[zqr10159]

Agent handoff

• Task ID: Windows import picker and Xshell encoding
• Stage: implementation
• Base SHA: a17dfa2fd61fd94128bbe69dad06fc20363c1988
• Allowed paths respected: yes (backend/)
• Depends on PR: none

Fix the Windows source picker whose OK button was outside the form client area, and decode BOM-marked UTF-16 Xshell session files inside .xts archives. UTF-8 files, including those with a BOM, remain supported.

Verification

• Repository identity, vendor lockstep, connection-form and mock host registry checks
• Frontend typecheck and build; 2,173 frontend tests passed with two workers (before unrelated local work)
• cargo fmt --manifest-path backend/Cargo.toml --check
• cargo clippy --locked --manifest-path backend/Cargo.toml --all-targets -- -D warnings
• cargo test --locked --manifest-path backend/Cargo.toml: 1,300 passed; triggers::tests::execute_command_strips_single_trailing_newline failed on Windows because its local printf command exited with code 1. This test and its code are unchanged by this PR.
• SSH container smoke and relevant MCP smoke: not run; no SSH server was contacted.

The Xshell UTF-16LE, UTF-16BE and UTF-8 BOM regression test passed. A WinForms client-area bounds check passed; live picker behavior at different Windows DPI settings still needs review. scripts/verify_rdp_vendor_integrity.py failed on unchanged vendor trees in this Windows checkout; case-sensitive path ordering reproduces the registered digest for six of seven trees, while sspi still needs investigation.

Security review

• No real credentials, private keys or production hosts used
• Authentication/secret/command-execution changes reviewed by a human: not applicable to this change; human review of the import handling is still requested.
• No install or DBX restart performed by the agent

Review notes

• Changed files: backend/src/local_fs.rs, backend/src/connection_import.rs.
• Risks or known limitations: the connection-form action still imports only the first session; this PR does not provide batch connection creation or credential migration.
• Follow-up task: investigate the Windows-only command test and vendor integrity check; verify the picker on scaled displays.