[zoster81]

Purpose

Fix a reproducible Windows standalone self-update/recovery failure: the staged helper executable lacked .exe and Windows could not dispatch it.

Scope

• Use helper.exe on Windows; preserve helper on Linux/macOS.
• Add a native executable-launch regression exercised on supported operating systems.
• Update architecture documentation and unreleased changelog.

Verification completed locally

• Windows real copied-helper launch: RED before fix / GREEN after fix.
• go test -timeout=30m -count=1 ./...: pass.
• go vet ./... and go mod verify: pass.
• node --test scripts/*.test.js: 327 passed, 4 platform-specific skips.
• Local Markdown links and diff whitespace checks: pass.
• Linux and macOS test compilation: pass (not native execution).

Acceptance before merge or 3.3.6 release

• Observe hosted Windows, Ubuntu and macOS native tests including helper dispatch and recovery; review race and security jobs.
• Verify release-facing docs and changelog; evaluate any CI failures against behavior, not brittle wording.
• Do not merge or publish until checks and review pass. Existing 3.3.0 Windows installation requires a separately approved safe bootstrap; do not operate on its pending-state quarantine or active launcher.