Add plugin isolation and sandboxing.

PR Details:
- Prevents cross-plugin interference
- Improves system stability

Author: DavidQ

docs/dev/CODEX_COMMANDS.md

@@ -2,8 +2,8 @@ MODEL: GPT-5.4
 REASONING: medium
 
 COMMAND:
-Implement plugin lifecycle:
-- Add init/activate/deactivate/destroy phases
-- Ensure safe transitions
-- Validate with test plugin
+Implement plugin isolation:
+- Enforce boundaries
+- Prevent interference
+- Handle failures safely
 - Update roadmap status only

docs/dev/COMMIT_COMMENT.txt

@@ -1,4 +1,5 @@
-Add overlay plugin lifecycle.
+Add plugin isolation and sandboxing.
 
 PR Details:
-- Standardizes plugin lifecycle behavior
+- Prevents cross-plugin interference
+- Improves system stability

docs/dev/reports/validation_checklist.txt

@@ -1,4 +1,4 @@
-[ ] Init works
-[ ] Activate/deactivate stable
-[ ] Destroy cleans up
+[ ] Plugins isolated
+[ ] Failures contained
+[ ] No interference
 [ ] Roadmap updated

docs/dev/roadmaps/MASTER_ROADMAP_HIGH_LEVEL.md

@@ -820,7 +820,7 @@
 ### Track G — Extensibility Readiness
 - [x] validate plugin/extension patterns
 - [.] validate adding new systems is clean
-- [ ] validate external integration points
+- [.] validate external integration points
 - [ ] ensure future phases can build cleanly
 
 ### Track H — Final Stability Gate

docs/pr/BUILD_PR.md

@@ -1,21 +1,21 @@
-# BUILD_PR_LEVEL_20_3_OVERLAY_PLUGIN_LIFECYCLE
+# BUILD_PR_LEVEL_20_4_OVERLAY_PLUGIN_ISOLATION_AND_SANDBOXING
 
 ## Purpose
-Define lifecycle for overlay plugins from init to teardown.
+Ensure overlay plugins operate in isolation without impacting core systems or other plugins.
 
 ## Roadmap Improvement
-Completes plugin system foundation by standardizing lifecycle behavior.
+Enhances stability and safety of the plugin system.
 
 ## Scope
-- Define init, activate, deactivate, destroy phases
-- Ensure safe transitions between states
-- Validate lifecycle with one plugin
+- Define isolation boundaries
+- Prevent cross-plugin interference
+- Ensure safe failure handling
 
 ## Test Steps
-1. Register plugin
-2. Activate/deactivate multiple times
-3. Destroy plugin
+1. Run multiple plugins
+2. Simulate plugin failure
+3. Verify isolation maintained
 
 ## Expected
-- Clean lifecycle transitions
-- No memory or state leaks
+- No cross-plugin impact
+- Safe failure containment