[enaboapps]

Strengthen word predictions when native caret text becomes unavailable. The existing worker now accepts ordered append, Backspace and reset edits, seeds its bounded field-scoped buffer from valid native context, and retains tracking across keyboard layouts. Without native context, predictions still require a typed boundary. Native context remains authoritative when available.

Backspace removes a complete Unicode grapheme only within known buffered text. Accepted prediction suffixes are recorded once after successful injection. Existing focus, protected-field, editable-target, external-input and observer-health checks remain required. Buffers stay in memory and are never logged. No settings schema or BLE changes.

Independent review found a race where an in-flight native read could already include an edit still queued by the parent. Stale suggestion replies now force a buffer reset before replaying later edits. Deterministic append and Backspace regressions cover that case.

Validation:

• Node 24 frontend lint, build, 163 tests and 5 script tests passed.
• Rust 1.97.1 format, Clippy, 489 unit tests and 7 configuration tests passed; one existing ignored benchmark.
• Coverage includes native/buffer transitions, ordered edits, Unicode deletion, boundaries, buffer limits, focus resets, protected fields, stale results, one-time acceptance and stable repeated batches.
• Independent latest-head review of 12e5f0c: no remaining actionable findings.
• Native Mac and Windows ARM builds and switch keyboard typing ran in disposable editors. Mac fixture withheld AX caret range; Windows fixture withheld UIA TextPattern while retaining ValuePattern.
• Native fallback qualification is unresolved: neither fixture produced visible buffered suggestions. Mac guard/fixture eligibility was not established. Windows manual navigation used Parallels Ctrl+Alt+F-key commands, which invalidate buffered context; an automatic-scanning retry was inconclusive. Native suggestion acceptance, correction and native-context recovery are not claimed as passed.
• Restored both VMs’ settings byte-for-byte, stopped owned fixtures, restarted the prior Windows build and returned Mac to suspended. Signed local Mac app was untouched.
• All CI checks passed, including Mac and Windows native packaging (run 35529684611).

Closes #811. No merge or release requested. Native end-to-end qualification remains required before treating this fallback as verified on either platform.