feat: add repo-local subminer workflow plugin

docs/workflow/README.md

@@ -13,6 +13,7 @@ This section is the internal workflow map for contributors and agents.
 
 - [Planning](./planning.md) - when to write a lightweight plan vs a full execution plan
 - [Verification](./verification.md) - maintained test/build lanes and handoff gate
+- [Agent Plugins](./agent-plugins.md) - repo-local plugin ownership for agent workflow skills
 - [Release Guide](../RELEASING.md) - tagged release workflow
 
 ## Default Flow

docs/workflow/agent-plugins.md

@@ -0,0 +1,32 @@
+<!-- read_when: using or modifying repo-local agent plugins -->
+
+# Agent Plugins
+
+Status: active
+Last verified: 2026-03-26
+Owner: Kyle Yasuda
+Read when: packaging or migrating repo-local agent workflow skills into plugins
+
+## SubMiner Workflow Plugin
+
+- Canonical plugin path: `plugins/subminer-workflow/`
+- Marketplace catalog: `.agents/plugins/marketplace.json`
+- Canonical skill sources:
+  - `plugins/subminer-workflow/skills/subminer-scrum-master/`
+  - `plugins/subminer-workflow/skills/subminer-change-verification/`
+
+## Migration Rule
+
+- Plugin-owned skills are the source of truth.
+- `.agents/skills/subminer-*` remain only as compatibility shims.
+- Existing script entrypoints under `.agents/skills/subminer-change-verification/scripts/` stay as wrappers so historical commands do not break.
+
+## Backlog
+
+- Prefer Backlog.md MCP when the host session exposes it.
+- If MCP is unavailable, use repo-local `backlog/` files and record that fallback.
+
+## Verification
+
+- For plugin/docs-only changes, start with `bun run test:docs:kb`.
+- Use the plugin-owned verifier when the change crosses from docs into scripts or workflow logic.