Summary
The Resources panel keys its list on resource.uri, so a server whose
resources/list result contains the same URI twice makes React log
Encountered two children with the same key on every render — and, per React's
own warning, may duplicate or omit one of the rows.
This is the same defect class as #1957 (duplicate tools/list names leaving
stale rows after filtering), which was fixed for tools. The resources list
appears not to have been covered by that change.
What was observed
While a third-party MCP Apps server was connected to web:dev, the browser
console logged this several hundred times — repeating on every re-render, in
bursts as the UI updated:
Encountered two children with the same key, `ui://hello-world/app.html`.
Keys should be unique so that components maintain their identity across
updates. Non-unique keys may cause children to be duplicated and/or omitted —
the behavior is unsupported and could change in a future version.
Where it comes from
clients/web/src/components/groups/ResourceControls/ResourceControls.tsx:317
{filteredResources.map((resource) => (
<ResourceListItem
key={resource.uri}
...Two neighbouring lists in the same file take the same shape and look equally
exposed: key={template.uriTemplate} (line 343) and key={sub.resource.uri}
(line 386). RootsTable.tsx:66 (key={root.uri}) is a fourth.
The store is not the source of the duplication: ManagedListState.applyItems
(core/mcp/state/managedListState.ts:351) replaces this.items wholesale rather
than appending, so repeated refreshes cannot accumulate copies. That points at
the fetched list itself carrying the URI twice — either because the server
advertises it twice, or because the paginating fetchAll overlaps pages.
Which of those two it is has not been established.
Status of this report — not reproduced
Filed from console output captured in a live session, not from a reproduction.
Specifically unconfirmed:
hello-world is not one of this repo's test-servers/, so the server
involved was external and is not identified here. No fixture in-repo currently
reproduces it.- Whether the duplicate URI originates server-side or in
fetchAll pagination.
- Whether a row was actually dropped or duplicated on screen, or the warning was
the only visible symptom.
First step for whoever picks this up is a synthetic fixture serving a
resources/list with a repeated URI — the same approach #1957 used for tools.
Expected
A duplicate URI in resources/list should render without a React key collision,
and every returned entry should be visible, matching the behavior #1957
established for duplicate tool names.
Summary
The Resources panel keys its list on
resource.uri, so a server whoseresources/listresult contains the same URI twice makes React logEncountered two children with the same keyon every render — and, per React'sown warning, may duplicate or omit one of the rows.
This is the same defect class as #1957 (duplicate
tools/listnames leavingstale rows after filtering), which was fixed for tools. The resources list
appears not to have been covered by that change.
What was observed
While a third-party MCP Apps server was connected to
web:dev, the browserconsole logged this several hundred times — repeating on every re-render, in
bursts as the UI updated:
Where it comes from
clients/web/src/components/groups/ResourceControls/ResourceControls.tsx:317Two neighbouring lists in the same file take the same shape and look equally
exposed:
key={template.uriTemplate}(line 343) andkey={sub.resource.uri}(line 386).
RootsTable.tsx:66(key={root.uri}) is a fourth.The store is not the source of the duplication:
ManagedListState.applyItems(
core/mcp/state/managedListState.ts:351) replacesthis.itemswholesale ratherthan appending, so repeated refreshes cannot accumulate copies. That points at
the fetched list itself carrying the URI twice — either because the server
advertises it twice, or because the paginating
fetchAlloverlaps pages.Which of those two it is has not been established.
Status of this report — not reproduced
Filed from console output captured in a live session, not from a reproduction.
Specifically unconfirmed:
hello-worldis not one of this repo'stest-servers/, so the serverinvolved was external and is not identified here. No fixture in-repo currently
reproduces it.
fetchAllpagination.the only visible symptom.
First step for whoever picks this up is a synthetic fixture serving a
resources/listwith a repeated URI — the same approach #1957 used for tools.Expected
A duplicate URI in
resources/listshould render without a React key collision,and every returned entry should be visible, matching the behavior #1957
established for duplicate tool names.