Plain interactive 'mcs sync' wipes component exclusions chosen via --customize

[bguidolim]

Problem

Component exclusions chosen via mcs sync --customize are silently discarded — and erased from state — by the next plain interactive mcs sync.

Configurator.interactiveConfigure (Sources/mcs/Sync/Configurator.swift:128-135) hardcodes an empty exclusion set and only populates it when --customize is passed:

var excludedComponents: [String: Set<String>] = [:]
if customize, !selectedPacks.isEmpty {
    excludedComponents = ConfiguratorSupport.selectComponentExclusions(...)
}

previousState is read only to seed the picker's checkboxes inside selectComponentExclusions — never to carry exclusions forward when the picker doesn't run.

Downstream, installAndReconcileArtifacts writes that empty set straight back to state:

// Configurator.swift:832
state.setExcludedComponents(excluded, for: pack.identifier)

So a plain mcs sync reinstalls every previously-excluded component and wipes the record that they were ever excluded.

Inconsistent with the non-interactive paths

--pack / --all get this right — SyncCommand loads persisted exclusions before delegating:

// SyncCommand.swift:87-89 (global), :145-147 (project)
persistedExclusions = try ProjectState(...).allExcludedComponents

and passes them at SyncCommand.swift:104 / :162. Only the interactive non-customize path drops them. Both scopes (project and --global) are affected, since interactiveConfigure is shared.

Reproduction

1. mcs sync --customize, deselect a component of some pack
2. mcs sync (plain, interactive, same pack selection)
3. The deselected component is reinstalled, and .claude/.mcs-project no longer lists it under excludedComponents

Fix sketch

Seed from persisted state when the picker doesn't run:

var excludedComponents = previousState.allExcludedComponents
if customize, !selectedPacks.isEmpty {
    excludedComponents = ConfiguratorSupport.selectComponentExclusions(...)
}

Newly-selected packs contribute no entry, so they install fully — correct. Deselected packs are removed by unconfigurePack, which already clears their state entry (ProjectState.swift:162).

Worth confirming while fixing: removeNewlyExcludedComponentArtifacts (Configurator.swift:538-545) diffs previousExcluded vs currentExcluded. With the fix those are equal on a plain sync, so it correctly becomes a no-op.

Tests

Tests/MCSTests/LifecycleIntegrationTests.swift:

• customize-exclude a component → plain re-sync → component still absent, still recorded in excludedComponents
• customize-exclude → plain re-sync → --customize again shows the component unchecked
• newly added pack on a plain sync installs all its components (regression guard: persisted exclusions from other packs must not leak)

Relation to #356

#356 (requiredBy on prompts) depends on the selected-component set being stable across syncs — a prompt skipped under --customize would otherwise be re-asked on the next plain sync. This should land first.