Gate iMessage local sync to macOS in serve to eliminate unsupported-platform warnings

[Copilot]

openmessage serve was attempting iMessage local DB sync on Windows, producing repeated warnings like load chats: unable to open database file under platform=imessage. This change limits iMessage background sync to supported OS behavior so Windows/Linux runs stop surfacing misleading iMessage importer errors.

• Behavior change: platform-gated iMessage sync

  • Wrapped periodic iMessage sync in an OS support check.
  • serve now skips iMessage local sync unless running on Darwin.

• Code structure: shared Darwin predicate

  • Introduced a shared isDarwin() helper and reused it from both notification gating and iMessage sync support checks.
  • Keeps platform checks consistent and avoids duplicated GOOS comparisons.

• Coverage: explicit sync support test

  • Added TestIMessageSyncSupported to verify:
    • darwin => supported
    • windows => unsupported

if iMessageSyncSupported() {
    syncPlatform("imessage", "iMessage sync complete", func(store *db.Store) (*importer.ImportResult, error) {
        return (&importer.IMessage{MyName: identityName}).ImportFromDB(store)
    })
}

[Copilot]

Pull request overview

This PR prevents openmessage serve from attempting iMessage local database sync on unsupported operating systems by gating the periodic iMessage sync path to macOS (Darwin). This reduces noisy/ misleading warnings on Windows/Linux while keeping existing macOS behavior intact.

Changes:

• Gate periodic iMessage local sync behind a iMessageSyncSupported() check (Darwin-only).
• Introduce a shared isDarwin() helper and reuse it from the macOS notifications default-path and iMessage sync gating.
• Add a unit test verifying iMessage sync support behavior across darwin vs windows.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
go.mod	Promotes several already-imported dependencies from indirect to direct requirements (module bookkeeping).
cmd/serve.go	Skips periodic iMessage local sync unless running on Darwin; centralizes GOOS check in isDarwin().
cmd/serve_test.go	Adds TestIMessageSyncSupported to validate Darwin-only support behavior.

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