diff --git a/src/agent/claude-code/binary.ts b/src/agent/claude-code/binary.ts
index 81b4a55..13e86e6 100644
--- a/src/agent/claude-code/binary.ts
+++ b/src/agent/claude-code/binary.ts
@@ -21,7 +21,9 @@ function getWindowsSearchSpec(env: BinaryLookup["env"], homeDir: string): Search
 
 	return {
 		paths,
-		names: ["claude.exe", "claude.cmd"],
+		// Direct spawn deliberately uses no shell. A .cmd-only npm install
+		// is not runnable and must not count as an available provider.
+		names: ["claude.exe"],
 		knownDirs: [
 			paths.join(homeDir, ".local", "bin"),
 			paths.join(homeDir, ".claude", "local"),
diff --git a/src/agent/claude-code/cli-events.ts b/src/agent/claude-code/cli-events.ts
index f532946..f3dddca 100644
--- a/src/agent/claude-code/cli-events.ts
+++ b/src/agent/claude-code/cli-events.ts
@@ -14,7 +14,8 @@ export type CliEvent =
 	| { type: "messageDelta"; stopReason: string | null; usage: CliUsage }
 	| { type: "messageStop" }
 	| { type: "assistantError"; error: string; text: string }
-	| { type: "resultError"; text: string };
+	| { type: "resultError"; text: string }
+	| { type: "toolResults"; ids: string[] };
 
 type RawUsage = {
 	input_tokens?: number | null;
@@ -46,7 +47,7 @@ type RawCliLine = {
 	type?: string;
 	event?: RawStreamEvent;
 	error?: string | null;
-	message?: { content?: { type: string; text?: string }[] };
+	message?: { content?: { type: string; text?: string; tool_use_id?: string }[] };
 	is_error?: boolean;
 	result?: string;
 	subtype?: string;
@@ -139,7 +140,7 @@ function parseStreamEvent(event: RawStreamEvent): CliEvent | null {
 }
 
 function getText(line: RawCliLine): string {
-	const blocks = line.message?.content ?? [];
+	const blocks = Array.isArray(line.message?.content) ? line.message.content : [];
 	const texts = blocks.flatMap((block) => (block.type === "text" && block.text ? [block.text] : []));
 
 	return texts.join("\n");
@@ -171,6 +172,12 @@ export function parseCliLine(text: string): CliEvent | null {
 			if (typeof line.error !== "string") return null;
 			return { type: "assistantError", error: line.error, text: getText(line) };
 
+		case "user": {
+			const blocks = Array.isArray(line.message?.content) ? line.message.content : [];
+			const ids = blocks.flatMap((block) => block.type === "tool_result" && typeof block.tool_use_id === "string" ? [block.tool_use_id] : []);
+			return ids.length ? { type: "toolResults", ids } : null;
+		}
+
 		case "result":
 			if (line.is_error !== true) return null;
 			return { type: "resultError", text: getResultErrorText(line) };
diff --git a/src/agent/claude-code/live-processes.ts b/src/agent/claude-code/live-processes.ts
index 61f036a..1a68672 100644
--- a/src/agent/claude-code/live-processes.ts
+++ b/src/agent/claude-code/live-processes.ts
@@ -1,4 +1,4 @@
-export type LiveProcess = { toolCallIds: string[]; kill(): void };
+export type LiveProcess = { readonly owner: symbol; toolCallIds: string[]; kill(): void };
 
 // Tools usually call back within seconds, but a question tool holds its call until the learner
 // answers. Past this, the process is killed and the answer starts a fresh one with a full replay.
@@ -12,6 +12,7 @@ export const liveProcessIdleTimeoutMs = { current: LIVE_PROCESS_IDLE_TIMEOUT_MS
 const liveProcesses = new Map<LiveProcess, NodeJS.Timeout>();
 
 export function addLiveProcess(process: LiveProcess): void {
+	removeLiveProcess(process);
 	const timer = setTimeout(() => {
 		removeLiveProcess(process);
 		process.kill();
@@ -23,14 +24,14 @@ export function addLiveProcess(process: LiveProcess): void {
 }
 
 function hasSameIds(ids: string[], otherIds: string[]): boolean {
-	return ids.length === otherIds.length && ids.every((id) => otherIds.includes(id));
+	return ids.length === otherIds.length && new Set(otherIds).size === otherIds.length && ids.every((id) => otherIds.includes(id));
 }
 
-export function getLiveProcess(toolCallIds: string[]): LiveProcess | null {
+export function getLiveProcess(toolCallIds: string[], owner: symbol): LiveProcess | null {
 	if (toolCallIds.length === 0) return null;
 
 	for (const process of liveProcesses.keys()) {
-		if (hasSameIds(process.toolCallIds, toolCallIds)) return process;
+		if (process.owner === owner && hasSameIds(process.toolCallIds, toolCallIds)) return process;
 	}
 
 	return null;
diff --git a/src/agent/claude-code/reuse-context.ts b/src/agent/claude-code/reuse-context.ts
new file mode 100644
index 0000000..63cbd7d
--- /dev/null
+++ b/src/agent/claude-code/reuse-context.ts
@@ -0,0 +1,27 @@
+import type { Api, Message, Model, TranscriptContext } from "@earendil-works/pi-ai";
+import { getCurrentSystemPrompt, getCurrentTools } from "@earendil-works/pi-ai/utils/transcript";
+
+/** Compare model-visible history, not app IDs, timestamps, usage, or Pi's added thinkingLevel. */
+export function conversationForReuse(messages: Message[]): unknown[] {
+	return messages.flatMap((message): unknown[] => {
+		switch (message.role) {
+			case "system": return [];
+			case "user": return [{ role: message.role, content: message.content }];
+			case "assistant": return [{ role: message.role, content: message.content }];
+			case "toolResult": return [{
+				role: message.role,
+				toolCallId: message.toolCallId,
+				toolName: message.toolName,
+				content: message.content,
+				isError: message.isError,
+			}];
+		}
+	});
+}
+
+export function configurationForReuse(model: Model<Api>, context: TranscriptContext, effort: string): unknown {
+	const systemPrompt = getCurrentSystemPrompt(context.messages);
+	const tools = getCurrentTools(context.messages);
+	// The wire is JSON: TypeBox's schema symbols are not CLI configuration.
+	return JSON.parse(JSON.stringify({ model, effort, systemPrompt, tools })) as unknown;
+}
diff --git a/src/agent/claude-code/stream.ts b/src/agent/claude-code/stream.ts
index 0f9dd4d..cd27167 100644
--- a/src/agent/claude-code/stream.ts
+++ b/src/agent/claude-code/stream.ts
@@ -16,11 +16,9 @@ import {
 	type StopReason,
 	type StreamFunction,
 	type ThinkingLevel,
-	type Tool,
 	type ToolCall,
 	type ToolResultMessage,
 	type TranscriptContext,
-	validateToolCall,
 } from "@earendil-works/pi-ai";
 import type { AnthropicEffort } from "@earendil-works/pi-ai/api/anthropic-messages";
 import { parseStreamingJson, parseToolCallArguments } from "@earendil-works/pi-ai/utils/json-parse";
@@ -29,7 +27,8 @@ import { getClaudeBinary } from "./binary.ts";
 import { parseCliLine, type CliBlock, type CliEvent, type CliUsage } from "./cli-events.ts";
 import { ClaudeCodeError } from "./constants.ts";
 import { addLiveProcess, getLiveProcess, removeLiveProcess, type LiveProcess } from "./live-processes.ts";
-import { createToolBridge, toolNameFromMcp, type PendingToolCall, type ToolBridge } from "./tool-bridge.ts";
+import { configurationForReuse, conversationForReuse } from "./reuse-context.ts";
+import { BRIDGE_SERVER_NAME, createToolBridge, toolNameFromMcp, type PendingToolCall, type ToolBridge } from "./tool-bridge.ts";
 import { toClaudeInput, toStreamJsonLine } from "./transcript.ts";
 
