below the cell. This is the primary way to introspect API responses:

- **Dicts/lists** render as collapsible JSON trees — click to expand nested fields
- **Polars/Pandas DataFrames** render as interactive sortable tables
- **Strings** render as plain text

To inspect a raw API response, just make it the last expression:

```python
@app.cell
def inspect_response(client, DATAINDEX):
    _resp = client.get(f"{DATAINDEX}/query", params={
        "entity_types": "meeting", "limit": 2,
    })
    _resp.json()  # This gets displayed as a collapsible JSON tree
```

To inspect an intermediate value alongside other work, use `mo.accordion` or return it:

```python
@app.cell
def debug_meetings(meetings, mo):
    mo.md(f"**Count:** {len(meetings)}")
    # Show first item structure for inspection
    mo.accordion({"First meeting raw": mo.json(meetings[0])}) if meetings else None
```

## Notebook Skeleton

Every notebook against InternalAI follows this structure:

```python
# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "marimo",
#     "httpx",
#     "polars",
#     "mirascope[openai]",
#     "pydantic",
#     "python-dotenv",
# ]
# ///

import marimo
app = marimo.App()

@app.cell
def params():
    """User parameters — edit these to change the workflow's behavior."""
    SEARCH_TERMS = ["greyhaven"]
    DATE_FROM = "2026-01-01T00:00:00Z"
    DATE_TO = "2026-02-01T00:00:00Z"
    TARGET_PERSON = None  # Set to a name like "Alice" to filter by person, or None for all
    return DATE_FROM, DATE_TO, SEARCH_TERMS, TARGET_PERSON

@app.cell
def config():
    BASE = "http://localhost:42000"
    CONTACTDB = f"{BASE}/contactdb-api"
    DATAINDEX = f"{BASE}/dataindex/api/v1"
    return (CONTACTDB, DATAINDEX,)

@app.cell
def setup():
    from dotenv import load_dotenv
    load_dotenv()  # Load .env from the project root

    import asyncio  # All imports go here — never import inside other cells
    import httpx
    import marimo as mo
    import polars as pl
    client = httpx.Client(timeout=30)
    return (asyncio, client, mo, pl,)

# --- your IN / ETL / OUT cells here ---

if __name__ == "__main__":
    app.run()
```

> **`load_dotenv()`** reads the `.env` file from the project root (walks up from the notebook's directory). This makes `LLM_API_KEY` and other env vars available to `os.getenv()` calls in `lib/llm.py` without requiring the shell to have them pre-set. Always include `python-dotenv` in PEP 723 dependencies and call `load_dotenv()` early in the setup cell.

**The `params` cell must always be the first cell** after `app = marimo.App()`. It contains all user-configurable constants (search terms, date ranges, target names, etc.) as plain Python values. This way the user can tweak the workflow by editing a single cell at the top — no need to hunt through the code for hardcoded values.

## Pagination Helper

The DataIndex `GET /query` endpoint paginates with `limit` and `offset`. Always paginate — result sets can be large.

```python
@app.cell
def helpers(client):
    def fetch_all(url, params):
        """Fetch all pages from a paginated DataIndex endpoint."""
        all_items = []
        limit = params.get("limit", 50)
        params = {**params, "limit": limit, "offset": 0}
        while True:
            resp = client.get(url, params=params)
            resp.raise_for_status()
            data = resp.json()
            all_items.extend(data["items"])
            if params["offset"] + limit >= data["total"]:
                break
            params["offset"] += limit
        return all_items

    def resolve_contact(name, contactdb_url):
        """Find a contact by name, return their ID."""
        resp = client.get(f"{contactdb_url}/api/contacts", params={"search": name})
        resp.raise_for_status()
        contacts = resp.json()["contacts"]
        if not contacts:
            raise ValueError(f"No contact found for '{name}'")
        return contacts[0]

    return (fetch_all, resolve_contact,)
```

