fix(cua-driver): preserve Linux pixel focus refusal details

[tanishqkancharla]

Preserve pixel-focus refusal details

Canonical Linux CI34558519742 at2e81b retains a failed background pixel typing case: the response says only focus pixel-click at (0,0) failed, losing the expected background_unavailable classification. The click implementation already returns the structured refusal before input; the shared Linux keyboard focus helper discards it. This prevents code and agent callers from distinguishing unsupported delivery from an uncertain failed input.

Scope: propagate the existing ToolResult unchanged when the prerequisite pixel focus action refuses. Keep input routes, fallback policy, focus, successful timing and public schemas unchanged. TypeText, PressKey and Hotkey share this helper. Stacked on the exact screen-origin candidate; unrelated hidden GTK fixture controls and scroll oracles stay separate. Fork issues are disabled, so the linked draft PR is the problem record.

Acceptance: unchanged canonical GTK3 background pixel typing must return background_unavailable with no leaked input and unchanged focus/z-order/cursor. Focused build/checks then the exact canonical row on a disposable remote Linux desktop; other affected keyboard callers must preserve the same response. Existing failing artifact remains retained. Complete certification remains required before readiness; no agent or cross-platform parity claim.

Exactce1b14809 compiled in focused CI34559870891; foreground typing passed but background setup failed because the diagnostic workflow omitted the required Electron sentinel. That failure remains retained. Workflow2190e9b restores the unchanged canonical sentinel dependency; run34560230870 passes both original canonical pixel-typing cases. Independent artifact inspection verifies source identity, background refusal with focus/z-order/cursor/no-leaked-input/fixture-state oracles, and foreground delivery with expected fixture state. This development-binary supporting check is not complete release/cross-platform certification. No model spending.

Full Linux release verification now passes on combined candidate403572f34dfbdc83b17bda7fe4c351060be32785, which includes the exact product/test changes from #5, #6 and #7 with source attribution. CI34561195062 passes all four jobs: shared83, native39, capture7 and canonical local installation. Independent inspection preserves every original case/expected behavior/oracle, verifies typed refusal codes, source/CI identities and finalized recording paths. All129canonical cases pass without skips. The release binary SHA256 is e65549f1a2d77d168581a2c2cc84585f90b51748a1cf85c2cf43bfca7a49ba85; installed identity/config and owned daemon/temp cleanup also pass.

Nine unchanged public-SDK cases then pass on that exact release binary in an isolated Linux desktop: four font edits, displaced Code replacement and four Calc/focus/dropdown checks. Saved files and owned cleanup were independently checked. This is supported X11 acceptance, not new Wayland/macOS GUI evidence or an agent parity score. A fresh matched Terra font pair on evaluator2d8879f is running separately. Its first OpenSky attempt passes in62.822seconds/10calls with full60/28pt, text and original font families preserved; native is pending. Prior failed agent outcomes remain retained. The user has explicitly authorized merging these fixes into this fork.