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flutter-mcp-cli-runtime-validation

Testing & Quality
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Run Flutter MCP runtime validation from CLI in two steps (launch app, then run validate-runtime), including toolkit-extension gating, screenshot/layout capture, app error collection, optional reload verification, and retry handling for transient first-connect failures.

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How to use this skill

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  2. Copy the prompt below and paste it into your agent.
  3. Review the proposed files and risks before you approve installation.
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I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/Arenukvern/mcp_flutter/blob/HEAD/plugin/skills/flutter-mcp-cli-runtime-validation/SKILL.md

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Copying this prompt does not install or run the skill. Review third-party files before use. Codex skill guide

Flutter MCP CLI Runtime Validation

Use this skill when you need agent-style runtime validation through flutter-mcp-toolkit with minimal operator steps.

Two-Step Flow

  1. Launch the Flutter app in debug mode.
  2. Run one CLI command:
dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart --save-images --output-dir .flutter_mcp/runtime_validation validate-runtime \
  --target ws://127.0.0.1:8181/<token>/ws \
  --timeout-ms 10000 \
  --post-reload-delay-ms 500 \
  --after-reload

Optional skill install in the same command:

dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart validate-runtime \
  --target ws://127.0.0.1:8181/<token>/ws \
  --install-skill

Permission behavior for this flow:

  • validate-runtime stays read/write only for visual capture and defaults to auto_request_once.
  • doctor remains read-only.
  • On macOS, Screen Recording permission belongs to the host process running flutter-mcp-toolkit.
  • On web: desktop_window uses macOS ScreenCaptureKit then Chrome CDP (Page.captureScreenshot); Linux/Windows use CDP when remote debugging is reachable. Pass --web-browser-debugging-port if discovery fails. For web targets, pass --flutter-device chrome so validation does not pick macOS host desktop_window by mistake.
  • Executor recovery retries host capture once (desktopCaptureRetried in screenshot payloads). If desktop_window still fails (including when platform views are detected), validate-runtime retries once with flutter_layer. Check data.summary.captureFallbackUsed.
  • You may pass the VM URI as global --vm-service-uri instead of validate-runtime --target when only one URI is needed.

What validate-runtime Must Prove

  • Doctor preflight passes critical checks.
  • Required toolkit extensions exist:
    • ext.mcp.toolkit.app_errors
    • ext.mcp.toolkit.view_details
    • ext.mcp.toolkit.view_screenshots
    • ext.mcp.toolkit.inspect_widget_at_point
  • Screenshot capture works.
  • View details (layout metadata) are available.
  • App errors are retrievable.
  • If --after-reload is enabled, post-reload screenshot also works.

Output Handling

  • Use data.summary as pass/fail status for automation.
  • Use data.summary.capturePlatformViewsDetected and captureFocusAttempted for platform-view routing.
  • Use data.summary.captureFallbackUsed to see whether a flutter_layer retry ran after a failed desktop_window attempt (including when platform views are detected).
  • Use data.steps for per-step evidence and retries.
  • Use data.doctor.checks to explain setup blockers.
  • Use data.summary.screenshotFiles for saved screenshot paths when --save-images is enabled.
  • When --save-images is enabled, read screenshot file URLs from step data.
  • For visual debugging reports, also run:
    • exec --name capture_ui_snapshot --args '{"errorsCount":4,"compress":true,"includeViewDetails":true,"includeErrors":true}'
    • exec --name inspect_widget_at_point --args '{"x":<int>,"y":<int>}'

Failure Rules

  • If toolkit extensions are missing, stop and report instrumentation gap with exact fix:
    • add mcp_toolkit to app dependencies
    • ensure MCPToolkitBinding.instance.bootstrapFlutter(...) or equivalent manual initialization runs before runApp
    • hot restart or rerun the app
  • If first explicit URI connect fails, retry is automatic for retryable connection errors.
  • If screenshots are blank, verify app window is visible and retry.
  • If macOS visual capture is denied, use:
    • dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart permissions status
    • dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart permissions request
    • dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart permissions open-settings
  • If app cannot be instrumented, do not claim screenshot/layout/error inspection success.

Visual QA + Source Mapping Rules

  • Always compare before/after screenshot evidence around changes.
  • For each reported visual issue, provide coordinate + inspect_widget_at_point output.
  • Map defects to source using get_app_errors top stack frame (file, line, column) when available.
  • Do not use debug_dump_* unless explicitly requested.

Challenge Cases (Always Call Out Explicitly)

  • No running debug app: doctor critical failure on vm_target_reachable; request app launch before continuing.
  • Wrong target URI/token: treat as connection mismatch and retry with exact app.debugPort.wsUri.
  • Toolkit added but still missing extensions: hot reload is often insufficient, require hot restart/full rerun.
  • Non-modifiable app (cannot add toolkit): report inspection as unavailable instead of guessing.