## Pattern 1: Emails Involving a Specific Person

Emails have `from_contact_id`, `to_contact_ids`, and `cc_contact_ids`. The query API's `contact_ids` filter matches entities where the contact appears in **any** of these roles.

```python
@app.cell
def find_person(resolve_contact, CONTACTDB):
    target = resolve_contact("Alice", CONTACTDB)
    target_id = target["id"]
    target_name = target["name"]
    return (target_id, target_name,)

@app.cell
def fetch_emails(fetch_all, DATAINDEX, target_id):
    emails = fetch_all(f"{DATAINDEX}/query", {
        "entity_types": "email",
        "contact_ids": str(target_id),
        "date_from": "2025-01-01T00:00:00Z",
        "sort_order": "desc",
    })
    return (emails,)

@app.cell
def email_table(emails, target_id, target_name, pl):
    email_df = pl.DataFrame([{
        "date": e["timestamp"][:10],
        "subject": e.get("title", "(no subject)"),
        "direction": (
            "sent" if str(target_id) == str(e.get("from_contact_id"))
            else "received"
        ),
        "snippet": (e.get("snippet") or e.get("text_content") or "")[:100],
    } for e in emails])
    return (email_df,)

@app.cell
def show_emails(email_df, target_name, mo):
    mo.md(f"## Emails involving {target_name} ({len(email_df)} total)")

@app.cell
def display_email_table(email_df):
    email_df  # Renders as interactive table in marimo edit
```

## Pattern 2: Meetings with a Specific Participant

Meetings have a `participants` list where each entry may or may not have a resolved `contact_id`. The query API's `contact_ids` filter only matches **resolved** participants.

**Strategy:** Query by `contact_ids` to get meetings with resolved participants, then optionally do a client-side check on `participants[].display_name` or `transcript` for unresolved ones.

```python
@app.cell
def fetch_meetings(fetch_all, DATAINDEX, target_id, my_id):
    # Get meetings where the target appears in contact_ids
    resolved_meetings = fetch_all(f"{DATAINDEX}/query", {
        "entity_types": "meeting",
        "contact_ids": str(target_id),
        "date_from": "2025-01-01T00:00:00Z",
    })
    return (resolved_meetings,)

@app.cell
def meeting_table(resolved_meetings, target_name, pl):
    _rows = []
    for _m in resolved_meetings:
        _participants = _m.get("participants", [])
        _names = [_p["display_name"] for _p in _participants]
        _rows.append({
            "date": (_m.get("start_time") or _m["timestamp"])[:10],
            "title": _m.get("title", _m.get("room_name", "Untitled")),
            "participants": ", ".join(_names),
            "has_transcript": _m.get("transcript") is not None,
            "has_summary": _m.get("summary") is not None,
        })
    meeting_df = pl.DataFrame(_rows)
    return (meeting_df,)
```

To also find meetings where the person was present but **not resolved** (guest), search the transcript:

```python
@app.cell
def search_unresolved(client, DATAINDEX, target_name):
    # Semantic search for the person's name in meeting transcripts
    _resp = client.post(f"{DATAINDEX}/search", json={
        "search_text": target_name,
        "entity_types": ["meeting"],
        "limit": 50,
    })
    _resp.raise_for_status()
    transcript_hits = _resp.json()["results"]
    return (transcript_hits,)
```

