diff --git a/.agents/aidevops/plugins.md b/.agents/aidevops/plugins.md
new file mode 100644
index 000000000..bebad43e0
--- /dev/null
+++ b/.agents/aidevops/plugins.md
@@ -0,0 +1,133 @@
+# Plugin System
+
+Third-party agent plugins extend aidevops with additional capabilities. Plugins are git repositories that deploy agents into namespaced directories, keeping them isolated from core agents.
+
+## Schema
+
+Plugins are configured in `.aidevops.json` under the `plugins` array:
+
+```json
+{
+  "plugins": [
+    {
+      "name": "pro",
+      "repo": "https://github.com/user/aidevops-pro.git",
+      "branch": "main",
+      "namespace": "pro",
+      "enabled": true
+    }
+  ]
+}
+```
+
+### Fields
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `name` | string | yes | Human-readable plugin name |
+| `repo` | string | yes | Git repository URL (HTTPS or SSH) |
+| `branch` | string | no | Branch to track (default: `main`) |
+| `namespace` | string | yes | Directory name under `~/.aidevops/agents/` |
+| `enabled` | boolean | no | Whether the plugin is active (default: `true`) |
+
+## Deployment
+
+Plugins deploy to `~/.aidevops/agents/<namespace>/`:
+
+```text
+~/.aidevops/agents/
+├── custom/          # User's private agents (tier: custom)
+├── draft/           # Experimental agents (tier: draft)
+├── pro/             # Example plugin namespace
+│   ├── AGENTS.md    # Plugin's agent definitions
+│   └── ...          # Plugin files
+└── ...              # Core agents (tier: shared)
+```
+
+## Namespacing Rules
+
+- Namespace must be a valid directory name (lowercase, alphanumeric, hyphens)
+- Namespace must NOT collide with core directories: `custom`, `draft`, `scripts`, `tools`, `services`, `workflows`, `templates`, `memory`, `plugins`
+- Each plugin gets its own isolated namespace directory
+- Plugins cannot write outside their namespace directory
+- Core agents are never overwritten by plugin deployment
+
+## Lifecycle
+
+### Add a Plugin
+
+```bash
+aidevops plugin add https://github.com/user/aidevops-pro.git --namespace pro
+```
+
+This:
+
+1. Validates the namespace doesn't collide with reserved names
+2. Adds the plugin entry to `.aidevops.json`
+3. Clones the repo to `~/.aidevops/agents/<namespace>/`
+4. Registers the plugin in the subagent index
+
+### Update Plugins
+
+```bash
+aidevops plugin update           # Update all enabled plugins
+aidevops plugin update pro       # Update a specific plugin
+```
+
+Pulls the latest from the tracked branch and redeploys.
+
+### Disable / Enable
+
+```bash
+aidevops plugin disable pro      # Sets enabled: false, removes deployed files
+aidevops plugin enable pro       # Sets enabled: true, redeploys
+```
+
+Disabling removes the deployed directory but preserves the config entry.
+
+### Remove a Plugin
+
+```bash
+aidevops plugin remove pro       # Removes config entry and deployed files
+```
+
+## Plugin Repository Structure
+
+A plugin repo should follow this structure:
+
+```text
+plugin-repo/
+├── AGENTS.md          # Plugin agent definitions (optional)
+├── *.md               # Agent/subagent files
+├── scripts/           # Helper scripts (optional)
+└── tools/             # Tool definitions (optional)
+```
+
+The entire repo contents are deployed to `~/.aidevops/agents/<namespace>/`.
+
+## Security
+
+- Plugins are user-installed and user-trusted
+- Plugin scripts are NOT auto-executed; they must be explicitly invoked
+- Plugin agents follow the same security rules as core agents (no credential exposure, pre-edit checks)
+- Review plugin source before installation
+
+## Integration with Agent Tiers
+
+Plugins occupy a distinct tier alongside existing tiers:
+
+| Tier | Location | Survives Update | Source |
+|------|----------|-----------------|--------|
+| Draft | `~/.aidevops/agents/draft/` | Yes | Auto-created by orchestration |
+| Custom | `~/.aidevops/agents/custom/` | Yes | User-created |
+| Plugin | `~/.aidevops/agents/<namespace>/` | Yes (managed separately) | Third-party git repos |
+| Shared | `.agents/` in repo | Overwritten on update | Open-source distribution |
+
+## Current Status
+
+The plugin schema is defined in `.aidevops.json`. The `aidevops plugin` subcommand is planned for a future release (t136.2+). Until then, plugins can be managed manually:
+
+1. Add the entry to `.aidevops.json` `plugins` array
+2. Clone the repo: `git clone <repo> ~/.aidevops/agents/<namespace>/`
+3. To update: `git -C ~/.aidevops/agents/<namespace>/ pull`
+4. To remove: delete the directory and remove the config entry
diff --git a/aidevops.sh b/aidevops.sh
index d95d7d84a..2734adb9b 100755
--- a/aidevops.sh
+++ b/aidevops.sh
@@ -948,8 +948,21 @@ cmd_init() {
       "backend": "age",
       "patterns": ["*.secret.yaml", "*.secret.json", "configs/*.enc.json", "configs/*.enc.yaml"]
     }
-  }
+  },
+  "plugins": []
+}
 EOF
+    # Note: plugins array is always present but empty by default.
+    # Users add plugins via: aidevops plugin add <repo-url> [--namespace <name>]
+    # Schema per plugin entry:
+    # {
+    #   "name": "pro",
+    #   "repo": "https://github.com/user/aidevops-pro.git",
+    #   "branch": "main",
+    #   "namespace": "pro",
+    #   "enabled": true
+    # }
+    # Plugins deploy to ~/.aidevops/agents/<namespace>/ (namespaced, no collisions)
     print_success "Created .aidevops.json"
     
     # Create .agents symlink (or migrate from legacy .agent)
@@ -1647,6 +1660,14 @@ cmd_features() {
     echo "                 - Patterns: *.secret.yaml, configs/*.enc.json"
     echo "                 - See: .agents/tools/credentials/sops.md"
     echo ""
+    echo "Extensibility:"
+    echo ""
+    echo "  plugins        Third-party agent plugins (configured in .aidevops.json)"
+    echo "                 - Git repos deployed to ~/.aidevops/agents/<namespace>/"
+    echo "                 - Namespaced to avoid collisions with core agents"
+    echo "                 - Enable/disable per-plugin without removal"
+    echo "                 - See: .agents/aidevops/plugins.md"
+    echo ""
     echo "Usage:"
     echo "  aidevops init                    # Enable all features (except sops)"
     echo "  aidevops init planning           # Enable only planning"