Summary

Fixes mock code generation for dependency cycles through Instantiator boundaries, and prevents optional mock parameters from shadowing non-optional local bindings.

Fix: __safeDI_mock_ internal parameter label prefix

All mock method parameters now use Swift's external/internal label syntax:

public static func mock(
    player __safeDI_mock_player: Player? = nil
) -> Parent {
    let player: Player = __safeDI_mock_player ?? __safeDI_player()
}

The external label is unchanged — call-site API is unaffected (Parent.mock(player: customPlayer)). The internal __safeDI_mock_ prefix prevents optional parameters from shadowing the non-optional local bindings that child scopes reference. Without this, closure-typed defaults and builder-internal bindings would resolve to stored properties or self-reference instead of the mock parameter.

Known issue: partially-lazy cycle forward references

The partially-lazy cycle pattern (A → B → Instantiator<C> → C → A, where C receives A through a single lazy hop) generates code with forward variable references that Swift's compiler rejects: closure captures 'X' before it is declared.

This is a pre-existing production code gen bug, not introduced by this PR. The production test run_writesConvenienceExtensionOnRootOfTree_whenPartiallyLazyInstantiationCycleExists only does string comparison — it never compiles the generated output. The bug is latent in production because types involved in partially-lazy cycles are never roots (so no convenience init is generated). Mock generation exposes it because generateMock: true generates for non-root types.

The mock_optionalNotPassedAsNonOptional_whenReceivedPropertyCyclesThroughInstantiatorBoundary test documents this case but its expected output contains the same forward-reference pattern that won't compile. A proper fix requires reworking how ScopeGenerator handles partially-lazy cycles for both production and mock code gen — tracked separately.

Fully-lazy cycles (all Instantiator hops) and self-forwarding cycles work correctly.

Cycle test coverage added

Other fixes in this PR

• Closure-typed default parameters now get let X = __safeDI_mock_X body bindings (no parens, since @escaping not @autoclosure)
• defaultValueBindings and uncoveredDependencyBindings inside builder functions use __safeDI_mock_ prefix
• CLAUDE.md updated: when updating test expected output, verify the new expected code would compile as valid Swift

Test plan

• 762 tests pass
• Lint clean
• 100% coverage on modified source
• __safeDI_mock_ prefix verified to compile via swiftc -o /dev/null (actual compilation, not just -typecheck)

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