PLAN-010 Phase 8: Create Window API Builder Protocol

[discreteds]

Phase 8: Create Window Protocol

Priority: P2 (Medium)
Effort: Medium
Methods: +12
New Files: 1
Depends on: PLAN-009 Phase 7 (#59)

Description

Create new API builder protocol file for window functions.

File to Create

src/mountainash_expressions/core/expression_protocols/api_builders/substrait/prtcl_api_bldr_window_arithmetic.py

Methods to Add

Ranking (5):

• row_number() -> BaseExpressionAPI
• rank() -> BaseExpressionAPI
• dense_rank() -> BaseExpressionAPI
• percent_rank() -> BaseExpressionAPI
• cume_dist() -> BaseExpressionAPI

Distribution (1):

• ntile(n) -> BaseExpressionAPI

Value (6):

• first_value() -> BaseExpressionAPI
• last_value() -> BaseExpressionAPI
• nth_value(n) -> BaseExpressionAPI
• lead(offset, default) -> BaseExpressionAPI
• lag(offset, default) -> BaseExpressionAPI

Acceptance Criteria

• Protocol file created
• All 12 methods defined
• Protocol follows existing naming conventions
• Update substrait/__init__.py with new import

Reference

• ADR-010: API Builder Protocol Alignment
• Substrait window extension