An MCP cursor is an opaque string: the spec constrains neither its content
nor its length, so `""` is a `nextCursor` a server may legitimately return
and the client is required to send back verbatim.
`listPrompts`, `listResources`, `listResourceTemplates` and
`listRequestorTasks` built their request params with `cursor ? { cursor } : {}`,
a truthiness check that cannot distinguish "no cursor" from "the cursor is
the empty string". Against a server that paginates with `""` they dropped it
and re-requested page one — a list that silently stops at the first page, or
a walk that loops on it forever. Nothing surfaced an error, because the
request was well-formed; it just asked the wrong question. `listTools` (and
the later `listSkills`) already used `cursor !== undefined`; this brings the
other four into line.
`getReplayableParams` in `protocolReplay.ts` existed partly to mirror the
asymmetry — its `method === "tools/list" || params.cursor !== ""` special
case collapses to `typeof params.cursor === "string"` now that the adapters
agree, and its long comment is updated rather than left describing a state
that no longer exists.
Coverage:
- `inspectorClient-list-cursor.test.ts` asserts the outbound params of all
five adapters — `""` carried, an absent cursor sending no `cursor` key,
a non-empty cursor forwarded unchanged. `listTools` is the control.
- `test-servers/configs/empty-cursor-http.json` (`emptyStringCursor`) hands
out `""` as the cursor for page two, the shape no other fixture produces,
and `empty-cursor.test.ts` walks all three of its lists end to end.
- Removing the fix from any one adapter fails exactly its two cases.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EN2UfrkQZvtrviMtqURRm4
Signed-off-by: cliffhall <cliff@futurescale.com>
