[rdlabo]

Related: rdlabo-dev/ionic-theme-ios27#269

What is the current behavior?

iOS sheet modals meet the side and bottom edges of the viewport at partial breakpoints. CSS alone cannot keep an inset sheet's visible bounds and rounded lower corners synchronized with interactive dragging and breakpoint transitions.

Independent iOS 27.0 simulator measurements show that native iPhone sheets have side and bottom gaps at partial detents and return to full width at the large detent. iPad uses a different presentation policy.

What is the new behavior?

• Add opt-in --sheet-inset for iOS sheet modals. Partial detents scale and clip the sheet with side/bottom gaps and rounded lower corners; breakpoint 1 returns to full width. The default is zero and MD is unchanged.
• Use shared keyframes for enter, leave, interactive dragging, snapping and programmatic breakpoint changes. The last configured partial breakpoint determines where the inset begins transitioning to full width.
• Keep footers in the scaled page, refresh geometry on resize, and clear owned clipping when responsive CSS disables the inset.

ion-modal.ios.phone-sheet {
  --sheet-inset: 8px;
  --border-radius: 32px;
}

Applications choose when to enable this property. It does not automatically identify devices or claim exact native spring or detent-height parity; existing Ionic breakpoint height semantics are retained.

Does this introduce a breaking change?

• Yes
• No

Other information

Validation:

• Core production/development builds, ESLint, Stylelint and formatting passed.
• New geometry/lifecycle E2E coverage: 12 passed across Chromium, WebKit and Firefox, including dragging, resize, responsive opt-out, footer placement, dismissal prevention and unchanged defaults/MD behavior.
• Existing sheet backdrop/breakpoint/scrolling regression tests: 13 passed.
• Existing modal unit tests: 25 passed.
• Theme CSS preview inspected at partial and full detents; screenshot baselines were not regenerated locally.

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[rdlabo]

Sorry for opening this PR before narrowing the scope sufficiently. The change reaches into modal animations and gestures, which is too broad for the original visual issue. I am closing it to reconsider a smaller approach. Apologies for the unnecessary review overhead.