# Sprint 124 Plan: Guarded Patch Application and Recovery

## Context

Sprints 121-123 produce deterministic failures, proposals, metrics, and
readiness signals. Sprint 124 adds guarded patch execution primitives:
proposal validation, dry-run/apply sequencing, rollback metadata, and
minimal bisect-oriented recovery workflows for low-context agents.

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## Goals

1. Add deterministic patch apply/rollback state models
2. Expose MCP tools for proposal validation, dry-run, apply, rollback
3. Add lightweight bisect helper for narrowing bad patch candidates
4. Keep full machine-readable audit packets for autonomous execution

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## Steps

### Step 1479: Patch execution record model (12 tests)
### Step 1480: Rollback ledger model (10 tests)
### Step 1481: Bisect candidate selector model (10 tests)
### Step 1482: `whetstone_validate_patch_proposal` MCP tool (8 tests)
### Step 1483: `whetstone_dry_run_patch` MCP tool (8 tests)
### Step 1484: `whetstone_apply_patch_packet` MCP tool (8 tests)
### Step 1485: `whetstone_rollback_last_patch` MCP tool (8 tests)
### Step 1486: `whetstone_run_bisect_debug` MCP tool (8 tests)
### Step 1487: Patch execution audit bundle (8 tests)
### Step 1488: Sprint 124 integration summary + regression (8 tests)

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## Architecture Gate

- Apply only after validate + dry-run success
- Rollback must be deterministic and explicit
- Bisect helper must produce stable candidate ordering
- Max 600 lines per header