This was erroneously added and later removed in PR #210. The visitor
override tracks visited nodes by id to prevent infinite recursion when
traversing cyclic AST structures created via MEMOIZE + GET opcodes.

Co-Authored-By: Dan Guido <dan@trailofbits.com>
Co-Authored-By: Claude Code <noreply@anthropic.com>

* Fix cyclic AST recursion DoS (issue #196)

Cyclic pickle structures (e.g., `L = []; L.append(L)`) caused
RecursionError when fickling analyzed them. This fix detects cycles
at mutation points (Append, Appends, SetItem, SetItems, AddItems)
and replaces self-references with `<cyclic-ref>` placeholder AST nodes.

Changes:
- Add `_has_cycle` flag to Interpreter to track cycle detection
- Modify mutation operations to check if value being added `is` the container
- Add `has_cycles` property to Pickled class for downstream awareness
- Update tests to verify the fix works correctly

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Restore cycle detection in ASTProperties visitor

This was erroneously added and later removed in PR #210. The visitor
override tracks visited nodes by id to prevent infinite recursion when
traversing cyclic AST structures created via MEMOIZE + GET opcodes.

Co-Authored-By: Dan Guido <dan@trailofbits.com>
Co-Authored-By: Claude Code <noreply@anthropic.com>

* Merge and uniformize tests

* Add tests for all cycle detection corner cases

Cover dict value cycles, dict key cycles, and set cycles
to ensure the cycle detection feature handles all supported
mutation opcodes (SetItem, AddItems).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Fix AddItems to peek instead of pop the set

Match Python's pickle implementation which uses stack[-1] to peek
at the set without removing it from the stack.

Ref: https://github.com/python/cpython/blob/6ea3f8cd7ff4ff9769ae276dabc0753e09dca998/Lib/pickle.py#L1840

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Use Python-style repr for cyclic references

Match Python's repr output for cyclic structures:
- List cycles: [[...]] instead of [<cyclic-ref>]
- Dict cycles: {'key': {...}} instead of {'key': <cyclic-ref>}
- Set cycles: {{...}} instead of {<cyclic-ref>}

This makes fickling's AST output directly comparable to what Python
displays when printing cyclic data structures.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Raise InterpretationError for impossible cyclic structures

Match Python's behavior for unhashable cyclic references:
- Dict key cycles: raise InterpretationError (Python raises TypeError)
- Set cycles: raise InterpretationError (Python raises TypeError)
- Dict value cycles: still allowed with {...} placeholder
- List cycles: still allowed with [...] placeholder

This distinguishes between valid cyclic structures that Python can
represent (lists containing themselves, dicts with self-referencing
values) and impossible structures that would fail at runtime.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Thomas Chauchefoin <thomas.chauchefoin@trailofbits.com>

Renames AGENTS.md to CLAUDE.md and expands it from vulnerability
reporting guidance into full project context: commands, architecture,
design rules, testing patterns, code style, and CI. Design rules
distilled from PR review history (#79, #87, #195, #207, #210, #220).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Renames AGENTS.md to CLAUDE.md and expands it from vulnerability
reporting guidance into full project context: commands, architecture,
design rules, testing patterns, code style, and CI. Design rules
distilled from PR review history (#79, #87, #195, #207, #210, #220).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>