feat: Memoize widget resolution to scan web/dist once

[jirispilka]

Part of #1066 (checkbox: memoize resolveWidgets()).

What we're solving

ActorsMcpServer.resolveWidgets() ran two dynamic imports and an fs.existsSync scan of web/dist (via resolveAvailableWidgets) on every initialize and every connect() — i.e. once per HTTP session. Widgets are static build artifacts and the scan depends only on a constant dirName (from import.meta.url), so the result never changes within a process.

How

Add a module-level cached promise in server.ts and a loadAvailableWidgetsOnce() helper that assigns the promise synchronously before its first await, so concurrent sessions share one in-flight scan instead of each starting their own. resolveWidgets() keeps its APPS-mode early return and soft-fail try/catch; it now awaits the shared cache and assigns this.availableWidgets. The ready/missing-widget logging moves into the once-path. On a rejected scan the cache is cleared so a later session can retry. The low-level resolveAvailableWidgets helper is left pure (unmemoized) so its direct unit tests keep working.

Alternatives considered

• Caching only the resolved value — rejected; concurrent sessions would both scan before either finished.
• Memoizing inside resolveAvailableWidgets — rejected; its unit tests mock the filesystem per test.

⚠️ Log-frequency note (hosted-server log consumers)

The "ready widgets" / "some widgets are not ready" log lines now fire once per process instead of once per session. Log content is unchanged — only frequency. Flagging per CLAUDE.md's public/internal rules since the hosted server (apify-mcp-server-internal) consumes these logs.

Verification

• New test tests/unit/mcp.server.resolve_widgets_memo.test.ts asserts the scan runs exactly once across two APPS-mode server initializations.
• Oracle green: type-check clean, lint 0/0, check:agents passed, test:unit 71 files / 960 passed / 2 skipped, format no-op.
• resolveAvailableWidgets (widgets.ts) untouched; utils.widgets.test.ts and mcp.server.capability_gating.test.ts pass unmodified.
• Scope: src/mcp/server.ts + the new test.

🤖 Generated with Claude Code

https://claude.ai/code/session_016pXZvhEoE6Lz3DpBSL3n1Y

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