# Schema

## Payload — one observation, four tar members

The tars are **uncompressed**, members of one observation are **consecutive**,
and the key is everything before the first `.` in a member name. Keys contain no
dots.

```
<key>.png             screenshot, PNG, never re-encoded
<key>.leaf.json       list of visible elements
<key>.screentag.txt   serialized markup
<key>.record.json     sanitized metadata
```

`<key>` is `<shard>__<stem>`, e.g. `shard-0106__scene-002ad3e5b23cbfd9-step00`.
It is shard-qualified because 152 capture stems and 128 scene ids repeat across
shards — a scene a run failed to finish was recaptured by a later run under the
same seed. `(shard, stem)` is unique across all 1,266,471 source rows.

## `leaf.json` — an element

```jsonc
{
  "type": "Button",                 // release class, 55 in the schema
  "role": "push button",            // AT-SPI role it came from
  "name": "Save",
  "visible_text": "Save",           // text a reader can actually see
  "visible_text_status": "visible",
  "rect":  {"x": 312, "y": 88, "w": 64, "h": 28},   // amodal: the whole element
  "visible_fragments": [                             // modal: pixels it occupies
    {"x": 312, "y": 88, "w": 40, "h": 28}
  ],
  "is_occluded": true,
  "occlusion_state": "partially_occluded",
  "app_name": "homebank",
  "reading_order_index": 41,
  "_window_stack_index": 2,
  "uid": "80b06ebf5db974e2"         // stable within an episode; action targets use it
}
```

**`rect` is amodal and `visible_fragments` is modal.** A box drawn from `rect`
alone claims pixels another window is covering. Train grounding on the
fragments; use `rect` when the question is where the whole element *is*.

## `screentag.txt`

One flat string per screenshot: `<Tag><loc_N>×4 [state] [text]</Tag>`, nested
to mirror the element tree. Coordinates are on a **0–500** grid, normalized to
the viewport (`record["screentag_grid"]`).

## `record.json`

Constructed field by field from an allow list, never by removing fields from
`meta.json`, so a change to the generator cannot quietly widen what is
published. Carries `observation_key`, `scene_id`, `episode_id`, `step_index`,
`split`, `group`, `width`, `height`, `apps`, `theme`, `scene`, `n_elements`,
`n_windows`, `window_stack`, `occlusion`, `flags`, `provenance`, and — on any
observation that an action led to — `action_into_this_state` and
`effect_of_that_action`.

`group` is `ep` for a frame of a click episode and `st` for a standalone scene.

## Indexes

| file | one row per | notable columns |
| --- | --- | --- |
| `index/scenes.parquet` | scene | `split`, `split_source`, `apps`, `theme`, `resolution` |
| `index/observations/<split>.parquet` | observation | `tar_path`, `*_member`, `occluded_ratio`, `n_elements`, `n_windows`, the flags |
| `index/transitions/<split>.parquet` | transition | `before_key`, `after_key`, action fields, `effect`, `exclusion_reasons` |
| `index/episodes/<split>.parquet` | episode | `observation_keys`, `transition_ids`, `episode_status` |
| `index/shard_members.parquet` | tar member | `byte_offset`, `byte_size`, `sha256` |
| `checksums/shard_stats.parquet` | tar | `bytes`, `sha256`, `observations` |

`split_source` is `v3` for a scene placed by the finalized split and `extended`
for one that split never had to place — 12,515 scenes, all of which are
publishable but not state-train-eligible, so they had no row in it.

## Transitions

An action is stored on the step it **produced**:

```
observation[k-1]  --  steps[k].action  -->  observation[k]
```

Step 0 has no action. Reading it the other way pairs every action with the
screen it was not taken on, and nothing downstream would notice.

Coordinates: `action_point_px` is authoritative. `action_point_norm_1000` and
`action_point_screentag_500` are derived and round-trip to within one grid cell;
`action_target_bbox_px` is `[x0, y0, x1, y1]`.

`effect` counts what changed between the endpoints — `changed`, `magnitude`,
`appeared`, `disappeared`, `moved`, `text_changed`, `state_changed`,
`newly_occluded`, `revealed`, `semantic_changes`, `persisted`.

`exclusion_reasons` is empty when `transition_train_eligible` is true and
otherwise names every rule the transition failed, so a count can always be
accounted for.