 type RunClaudeOptions = { cwd: string; env: NodeJS.ProcessEnv };
@@ -137,6 +136,8 @@ class ClaudeTurn {
 	private readonly output: AssistantMessage;
 	private readonly contentIndexes = new Map<number, number>();
 	private readonly partialJson = new Map<number, string>();
+	private readonly toolBlocks = new Map<number, ToolCall>();
+	private readonly intents: ToolCall[] = [];
 	started = false;
 	finished = false;
 
@@ -188,13 +189,12 @@ class ClaudeTurn {
 				const found = this.getBlock(event.index);
 				if (!found) return;
 
-				const { contentIndex, block } = found;
+				const { block } = found;
 				if (block.type !== "toolCall") return;
 
 				const partialJson = (this.partialJson.get(event.index) ?? "") + event.partialJson;
 				this.partialJson.set(event.index, partialJson);
 				block.arguments = parseStreamingJson(partialJson);
-				this.stream.push({ type: "toolcall_delta", contentIndex, delta: event.partialJson, partial: this.output });
 				return;
 			}
 
@@ -208,7 +208,9 @@ class ClaudeTurn {
 				return;
 
 			case "messageStop":
-				this.finish();
+				// Tool intent is not execution admission. The process publishes only
+				// calls that actually reach the authenticated MCP bridge.
+				if (this.output.stopReason !== "toolUse") this.finish();
 				return;
 
 			case "assistantError":
@@ -221,10 +223,22 @@ class ClaudeTurn {
 		}
 	}
 
-	getToolCalls(): ToolCall[] {
-		if (!this.finished || this.output.stopReason !== "toolUse") return [];
+	get waitingForAdmission(): boolean { return !this.finished && this.output.stopReason === "toolUse"; }
 
-		return this.output.content.filter((block) => block.type === "toolCall");
+	getIntents(): ToolCall[] { return this.intents; }
+
+	getMessage(): AssistantMessage { return this.output; }
+
+	admit(calls: ToolCall[]): void {
+		this.start();
+		for (const call of calls) {
+			const contentIndex = this.output.content.length;
+			this.output.content.push(call);
+			this.stream.push({ type: "toolcall_start", contentIndex, partial: this.output });
+			this.stream.push({ type: "toolcall_end", contentIndex, toolCall: call, partial: this.output });
+		}
+		this.output.stopReason = "toolUse";
+		this.finish();
 	}
 
 	fail(message: string, reason: "aborted" | "error"): void {
@@ -260,13 +274,18 @@ class ClaudeTurn {
 				return;
 
 			case "toolUse":
-				this.output.content.push({ type: "toolCall", id: block.id, name: toolNameFromMcp(block.name), arguments: {} });
-				this.stream.push({ type: "toolcall_start", contentIndex, partial: this.output });
+				if (!block.name.startsWith(`mcp__${BRIDGE_SERVER_NAME}__`)) {
+					this.fail("claude CLI emitted an unsupported native tool call", "error");
+					return;
+				}
+				this.toolBlocks.set(index, { type: "toolCall", id: block.id, name: toolNameFromMcp(block.name), arguments: {} });
 				return;
 		}
 	}
 
 	private getBlock(index: number): { contentIndex: number; block: AssistantMessage["content"][number] } | null {
+		const tool = this.toolBlocks.get(index);
+		if (tool) return { contentIndex: -1, block: tool };
 		const contentIndex = this.contentIndexes.get(index);
 		if (contentIndex === undefined) return null;
 
@@ -293,7 +312,8 @@ class ClaudeTurn {
 			case "toolCall":
 				Object.assign(block, parseToolCallArguments(this.partialJson.get(index) ?? ""));
 				this.partialJson.delete(index);
-				this.stream.push({ type: "toolcall_end", contentIndex, toolCall: block satisfies ToolCall, partial: this.output });
+				this.toolBlocks.delete(index);
+				this.intents.push(block);
 				return;
 		}
 	}
@@ -340,51 +360,48 @@ type TurnFiles = { cwd: string; privateDir: string; systemPromptFile: string; mc
 
 async function createTurnFiles(systemPrompt: string, mcpConfig: string): Promise<TurnFiles> {
 	const cwd = await mkdtemp(join(tmpdir(), "claude-code-cwd-"));
-	const privateDir = await mkdtemp(join(tmpdir(), "claude-code-private-"));
-
-	const systemPromptFile = join(privateDir, "system-prompt.md");
-	const mcpConfigFile = join(privateDir, "mcp.json");
-
-	await writeFile(systemPromptFile, systemPrompt, { mode: PRIVATE_FILE_MODE });
-	await writeFile(mcpConfigFile, mcpConfig, { mode: PRIVATE_FILE_MODE });
-
-	return { cwd, privateDir, systemPromptFile, mcpConfigFile };
-}
-
-async function removeTurnResources(bridge: ToolBridge, files: TurnFiles): Promise<void> {
-	await bridge.close();
-	await rm(files.cwd, { recursive: true, force: true });
-	await rm(files.privateDir, { recursive: true, force: true });
-}
-
-type UnansweredToolCall = { toolCall: ToolCall; result: ToolResultMessage };
-
-// The CLI answers calls to undeclared tools or with invalid arguments itself, without reaching the bridge.
-function isValidToolCall(tools: Tool[], toolCall: ToolCall): boolean {
+	let privateDir: string | undefined;
 	try {
-		validateToolCall(tools, toolCall);
-		return true;
-	} catch {
-		return false;
+		privateDir = await mkdtemp(join(tmpdir(), "claude-code-private-"));
+		const systemPromptFile = join(privateDir, "system-prompt.md");
+		const mcpConfigFile = join(privateDir, "mcp.json");
+		await writeFile(systemPromptFile, systemPrompt, { mode: PRIVATE_FILE_MODE });
+		await writeFile(mcpConfigFile, mcpConfig, { mode: PRIVATE_FILE_MODE });
+		return { cwd, privateDir, systemPromptFile, mcpConfigFile };
+	} catch (error) {
+		await Promise.all([rm(cwd, { recursive: true, force: true }), ...(privateDir ? [rm(privateDir, { recursive: true, force: true })] : [])]);
+		throw error;
 	}
 }
 
