Gesture viewport should expose content-safe bounds (app window minus system bars) so scroll planning clamps to real geometry #1821

Follow-up from #1820 (#1781 A1), asked for in its review.

Today

buildScrollGesturePlan (packages/contracts/src/scroll-gesture.ts) keeps scroll gestures out of the outer DEFAULT_EDGE_PADDING_FRACTION = 10 % of each axis. That fraction is a proxy for the real invariant — a scroll must never touch down inside a system bar — tuned to exceed the tallest known bar (Pixel 7 cutout status bar 136/2400 = 5.7 %, iPhone Dynamic Island 59/852 = 6.9 %). It lives in a device-agnostic pure planner because the viewport it receives is the raw application window, which on edge-to-edge apps (API 35+, every system app, iOS) starts at y=0 and includes the bars. #1820 raised it from 5 % after scroll up 3 on a Pixel 7-geometry emulator touched down at y=120, inside the bar, and pulled the notification shade instead of scrolling.

Costs of the proxy: every user pays 10 points of max single-gesture travel (90 % → 80 % for amount ≥ 0.8) whether or not their device has a cutout, and a device with a taller bar than the tuned constant reintroduces the shade pull silently.

Proposed

The layer that knows where the bars are should say so:

• Android — GestureViewportReader.read() (android/snapshot-helper/.../GestureViewportReader.java) already iterates UiAutomation.getWindows() and keeps only TYPE_APPLICATION; the StatusBar / NavigationBar system windows are right there to subtract (or read the status/navigation-bar insets). Expose content-safe bounds alongside the raw window bounds in the viewport action (helper protocol/API version bump).
• Apple — the runner has safe-area insets; report the same content-safe rect in the resolved scroll frame.
• Planner — clamp scroll travel to the content-safe rect and return DEFAULT_EDGE_PADDING_FRACTION to a small generic margin (the original 5 % or less). Keep the raw window rect for absolute swipe/gesture validation so an agent can still deliberately swipe down from the status bar.
• Parity table contracts/fixtures/scroll-gesture.json (added in fix(scroll): keep saturated scroll gestures out of the status bar; gate Android replays from android/emulator (#1781 A1) #1820) is where the new vectors go — both the TS and Swift suites iterate it.

Also on this issue: suite discovery order

The masking in #1781 A1 came from discoverReplaySourcePaths (src/daemon/replay-source-discovery.ts) enumerating directory inputs in native readdir order (03,05,06,…,04 on the ubuntu runner vs 01…06 locally). The header documents this as deliberate Maestro parity, and it is accurate — Maestro's WorkspaceExecutionPlanner uses Files.walk and names the result unsortedFlowFiles, no sort. Sorting directory inputs would make results reproducible across machines but is a deliberate departure from that parity; decide it here rather than silently. Order-sensitive tests currently pass explicit positionals (see session-test-suite.test.ts).