# Explain Block CLI Command

## Module
Cli

## Status
IMPLEMENTED

## Description
CLI command `stella explain block <digest>` that provides a complete "why is this blocked?" explanation with evidence linking, policy rule identification, and deterministic output formatting for audit trails.

## Implementation Details
- **Command Group**: `src/Cli/StellaOps.Cli/Commands/ExplainCommandGroup.cs` -- `ExplainCommandGroup` for `stella explain` commands
- **Verdict Rationale**: `src/Cli/StellaOps.Cli/Commands/CommandHandlers.VerdictRationale.cs` -- verdict rationale handlers
- **Rationale Client**: `src/Cli/StellaOps.Cli/Services/RationaleClient.cs` / `IRationaleClient.cs` -- rationale API client
- **Commands**:
  - `stella explain block <digest>` -- explain why an artifact is blocked. Options: `--format text|json`, `--verbose`
- **Output includes**: blocking policy rule, triggering findings, evidence links, remediation suggestions

## E2E Test Plan
- [ ] Run `stella explain block sha256:abc123` and verify block explanation with policy rule identification
- [ ] Verify evidence links are included in the explanation
- [ ] Verify `--format json` produces structured explanation with policy, findings, evidence
- [ ] Verify `--verbose` shows additional rule evaluation details
- [ ] Verify deterministic output (same digest produces identical explanation)
- [ ] Verify error handling for non-blocked artifacts (shows "not blocked" message)