# Sprint 139 Plan: MCP Backward Compatibility and Deprecation Governance

## Context

Wiring closure must not break existing clients. Sprint 139 adds compatibility and
deprecation governance for evolving MCP tool surfaces.

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## Goals

1. Define deterministic backward-compatibility policy for tool changes
2. Model deprecation lifecycle with explicit timeline states
3. Add compatibility simulation against client capability profiles
4. Publish machine-readable deprecation and migration guidance

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## Steps

### Step 1629: MCP compatibility policy schema (10 tests)
### Step 1630: Tool deprecation lifecycle model (10 tests)
### Step 1631: Client capability profile schema (10 tests)
### Step 1632: Compatibility simulation runner model (10 tests)
### Step 1633: `whetstone_check_tool_compatibility` MCP tool (8 tests)
### Step 1634: `whetstone_get_tool_deprecations` MCP tool (8 tests)
### Step 1635: `whetstone_plan_tool_migrations` MCP tool (8 tests)
### Step 1636: Compatibility risk packet model (8 tests)
### Step 1637: Compatibility/deprecation report artifact (8 tests)
### Step 1638: Sprint 139 integration summary + regression (8 tests)

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## Architecture Gate

- Compatibility simulation must be deterministic for identical profiles
- Deprecation states must be explicit and auditable
- Migration guidance must be structured and machine-readable
- Max 600 lines per header