fix(flow): apply deferred narrows after antecedent resolution

[lewis6991]

When walking backward through flow, collect condition narrows as pending
actions instead of applying them while recursively querying antecedent
types. The eager path mixed narrowing with antecedent resolution, so
stacked guards could re-enter flow inference from inside condition
evaluation and build deep recursive chains across repeated truthiness,
type-guard, signature-cast, and correlated return-overload checks.

Resolve the antecedent type first, then apply the pending narrows in
reverse order. That keeps narrowing as a post-pass over an
already-resolved input, avoids re-entering the same condition chain
while answering the current flow query, and lets same-variable
self/member guards wait until earlier guards have narrowed the receiver
enough for reliable lookup.

Key the flow cache by whether condition narrowing is enabled, and
separate assignment source lookup from condition application. Reuse a
narrowed source only when the RHS preserves that precision; broader RHS
expressions fall back to the antecedent type with condition narrowing
disabled so reassignment clears stale branch narrows, while exact
literals and compatible partial table/object rewrites still preserve
useful narrowing.

Add regression coverage for stacked guards, correlated overload joins,
pcall aliases, and assign/return diagnostics.

---

These added tests fail on main:

• test_stacked_same_var_type_guards_build_semantic_model
• test_stacked_same_field_truthiness_guards_build_semantic_model
• test_stacked_return_cast_guards_build_semantic_model
• test_stacked_return_cast_self_guards_build_semantic_model
• test_assignment_from_wider_single_return_call_drops_branch_narrowing
• test_assignment_after_pending_return_cast_guard_drops_branch_narrowing
• test_assignment_after_binary_call_guard_eq_false_drops_branch_narrowing
• test_assignment_after_mixed_eager_and_pending_guards_drops_branch_narrowing
• test_assignment_from_nullable_union_keeps_rhs_members
• test_assignment_from_partially_overlapping_union_keeps_rhs_members
• test_assignment_from_broad_string_drops_literal_branch_narrowing
• test_partial_table_reassignment_with_conflicting_discriminant_drops_branch_narrowing
• test_pcall_stacked_alias_guards_build_semantic_model
• test_return_overload_stacked_eq_guards_build_semantic_model
• test_return_overload_stacked_mixed_guards_build_semantic_model
• test_return_overload_uncorrelated_later_guard_keeps_prior_narrowing
• test_return_overload_unmatched_target_call_keeps_guard_union
• test_return_overload_unmatched_target_root_then_truthiness_guard
• test_return_overload_unmatched_target_root_then_type_guard
• test_return_overload_post_guard_reassign_clears_mixed_root_narrowing
• test_return_overload_branch_reassign_to_different_call_preserves_matching_root_narrowing
• test_return_overload_branch_reassign_to_different_call_narrows_alternate_matching_root

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical recursion bug within the type inference system, specifically affecting correlated @return_overload narrowing. By introducing a guard mechanism, it prevents infinite loops and stack overflows during complex type analysis, significantly enhancing the stability and reliability of the semantic model generation without altering the core inference logic for valid cases.

Highlights

• Addressed recursive re-entry in @return_overload narrowing: Fixed an issue where correlated @return_overload narrowing could recursively re-enter itself for the same target return slot, leading to stack overflows or hung indexing due to a missing in-flight recursion break.
• Introduced a recursion guard: Implemented a correlated_condition_guard (a HashSet) within LuaInferCache to prevent re-entry into narrow_var_from_return_overload_condition for an already in-flight correlated query.
• Improved type inference stability: When re-entry is detected by the guard, the inference process now returns Continue, allowing the flow walk to fall back to non-correlated inference instead of repeating the problematic correlated query.
• Added a regression test: Included a new regression test case that specifically reproduces the stack overflow issue with many repeated if-not-ok guards, confirming the fix allows the semantic model to build correctly.

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[gemini-code-assist]

Code Review

This pull request correctly identifies and fixes a potential stack overflow issue caused by recursive re-entry in correlated @return_overload narrowing. The approach of adding a guard to LuaInferCache is sound. The added regression test is also a great way to ensure this issue does not reappear. I have one suggestion to improve the robustness of the re-entrancy guard implementation.

[lewis6991]

/gemini review

[gemini-code-assist]

Code Review

This pull request significantly refactors the control flow analysis to defer type narrowing. By collecting narrowing actions and applying them after resolving the antecedent type, you've addressed potential deep recursion issues and improved the correctness of type inference, especially for complex scenarios involving stacked guards and reassignments. The changes are substantial and well-supported by an impressive suite of new regression tests, which gives great confidence in the robustness of this new approach. The implementation of pending narrows and the updated caching strategy are well-executed. Overall, this is a high-quality improvement to the type system's core logic.