feat: add verification and debugging workflow skills

.config/opencode/skills/systematic-debugging/defense-in-depth.md

@@ -0,0 +1,64 @@
+---
+title: defense-in-depth
+type: note
+permalink: opencode-config/skills/systematic-debugging/defense-in-depth
+---
+
+# Defense in Depth
+
+## Overview
+
+A single validation check can be bypassed by alternate paths, refactors, or test setup differences.
+
+**Core principle:** add validation at multiple layers so one missed check does not recreate the same failure.
+
+## Layered Validation Model
+
+### Layer 1: Entry Validation
+Reject obviously invalid input at boundaries (CLI/API/public methods).
+
+### Layer 2: Business-Logic Validation
+Re-validate assumptions where operations are performed.
+
+### Layer 3: Environment Guards
+Block dangerous operations in sensitive contexts (for example, test/runtime safety guards).
+
+### Layer 4: Diagnostic Context
+Emit enough structured debug information to support future root-cause analysis.
+
+## Applying the Pattern
+
+1. Trace real data flow from entry to failure.
+2. Mark all checkpoints where invalid state could be detected.
+3. Add targeted validation at each relevant layer.
+4. Verify each layer can catch invalid input independently.
+
+## Example Shape
+
+```ts
+function createWorkspace(path: string) {
+  // Layer 1: entry
+  if (!path || path.trim() === '') {
+    throw new Error('path is required');
+  }
+
+  // Layer 2: operation-specific
+  if (!isPathAllowed(path)) {
+    throw new Error(`path not allowed: ${path}`);
+  }
+}
+
+async function dangerousOperation(path: string) {
+  // Layer 3: environment guard
+  if (process.env.NODE_ENV === 'test' && !isSafeTestPath(path)) {
+    throw new Error(`refusing unsafe path in test mode: ${path}`);
+  }
+
+  // Layer 4: diagnostic context
+  console.error('operation context', { path, cwd: process.cwd(), stack: new Error().stack });
+}
+```
+
+## Key Outcome
+
+Root-cause fixes prevent recurrence at the origin. Layered validation reduces the chance that adjacent paths can reintroduce the same class of bug.