LAST_INDEX serialization does not preserve RFC 6901 sentinel on round-trip

[coderabbitai]

Context

This issue tracks a pre-existing serialization concern with the LAST_INDEX constant identified during code review of PR #221.

Description

When LAST_INDEX (currently Integer.MIN_VALUE) is used in the append(int) method of AbstractJsonPointer (previously in JsonPointer), it creates a RefToken with the numeric string "-2147483648". Upon serialization via toString() and re-parsing:

• The numeric string "-2147483648" does not match the VALID_ARRAY_IND regex pattern
• The parser treats it as a property name instead of an array index sentinel
• The semantic meaning (append-to-end) is lost in the round-trip

This affects the RFC 6901 compliance where "-" is the standard sentinel for array append operations.

Source

Identified in code review of PR #221 (Jackson 3 support):

• PR: Add Jackson 3 support #221
• Comment: Add Jackson 3 support #221 (comment)

Requested by: @sondemar

Location

The logic exists in:

• src/main/java/com/flipkart/zjsonpatch/AbstractJsonPointer.java (lines 115-132 after PR Add Jackson 3 support #221)
• Originally in src/main/java/com/flipkart/zjsonpatch/JsonPointer.java on master branch