fix: drop registered MCP tools when the conversation rotates

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JgzuxyafKNF2uaEeL35XQw

frontend/src/lib/components/copilot/chat/AIChatManager.svelte.ts

@@ -4170,6 +4170,11 @@ export class AIChatManager {
 		this.#syncMessageFiles()
 		this.syncArtifactsSession()
 		this.planMode.resetRound()
+		// Remote MCP tools are registered by a search in the conversation being left.
+		// Carrying them forward would put their schemas in the next conversation's tool
+		// list — the cost the search indirection exists to avoid — and offer the model a
+		// remote tool nobody there asked for.
+		forgetLoadedMcpTools()
 		this.onChatRotated?.(this.historyManager.getCurrentChatId())
 	}
 
@@ -4221,6 +4226,7 @@ export class AIChatManager {
 			this.#automaticScroll = true
 			this.syncArtifactsSession()
 			this.planMode.resetRound()
+			forgetLoadedMcpTools()
 			this.onChatRotated?.(id)
 		}
 	}

frontend/src/lib/components/copilot/chat/global/mcpTools.test.ts

@@ -11,7 +11,20 @@ vi.mock('../shared', () => ({
 	createToolDef: (_schema: unknown, name: string, description: string) => ({
 		type: 'function',
 		function: { name, description, parameters: {} }
-	})
+	}),
+	// Mirrors the real normalizer closely enough to keep assertions about what
+	// reaches a provider honest: it strips empty/null `format`, recursively.
+	normalizeToolParameterSchema: function strip(schema: any): void {
+		if (!schema || typeof schema !== 'object') return
+		if (schema.format === null || schema.format === '') delete schema.format
+		for (const child of Object.values(schema.properties ?? {})) strip(child)
+		if (Array.isArray(schema.items)) schema.items.forEach(strip)
+		else strip(schema.items)
+		for (const kw of ['allOf', 'anyOf', 'oneOf']) {
+			if (Array.isArray(schema[kw])) schema[kw].forEach(strip)
+		}
+		if (typeof schema.additionalProperties === 'object') strip(schema.additionalProperties)
+	}
 }))
 
 vi.mock('$lib/gen', () => ({
@@ -194,7 +207,9 @@ describe('loaded remote tools', () => {
 				inputSchema: {
 					$schema: 'https://json-schema.org/draft/2020-12/schema',
 					type: 'string',
-					properties: { a: { type: 'string' } },
+					// `format: ''` is what Windmill's own MCP server emits for an untyped
+					// field, and only the recursive normalizer removes it.
+					properties: { a: { type: 'string', format: '' } },
 					required: ['a', 'a', 'ghost']
 				}
 			} as any
@@ -204,6 +219,7 @@ describe('loaded remote tools', () => {
 		expect(params.type).toBe('object')
 		expect(params.required).toEqual(['a'])
 		expect(params.$schema).toBeUndefined()
+		expect(params.properties.a.format).toBeUndefined()
 	})
 
 	it('falls back to an empty object schema when the remote sends no usable one', () => {

frontend/src/lib/components/copilot/chat/global/mcpTools.ts

@@ -1,6 +1,6 @@
 import { z } from 'zod'
 import { ResourceService, type GetMcpToolsResponse } from '$lib/gen'
-import { createToolDef, type Tool } from '../shared'
+import { createToolDef, normalizeToolParameterSchema, type Tool } from '../shared'
 import { enabledMcpPaths } from '$lib/components/mcp/enabledServers'
 
 /**
@@ -78,9 +78,11 @@ export function clearMcpToolsCache() {
 }
 
 /**
- * Remote tools promoted to first-class chat tools for this session, keyed
- * `${server}::${tool}`. `chatLoop` re-reads its tool list on every iteration, so
- * one registered while a call is running is callable on the next one.
+ * Remote tools promoted to first-class chat tools for the current conversation,
+ * keyed `${server}::${tool}`. `chatLoop` re-reads its tool list on every iteration,
+ * so one registered while a call is running is callable on the next one, and the
+ * whole set is dropped when the conversation rotates — a tool the model was never
+ * told about in a fresh chat should not be in its list, nor its schema in the bill.
  *
  * A registered tool is a frozen copy of an input schema *and* of `readOnlyHint`,
  * which is the thing `TOOLS_CACHE_TTL_MS` exists to bound — so these are dropped
@@ -530,7 +532,12 @@ function safeInputSchema(schema: unknown): Record<string, unknown> {
 				)
 			]
 		: []
-	return { ...rest, type: 'object', properties, required }
+	const safe = { ...rest, type: 'object', properties, required }
+	// The same pass `createToolDef` runs on every other tool, so a remote schema is not
+	// the one that reaches a provider unnormalized. It recurses, which this does not:
+	// Windmill's own MCP server emits `format: ""` on untyped fields.
+	normalizeToolParameterSchema(safe)
+	return safe
 }
 
 function evictLoadedTools() {

frontend/src/lib/components/copilot/chat/shared.ts

@@ -1398,7 +1398,7 @@ export const createSearchHubScriptsTool = (withContent: boolean = false) => ({
 /**
  * Recursively normalizes JSON Schema quirks that specific providers reject.
  */
-function normalizeToolParameterSchema(schema: Record<string, any> | undefined): void {
+export function normalizeToolParameterSchema(schema: Record<string, any> | undefined): void {
 	if (!schema || typeof schema !== 'object') {
 		return
 	}