# Sprint 84 Plan: Semantic Diff and Explainability Layer

## Context

Trust improves when developers can see exactly what changed semantically.
Sprint 84 adds human-readable semantic diffs and explainability traces.

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## Goals

1. Generate semantic-level diffs between source and projections
2. Explain adapter decisions and policy selections per transformation
3. Surface uncertainty and alternatives in reviewer-friendly form
4. Reduce manual review latency through better diagnostics

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## Steps

### Step 1069: Semantic diff canonical model (12 tests)
### Step 1070: Adapter decision trace packet schema (10 tests)
### Step 1071: Policy decision explainability renderer (10 tests)
### Step 1072: Uncertainty and alternative-path explainer (10 tests)
### Step 1073: Reviewer-focused semantic diff summarizer (10 tests)
### Step 1074: Explainability data retention policy integration (8 tests)
### Step 1075: `whetstone_get_semantic_diff` MCP tool (8 tests)
### Step 1076: `whetstone_explain_transpilation_decision` MCP tool (8 tests)
### Step 1077: Explainability report template pack (8 tests)
### Step 1078: Sprint 84 integration summary + regression (8 tests)

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## Explainability Rule

- Stable-tier promotions require available semantic diff and decision traces.