fix(desktop): fence stale update status responses - #5693

Goal And Delivered Outcome

• Outcome basis / optional anchor: Desktop update freshness gap identified under [Task][RFC]: Complete the Desktop execution frontend journeys #5204.
• Goal/source and gap: desktop_update_status could capture state before bounded diagnostics, while both desktop frontends accepted delayed polling responses after a newer update action completed.
• Observable before -> after, with the validation row that proves it: a delayed downloading response previously replaced restart_required and could expose Apply again; the same deterministic browser scenario now keeps Restart visible and records exactly one Apply request.
• Issue/task and intended base: Related to [Task][RFC]: Complete the Desktop execution frontend journeys #5204; targets main.

Author Declaration

• Written by: model agent (OpenAI Codex), operated by Duang777.

Implemented against

• Specification and revision: Issue [Task][RFC]: Complete the Desktop execution frontend journeys #5204 plus the public scope comment on 2026-10-05; no narrower maintainer-authored specification.
• Criteria:

• Self-check before submission: Reviewed the four-file diff, rebased onto current upstream/main, checked DCO, public/private boundaries, formatting, static analysis, unit tests, production frontend bundles, exact runtime bundle generation, and the browser journey. A signed packaged App was deliberately not built because release signing fixtures are unavailable.

Scope And Continuation

• Completed scope and remaining work: Complete within the claimed freshness-race scope. The parent desktop journey task remains broader.
• Slice boundary / successor: Packaged macOS validation remains CI/release-owned; this PR verifies the exact source bundle and production web assets without signing or installing an App.

Validation

• Tested revision: 647188f74eb961731a6dcc0f502b3e0379d10d26
• Run state: finished
• Input classes: synthetic, public_fixture

• Coverage and gaps: No signed .app was installed or exercised. The deterministic IPC double covers response ordering, while Rust tests compile and execute the backend with the exact generated runtime resources.

Frontend / Visual Evidence

• UI impact: none
• Before: N/A
• After: N/A
• States and viewports shown: Existing desktop and mobile states were exercised; no layout, style, or copy changed.
• Source data: synthetic
• Attention review: No visual elements were added or moved. Existing loading, failure, recovery, and one-step update controls remain available.

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring (no functional changes)
• Documentation update
• Test update

LoopX Area

• Control plane (goals, todos, quota, scheduler, registry, runtime)
• Benchmark boundary (adapters, runners, verifiers, scoring, evidence)
• Capability or extension (providers, adapters, skills)
• Public docs or presentation surface (README, protocols, dashboard)
• Build, packaging, installer, or CI
• Host or runtime integration

Technical Direction

• Direction / acceptance reference, when applicable: Desktop execution frontend journey reliability under [Task][RFC]: Complete the Desktop execution frontend journeys #5204.

Shared-authority RFC fixture impact

N/A. This change does not claim progress against the TypeScript control-plane migration or shared Goal Authority RFC.

Boundary Checklist

• Neither the diff nor this PR body/comments/attachments disclose private state, credentials, raw traces or verifier output, internal links, or local machine paths.
• I did not duplicate maintainer-owned benchmark work unless a maintainer split out a public issue for it.
• I kept the change scoped to the linked issue/task.
• I completed the visual evidence section for UI changes, or marked UI impact none.
• Every commit includes a DCO Signed-off-by trailer (git commit -s).