fix(windows): sign inner Atomic-Chat.exe at bundle time to fix AV false positives (ATO-248)

[cursor]

Describe Your Changes

• Add bundle.windows.signCommand to src-tauri/tauri.windows.conf.json pointing to a new wrapper script src-tauri/windows/sign-binary.bat
• New script calls signtool.exe with the DigiCert KSP (/csp "DigiCert Signing Manager KSP" /kc "%SM_CERT_ALIAS%"); exits 0 gracefully when SM_CERT_ALIAS is absent (local dev / fork-PR builds)
• Update the Windows CI build step to pass the four DigiCert KSP secrets (SM_API_KEY, SM_CLIENT_CERT_PASSWORD, SM_HOST, SM_CERT_ALIAS) so the KSP DLL can authenticate during yarn tauri build
• Add ADR entry in AGENTS.md §7

Root cause

The post-build jsign step in .github/workflows/release.yml signed only the NSIS installer and MSI. The inner Atomic-Chat.exe embedded in the NSIS installer was left unsigned. Kaspersky unpacks installers before scanning and finds the unsigned binary, triggering:

• Trojan-Downloader.Win32.Agent.xydtva (heuristic on unsigned binary that downloads/launches executables at runtime)
• UDS:DangerousObject.Multi.Generic (KSN cloud reputation: new hash, low prevalence)

The fix

Tauri's bundle.windows.signCommand runs before NSIS packaging — the bundler calls it for every binary (main exe + sidecar EXEs). This ensures Atomic-Chat.exe carries a valid Authenticode signature before it is embedded in the installer.

// src-tauri/tauri.windows.conf.json
"signCommand": "cmd /c windows\\sign-binary.bat %1"

The sign-binary.bat wrapper exits 0 (skip) when SM_CERT_ALIAS is absent, keeping local dev builds unaffected. The existing jsign post-build step that signs the installer itself is unchanged.

Verification

• tauri.windows.conf.json validates as valid JSON ✓
• sign-binary.bat exits 0 when SM_CERT_ALIAS is unset ✓
• Residual manual step: build a tagged release, extract Atomic-Chat.exe from the NSIS installer, run signtool verify /pa Atomic-Chat.exe to confirm the signature

Fixes Issues

• Closes ATO-248

Self Checklist

• Added relevant comments, esp in complex areas
• Updated docs (ADR entry in AGENTS.md §7)
• Created issues for follow-up changes or refactoring needed
  • Follow-up: sign jan-cli.exe and bundled llama-server DLLs (lower-risk, resources not in externalBin so not handled by signCommand)