Add opt-in state retention for plugin WebUI pages

[BernardXiong]

Summary

• Add optional manifest.webui.keep_alive, defaulting to false.
• Keep opted-in plugin iframes mounted while navigating between plugin pages, settings, and the plugin center.
• Preserve the existing reload behavior for plugins without keep_alive.
• Remove the top bar and move the “Exit WebUI” action to the bottom of the sidebar.
• Scope plugin assets per plugin and expose optional backend HTTP/WebSocket context to sandboxed WebUI pages.

Implementation

• Track iframe state, refs, and timeout timers per plugin.
• Clean up iframe state when a plugin is disabled, uninstalled, upgraded, or its WebUI entry changes.
• Support explicit iframe reload from the error state.
• Update the manifest schema, validation, project scaffolding, documentation, and frontend/server API contracts.
• Add WebSocket negotiation header forwarding and CSP declarations for plugin backend connections.

Validation

• npm run typecheck
• npm test -- --run
• npm run test:e2e
• pytest -q plugins/tests/test_manifest_package.py plugins/tests/test_epack_cli.py plugins/tests/test_webui_package.py plugins/tests/ test_webui_server.py

All targeted tests pass.

Compatibility

Existing plugin manifests remain valid. If keep_alive is omitted, the value is treated as false, so existing plugins retain the original
reload behavior.

[Copilot]

🟡 Changes recommended

Asynchronous plugin checks can overwrite newer lifecycle state, and cleanup behavior lacks direct coverage.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds opt-in iframe state retention and plugin-scoped backend transport support while simplifying WebUI navigation.

Changes:

• Adds webui.keep_alive across manifests, scaffolding, documentation, and tests.
• Retains opted-in plugin iframes and exposes scoped HTTP/WebSocket contexts.
• Moves WebUI exit controls into the sidebar.

File summaries

File	Description
plugins/webui/static/index.html	References rebuilt frontend assets.
plugins/webui/server.py	Adds scoped asset tokens and backend contexts.
plugins/webui/frontend/src/utils/plugins.ts	Builds browser backend endpoints.
plugins/webui/frontend/src/utils/plugins.test.ts	Tests endpoint conversion.
plugins/webui/frontend/src/types/api.ts	Extends plugin and session contracts.
plugins/webui/frontend/src/styles.css	Updates layout and iframe stacking.
plugins/webui/frontend/src/App.vue	Implements retained iframe lifecycle and sidebar exit.
plugins/webui/frontend/e2e/webui.spec.ts	Tests navigation retention and UI changes.
plugins/tests/test_webui_server.py	Tests scoped assets, CSP, and WebSockets.
plugins/tests/test_manifest_package.py	Validates keep_alive.
plugins/tests/test_epack_cli.py	Verifies scaffold defaults.
plugins/spec/README.md	Documents retention and backend transport.
plugins/spec/manifest-v1.schema.json	Adds the schema field.
plugins/README.zh-CN.md	Updates Chinese plugin documentation.
plugins/README.md	Updates plugin documentation.
plugins/manifest.py	Validates the optional field.
plugins/examples/build-insight-1.0.0/README.md	Documents example host context.
plugins/epack/project.py	Adds the scaffold default.

Review details

• Files reviewed: 18/21 changed files
• Comments generated: 2
• Review effort level: Balanced

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