PPTX adapter: preserve slide structure, notes, media, and reading order #22

Migrated from private source issue alphazede/bran-dev#7

Parent: #5

Goal

Add a local PPTX adapter that maps PresentationML into the presentation-content payload defined by the enterprise-document RFC and can emit a supported deterministic PPTX projection.

Import scope

Preserve, where supported:

• deck and slide order, slide identifiers, sections, and layouts
• shapes, text, tables, hyperlinks, and grouped elements
• speaker notes, comments, alt text, and reading order
• themes and style references needed to interpret content
• images and permitted media as content-addressed assets
• stable slide/shape/text locators for BRAN citations

Unsupported transitions, animations, charts, SmartArt, or media behavior must appear in the fidelity receipt rather than disappearing silently.

Safety boundary

• Treat PPTX as an untrusted OPC/ZIP package.
• Do not execute macros, actions, embedded objects, scripts, or media.
• Do not follow external relationships or remote media.
• Enforce part-count, relationship, nesting, decompression, and total-byte limits.

Acceptance criteria

• Import is deterministic regardless of ZIP ordering and timestamps.
• Fixtures cover layouts, text boxes, grouped shapes, tables, notes, comments, alt text, links, images, and reading order.
• Adversarial fixtures cover external media, macro-enabled decks, malformed relationships, path escape, and decompression limits.
• Exported decks open in at least two independent readers and include a fidelity receipt.
• Import-export-import preserves supported slide order, structural identities, notes, accessibility metadata, and citation anchors.
• DLP and public-boundary checks complete before export.
• No PowerPoint installation or cloud service is required.

Non-goals

Running slide shows, executing transitions or macros, or promising pixel-identical layout across rendering engines.