feat(ui): remove MCP UI A/B test — widgets on for everyone, with showMcpUI opt-out setting

[edgarsskore]

Add a user-editable showMcpUI config field that explicitly controls whether tools advertise interactive UI widgets. Decision priority: explicit override > A/B experiment assignment > default ON.

• The decision is resolved once per server process so a session renders consistently; changing the setting takes effect after the client restarts the MCP server (mid-session tools-list flips confuse hosts that bind UI to the cached list).
• set_config_value response and the field description note the restart requirement.
• Config editor shows the effective decision when the value is unset, so the toggle reflects reality instead of rendering unset as off.
• Config editor now shows a quiet inline "Saved" confirmation next to the setting that changed (covers toggles, inputs, shell select, and list modals); errors keep the floating tooltip.

Summary by CodeRabbit

• New Features
  • Updated the showMcpUI configuration so leaving it unset now shows MCP UI widgets by default (effective value is used in the config viewer).
  • Changing showMcpUI includes an in-app note that it takes effect after restarting.
• UI Improvements
  • Config editor now shows per-setting “Saved” confirmation chips after successful updates (with inline success feedback).
• Bug Fixes
  • UI-origin config/tool calls now have improved telemetry and UI-specific handling.
  • Tool execution now returns gentle warnings for unsupported parameters instead of failing.
• Tests
  • Added tests for MCP UI enablement/override boolean handling, and adjusted A/B related test coverage.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR changes showMcpUI so widgets are shown unless explicitly disabled, adds serialized and non-blocking config persistence, updates server and config-tool behavior, removes the prior A/B override path, and adds inline saved indicators to the configuration editor.

Changes

MCP UI configuration and editor flow

Layer / File(s)	Summary
Configuration persistence and onboarding state src/config-manager.ts	Config writes are serialized or coalesced in the background, setValueNonBlocking() is added, onboarding eligibility is defaulted and backfilled, and unset showMcpUI is documented as shown.
MCP UI visibility decision src/utils/mcp-ui.ts, src/utils/mcp-ui-ab-test.ts, src/utils/ab-test.ts	MCP UI settings accept boolean overrides, cache the process-wide decision, and no longer use explicit overrides in the previous A/B preview resolver; the unused variant helper is removed.
Config tools and server integration src/config-field-definitions.ts, src/tools/config.ts, src/server.ts	Tool metadata and config responses use shouldShowMcpUi(), descriptions document restart behavior, and showMcpUI updates emit dedicated telemetry.
Inline configuration save feedback src/ui/config-editor/src/app.ts, src/ui/styles/apps/config-editor.css	Successful updates display keyed, temporary “Saved” indicators beside the affected setting controls, with fallback tooltip handling.
MCP UI behavior tests test/test-mcp-ui-toggle.js, test/ab-test.test.js	Tests cover boolean and non-boolean MCP UI values, while obsolete A/B override decision tests and helpers are removed.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant MCPClient
  participant ConfigTools
  participant ConfigManager
  participant MCPServer
  MCPClient->>ConfigTools: get_config
  ConfigTools->>ConfigManager: read showMcpUI
  ConfigTools-->>MCPClient: effective showMcpUI value
  MCPClient->>MCPServer: list_tools
  MCPServer->>ConfigManager: resolve MCP UI decision
  MCPServer-->>MCPClient: tool metadata with UI visibility

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Possibly related PRs

• wonderwhy-er/DesktopCommanderMCP#491: Both modify MCP UI preview gating and decision logic.
• wonderwhy-er/DesktopCommanderMCP#535: Both refactor config persistence with serialized and non-blocking saves.
• wonderwhy-er/DesktopCommanderMCP#486: Both modify remote-client attribution in server tool-call telemetry.

Suggested reviewers: wonderwhy-er

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: removing the MCP UI A/B test and making widgets enabled by default with a showMcpUI opt-out.

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/config-ui-enable

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/ui/config-editor/src/app.ts`:
- Line 593: The inline save-status chip (the <span class="setting-save-status"
data-save-status-key="${escapeHtml(entry.key)}" ...>) lacks live-region
semantics; update the span rendered in app.ts (the element that uses class
"setting-save-status" and data-save-status-key) to include role="status",
aria-live="polite", and aria-atomic="true" so assistive tech announces save
confirmations, and apply the same attributes to the other occurrences of the
same span (lines around where controlHtml is injected).
- Around line 642-643: The selector built with
querySelector(`[data-save-status-key="${key}"]`) can break for keys containing
CSS-special characters; update the lookup to escape the key using CSS.escape
before embedding it in the selector so the element is reliably found (i.e.,
replace the plain `${key}` usage when constructing the selector for
data-save-status-key used to set const chip = container.querySelector(...)).
Ensure you reference CSS.escape(key) so the selection logic always returns the
correct HTMLElement or null.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 4c5429b6-1fa3-4dd9-b532-09f72ca58612

📥 Commits

Reviewing files that changed from the base of the PR and between 7126346 and d3f6696.

📒 Files selected for processing (8)

• src/config-field-definitions.ts
• src/config-manager.ts
• src/server.ts
• src/tools/config.ts
• src/ui/config-editor/src/app.ts
• src/ui/styles/apps/config-editor.css
• src/utils/mcp-ui-ab-test.ts
• test/ab-test.test.js

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/server.ts`:
- Around line 1231-1233: The telemetry capture for the showMcpUI configuration
is not validating the input type before stringifying it. Add a type guard to
verify that the value is actually a boolean using typeof check before setting
telemetryData.set_config_value_bool. Only when the value passes the boolean type
check should you then stringify it and assign it to the telemetry field. This
prevents malformed client payloads from leaking arbitrary text into the
telemetry metric.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: a0023003-4c9c-4b51-a2dc-71865b001252

📥 Commits

Reviewing files that changed from the base of the PR and between 6e685ea and c2c70c0.

📒 Files selected for processing (1)

• src/server.ts

[kemo04]

AI Code Review (PR Review Agent)

• [Test Coverage · High] — src/utils/mcp-ui-ab-test.ts (diff line 307): New session-level memoization (sessionDecision) lacks tests to verify it persists across multiple calls.

[kemo04]

AI Code Review (PR Review Agent)

• [Test Coverage · High] — src/utils/mcp-ui-ab-test.ts (diff line 307): New session-level memoization (sessionDecision) lacks tests to verify it persists across multiple calls.

[rajpratham1]

Nice addition! The showMcpUI override is well integrated with the existing A/B test flow, the session-level caching avoids inconsistent UI during runtime, and the accompanying tests cover the important decision paths. The config editor UX improvements (inline save status and restart note) are also a nice touch.

One small non-blocking suggestion: when recording showMcpUI telemetry, consider only capturing the value if it's actually a boolean to avoid malformed client payloads being stringified into telemetry. Otherwise, this looks good to me.