-function isSameToolCall(toolCall: ToolCall, call: PendingToolCall): boolean {
-	return toolCall.name === call.name && isDeepStrictEqual(toolCall.arguments, call.arguments);
+async function removeTurnResources(bridge: ToolBridge, files: TurnFiles): Promise<void> {
+	await Promise.all([
+		bridge.close(),
+		rm(files.cwd, { recursive: true, force: true }),
+		rm(files.privateDir, { recursive: true, force: true }),
+	]);
 }
 
 class ClaudeProcess implements LiveProcess {
 	toolCallIds: string[] = [];
 	private stderr = "";
 	private closed = false;
+	private stopping = false;
+	private killTimer: NodeJS.Timeout | undefined;
 	private signal: AbortSignal | undefined;
+	private sourceCalls: ToolCall[] = [];
+	private sourceComplete = false;
+	private admitted: PendingToolCall[] = [];
+	private pendingError: string | undefined;
 
 	constructor(
 		private readonly child: ChildProcessWithoutNullStreams,
 		private readonly bridge: ToolBridge,
 		private readonly files: TurnFiles,
-		private readonly tools: Tool[],
 		private turn: ClaudeTurn,
+		readonly owner: symbol,
+		private readonly configuration: unknown,
+		private conversation: unknown[],
 	) {}
 
 	start(stdinLine: string, signal: AbortSignal | undefined): void {
@@ -394,39 +411,92 @@ class ClaudeProcess implements LiveProcess {
 			this.turn.fail(START_FAILED_MESSAGE, "error");
 			this.handleClose(START_FAILED_MESSAGE);
 		});
-
 		this.child.stderr.setEncoding("utf8");
-		this.child.stderr.on("data", (chunk: string) => (this.stderr += chunk));
-
+		this.child.stderr.on("data", (chunk: string) => { this.stderr = (this.stderr + chunk).slice(-65_536); });
 		this.child.stdin.on("error", (error) => console.error("claude CLI stdin closed early:", error));
 		this.child.stdin.end(`${stdinLine}\n`);
-
-		createInterface({ input: this.child.stdout }).on("line", (line) => this.handleLine(line));
-
+		createInterface({ input: this.child.stdout }).on("line", (line) => {
+			try { this.handleLine(line); }
+			catch { this.fail("claude CLI emitted malformed stream output"); }
+		});
 		this.setSignal(signal);
 	}
 
-	continueTurn(turn: ClaudeTurn, toolResults: ToolResultMessage[], signal: AbortSignal | undefined): void {
+	canContinue(owner: symbol, configuration: unknown, messages: Message[], results: ToolResultMessage[]): boolean {
+		const conversation = conversationForReuse(messages);
+		return !this.stopping && owner === this.owner
+			&& isDeepStrictEqual(configuration, this.configuration)
+			&& isDeepStrictEqual(conversation.slice(0, this.conversation.length), this.conversation)
+			&& conversation.length === this.conversation.length + this.admitted.length
+			&& results.length === this.admitted.length
+			&& new Set(results.map((result) => result.toolCallId)).size === results.length
+			&& this.admitted.every((call) => results.some((result) => result.toolCallId === call.id && result.toolName === call.name));
+	}
+
+	continueTurn(turn: ClaudeTurn, messages: Message[], results: ToolResultMessage[], signal: AbortSignal | undefined): void {
 		removeLiveProcess(this);
-
-		const unanswered = this.turn.getToolCalls().flatMap((toolCall) => {
-			const result = toolResults.find((toolResult) => toolResult.toolCallId === toolCall.id);
-			return result ? [{ toolCall, result }] : [];
-		});
-
+		const admitted = this.admitted;
+		this.admitted = [];
+		this.conversation = structuredClone(conversationForReuse(messages));
 		this.turn = turn;
+		this.sourceComplete = this.sourceCalls.length > 0;
 		this.setSignal(signal);
-
-		this.answerToolCalls(turn, unanswered).catch((error: unknown) => {
-			console.error("claude CLI tool results failed:", error);
-			turn.fail(START_FAILED_MESSAGE, "error");
-			this.kill();
-		});
+		if (this.stopping) return;
+		for (const call of admitted) {
+			const result = results.find((candidate) => candidate.toolCallId === call.id)!;
+			this.bridge.resolveToolCall(call, result);
+		}
+		this.flushAdmissions();
 	}
 
 	kill(): void {
 		removeLiveProcess(this);
+		if (this.stopping || this.closed) return;
+		this.stopping = true;
 		this.child.kill();
+		this.killTimer = setTimeout(() => this.child.kill("SIGKILL"), 1000);
+		this.killTimer.unref();
+	}
+
+	fail(message: string): void {
+		// A parallel request can fail after the admitted slice was handed to
+		// Pi. Retain that failure for its continuation instead of silently
+		// replaying and hiding the compatibility error.
+		if (this.turn.finished && this.toolCallIds.length > 0) this.pendingError = message;
+		this.turn.fail(message, "error");
+		this.kill();
+		if (this.pendingError) addLiveProcess(this);
+	}
+
+	consumeFailure(owner: symbol, turn: ClaudeTurn): boolean {
+		if (owner !== this.owner || !this.pendingError) return false;
+		const message = this.pendingError;
+		this.pendingError = undefined;
+		this.kill();
+		turn.fail(message, "error");
+		return true;
+	}
+
+	/** Only authenticated MCP requests, never stdout intent alone, admit side effects. */
+	flushAdmissions(): void {
+		if (this.stopping || this.turn.finished || !this.sourceComplete) return;
+		const pending = this.bridge.getPendingToolCalls();
+		if (pending.length === 0) return;
+		const calls: ToolCall[] = [];
+		for (const call of pending) {
+			const intent = this.sourceCalls.find((candidate) => candidate.id === call.id);
+			if (!intent || intent.name !== call.name || !isDeepStrictEqual(intent.arguments, call.arguments)) {
+				this.fail("claude CLI compatibility error: MCP call does not match its streamed tool intent");
+				return;
+			}
+			calls.push(intent);
+		}
+		this.sourceCalls = this.sourceCalls.filter((call) => !pending.some((admitted) => admitted.id === call.id));
+		this.admitted = pending;
+		this.toolCallIds = pending.map((call) => call.id);
+		this.turn.admit(calls);
+		this.conversation.push(...structuredClone(conversationForReuse([this.turn.getMessage()])));
+		addLiveProcess(this);
 	}
 
 	private readonly abort = () => {
@@ -438,96 +508,72 @@ class ClaudeProcess implements LiveProcess {
 		this.signal?.removeEventListener("abort", this.abort);
 		this.signal = signal;
 		signal?.addEventListener("abort", this.abort, { once: true });
-
 		if (signal?.aborted) this.abort();
 	}
 
 	private handleLine(line: string): void {
+		if (this.stopping) return;
 		const event = parseCliLine(line);
 		if (!event) return;
-
-		// Output after a finished message means the CLI moved on without waiting for our tool results.
-		if (this.turn.finished) {
-			this.kill();
-			return;
-		}
-
-		this.turn.handle(event);
-		if (!this.turn.finished) return;
-
-		const toolCalls = this.turn.getToolCalls();
-		this.toolCallIds = toolCalls.map((toolCall) => toolCall.id);
-
-		const reachesBridge = toolCalls.length > 0 && toolCalls.every((toolCall) => isValidToolCall(this.tools, toolCall));
-		if (!reachesBridge) {
-			this.kill();
-			return;
-		}
-
-		addLiveProcess(this);
-	}
-
-	private async answerToolCalls(turn: ClaudeTurn, unanswered: UnansweredToolCall[]): Promise<void> {
-		while (unanswered.length > 0 && !turn.started) {
-			const pending = this.bridge.getPendingToolCalls();
-			let answered = false;
-
-			for (const call of pending) {
-				const index = unanswered.findIndex(({ toolCall }) => isSameToolCall(toolCall, call));
-				const match = unanswered[index];
-				if (!match) continue;
-
-				this.bridge.resolveToolCall(call, match.result);
-				unanswered.splice(index, 1);
-				answered = true;
+		if (event.type === "toolResults") {
+			if (event.ids.some((id) => this.sourceCalls.some((call) => call.id === id))) {
+				this.fail("claude CLI refused a harness tool call before MCP admission");
 			}
-
-			if (answered) continue;
-
-			// Rejects only once the bridge has closed, which means the process is already gone.
-			const next = await this.bridge.waitForToolCalls(pending.length + 1).catch(() => null);
-			if (!next) return;
+			return;
+		}
+		// Moving on before held calls were answered means the CLI did not
+		// honor this tool wait. Never execute further stdout-only intentions.
+		if (this.turn.finished) {
+			this.fail("claude CLI moved on while harness tool calls were waiting for results");
+			return;
+		}
+		if (event.type === "messageStart" && this.sourceComplete && this.sourceCalls.length > 0) {
+			this.fail("claude CLI moved on without admitting its harness tool calls");
+			return;
+		}
+		this.turn.handle(event);
+		if (this.turn.finished) { this.kill(); return; }
+		if (event.type === "messageStop" && this.turn.waitingForAdmission) {
+			this.sourceCalls = this.turn.getIntents();
+			if (this.sourceCalls.length === 0 || new Set(this.sourceCalls.map((call) => call.id)).size !== this.sourceCalls.length) {
+				this.fail("claude CLI emitted an invalid tool batch");
+				return;
+			}
+			this.sourceComplete = true;
+			this.flushAdmissions();
 		}
 	}
 
 	private handleClose(message: string): void {
 		if (this.closed) return;
-
 		this.closed = true;
+		clearTimeout(this.killTimer);
 		removeLiveProcess(this);
+		if (this.pendingError) addLiveProcess(this);
 		this.signal?.removeEventListener("abort", this.abort);
-
 		if (this.stderr.trim()) console.error("claude CLI stderr:", this.stderr.trim());
-
 		this.turn.fail(message, "error");
-
 		removeTurnResources(this.bridge, this.files).catch((error: unknown) => {
 			console.error("claude CLI cleanup failed:", error);
 		});
 	}
 }
 
-function continueLiveProcess(turn: ClaudeTurn, messages: Message[], signal: AbortSignal | undefined): boolean {
+function continueLiveProcess(turn: ClaudeTurn, owner: symbol, configuration: unknown, messages: Message[], signal: AbortSignal | undefined): boolean {
 	const assistantIndex = messages.findLastIndex((message) => message.role === "assistant");
 	const assistant = messages[assistantIndex];
 	if (assistant?.role !== "assistant") return false;
-
-	const toolCallIds = assistant.content.flatMap((block) => (block.type === "toolCall" ? [block.id] : []));
-	const process = getLiveProcess(toolCallIds);
+	const ids = assistant.content.flatMap((block) => block.type === "toolCall" ? [block.id] : []);
+	const process = getLiveProcess(ids, owner);
 	if (!(process instanceof ClaudeProcess)) return false;
-
+	if (process.consumeFailure(owner, turn)) return true;
 	const trailing = messages.slice(assistantIndex + 1);
-	const toolResults = trailing.filter((message) => message.role === "toolResult");
-
-	const onlyToolResults = toolResults.length === trailing.length;
-	const answersEveryCall = toolCallIds.every((id) => toolResults.some((toolResult) => toolResult.toolCallId === id));
-
-	if (!onlyToolResults || !answersEveryCall) {
+	const results = trailing.filter((message) => message.role === "toolResult");
+	if (trailing.length !== results.length || !process.canContinue(owner, configuration, messages, results)) {
 		process.kill();
 		return false;
 	}
-
-	process.continueTurn(turn, toolResults, signal);
+	process.continueTurn(turn, messages, results, signal);
 	return true;
 }
 
@@ -549,10 +595,28 @@ async function startProcess(
 	model: Model<Api>,
 	context: TranscriptContext,
 	options: SimpleStreamOptions | undefined,
+	owner: symbol,
+	configuration: unknown,
 ): Promise<void> {
+	if (options?.signal?.aborted) { turn.fail(ABORT_MESSAGE, "aborted"); return; }
 	const input = toClaudeInput(context.messages);
-	const bridge = await createToolBridge(input.tools);
-	const files = await createTurnFiles(input.systemPrompt, bridge.mcpConfig);
+	let cliProcess: ClaudeProcess | undefined;
+	const bridge = await createToolBridge(input.tools, {
+		onCall: () => cliProcess?.flushAdmissions(),
+		onError: (error) => cliProcess?.fail(error.message),
+	});
+	let files: TurnFiles;
+	try {
+		files = await createTurnFiles(input.systemPrompt, bridge.mcpConfig);
+	} catch (error) {
+		await bridge.close();
+		throw error;
+	}
+	if (options?.signal?.aborted) {
+		turn.fail(ABORT_MESSAGE, "aborted");
+		await removeTurnResources(bridge, files);
+		return;
+	}
 
 	let child: ChildProcessWithoutNullStreams | null;
 	try {
@@ -575,17 +639,20 @@ async function startProcess(
 		return;
 	}
 
-	new ClaudeProcess(child, bridge, files, input.tools, turn).start(toStreamJsonLine(input.userContent), options?.signal);
+	cliProcess = new ClaudeProcess(child, bridge, files, turn, owner, configuration, structuredClone(conversationForReuse(context.messages)));
+	cliProcess.start(toStreamJsonLine(input.userContent), options?.signal);
 }
 
 export function createClaudeCodeStreamFunction(runClaude: RunClaude): StreamFunction<Api, SimpleStreamOptions> {
+	const owner = Symbol("claude-code stream owner");
 	return (model, context, options) => {
 		const stream = createAssistantMessageEventStream();
 		const turn = new ClaudeTurn(stream, model);
 
-		if (continueLiveProcess(turn, context.messages, options?.signal)) return stream;
+		const configuration = configurationForReuse(model, context, toEffort(options?.reasoning));
+		if (continueLiveProcess(turn, owner, configuration, context.messages, options?.signal)) return stream;
 
-		startProcess(runClaude, turn, model, context, options).catch((error: unknown) => {
+		startProcess(runClaude, turn, model, context, options, owner, configuration).catch((error: unknown) => {
 			console.error("claude CLI turn failed:", error);
 			turn.fail(START_FAILED_MESSAGE, "error");
 		});
diff --git a/src/agent/claude-code/tool-bridge.ts b/src/agent/claude-code/tool-bridge.ts
index 92e2aad..db9f4da 100644
--- a/src/agent/claude-code/tool-bridge.ts
+++ b/src/agent/claude-code/tool-bridge.ts
@@ -7,7 +7,9 @@ import { Server } from "@modelcontextprotocol/sdk/server/index.js";
 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
 import {
 	CallToolRequestSchema,
+	ErrorCode,
 	ListToolsRequestSchema,
+	McpError,
 	type CallToolResult,
 	type Tool as McpTool,
 } from "@modelcontextprotocol/sdk/types.js";
@@ -18,7 +20,11 @@ const MCP_TOOL_PREFIX = `mcp__${BRIDGE_SERVER_NAME}__`;
 const LOOPBACK_HOST = "127.0.0.1";
 const TOKEN_BYTES = 32;
 
-export type PendingToolCall = { name: string; arguments: JsonObject };
+export type PendingToolCall = { id: string; name: string; arguments: JsonObject };
+
+type BridgeCallbacks = { onCall(): void; onError(error: Error): void };
+
+export const MCP_IDENTITY_ERROR = "claude CLI compatibility error: MCP calls must include a unique claudecode/toolUseId";
 
 export type ToolBridge = {
 	mcpConfig: string;
@@ -104,14 +110,28 @@ class ToolCallQueue {
 
 // Low-level Server on purpose: McpServer.registerTool only takes zod schemas, and pi tools carry
 // JSON Schema that must reach the CLI unchanged.
-function createMcpServer(tools: Tool[], queue: ToolCallQueue): Server {
+function createMcpServer(tools: Tool[], queue: ToolCallQueue, callbacks?: BridgeCallbacks): Server {
 	const server = new Server({ name: BRIDGE_SERVER_NAME, version: "1.0.0" }, { capabilities: { tools: {} } });
 
 	server.setRequestHandler(ListToolsRequestSchema, () => ({ tools: tools.map(toMcpTool) }));
 
+	const seenIds = new Set<string>();
 	server.setRequestHandler(CallToolRequestSchema, (request) => {
-		const call = { name: request.params.name, arguments: (request.params.arguments ?? {}) as JsonObject };
-		return queue.add(call);
+		const id = request.params._meta?.["claudecode/toolUseId"];
+		if (typeof id !== "string" || !id.trim() || seenIds.has(id)) {
+			const error = new McpError(ErrorCode.InvalidParams, MCP_IDENTITY_ERROR);
+			callbacks?.onError(error);
+			throw error;
+		}
+		if (!tools.some((tool) => tool.name === request.params.name)) {
+			const error = new McpError(ErrorCode.InvalidParams, "claude CLI requested an undeclared harness tool");
+			callbacks?.onError(error);
+			throw error;
+		}
+		seenIds.add(id);
+		const result = queue.add({ id, name: request.params.name, arguments: (request.params.arguments ?? {}) as JsonObject });
+		callbacks?.onCall();
+		return result;
 	});
 
 	return server;
@@ -167,16 +187,22 @@ function toMcpConfig(port: number, authorization: string): string {
 	return JSON.stringify({ mcpServers: { [BRIDGE_SERVER_NAME]: server } });
 }
 
-export async function createToolBridge(tools: Tool[]): Promise<ToolBridge> {
+export async function createToolBridge(tools: Tool[], callbacks?: BridgeCallbacks): Promise<ToolBridge> {
 	const authorization = `Bearer ${randomBytes(TOKEN_BYTES).toString("hex")}`;
 
 	const queue = new ToolCallQueue();
-	const mcpServer = createMcpServer(tools, queue);
+	const mcpServer = createMcpServer(tools, queue, callbacks);
 	const transport = new StreamableHTTPServerTransport({ sessionIdGenerator: () => randomUUID() });
 	await mcpServer.connect(transport);
 
 	const httpServer = createHttpServer(transport, authorization);
-	const { port } = await listen(httpServer);
+	let port: number;
+	try {
+		({ port } = await listen(httpServer));
+	} catch (error) {
+		await mcpServer.close();
+		throw error;
+	}
 
 	return {
 		mcpConfig: toMcpConfig(port, authorization),
diff --git a/src/agent/teacher-agent.ts b/src/agent/teacher-agent.ts
index 6fe6ac1..cfdab68 100644
--- a/src/agent/teacher-agent.ts
+++ b/src/agent/teacher-agent.ts
@@ -17,6 +17,7 @@ import {
 import { practiceTools, type PracticeToolContext } from "./tools/practice.ts";
 import { healToolRecord, withArgumentHeal } from "./tools/heal.ts";
 import { sendToUserTool } from "./tools/send-to-user.ts";
+import { CLAUDE_CODE_PROVIDER } from "./claude-code/constants.ts";
 import { quizInputObject, quizInputProblems } from "../core/question-core.ts";
 import { QUESTION_TOOLS, type EnabledTools } from "../core/pending.ts";
 import { toLlmMessages, nativeInputCause, PRACTICE_PROBLEM_TOOL } from "../core/native-messages.ts";
@@ -202,7 +203,7 @@ function baseAgentOptions(kind: AgentKind, opts: AgentBuildOptions, tools: Agent
 			// transport. Explicit test registries remain caller-owned.
 			tools: [
 				...tools,
-				...(opts.tools === undefined && engine.model.id.toLowerCase().includes("claude")
+				...(opts.tools === undefined && (engine.model.provider === CLAUDE_CODE_PROVIDER || engine.model.id.toLowerCase().includes("claude"))
 					? [withArgumentHeal(sendToUserTool)]
 					: []),
 			],
diff --git a/tests/claude-code-binary.test.ts b/tests/claude-code-binary.test.ts
index 66a716a..599f5d9 100644
--- a/tests/claude-code-binary.test.ts
+++ b/tests/claude-code-binary.test.ts
@@ -39,15 +39,15 @@ test("npm global bin follows npm_config_prefix when set", () => {
 	assert.equal(binary, "/opt/npm/bin/claude");
 });
 
-test("windows looks for claude.cmd and claude.exe", () => {
+test("windows finds native claude.exe and does not advertise unsupported .cmd-only installs", () => {
 	const winHome = "C:\\Users\\u";
 	const env = { PATH: "C:\\tools;C:\\bin", APPDATA: `${winHome}\\AppData\\Roaming` };
-	assert.equal(resolveWith(["C:\\bin\\claude.cmd"], env, "win32", winHome), "C:\\bin\\claude.cmd");
+	assert.equal(resolveWith(["C:\\bin\\claude.cmd"], env, "win32", winHome), null);
 	assert.equal(resolveWith(["C:\\bin\\claude.exe"], env, "win32", winHome), "C:\\bin\\claude.exe");
 	assert.equal(resolveWith([`${winHome}\\.local\\bin\\claude.exe`], env, "win32", winHome), `${winHome}\\.local\\bin\\claude.exe`);
 	assert.equal(
 		resolveWith([`${winHome}\\AppData\\Roaming\\npm\\claude.cmd`], env, "win32", winHome),
-		`${winHome}\\AppData\\Roaming\\npm\\claude.cmd`,
+		null,
 	);
 	assert.equal(resolveWith(["C:\\bin\\claude"], env, "win32", winHome), null);
 });
diff --git a/tests/claude-code-harness.test.ts b/tests/claude-code-harness.test.ts
index 1dcd8c2..d300b35 100644
--- a/tests/claude-code-harness.test.ts
+++ b/tests/claude-code-harness.test.ts
@@ -55,7 +55,7 @@ function toAskScenario(): string[] {
 		streamEvent({ type: "content_block_stop", index: 0 }),
 		streamEvent({ type: "message_delta", delta: { stop_reason: "tool_use" }, usage: {} }),
 		streamEvent({ type: "message_stop" }),
-		JSON.stringify({ fake: "call", name: "ask_user_question", arguments: ASK_INPUT }),
+		JSON.stringify({ fake: "call", id: ASK_ID, name: "ask_user_question", arguments: ASK_INPUT }),
 		JSON.stringify({ fake: "reply" }),
 	];
 }
@@ -168,6 +168,34 @@ test("a question answered before the idle timeout continues the waiting CLI proc
 	await waitForExit(waiting);
 });
 
+test("a question pauses later calls from the same CLI response until the learner answers", async (t) => {
+	const secondId = "toolu_second_question";
+	const secondQuestion = "What do you want to learn next?";
+	const scenario = toAskScenario();
+	scenario.splice(4, 0,
+		streamEvent({ type: "content_block_start", index: 1, content_block: { type: "tool_use", id: secondId, name: "mcp__learnharness__ask_user_question", input: {} } }),
+		streamEvent({ type: "content_block_delta", index: 1, delta: { type: "input_json_delta", partial_json: JSON.stringify({ question: secondQuestion }) } }),
+		streamEvent({ type: "content_block_stop", index: 1 }),
+	);
+	scenario.splice(scenario.length - 1, 0, JSON.stringify({ fake: "call", id: secondId, name: "ask_user_question", arguments: { question: secondQuestion } }));
+	const fakeRun = createFakeRun(t, [scenario]);
+	const factory = createAgentFactory(fakeRun);
+	const chatId = createClaudeCodeChat(t);
+	await runChatTurn(chatId, { type: "text", text: "teach me sockets" }, factory);
+	assert.equal(danglingQuestionOf(chatStore.getChat(chatId)?.messages ?? [])?.toolCallId, ASK_ID);
+	assert.equal(JSON.stringify(chatStore.getChat(chatId)?.messages).includes(secondId), false, "unadmitted second question must not be posed or persisted");
+	await runChatTurn(chatId, toAnswerInput(), factory);
+	assert.equal(danglingQuestionOf(chatStore.getChat(chatId)?.messages ?? [])?.toolCallId, secondId);
+	await runChatTurn(chatId, {
+		type: "answer", toolCallId: secondId,
+		answer: { kind: "ask", questionText: secondQuestion, dontKnow: false, answers: [], text: "HTTP next", answeredAt: new Date().toISOString() },
+	}, factory);
+	assert.equal(fakeRun.children.length, 1);
+	assert.ok(getLastAssistantText(chatId).includes(ANSWER_TEXT));
+	assert.ok(getLastAssistantText(chatId).includes("HTTP next"));
+	await waitForExit(fakeRun.children[0]!);
+});
+
 test("a question answered after the idle timeout starts a fresh CLI process that replays the question and answer", async (t) => {
 	liveProcessIdleTimeoutMs.current = 300;
 	t.after(() => (liveProcessIdleTimeoutMs.current = LIVE_PROCESS_IDLE_TIMEOUT_MS));
diff --git a/tests/claude-code-stream.test.ts b/tests/claude-code-stream.test.ts
index d5e48b3..efdd322 100644
--- a/tests/claude-code-stream.test.ts
+++ b/tests/claude-code-stream.test.ts
@@ -29,6 +29,8 @@ import type {
 	ToolResultMessage,
 } from "@earendil-works/pi-ai";
 import { normalizeContext } from "@earendil-works/pi-ai/utils/transcript";
+import { Agent } from "@earendil-works/pi-agent-core";
+import { Type } from "typebox";
 
 import { parseCliLine } from "../src/agent/claude-code/cli-events.ts";
 import { ClaudeCodeError } from "../src/agent/claude-code/constants.ts";
@@ -83,7 +85,8 @@ function exitWith(code: number, stderr: string): string {
 function getToolScenario(): string[] {
 	const lines = readFixtureLines("tool.jsonl");
 	const firstMessageStop = lines.findIndex((line) => line.includes('"type":"message_stop"'));
-	return [...lines.slice(0, firstMessageStop + 1).filter((line) => !line.startsWith('{"type":"user"')), HOLD];
+	return [...lines.slice(0, firstMessageStop + 1).filter((line) => !line.startsWith('{"type":"user"')),
+		callTool({ id: "toolu_01JBB4cJsPa585FWb1XrfbNX", name: "get_weather", arguments: { city: "Paris" } }), HOLD];
 }
 
 function createFakeRun(
@@ -104,9 +107,9 @@ function createFakeRun(
 		const child = spawn(process.execPath, [FAKE_CLAUDE, ...args], {
 			cwd: options.cwd,
 			env: { ...options.env, FAKE_CLAUDE_SCENARIO: scenarioFile, ...extraEnv },
-			stdio: "pipe",
-		});
-		t.after(() => child.kill());
+			stdio: ["pipe", "pipe", "pipe", "ipc"],
+		}) as ChildProcessWithoutNullStreams;
+		t.after(() => child.kill("SIGKILL"));
 		calls.push({
 			args,
 			cwd: options.cwd,
@@ -151,7 +154,7 @@ async function runScenario(
 	const context = normalizeContext({
 		systemPrompt: "You are a tutor.",
 		messages: [{ role: "user", content: "hi", timestamp: 0 }],
-		tools: [READ_TOOL],
+		tools: [READ_TOOL, { name: "get_weather", description: "Weather", parameters: { type: "object", properties: {} } }],
 	});
 	const events = await collectEvents(createClaudeCodeStreamFunction(runClaude)(model, context, options));
 
@@ -180,7 +183,7 @@ function toToolUseMessage(toolUses: ToolUse[]): string[] {
 }
 
 function callTool(toolUse: ToolUse): string {
-	return JSON.stringify({ fake: "call", name: toolUse.name, arguments: toolUse.arguments });
+	return JSON.stringify({ fake: "call", id: toolUse.id, name: toolUse.name, arguments: toolUse.arguments });
 }
 
 function toToolResult(toolUse: ToolUse, text: string): ToolResultMessage {
@@ -368,7 +371,7 @@ test("tool scenario ends with toolcall_end (Claude's tool_use id, unprefixed nam
 
 	assert.deepEqual(
 		events.map((event) => event.type),
-		["start", "toolcall_start", "toolcall_delta", "toolcall_delta", "toolcall_delta", "toolcall_end", "done"],
+		["start", "toolcall_start", "toolcall_end", "done"],
 	);
 
 	const toolCallEnd = events.find((event) => event.type === "toolcall_end");
@@ -386,7 +389,7 @@ test("tool scenario ends with toolcall_end (Claude's tool_use id, unprefixed nam
 	assert.deepEqual(done.message.content, [toolCallEnd.toolCall]);
 });
 
-test("unknown tool name and bad JSON args still surface as tool calls", async (t) => {
+test("unsupported native tool intent fails without exposing executable calls", async (t) => {
 	const { events } = await runScenario(t, [
 		streamEvent({ type: "message_start", message: { usage: {} } }),
 		streamEvent({
@@ -404,21 +407,8 @@ test("unknown tool name and bad JSON args still surface as tool calls", async (t
 		HOLD,
 	]);
 
-	const toolCalls = events.flatMap((event) => (event.type === "toolcall_end" ? [event.toolCall] : []));
-	assert.deepEqual(
-		toolCalls.map((call) => ({ id: call.id, name: call.name, arguments: call.arguments })),
-		[
-			{ id: "toolu_a", name: "nope", arguments: {} },
-			{ id: "toolu_b", name: "Bash", arguments: { command: "ls" } },
-		],
-	);
-
-	assert.match(toolCalls[0]?.argumentsError ?? "", /\{"path": /);
-	assert.equal(toolCalls[1]?.argumentsError, undefined);
-
-	const done = getLastEvent(events);
-	assert.ok(done.type === "done");
-	assert.equal(done.reason, "toolUse");
+	assert.equal(events.some((event) => event.type === "toolcall_end"), false);
+	assert.match(getErrorMessage(events) ?? "", /unsupported native tool/);
 });
 
 test("usage maps input/output/cacheRead/cacheWrite with zero cost, message_delta overriding message_start", async (t) => {
@@ -585,7 +575,7 @@ test("spawns with the model alias, effort, bridge tools, MCP_TOOL_TIMEOUT and th
 	const call = getOnlyCall(calls);
 	assert.equal(getFlagValue(call.args, "--model"), "opus");
 	assert.equal(getFlagValue(call.args, "--effort"), "xhigh");
-	assert.equal(getFlagValue(call.args, "--allowedTools"), "mcp__learnharness__read");
+	assert.equal(getFlagValue(call.args, "--allowedTools"), "mcp__learnharness__read,mcp__learnharness__get_weather");
 	assert.equal(call.env.MCP_TOOL_TIMEOUT, "1800000");
 	assert.equal(call.env.HOME, process.env.HOME);
 	assert.equal(call.env.CLAUDE_CONFIG_DIR, process.env.CLAUDE_CONFIG_DIR);
@@ -641,27 +631,35 @@ test("trailing toolResults matching a live process continue it: held calls answe
 	await assertCleanedUp(getOnlyCall(calls));
 });
 
-test("multiple tool calls in one message are all answered by id", async (t) => {
+test("sequential identical calls split one response and correlate results by id, not arguments", async (t) => {
 	const readA: ToolUse = { id: "toolu_many_a", name: "read", arguments: { path: "a" } };
-	const readB: ToolUse = { id: "toolu_many_b", name: "read", arguments: { path: "b" } };
-	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([readA, readB]), callTool(readB), callTool(readA), REPLY]);
+	const readB: ToolUse = { id: "toolu_many_b", name: "read", arguments: { path: "a" } };
+	const source = toToolUseMessage([readA, readB]);
+	source[0] = streamEvent({ type: "message_start", message: { usage: { input_tokens: 7, output_tokens: 2 } } });
+	const { runClaude, calls } = createFakeRun(t, [...source, callTool(readB), callTool(readA), REPLY]);
 	const streamFunction = createClaudeCodeStreamFunction(runClaude);
 	const toolMessage = await runTurn(streamFunction, [HI]);
 
-	const reply = await runTurn(streamFunction, [HI, toolMessage, toToolResult(readA, "A"), toToolResult(readB, "B")]);
+	assert.deepEqual(toolMessage.content.filter((block) => block.type === "toolCall").map((call) => call.id), [readB.id]);
+	const history = [HI, toolMessage, toToolResult(readB, "B")];
+	const second = await runTurn(streamFunction, history);
+	assert.deepEqual(second.content.filter((block) => block.type === "toolCall").map((call) => call.id), [readA.id]);
+	const reply = await runTurn(streamFunction, [...history, second, toToolResult(readA, "A")]);
 
 	assert.equal(getText(reply), "B | A");
+	assert.equal(toolMessage.usage.totalTokens, 9);
+	assert.equal(second.usage.totalTokens, 0, "splitting one response must not charge its tokens twice");
 	assert.equal(calls.length, 1);
 });
 
-test("partial id match starts fresh and kills the old process", async (t) => {
+test("mismatched result id starts fresh and kills the old process", async (t) => {
 	const readA: ToolUse = { id: "toolu_partial_a", name: "read", arguments: { path: "a" } };
 	const readB: ToolUse = { id: "toolu_partial_b", name: "read", arguments: { path: "b" } };
 	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([readA, readB]), callTool(readA), callTool(readB), REPLY]);
 	const streamFunction = createClaudeCodeStreamFunction(runClaude);
 	const toolMessage = await runTurn(streamFunction, [HI]);
 
-	await runTurn(streamFunction, [HI, toolMessage, toToolResult(readA, "A")]);
+	await runTurn(streamFunction, [HI, toolMessage, toToolResult(readB, "B")]);
 
 	assert.equal(calls.length, 2);
 	const [oldCall] = calls;
@@ -695,24 +693,23 @@ test("user message after tool results starts fresh with unfinished calls in the
 test("output while waiting for tool results kills the process", async (t) => {
 	const readA: ToolUse = { id: "toolu_moved_on_a", name: "read", arguments: { path: "a" } };
 	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([readA]), REPLY, HOLD]);
-
-	await runTurn(createClaudeCodeStreamFunction(runClaude), [HI]);
-
+	const events = await collectEvents(createClaudeCodeStreamFunction(runClaude)(getModel(), normalizeContext({ messages: [HI], tools: [READ_TOOL] })));
+	assert.match(getErrorMessage(events) ?? "", /moved on without admitting/);
+	assert.equal(events.some((event) => event.type === "toolcall_end"), false);
 	await assertCleanedUp(getOnlyCall(calls));
 });
 