## Pattern 3: Calendar Events → Meeting Correlation

Calendar events and meetings are separate entities from different connectors. To find which calendar events had a corresponding recorded meeting, match by time overlap.

```python
@app.cell
def fetch_calendar_and_meetings(fetch_all, DATAINDEX, my_id):
    events = fetch_all(f"{DATAINDEX}/query", {
        "entity_types": "calendar_event",
        "contact_ids": str(my_id),
        "date_from": "2025-01-01T00:00:00Z",
        "sort_by": "timestamp",
        "sort_order": "asc",
    })
    meetings = fetch_all(f"{DATAINDEX}/query", {
        "entity_types": "meeting",
        "contact_ids": str(my_id),
        "date_from": "2025-01-01T00:00:00Z",
    })
    return (events, meetings,)

@app.cell
def correlate(events, meetings, pl):
    from datetime import datetime, timedelta

    def _parse_dt(s):
        if not s:
            return None
        return datetime.fromisoformat(s.replace("Z", "+00:00"))

    # Index meetings by start_time for matching
    _meeting_by_time = {}
    for _m in meetings:
        _start = _parse_dt(_m.get("start_time"))
        if _start:
            _meeting_by_time[_start] = _m

    _rows = []
    for _ev in events:
        _ev_start = _parse_dt(_ev.get("start_time"))
        _ev_end = _parse_dt(_ev.get("end_time"))
        if not _ev_start:
            continue

        # Find meeting within 15-min window of calendar event start
        _matched = None
        for _m_start, _m in _meeting_by_time.items():
            if abs((_m_start - _ev_start).total_seconds()) < 900:
                _matched = _m
                break

        _rows.append({
            "date": _ev_start.strftime("%Y-%m-%d"),
            "time": _ev_start.strftime("%H:%M"),
            "event_title": _ev.get("title", "(untitled)"),
            "has_recording": _matched is not None,
            "meeting_title": _matched.get("title", "") if _matched else "",
            "attendee_count": len(_ev.get("attendees", [])),
        })

    calendar_df = pl.DataFrame(_rows)
    return (calendar_df,)
```

## Pattern 4: Full Interaction Timeline for a Person

Combine emails, meetings, and Zulip messages into a single chronological view.

```python
@app.cell
def fetch_all_interactions(fetch_all, DATAINDEX, target_id):
    all_entities = fetch_all(f"{DATAINDEX}/query", {
        "contact_ids": str(target_id),
        "date_from": "2025-01-01T00:00:00Z",
        "sort_by": "timestamp",
        "sort_order": "desc",
    })
    return (all_entities,)

@app.cell
def interaction_timeline(all_entities, target_name, pl):
    _rows = []
    for _e in all_entities:
        _etype = _e["entity_type"]
        _summary = ""
        if _etype == "email":
            _summary = _e.get("snippet") or _e.get("title") or ""
        elif _etype == "meeting":
            _summary = _e.get("summary") or _e.get("title") or ""
        elif _etype == "conversation_message":
            _summary = (_e.get("message") or "")[:120]
        elif _etype == "threaded_conversation":
            _summary = _e.get("title") or ""
        elif _etype == "calendar_event":
            _summary = _e.get("title") or ""
        else:
            _summary = _e.get("title") or _e["entity_type"]

        _rows.append({
            "date": _e["timestamp"][:10],
            "type": _etype,
            "source": _e["connector_id"],
            "summary": _summary[:120],
        })

    timeline_df = pl.DataFrame(_rows)
    return (timeline_df,)

@app.cell
def show_timeline(timeline_df, target_name, mo):
    mo.md(f"## Interaction Timeline: {target_name} ({len(timeline_df)} events)")

@app.cell
def display_timeline(timeline_df):
    timeline_df
```

## Pattern 5: LLM Filtering with `lib.llm`

When you need to classify, score, or extract structured information from each entity (e.g. "is this meeting about project X?", "rate the relevance of this email"), use the `llm_call` helper from `workflows/lib`. It sends each item to an LLM and parses the response into a typed Pydantic model.

**Prerequisites:** Copy `.env.example` to `.env` and fill in your `LLM_API_KEY`. Add `mirascope`, `pydantic`, and `python-dotenv` to the notebook's PEP 723 dependencies.

```python
# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "marimo",
#     "httpx",
#     "polars",
#     "mirascope[openai]",
#     "pydantic",
#     "python-dotenv",
# ]
# ///
```

### Setup cell — load `.env` and import `llm_call`

```python
@app.cell
def setup():
    from dotenv import load_dotenv
    load_dotenv()  # Makes LLM_API_KEY available to lib/llm.py

    import asyncio
    import httpx
    import marimo as mo
    import polars as pl
    from lib.llm import llm_call
    client = httpx.Client(timeout=30)
    return (asyncio, client, llm_call, mo, pl,)
```

### Define a response model

Create a Pydantic model that describes the structured output you want from the LLM:

```python
@app.cell
def models():
    from pydantic import BaseModel

    class RelevanceScore(BaseModel):
        relevant: bool
        reason: str
        score: int  # 0-10

    return (RelevanceScore,)
```

