docs(mcp): describe the 100-value completion reply limit (#4086)

* docs(mcp): describe the 100-value completion reply limit

The prompt guide said completion returns all matching values. A reply
carries at most 100 values, the MCP limit, with total and hasMore
reporting omitted matches. Describe that and how to reach omitted values
with a longer prefix.

Fixes #3866

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* docs(mcp): qualify longer-prefix completion recovery

Review follow-up. A longer prefix reaches an omitted value only when it
excludes other matches; values whose normalized forms share a prefix
with more than 100 matches stay unreachable.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/mcp-prompts.md

@@ -111,8 +111,12 @@ list does not establish that the target has no procedures.
 Suggestions are Unicode-normalized, case-insensitive prefix matches. The server
 deduplicates them and sorts by code point for deterministic results. Procedure
 completion derives candidates from the complete inventory, so a name is offered
-only when it identifies one address in that inventory. Completion returns all
-matching values; it does not expose paging controls.
+only when it identifies one address in that inventory. A completion reply
+carries at most 100 values, the MCP limit. `total` counts every match and
+`hasMore` is `true` when values were omitted. Completion has no paging
+controls. A longer prefix reaches an omitted value only when it excludes other
+matches; matching uses normalized, case-insensitive forms, so a value can stay
+unreachable when more than 100 matches share its normalized prefix.
 
 ## Lifecycle and safety