chore: install openagent opencode

Signed-off-by: Dmytro Stanchiev <git@dmytros.dev>

.opencode/context/core/context-system/standards/frontmatter.md

@@ -0,0 +1,64 @@
+# Frontmatter Format
+
+**Purpose**: HTML comment frontmatter format for all context files
+
+**Last Updated**: 2026-01-27
+
+---
+
+## Format
+
+<rule id="frontmatter_required" enforcement="strict">
+  ALL context files MUST start with:
+  
+  ```markdown
+  <!-- Context: {category}/{function} | Priority: {level} | Version: X.Y | Updated: YYYY-MM-DD -->
+  ```
+</rule>
+
+---
+
+## Components
+
+**Category/Function**: `{category}/{function}`
+- Examples: `ecommerce/concepts`, `development/examples`, `core/standards`
+- Category = domain (ecommerce, payments, development)
+- Function = file type (concepts, examples, guides, lookup, errors)
+
+**Priority**: `critical` | `high` | `medium` | `low`
+- critical: 80% of use cases (business logic, core concepts)
+- high: 15% of use cases (common workflows, examples)
+- medium: 4% of use cases (edge cases)
+- low: 1% of use cases (rare scenarios)
+
+**Version**: `X.Y` (start 1.0, increment on changes)
+
+**Updated**: `YYYY-MM-DD` (ISO 8601, must match metadata section)
+
+---
+
+## Examples
+
+```markdown
+<!-- Context: ecommerce/concepts | Priority: critical | Version: 1.0 | Updated: 2026-01-27 -->
+<!-- Context: payments/guides | Priority: high | Version: 1.2 | Updated: 2026-01-27 -->
+<!-- Context: development/examples | Priority: medium | Version: 1.0 | Updated: 2026-01-27 -->
+```
+
+---
+
+## Validation
+
+- [ ] Frontmatter is first line?
+- [ ] Format exact: `<!-- Context: ... -->`?
+- [ ] Priority is critical|high|medium|low?
+- [ ] Version is X.Y?
+- [ ] Date is YYYY-MM-DD?
+
+---
+
+## Related
+
+- structure.md - File organization
+- templates.md - File templates
+- codebase-references.md - Linking to code