Reading in-cell ("Place in Cell") rich-value images

Cluster: images

Scenario

Excel's "Place in Cell" feature stores an image inside a cell value rather than as a floating drawing anchored over the grid. This uses the rich-value mechanism: the cell carries a value-metadata (vm) index that points through the workbook metadata part to a rich-value record, which references the image via a rich-value relationship to a media part. The legacy #VALUE! error is stored in the cell as a fallback for applications that don't understand rich values.

A reader that only understands drawing-anchored images (twoCell and oneCell anchors) surfaces none of these: getImages() returns nothing, and the image-bearing cells look empty or like errors. The image is silently invisible to the caller.

Desired behavior

• Reading a workbook whose cells use in-cell rich-value images surfaces those images, each associated with its host cell such as C2, not with a drawing-anchor position.
• Resolution follows the real chain: cell vm index, then workbook metadata, then the rich-value record, then the rich-value relationship, then the media part, yielding the correct image bytes for each cell.
• The legacy #VALUE! error fallback stored in the cell must not mask the presence of the in-cell image. The model should expose the image and treat the error as the documented fallback.
• This is distinct from drawing-anchored images: the API should make clear which images are in-cell, part of a cell's value, and which are floating, anchored over the grid.

Open questions

• The public model shape for an in-cell image: a distinct cell value kind, such as an image value, or a parallel per-cell image accessor. It must round-trip.
• Write-side authoring of in-cell images, creating a "Place in Cell" image: in scope, or read and preserve only for now?
• Hostile-input hardening: the metadata to rich-value to media indirection is attacker-influenced, so bound the indirection depth and validate indices, and a crafted file must not force unbounded work or dangling-reference crashes.
• Interaction with getImages() (drawing-anchored) so callers can enumerate both kinds without conflating them.

Related: image-by-filename-is-node-only, image-anchor-emu-from-real-column-geometry (the drawing-anchored image model this extends beyond).