fix: accept shared objects in boolean object guards

[gjbkz]

Requested by Kei · project thread

Before: isPair({ left: person, right: person }) threw CircularReference: T.left -> T.right when the same object appeared under two sibling properties, while validate() and validateAll() accepted it.

After: shared, acyclic objects pass the boolean guard, matching structured validation. Real cycles still throw CircularReference.

How: the object guard now removes the object from its reference map in a finally block once the branch is done, so the map only holds the active recursion path, as the diagnosis path already does. Tests cover exact and open object checkers, a shared object checked against two different shapes, nesting, and a real cycle reached through a shared object; the shared-object test fails on main and passes here.

Closes #449

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https://claude.ai/code/session_019BJENnU8SXcDH2Tcx5EWE4

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.46%. Comparing base (9225421) to head (5550cb1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #454   +/-   ##
=======================================
  Coverage   98.45%   98.46%           
=======================================
  Files          52       52           
  Lines        3049     3055    +6     
  Branches      327      327           
=======================================
+ Hits         3002     3008    +6     
  Misses         46       46           
  Partials        1        1           

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[gjbkz]

Reviewed commit c06fd0e050765e68a1ef1595f8f27d9cf36f9c26. No actionable issues found in this change.

Removing each object from refs in a finally block restricts tracking to the active recursion path, allowing shared acyclic children while retaining the existing exception for actual cycles. The added coverage exercises exact/open shapes and nested shared references. I also checked a shared object against distinct constraints.

Validation: the complete source unit-test suite passed locally on this reviewed version, and the GitHub Actions test workflow for this commit completed successfully. The latest head is unchanged from the locally tested version.