### Filter entities through the LLM

Iterate over fetched entities and call `llm_call` for each one. Since `llm_call` is async, use `asyncio.gather` to process items concurrently:

```python
@app.cell
async def llm_filter(meetings, llm_call, RelevanceScore, pl, mo, asyncio):
    _topic = "Greyhaven"

    async def _score(meeting):
        _text = meeting.get("summary") or meeting.get("title") or ""
        _result = await llm_call(
            prompt=f"Is this meeting about '{_topic}'?\n\nMeeting: {_text}",
            response_model=RelevanceScore,
            system_prompt="Score the relevance of this meeting to the given topic. Set relevant=true if score >= 5.",
        )
        return {**meeting, "llm_relevant": _result.relevant, "llm_reason": _result.reason, "llm_score": _result.score}

    scored_meetings = await asyncio.gather(*[_score(_m) for _m in meetings])
    relevant_meetings = [_m for _m in scored_meetings if _m["llm_relevant"]]

    mo.md(f"**LLM filter:** {len(relevant_meetings)}/{len(meetings)} meetings relevant to '{_topic}'")
    return (relevant_meetings,)
```

### Tips for LLM filtering

- **Keep prompts short** — only include the fields the LLM needs (title, summary, snippet), not the entire raw entity.
- **Use structured output** — always pass a `response_model` so you get typed fields back, not free-text.
- **Batch wisely** — `asyncio.gather` sends all requests concurrently. For large datasets (100+ items), process in chunks to avoid rate limits.
- **Cache results** — LLM calls are slow and cost money. If iterating on a notebook, consider storing scored results in a cell variable so you don't re-score on every edit.

## Do / Don't — Quick Reference for LLM Agents

When generating marimo notebooks, follow these rules strictly. Violations cause `MultipleDefinitionError` at runtime.

### Do

- **Prefix cell-local variables with `_`** — `_resp`, `_rows`, `_m`, `_data`, `_chunk`. Marimo ignores `_`-prefixed names so they won't clash across cells.
- **Put all imports in the `setup` cell** and pass them as cell parameters: `def my_cell(client, mo, pl, asyncio):`. Never `import` inside other cells — even `import asyncio` in two async cells causes `MultipleDefinitionError`.
- **Give returned DataFrames unique names** — `email_df`, `meeting_df`, `timeline_df`. Never use a bare `df` that might collide with another cell.
- **Return only values other cells need** — everything else should be `_`-prefixed and stays private to the cell.
- **Import stdlib modules in `setup` too** — even `from datetime import datetime` creates a top-level name. If two cells both import `datetime`, marimo errors. Import it once in `setup` and receive it as a parameter, or use it inside a `_`-prefixed helper function where it's naturally scoped.
- **Every non-utility cell must show a preview** — see the "Cell Output Previews" section below.
- **Keep cell output expressions at the top level** — if a cell conditionally displays a DataFrame, initialize `_output = None` before the `if`/`else`, assign inside the branches, then put `_output` as the last top-level expression. Expressions inside `if`/`else`/`for` blocks are silently ignored by marimo.
- **Put all user parameters in a `params` cell as the first cell** — date ranges, search terms, target names, limits. Never hardcode these values deeper in the notebook.
- **Declare cells as `async def` when using `await`** — `@app.cell` followed by `async def cell_name(...)`. This includes cells using `asyncio.gather`, `await llm_call(...)`, or any async API.
- **Return classes/models from cells that define them** — if a cell defines `class MyModel(BaseModel)`, return it so other cells can use it as a parameter: `return (MyModel,)`.
- **Use `python-dotenv` to load `.env`** — add `python-dotenv` to PEP 723 dependencies and call `load_dotenv()` early in the setup cell (before importing `lib.llm`). This ensures `LLM_API_KEY` and other env vars are available without requiring them to be pre-set in the shell.

