[tiensonqin]

Summary

Add Element.HandleNavigationKeys(keys, fn) for node-local handling of arrows left by a focused child, before default scrolling. Preserve child/native/shortcut priority, stop at the nearest declared owner, and respect editing/compound-control/overlay boundaries. Only arrows with no modifiers or Shift are eligible; unsupported declarations panic and empty/nil/omitted registrations unregister. No global capture, new queue, or default opt-in.

Testing

• CGO_ENABLED=0 go test ./ui ./internal/uimigrate: passed; focused arrow contract also verified red without the route, green with it.
• Full CGO_ENABLED=0 go test ./...: all change-related tests pass after API-index regeneration; internal/darwin.TestLocales fails preferred-language isolation identically on untouched base 5c865d27 in a separate worktree. No locale source changed.
• CGO_ENABLED=0 build/vet for Darwin, Linux and Windows (arm64), production mygo_noinspector vet, and js/wasm vet: passed. No GUI validation.
• Public API and production migrator index regenerated; layout-cache completeness records navigation as event-only.

Production sizes in bytes (arm64, trimpath, noinspector, stripped):

OS	counter-native before	after	delta	hello delta
macOS	9,781,938	9,782,050	+112	0
Linux	9,175,303	9,175,303	0	0
Windows	9,569,792	9,570,816	+1,024	0

-dumpdep plus go tool nm -size confirms unused navigation implementations are dead-stripped. The small native-only growth comes from the optional dispatch call, committed registration/barrier writes, and type/section alignment; no feature implementation or heavy dependency is retained by non-users. Webview hello is unchanged on all platforms.

Tested on:

• macOS (headless tests/build/vet only)
• Windows (cross-build/vet only)
• Linux (cross-build/vet only)
• Web (wasm vet only)
• Other: (specify here)

AI disclosure

• Tool and model: Devin (Cognition AI; underlying model version is not exposed).
• Used for: implementation, contract tests, source review, and this description.
• A human read every line of this change and can explain it.

Link to Devin session: https://app.devin.ai/sessions/90fc05f0cb694a4292bb80a3a7186778
Open in Devin Desktop: https://app.devin.ai/desktop/session/90fc05f0cb694a4292bb80a3a7186778?variant=devin
Requested by: @tiensonqin

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring