[Fix] Over-long MCP tool names reach API history and break the task

src/core/assistant-message/NativeToolCallParser.ts

@@ -16,7 +16,14 @@
 	ApiStreamToolCallDeltaChunk,
 	ApiStreamToolCallEndChunk,
 } from "../../api/transform/stream"
-import { MCP_TOOL_PREFIX, MCP_TOOL_SEPARATOR, parseMcpToolName, normalizeMcpToolName } from "../../utils/mcp-name"
+import {
+	MAX_TOOL_NAME_LENGTH,
+	MCP_TOOL_PREFIX,
+	MCP_TOOL_SEPARATOR,
+	buildMcpToolName,
+	parseMcpToolName,
+	normalizeMcpToolName,
+} from "../../utils/mcp-name"
 
 /**
  * Helper type to extract properly typed native arguments for a given tool.
@@ -1141,8 +1148,13 @@
 			const result: McpToolUse = {
 				type: "mcp_tool_use" as const,
 				id: toolCall.id,
-				// Keep the original tool name (e.g., "mcp--serverName--toolName") for API history
-				name: toolCall.name,
+				// Keep the original tool name (e.g., "mcp--serverName--toolName") for API history.
+				// A name over the provider limit can only be the uncut name; providers reject it in
+				// history, so record it under the name that was declared to the model instead.
+				name:
+					toolCall.name.length > MAX_TOOL_NAME_LENGTH
+						? buildMcpToolName(serverName, toolName)
+						: toolCall.name,
 				serverName,
 				toolName,
 				arguments: args,

src/core/assistant-message/__tests__/NativeToolCallParser-mcp-long-name.spec.ts

@@ -0,0 +1,59 @@
+import { buildMcpToolName, resolveMcpToolByName, toolNamesMatch } from "../../../utils/mcp-name"
+import { NativeToolCallParser } from "../NativeToolCallParser"
+
+const SERVER = "company-gateway-tools"
+const TOOL = "confluence-confluence_get_space_page_tree"
+
+describe("NativeToolCallParser.parseDynamicMcpTool name for API history", () => {
+	it("records an over-long uncut name under the declared name", () => {
+		const result = NativeToolCallParser.parseDynamicMcpTool({
+			id: "toolu_1",
+			name: `mcp--${SERVER}--${TOOL}`,
+			arguments: "{}",
+		})
+
+		expect(result?.name).toBe(buildMcpToolName(SERVER, TOOL))
+		expect(result?.name.length).toBeLessThanOrEqual(64)
+	})
+
+	it("resolves an over-long uncut name whose hyphens the model turned into underscores", () => {
+		const mangled = `mcp--${SERVER}--${TOOL}`.replace(/-/g, "_")
+
+		const result = NativeToolCallParser.parseDynamicMcpTool({ id: "toolu_5", name: mangled, arguments: "{}" })
+
+		expect(result).not.toBeNull()
+		expect(result!.name.length).toBeLessThanOrEqual(64)
+		// The recorded name is the declared one, up to the hyphen/underscore spelling.
+		expect(toolNamesMatch(result!.name, buildMcpToolName(SERVER, TOOL))).toBe(true)
+		expect(resolveMcpToolByName([{ name: SERVER, tools: [{ name: TOOL }] }], result!.name)).toEqual({
+			serverName: SERVER,
+			toolName: TOOL,
+		})
+	})
+
+	it("keeps the declared name the model returned", () => {
+		const declared = buildMcpToolName(SERVER, TOOL)
+
+		const result = NativeToolCallParser.parseDynamicMcpTool({ id: "toolu_2", name: declared, arguments: "{}" })
+
+		expect(result?.name).toBe(declared)
+	})
+
+	it("parses the declared name of a tool on a server with a very long name", () => {
+		const declared = buildMcpToolName("s".repeat(60), TOOL)
+
+		const result = NativeToolCallParser.parseDynamicMcpTool({ id: "toolu_4", name: declared, arguments: "{}" })
+
+		expect(result).toMatchObject({ type: "mcp_tool_use", name: declared })
+	})
+
+	it("keeps a short name verbatim", () => {
+		const result = NativeToolCallParser.parseDynamicMcpTool({
+			id: "toolu_3",
+			name: "mcp--weather--get_forecast",
+			arguments: "{}",
+		})
+
+		expect(result).toMatchObject({ name: "mcp--weather--get_forecast", serverName: "weather" })
+	})
+})

src/core/assistant-message/__tests__/presentAssistantMessage-auto-deny.spec.ts

@@ -88,7 +88,10 @@ interface MockTask {
 	providerRef: {
 		deref: () => {
 			getState: ReturnType<typeof vi.fn>
-			getMcpHub?: () => { findServerNameBySanitizedName: (name: string) => string | undefined }
+			getMcpHub?: () => {
+				findServerNameBySanitizedName: (name: string) => string | undefined
+				getAllServers: () => Array<{ name: string; tools?: Array<{ name: string }> }>
+			}
 		}
 	}
 	say: ReturnType<typeof vi.fn>
@@ -368,7 +371,7 @@ describe("presentAssistantMessage - automatic (policy) denials", () => {
 		mockTask.providerRef = {
 			deref: () => ({
 				getState: vi.fn().mockResolvedValue({ mode: "code", customModes: [] }),
-				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined }),
+				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined, getAllServers: () => [] }),
 			}),
 		}
 
@@ -428,7 +431,7 @@ describe("presentAssistantMessage - automatic (policy) denials", () => {
 		mockTask.providerRef = {
 			deref: () => ({
 				getState: vi.fn().mockResolvedValue({ mode: "code", customModes: [] }),
-				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined }),
+				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined, getAllServers: () => [] }),
 			}),
 		}
 
@@ -541,7 +544,7 @@ describe("presentAssistantMessage - automatic (policy) denials", () => {
 		mockTask.providerRef = {
 			deref: () => ({
 				getState: vi.fn().mockResolvedValue({ mode: "code", customModes: [] }),
-				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined }),
+				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined, getAllServers: () => [] }),
 			}),
 		}
 
@@ -581,7 +584,7 @@ describe("presentAssistantMessage - automatic (policy) denials", () => {
 		mockTask.providerRef = {
 			deref: () => ({
 				getState: vi.fn().mockResolvedValue({ mode: "code", customModes: [] }),
-				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined }),
+				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined, getAllServers: () => [] }),
 			}),
 		}
 
@@ -642,7 +645,7 @@ describe("presentAssistantMessage - automatic (policy) denials", () => {
 		mockTask.providerRef = {
 			deref: () => ({
 				getState: vi.fn().mockResolvedValue({ mode: "code", customModes: [] }),
-				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined }),
+				getMcpHub: () => ({ findServerNameBySanitizedName: () => undefined, getAllServers: () => [] }),
 			}),
 		}
 

src/core/assistant-message/__tests__/presentAssistantMessage-custom-tool.spec.ts

@@ -491,6 +491,7 @@ describe("presentAssistantMessage - Custom Tool Recording", () => {
 					}),
 					getMcpHub: () => ({
 						findServerNameBySanitizedName: () => "test-server",
+						getAllServers: () => [],
 						executeToolCall: vi.fn().mockResolvedValue({ content: [{ type: "text", text: "result" }] }),
 					}),
 				}),

src/core/assistant-message/__tests__/presentAssistantMessage-tool-usage-attribution.spec.ts

@@ -9,6 +9,7 @@ import { getModeBySlug } from "../../../shared/modes"
 import type { Task } from "../../task/Task"
 import type { RequestPolicySnapshot } from "../../prompts/tools/effective-tool-policy"
 import { useMcpToolTool } from "../../tools/UseMcpToolTool"
+import { buildMcpToolName, parseMcpToolName } from "../../../utils/mcp-name"
 
