fix(coding-agent): preserved mixed-case plugin tool names on refresh

packages/coding-agent/CHANGELOG.md

@@ -51,6 +51,10 @@
 
 - Continued Cursor turns that died with `NGHTTP2_INTERNAL_ERROR` / `NGHTTP2_REFUSED_STREAM` after tool calls already had results, instead of leaving the agent idle until the user typed "continue". HTTP/2 stream resets now use the same preserve-and-continue path as idle stream stalls, without requiring the Cursor exec-resolved marker that MCP/todo blocks never carry.
 
+### Fixed
+
+- Stopped mixed-case plugin tool names from being lowercased during tool-set refresh, which unmounted them from `xd://` whenever MCP tools connected.
+
 ## [17.3.3] - 2026-08-14
 
 ### Fixed

packages/coding-agent/src/tools/builtin-names.ts

@@ -41,10 +41,14 @@ const LEGACY_BUILTIN_TOOL_NAME_ALIASES: ReadonlyMap<string, BuiltinToolName> = n
 	["find", "glob"],
 ]);
 
-/** Return the canonical tool name for current and legacy built-in tool IDs. */
+const CANONICAL_TOOL_NAMES: Record<string, true> = Object.fromEntries(
+	[...BUILTIN_TOOL_NAMES, ...HIDDEN_TOOL_NAMES].map(name => [name, true]),
+);
+
+/** Canonicalize built-in IDs and legacy aliases. Leave plugin names unchanged. */
 export function normalizeToolName(name: string): string {
-	const normalized = name.toLowerCase();
-	return LEGACY_BUILTIN_TOOL_NAME_ALIASES.get(normalized) ?? normalized;
+	const lower = name.toLowerCase();
+	return LEGACY_BUILTIN_TOOL_NAME_ALIASES.get(lower) ?? (Object.hasOwn(CANONICAL_TOOL_NAMES, lower) ? lower : name);
 }
 
 /** Normalize and deduplicate tool names while preserving first-seen order. */

packages/coding-agent/test/agent-session-tool-rebuild-skip.test.ts

@@ -1289,4 +1289,21 @@ These tools became available:
 		expect(session.getToolByName(newTool.name)).toBeDefined();
 		expect(session.getActiveToolNames()).toContain(newTool.name);
 	});
+
+	it("keeps mixed-case plugin devices mounted when MCP tools refresh", async () => {
+		const xdevState = createTestXdevState();
+		const { session, toolRegistry } = newSession(async toolNames => `tools:${toolNames.join(",")}`, {
+			xdev: xdevState,
+		});
+		const pluginTool = { ...createBasicTool("CaseAdd", "Case Add"), loadMode: "discoverable" as const };
+		toolRegistry.set(pluginTool.name, pluginTool);
+		xdevState.mountedNames.add(pluginTool.name);
+
+		await session.refreshMCPTools([
+			createMcpCustomTool("mcp__nucleus_search", "nucleus", "search", "Search nucleus"),
+		]);
+
+		expect(session.getMountedXdevToolNames()).toContain("CaseAdd");
+		expect(session.getToolByName("CaseAdd")).toBeDefined();
+	});
 });

packages/coding-agent/test/builtin-names.test.ts

@@ -0,0 +1,11 @@
+import { describe, expect, it } from "bun:test";
+import { normalizeToolName } from "../src/tools/builtin-names";
+
+describe("normalizeToolName", () => {
+	it("maps legacy builtin aliases without touching plugin case", () => {
+		expect(normalizeToolName("search")).toBe("grep");
+		expect(normalizeToolName("Read")).toBe("read");
+		expect(normalizeToolName("CaseAdd")).toBe("CaseAdd");
+		expect(normalizeToolName("Constructor")).toBe("Constructor");
+	});
+});