fix: surface list-fetch failures in paginated mode (#1998)

[cliffhall]

Closes #1998

With Fetch Lists One Page at a Time on, a failing tools/list / prompts/list / resources/list showed an empty sidebar with no alert and no Retry — the exact behavior #1954 set out to remove — and the connect-time load left an unhandled rejection.

The cause is that #1954 wired the error off the aggregate stores only. In paginated mode those stores deliberately skip their all-page walk (deferWhenPaginated), so their error is permanently null; the paged stores that actually drive the sidebar had no error state at all, and loadPage() had a try/finally with no catch.

What changed

1. The three paged stores get observable error state (core/mcp/state/paged{Tools,Prompts,Resources}State.ts): an errorChange event plus getError(), set in a new catch in loadPage, cleared on the next successful load and on disconnect. The rejection is still re-thrown, matching ManagedListState — the state drives the panel, while the rejection is what a caller's auth-recovery wrapper keys off to detect a 401.
2. The connect-time load no longer floats its rejection: void this.loadPage(undefined) became void this.loadPage(undefined).catch(() => {}). Not a swallow — loadPage has already recorded the failure, and the panel renders it. (This is the same shape ManagedListState's connect handler already used, and it keeps Enable @typescript-eslint/no-floating-promises so an unhandled rejection can't fail the gate again #1959's no-floating-promises honest.)
3. usePaginatedList selects the error by mode, the same way it already selects items: error: paginated ? pagedError : managedError. App.tsx now passes toolsPagination.error / promptsPagination.error / resourcesPagination.error instead of always reading the managed stores.
4. useManagedListError → useListError (core/react/useListError.ts). Both store families expose the identical errorChange: Error | null, so the hook now serves both and no longer imports ManagedListEventMap — it declares the one-event contract it actually needs. The four useManaged* hooks and the three usePaged* hooks share it.

Retry already does the right thing in paginated mode: onRefreshTools routes to usePaginatedList.onRefresh, which reloads page 1 from the paged store.

Screenshots

Paginated mode against a server whose tools/list rejects with -32603.

Before — empty panel, no alert, no Retry (and an unhandled rejection from the connect-time load):

After — the same alert + Retry the aggregate path has shown since #1954:

Tests

• paged{Tools,Prompts,Resources}State.test.ts: records + dispatches + re-throws, wraps a non-Error rejection, clears on the next success, clears on disconnect, and records a connect-time auto-load failure rather than floating it.
• usePaged{Tools,Prompts,Resources}.test.tsx: the hook surfaces and clears the store's error, and reports null for a null store.
• usePaginatedList.test.tsx: reports the managed error in all-pages mode and the paged error in paginated mode.

Deliberately out of scope

ManagedListState.refresh also calls markResponseRejected for an SDK decode rejection, so the Protocol entry stops rendering a rejected result as a clean success. The paged stores don't, and this PR doesn't add it — that is #1953's surface, and the issue's suggested shape doesn't ask for it. Worth a follow-up issue if we want the two paths identical there.

npm run ci passes locally.

[Copilot]

Pull request overview

Fixes #1998 by surfacing paginated list-fetch failures in the existing alert and Retry UI.

Changes:

• Adds observable error state to paged tools, prompts, and resources stores.
• Selects managed or paged errors based on pagination mode.
• Prevents connect-time load failures from becoming unhandled rejections and adds comprehensive tests.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
core/react/usePagedTools.ts	Exposes paged tools errors.
core/react/usePagedResources.ts	Exposes paged resources errors.
core/react/usePagedPrompts.ts	Exposes paged prompts errors.
core/react/useManagedTools.ts	Uses the generalized error hook.
core/react/useManagedResourceTemplates.ts	Uses the generalized error hook.
core/react/useManagedResources.ts	Uses the generalized error hook.
core/react/useManagedPrompts.ts	Uses the generalized error hook.
core/react/useListError.ts	Generalizes error subscriptions across list-store families.
core/mcp/state/pagedToolsState.ts	Records, emits, clears, and rethrows tools errors.
core/mcp/state/pagedResourcesState.ts	Records, emits, clears, and rethrows resources errors.
core/mcp/state/pagedPromptsState.ts	Records, emits, clears, and rethrows prompts errors.
clients/web/src/test/core/react/usePagedTools.test.tsx	Tests paged tools error propagation.
clients/web/src/test/core/react/usePagedResources.test.tsx	Tests paged resources error propagation.
clients/web/src/test/core/react/usePagedPrompts.test.tsx	Tests paged prompts error propagation.
clients/web/src/test/core/react/useListError.test.tsx	Updates generalized error-hook coverage.
clients/web/src/test/core/mcp/state/pagedToolsState.test.ts	Tests tools error lifecycle and connect failures.
clients/web/src/test/core/mcp/state/pagedResourcesState.test.ts	Tests resources error lifecycle and connect failures.
clients/web/src/test/core/mcp/state/pagedPromptsState.test.ts	Tests prompts error lifecycle and connect failures.
clients/web/src/hooks/usePaginatedList.ts	Selects errors from the active list source.
clients/web/src/hooks/usePaginatedList.test.tsx	Tests mode-aware error selection.
clients/web/src/App.tsx	Routes active paginated errors into list panels.

---

💡 Add a code-review agent skill for context-aware, tailored reviews. Learn more in the docs.