 vi.mock("../../task/Task")
 vi.mock("../../../shared/modes", async (importOriginal) => {
@@ -80,7 +81,10 @@ interface MockTask {
 		deref: () =>
 			| {
 					getState: ReturnType<typeof vi.fn>
-					getMcpHub?: () => { findServerNameBySanitizedName: (name: string) => string | undefined }
+					getMcpHub?: () => {
+						findServerNameBySanitizedName: (name: string) => string | undefined
+						getAllServers: () => Array<{ name: string; tools?: Array<{ name: string }> }>
+					}
 			  }
 			| undefined
 	}
@@ -379,6 +383,7 @@ describe("presentAssistantMessage - tool usage attribution", () => {
 					}),
 					getMcpHub: () => ({
 						findServerNameBySanitizedName: () => "my_server",
+						getAllServers: () => [],
 					}),
 				}),
 			}
@@ -548,6 +553,7 @@ describe("presentAssistantMessage - tool usage attribution", () => {
 					}),
 					getMcpHub: () => ({
 						findServerNameBySanitizedName: () => "my_server",
+						getAllServers: () => [],
 					}),
 				}),
 			}
@@ -638,6 +644,7 @@ describe("presentAssistantMessage - tool usage attribution", () => {
 					}),
 					getMcpHub: () => ({
 						findServerNameBySanitizedName: () => "my_server",
+						getAllServers: () => [],
 					}),
 				}),
 			}
@@ -680,6 +687,7 @@ describe("presentAssistantMessage - tool usage attribution", () => {
 					}),
 					getMcpHub: () => ({
 						findServerNameBySanitizedName: () => "my_server",
+						getAllServers: () => [],
 					}),
 				}),
 			}
@@ -787,6 +795,7 @@ describe("presentAssistantMessage - tool usage attribution", () => {
 					}),
 					getMcpHub: () => ({
 						findServerNameBySanitizedName: () => "my_server",
+						getAllServers: () => [],
 					}),
 				}),
 			}
@@ -932,6 +941,43 @@ describe("presentAssistantMessage - tool usage attribution", () => {
 			expect(handleSpy).toHaveBeenCalledTimes(1)
 		})
 
+		it("resolves a hash-shortened MCP tool name to its server and tool before executing", async () => {
+			const serverName = "company-gateway-tools"
+			const realToolName = "confluence-confluence_get_space_page_tree"
+			const declaredName = buildMcpToolName(serverName, realToolName)
+			const mockHub = {
+				findServerNameBySanitizedName: () => serverName,
+				getAllServers: () => [{ name: serverName, tools: [{ name: realToolName, enabledForPrompt: true }] }],
+			}
+			mockTask.providerRef = {
+				deref: () => ({
+					getState: vi.fn().mockResolvedValue({ mode: "code", customModes: [], disabledTools: [] }),
+					getMcpHub: () => mockHub,
+				}),
+			}
+			const handleSpy = vi.spyOn(useMcpToolTool, "handle").mockResolvedValue(undefined)
+			// The parser can only recover a cut tool name from the shortened one.
+			const parsed = parseMcpToolName(declaredName)!
+			mockTask.assistantMessageContent = [
+				{
+					type: "mcp_tool_use",
+					id: "call_hashed_name",
+					name: declaredName,
+					serverName: parsed.serverName,
+					toolName: parsed.toolName,
+					arguments: {},
+					partial: false,
+				},
+			]
+
+			await presentAssistantMessage(mockTask as unknown as Task, baseSnapshot)
+
+			expect(handleSpy).toHaveBeenCalledTimes(1)
+			expect(handleSpy.mock.calls[0][1]).toMatchObject({
+				nativeArgs: { server_name: serverName, tool_name: realToolName },
+			})
+		})
+
 		it("performs no provider-state read on the native validation path", async () => {
 			// Handler mocked so the only reachable pre-handler code is the
 			// validation arm itself; any getState call inside the presenter's
@@ -947,6 +993,7 @@ describe("presentAssistantMessage - tool usage attribution", () => {
 					getState,
 					getMcpHub: () => ({
 						findServerNameBySanitizedName: () => "my_server",
+						getAllServers: () => [],
 					}),
 				}),
 			}

src/core/assistant-message/presentAssistantMessage.ts

@@ -44,6 +44,7 @@
 
 import { formatResponse } from "../prompts/responses"
 import { sanitizeToolUseId } from "../../utils/tool-id"
+import { resolveMcpToolByName, toolNamesMatch } from "../../utils/mcp-name"
 
 /**
  * Maps a raw, potentially model-controlled tool name to a safe analytics key.
@@ -329,6 +330,25 @@
 				}
 			}
 
