#17417 fix(cloud): prevent Cmd-Y picker crashes from duplicate machines

Summary

• Deduplicate Cloud machine IDs before rendering the New Machine Base picker.
• Prevent duplicate SwiftUI picker identities during a live nightly refresh while Cmd-Y opens the sheet.

Testing

• git diff --check
• Added NewMachineModelTests.sourceRefreshDeduplicatesMachineIDs (hosted Swift test required for execution).

Changelog

• Fixed Cmd-Y crashing when overlapping Cloud refreshes briefly return duplicate machine IDs.

Impact map

• Source of truth: NewMachineModel.applySourceMachines.
• Direct caller: NewMachineSheetPresenter cache refresh path; all New Machine entrypoints share this model.
• Cross-surface effects: Base picker receives one stable row per machine ID; first occurrence wins.
• Residual risk: full macOS test execution is delegated to CI.

Mergeability

• Conflict-only gate: pending PR creation.

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Summary by cubic

Fixes the Cmd-Y New Machine Base picker crashing when overlapping Cloud refreshes briefly return duplicate machine IDs, and keeps the picker inside the sheet when the cache holds many machines.

• Deduplicates machine IDs in NewMachineModel.applySourceMachines so each ID maps to one stable row, with the first occurrence winning.
• Constrains the Base picker frame so a long machine list no longer widens the sheet.
• Freezes the sheet's initial size during presentation so a mid-animation cache refresh can't resize the window from inside AppKit's constraint pass.

Mergeability

• Base SHA: 7e315c5acbf1aab0e0a87e8e0011be69d848684d
• Head SHA: 14b2b8043a8ca0758aa427c8c716ffc92c2ed4ce
• Conflict-only gate: PASS (91914df8173fa67cc08dde20864d08336ac508ff), no conflicted paths

Summary by CodeRabbit

• Bug Fixes
  • Duplicate source machines are now shown only once, with the first entry’s name retained.
  • The base image picker now uses the available sheet width, preventing cached machines from making the sheet wider.