### Don't

- **Don't define the same variable name in two cells** — even `resp = ...` in cell A and `resp = ...` in cell B is a fatal error.
- **Don't `import` inside non-setup cells** — every `import X` defines a top-level variable `X`. If two cells both `import asyncio`, marimo raises `MultipleDefinitionError` and refuses to run. Put all imports in the `setup` cell and receive them as function parameters.
- **Don't use generic top-level names** like `df`, `rows`, `resp`, `data`, `result` — either prefix with `_` or give them a unique descriptive name.
- **Don't return temporary variables** — if `_rows` is only used to build a DataFrame, keep it `_`-prefixed and only return the DataFrame.
- **Don't use `await` in a non-async cell** — this causes marimo to save the cell as `_unparsable_cell` (a string literal that won't execute). Always use `async def` for cells that call async functions.
- **Don't define classes in a cell without returning them** — a bare `return` or no return makes classes invisible to the DAG. Other cells can't receive them as parameters.
- **Don't put display expressions inside `if`/`else`/`for` blocks** — marimo only renders the last top-level expression. A DataFrame inside an `if` branch is silently discarded. Use the `_output = None` pattern instead (see [Cell Output Must Be at the Top Level](#cell-output-must-be-at-the-top-level)).

## Cell Output Previews

Every cell that fetches, transforms, or produces data **must display a preview** so the user can validate results at each step. The only exceptions are **utility cells** (config, setup, helpers) that only define constants or functions.

Think from the user's perspective: when they open the notebook in `marimo edit`, each cell should tell them something useful — a count, a sample, a summary. Silent cells that do work but show nothing are hard to debug and validate.

### What to show

| Cell type | What to preview |
|-----------|----------------|
| API fetch (list of items) | `mo.md(f"**Fetched {len(items)} meetings**")` |
| DataFrame build | The DataFrame itself as last expression (renders as interactive table) |
| Scalar result | `mo.md(f"**Contact:** {name} (id={contact_id})")` |
| Search / filter | `mo.md(f"**{len(hits)} results** matching '{term}'")` |
| Final output | Full DataFrame or `mo.md()` summary as last expression |

### Example: fetch cell with preview

**Bad** — cell runs silently, user sees nothing:

```python
@app.cell
def fetch_meetings(fetch_all, DATAINDEX, my_id):
    meetings = fetch_all(f"{DATAINDEX}/query", {
        "entity_types": "meeting",
        "contact_ids": str(my_id),
    })
    return (meetings,)
```

**Good** — cell shows a count so the user knows it worked:

```python
@app.cell
def fetch_meetings(fetch_all, DATAINDEX, my_id, mo):
    meetings = fetch_all(f"{DATAINDEX}/query", {
        "entity_types": "meeting",
        "contact_ids": str(my_id),
    })
    mo.md(f"**Fetched {len(meetings)} meetings**")
    return (meetings,)
```

### Example: transform cell with table preview

**Bad** — builds DataFrame but doesn't display it:

```python
@app.cell
def build_table(meetings, pl):
    _rows = [{"date": _m["timestamp"][:10], "title": _m.get("title", "")} for _m in meetings]
    meeting_df = pl.DataFrame(_rows)
    return (meeting_df,)
```

**Good** — DataFrame is the last expression, so marimo renders it as an interactive table:

```python
@app.cell
def build_table(meetings, pl, mo):
    _rows = [{"date": _m["timestamp"][:10], "title": _m.get("title", "")} for _m in meetings]
    meeting_df = pl.DataFrame(_rows).sort("date")
    mo.md(f"### Meetings ({len(meeting_df)} results)")
    return (meeting_df,)

@app.cell
def show_meeting_table(meeting_df):
    meeting_df  # Renders as interactive sortable table
```

### Utility cells (no preview needed)

Config, setup, and helper cells that only define constants or functions don't need previews:

```python
@app.cell
def config():
    BASE = "http://localhost:42000"
    CONTACTDB = f"{BASE}/contactdb-api"
    DATAINDEX = f"{BASE}/dataindex/api/v1"
    return CONTACTDB, DATAINDEX

@app.cell
def helpers(client):
    def fetch_all(url, params):
        ...
    return (fetch_all,)
```

## Tips

- Use `marimo edit` during development to see cell outputs interactively
- Make raw API responses the last expression in a cell to inspect their structure
- Use `polars` over `pandas` for better performance and type safety
- Set `timeout=30` on httpx clients — some queries over large date ranges are slow
- Name cells descriptively — function names appear in the marimo sidebar