mcp: prefer announced server title for tool prefixes and picker labels

[connor4312]

mcp: prefer announced server title for tool prefixes and picker labels

Reworks how MCP tool prefixes are generated and how MCP servers are labelled
in the Configure Tools picker so that the server-announced serverInfo.title
(falling back to serverInfo.name) is preferred over the mcp.json key.

• Introduces a shared McpPrefixGenerator with a take(name): IReference<string>
  API that hands out collision-resolved tool prefixes and releases them on
  dispose. Replaces the eager one-shot generator that used to live in
  McpService.
• McpServer now derives its tool prefix from its preferred name (announced
  title when known, otherwise the mcp.json label) so registry-style names
  like io.github.upstash/context7 no longer end up as truncated
  mcp_io_github_ups_* prefixes.
• Configure Tools picker and ToolDataSource.classify for MCP sources now
  prefer serverLabel (the announced title) over label.
• Adds unit tests for McpPrefixGenerator covering collisions, slot reuse on
  dispose, bucket cleanup, and name sanitization.

Fixes #299749
Fixes #299787

(Commit message generated by Copilot)

[Copilot]

Pull request overview

Updates MCP tool prefix generation and MCP server labeling to prefer server-announced serverInfo.title/name over the mcp.json key, improving readability and avoiding truncated registry-style identifiers in tool names and UI.

Changes:

• Introduces a shared McpPrefixGenerator.take(name): IReference<string> that manages collision-resolved prefixes with reuse on dispose.
• Updates McpServer to derive its tool prefix from server-announced metadata when available, and updates MCP source labeling in the tool picker and source classification.
• Adds unit tests for prefix collisions, reuse, bucket cleanup, and name sanitization.

Show a summary per file

File	Description
src/vs/workbench/contrib/mcp/test/common/mcpPrefixGenerator.test.ts	Adds unit tests for the new prefix generator behavior.
src/vs/workbench/contrib/mcp/common/mcpService.ts	Switches to a shared prefix generator and removes per-refresh eager prefix allocation.
src/vs/workbench/contrib/mcp/common/mcpServer.ts	Adds McpPrefixGenerator and updates servers to compute prefixes from preferred (announced) names.
src/vs/workbench/contrib/chat/common/tools/languageModelToolsService.ts	Prefers serverLabel for MCP tool source classification labels.
src/vs/workbench/contrib/chat/browser/actions/chatToolPicker.ts	Prefers serverLabel for MCP server bucket labels in the Configure Tools picker.

Copilot's findings

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/mcp/common/mcpService.ts:205

• updateCollectedServers() used to require server.toolPrefix === d.toolPrefix to reuse an existing server. Now it matches only by IDs, so a definition label change (possible for extension-provided definitions where id is stable) won’t recreate/update the server and it will keep using the old definition.label as fallback display/prefix. Consider including serverDefinition.label in the reuse criteria or updating the server’s label when the definition changes.

		// Transfer over any servers that are still valid.
		for (const server of currentServers) {
			const match = definitions.find(d => defsEqual(server.object, d));
			if (match) {
				pushMatch(match, server);
			} else {
				server.object.dispose();

• Files reviewed: 5/5 changed files
• Comments generated: 3