+			// A name shortened to fit the provider limit cannot be parsed back into its tool, so
+			// when the parsed names match nothing, look the called name up among the declared ones.
+			let resolvedToolName = mcpBlock.toolName
+			if (mcpHub && !mcpBlock.partial) {
+				const servers = mcpHub.getAllServers()
+				const parsedServer = servers.find((server) => server.name === resolvedServerName)
+				const parsedToolExists = parsedServer?.tools?.some((tool) =>
+					toolNamesMatch(tool.name, resolvedToolName),
+				)
+
+				if (!parsedToolExists) {
+					const resolved = resolveMcpToolByName(servers, mcpBlock.name)
+					if (resolved) {
+						resolvedServerName = resolved.serverName
+						resolvedToolName = resolved.toolName
+					}
+				}
+			}
+
 			// Execute the MCP tool using the same handler as use_mcp_tool
 			// Create a synthetic ToolUse block that the useMcpToolTool can handle
 			const syntheticToolUse: ToolUse<"use_mcp_tool"> = {
@@ -337,13 +357,13 @@
 				name: "use_mcp_tool",
 				params: {
 					server_name: resolvedServerName,
-					tool_name: mcpBlock.toolName,
+					tool_name: resolvedToolName,
 					arguments: JSON.stringify(mcpBlock.arguments),
 				},
 				partial: mcpBlock.partial,
 				nativeArgs: {
 					server_name: resolvedServerName,
-					tool_name: mcpBlock.toolName,
+					tool_name: resolvedToolName,
 					arguments: mcpBlock.arguments,
 				},
 			}

src/core/task/Task.ts

@@ -140,6 +140,7 @@ import { type AutoDenyDetail, AutoApprovalHandler, checkAutoApproval } from "../
 import { MessageManager } from "../message-manager"
 import { validateAndFixToolResultIds } from "./validateToolResultIds"
 import { mergeConsecutiveApiMessages } from "./mergeConsecutiveApiMessages"
+import { capMcpToolUseNames } from "./capMcpToolUseNames"
 import { prepareApiConversationMessage } from "./apiConversationHistory"
 import { shouldAddUserMessageToHistory } from "./messageCounting"
 import { type TaskExecutionContext } from "./providerHandoff"
@@ -5831,7 +5832,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 		// For API only: merge consecutive user messages (excludes summary messages per
 		// mergeConsecutiveApiMessages implementation) without mutating stored history.
 		const mergedForApi = mergeConsecutiveApiMessages(messagesSinceLastSummary, { roles: ["user"] })
-		const messagesWithoutImages = maybeRemoveImageBlocks(mergedForApi, this.api)
+		const messagesWithoutImages = maybeRemoveImageBlocks(capMcpToolUseNames(mergedForApi), this.api)
 		const cleanConversationHistory = this.buildCleanConversationHistory(
 			messagesWithoutImages as ApiMessage[],
 			requestModelInfo,

src/core/task/__tests__/capMcpToolUseNames.spec.ts

@@ -0,0 +1,46 @@
+import type { Anthropic } from "@anthropic-ai/sdk"
+
+import type { ApiMessage } from "../../task-persistence"
+import { buildMcpToolName } from "../../../utils/mcp-name"
+import { capMcpToolUseNames } from "../capMcpToolUseNames"
+
+type Block = Anthropic.Messages.ContentBlockParam
+
+const SERVER = "company-gateway-tools"
+const TOOL = "confluence-confluence_get_space_page_tree"
+const UNCUT = `mcp--${SERVER}--${TOOL}`
+
+const use = (name: string): Block => ({ type: "tool_use", id: "toolu_1", name, input: {} })
+const assistant = (...content: Block[]): ApiMessage => ({ role: "assistant", content })
+
+describe("capMcpToolUseNames", () => {
+	it("renames an over-long MCP tool_use to the declared name", () => {
+		const [message] = capMcpToolUseNames([assistant({ type: "text", text: "calling" }, use(UNCUT))])
+
+		expect(message.content).toEqual([{ type: "text", text: "calling" }, use(buildMcpToolName(SERVER, TOOL))])
+	})
+
+	it("leaves short names, non-MCP names and other roles untouched", () => {
+		const messages: ApiMessage[] = [
+			{ role: "user", content: "hi" },
+			assistant(use("read_file"), use("mcp--weather--get_forecast")),
+		]
+
+		expect(capMcpToolUseNames(messages)).toEqual(messages)
+	})
+
+	it("leaves an over-long name it cannot parse as an MCP tool", () => {
+		const name = "x".repeat(70)
+
+		expect(capMcpToolUseNames([assistant(use(name))])[0].content).toEqual([use(name)])
+	})
+
+	it("does not mutate its input", () => {
+		const input = [assistant(use(UNCUT))]
+		const snapshot = structuredClone(input)
+
+		capMcpToolUseNames(input)
+
+		expect(input).toEqual(snapshot)
+	})
+})