# Sprint 49 Plan: Executable Equivalence Harness

## Context

Current equivalence signals are heuristic-heavy. Sprint 49 introduces executable,
repeatable differential verification between source and transpiled targets.

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## Goals

1. Execute source and target against identical test vectors
2. Add property-based and fuzz-based differential checks
3. Persist equivalence evidence for migration reports
4. Replace heuristic-only confidence with measured confidence

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## Steps

### Step 719: Differential execution harness core (12 tests)
### Step 720: Deterministic test vector specification format (10 tests)
### Step 721: Rust runner adapter for harness (10 tests)
### Step 722: C++ runner adapter for harness (10 tests)
### Step 723: Property-based equivalence runner (10 tests)
### Step 724: Fuzz differential runner with seed replay (10 tests)
### Step 725: Behavioral divergence packet + minimization (8 tests)
### Step 726: `whetstone_verify_executable_equivalence` MCP tool (8 tests)
### Step 727: Equivalence evidence bundle exporter (8 tests)
### Step 728: Sprint 49 integration summary + regression (8 tests)

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## Equivalence Rules

- Same output shape and semantic value for approved domains
- Error behavior classified as equivalent/acceptable divergence/unacceptable divergence
- Confidence scores derive from measured pass rates, not syntax patterns