feat(pptx): patch-mode saves + IndexedDB-backed source persistence

[karthikmudunuri]

The user complaint

After 1.12.1 the user re-uploaded KBC-More_sample_slides.pptx, edited a small text, exported, and the save dropped:

• 1 / 2 slide masters
• 1 / 50 slide layouts
• 1 / 3 themes
• 18 / 25 media files

Plus the edited text element lost its themed colors and brand fonts — pptxgenjs flattens <a:schemeClr> to inline <a:srgbClr> and drops <a:latin> typeface refs.

Two distinct root causes, two fixes.

1. Patch-mode saves (Univer-inspired)

When the user edits a text or drags a shape, the old path regenerates the entire <p:sp> via pptxgenjs — which only knows a fraction of the OOXML schema, so themed colors, brand fonts, custGeom paths, gradient fills, body padding, effects, autofit hints all drop on the floor.

tryPatchEditedElement now splices the edit into the source XML in place:

• Text content — splice the new text into <p:txBody>, preserving the first paragraph's <a:pPr> (alignment, bullets, indent) and the first run's <a:rPr> (themed colors, fonts, bold/italic/underline/strike). Multi-line text becomes multi-paragraph; mixed-style runs still fall back to pptxgenjs.
• Geometry — replace <a:xfrm> (or <p:xfrm> on <p:graphicFrame>) and keep everything else. Works for <p:sp>, <p:pic>, <p:cxnSp>, <p:graphicFrame>.
• Placeholder-inherited shapes — now registered too. Patch-mode always splices geometry into the patched output, so themed styling on title / body / content placeholders survives text edits.

pptxgenjs remains the fallback for unpatchable cases (newly added elements, color/font picker edits, mixed-style run restyling, shape kind changes). Architecture matches Univer's "edit the source doc tree, never round-trip through a lossy intermediate model."

2. IndexedDB-backed source persistence

Even with patch-mode, the chrome / EMF / slide-bg preservation pipeline still needs the source PPTX bytes at save time. PR #47 introduced an enumerable Deck.sourcePptxId plus a module-level cache so the bytes survive structuredClone and reducer spreads — but the cache was in-memory only, so a full page reload (host loads deck from localStorage, fresh module instance) emptied it.

parsePptx now mirrors source bytes to IndexedDB keyed by sourcePptxId. serializeDeck's source resolution walks: explicit options.source → in-memory cache → IndexedDB → legacy non-enumerable attachment. The IDB layer is best-effort (private mode / quota exceeded gracefully no-op) and falls back to nothing in SSR / Node environments.

Bonus: Export topbar now downloads .pptx

The package's <TopBar.Export> button used to download a .slidewise.json dump when the host didn't register onExport. It now calls serializeDeck directly and downloads a real .pptx, so hosts can verify the full edit → save round trip without wiring onExport at all (and so I can test the dev server locally with one click).

Validation

End-to-end against KBC-More_sample_slides.pptx with parsePptx → structuredClone + spread → serializeDeck(deck) and no source passed:

	Source	Before this PR	After
Slide masters	2	1	2 ✅
Slide layouts	50	1	50 ✅
Themes	3	1	3 ✅
Media	25	18	27 (25 + 2 from pptxgenjs) ✅
Slides with content	6/6	6/6	6/6 ✅

New regression tests in patch-mode.test.ts: edit text on eon-deck slide 10 column 2 → asserts the source <a:schemeClr val="accent1"/> fill AND the <a:schemeClr val="bg1"/> text color both survive verbatim. Geometry drag test asserts the same theme refs survive after an x-coordinate change.

pnpm typecheck clean. pnpm --filter @textcortex/slidewise test → 41/41 passing.

Test plan

• Typecheck + tests green locally
• End-to-end script on KBC reproduces full chrome preservation
• Regression test for theme refs on text edit (eon-deck)
• Regression test for theme refs on geometry edit (eon-deck)
• Reviewer: open KBC-More_sample_slides.pptx → edit a text → export → verify in PowerPoint that the 50 layouts and 3 themes are intact

Changeset

Minor bump on @textcortex/slidewise (1.12.1 → 1.13.0). New optional Deck.sourcePptxId field is additive; patch-mode kicks in automatically, no API changes.

Known not-yet-patched

• Multi-run text edits with mixed styling — still fall through to pptxgenjs. The contentEditable surface collapses heterogeneous runs to a flat runs array which the patch path can't yet faithfully serialize. Follow-up: rebuild <p:txBody> from el.runs while preserving paragraph-level <a:pPr>.
• Color / font / weight picker changes — not yet a patch category. They go through pptxgenjs. Adding color and fontFamily to the patch field set is straightforward; will follow once the contentEditable run handling is sorted.
• 4:3 source chrome preservation — still skipped by the aspect-ratio guard. Needs the deeper inverse-fit refactor.