-test("an undeclared tool call is not kept waiting, since the CLI answers it itself", async (t) => {
+test("unadmitted tool intent never becomes an executable call", async (t) => {
 	const readA: ToolUse = { id: "toolu_undeclared_a", name: "read", arguments: { path: "a" } };
 	const nope: ToolUse = { id: "toolu_undeclared_nope", name: "nope", arguments: {} };
-	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([readA, nope]), HOLD]);
-
-	const toolMessage = await runTurn(createClaudeCodeStreamFunction(runClaude), [HI]);
-
-	assert.equal(toolMessage.stopReason, "toolUse");
+	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([readA, nope]), exitWith(1, "tool denied")]);
+	const events = await collectEvents(createClaudeCodeStreamFunction(runClaude)(getModel(), normalizeContext({ messages: [HI], tools: [READ_TOOL] })));
+	assert.equal(events.some((event) => event.type === "toolcall_end"), false);
+	assert.match(getErrorMessage(events) ?? "", /exited with code 1/);
 	await assertCleanedUp(getOnlyCall(calls));
 });
 
-test("a tool call with invalid JSON arguments is not kept waiting, since the CLI answers it itself", async (t) => {
+test("a CLI-rejected malformed call is not exposed for execution", async (t) => {
 	const { runClaude, calls } = createFakeRun(t, [
 		streamEvent({ type: "message_start", message: { usage: {} } }),
 		streamEvent({
@@ -724,12 +721,13 @@ test("a tool call with invalid JSON arguments is not kept waiting, since the CLI
 		streamEvent({ type: "content_block_stop", index: 0 }),
 		streamEvent({ type: "message_delta", delta: { stop_reason: "tool_use" }, usage: {} }),
 		streamEvent({ type: "message_stop" }),
+		JSON.stringify({ type: "user", message: { content: [{ type: "tool_result", tool_use_id: "toolu_bad_json", is_error: true, content: "invalid arguments" }] } }),
 		HOLD,
 	]);
 
-	const toolMessage = await runTurn(createClaudeCodeStreamFunction(runClaude), [HI]);
-
-	assert.equal(toolMessage.stopReason, "toolUse");
+	const events = await collectEvents(createClaudeCodeStreamFunction(runClaude)(getModel(), normalizeContext({ messages: [HI], tools: [READ_TOOL] })));
+	assert.equal(events.some((event) => event.type === "toolcall_end"), false);
+	assert.match(getErrorMessage(events) ?? "", /refused.*before MCP admission/);
 	await assertCleanedUp(getOnlyCall(calls));
 });
 
@@ -805,9 +803,140 @@ test("a tool result arriving late but before the idle timeout still continues th
 	await assertCleanedUp(getOnlyCall(calls));
 });
 
-test("two concurrent streams keep separate processes and results never cross", async (t) => {
+test("CLI denial cannot execute a tool in the native Pi loop", async (t) => {
+	const read: ToolUse = { id: "toolu_denied", name: "read", arguments: { path: "a" } };
+	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([read]), JSON.stringify({ type: "user", message: { content: [
+		{ type: "tool_result", tool_use_id: read.id, is_error: true, content: "Denied by managed policy" },
+	] } }), HOLD]);
+	let executed = 0;
+	const agent = new Agent({ initialState: { model: getModel(), tools: [{
+		name: "read", label: "Read", description: "Read", parameters: Type.Object({ path: Type.String() }),
+		execute: async () => { executed++; return { content: [{ type: "text", text: "must not run" }], details: null }; },
+	}] }, streamFn: createClaudeCodeStreamFunction(runClaude) });
+	await agent.prompt("hi");
+	assert.equal(executed, 0);
+	const last = agent.state.messages.at(-1);
+	assert.ok(last?.role === "assistant");
+	assert.equal(last.stopReason, "error");
+	assert.match(last.errorMessage ?? "", /refused.*before MCP admission/);
+	await assertCleanedUp(getOnlyCall(calls));
+});
+
+test("pre-aborted requests do not spawn a process", async () => {
+	const controller = new AbortController();
+	controller.abort();
+	let spawned = false;
+	const stream = createClaudeCodeStreamFunction(() => { spawned = true; return null; });
+	const events = await collectEvents(stream(getModel(), normalizeContext({ messages: [HI] }), { signal: controller.signal }));
+	assert.equal(spawned, false);
+	assert.match(getErrorMessage(events) ?? "", /aborted/);
+});
+
+test("missing MCP identity fails closed without emitting executable calls", async (t) => {
+	const read: ToolUse = { id: "toolu_no_meta", name: "read", arguments: { path: "a" } };
+	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([read]), JSON.stringify({ fake: "call", name: read.name, arguments: read.arguments })]);
+	const events = await collectEvents(createClaudeCodeStreamFunction(runClaude)(getModel(), normalizeContext({ messages: [HI], tools: [READ_TOOL] })));
+	assert.equal(events.some((event) => event.type === "toolcall_end"), false);
+	assert.match(getErrorMessage(events) ?? "", /compatibility error.*claudecode\/toolUseId/);
+	await assertCleanedUp(getOnlyCall(calls));
+});
+
+test("a parallel identity failure after an admitted slice is reported on continuation, not hidden by replay", async (t) => {
+	const first: ToolUse = { id: "toolu_good_parallel", name: "read", arguments: { path: "a" } };
+	const second: ToolUse = { id: "toolu_bad_parallel", name: "read", arguments: { path: "b" } };
+	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([first, second]),
+		JSON.stringify({ fake: "start-call", id: first.id, name: first.name, arguments: first.arguments }),
+		JSON.stringify({ fake: "wait-for-message" }),
+		JSON.stringify({ fake: "call", name: second.name, arguments: second.arguments }), HOLD]);
+	const stream = createClaudeCodeStreamFunction(runClaude);
+	const message = await runTurn(stream, [HI]);
+	getOnlyCall(calls).child.send("continue");
+	await waitForExit(getOnlyCall(calls).child);
+	const events = await collectEvents(stream(getModel(), normalizeContext({ systemPrompt: "You are a tutor.", messages: [HI, message, toToolResult(first, "A")], tools: [READ_TOOL] })));
+	assert.match(getErrorMessage(events) ?? "", /compatibility error.*claudecode\/toolUseId/);
+	assert.equal(calls.length, 1, "must not hide the compatibility failure by spawning again");
+	await assertCleanedUp(getOnlyCall(calls));
+});
+
+test("output after MCP admission fails continuation instead of silently replaying", async (t) => {
+	const call: ToolUse = { id: "toolu_moved_on", name: "read", arguments: { path: "a" } };
+	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([call]),
+		JSON.stringify({ fake: "start-call", id: call.id, name: call.name, arguments: call.arguments }),
+		JSON.stringify({ fake: "wait-for-message" }), ...toToolUseMessage([call]), HOLD]);
+	const stream = createClaudeCodeStreamFunction(runClaude);
+	const message = await runTurn(stream, [HI]);
+	getOnlyCall(calls).child.send("continue");
+	await waitForExit(getOnlyCall(calls).child);
+	const events = await collectEvents(stream(getModel(), normalizeContext({ systemPrompt: "You are a tutor.", messages: [HI, message, toToolResult(call, "A")], tools: [READ_TOOL] })));
+	assert.match(getErrorMessage(events) ?? "", /moved on while.*waiting for results/);
+	assert.equal(calls.length, 1);
+	await assertCleanedUp(getOnlyCall(calls));
+});
+
+test("normal completion escalates termination when the child ignores SIGTERM", async (t) => {
+	const { events, calls } = await runScenario(t, [JSON.stringify({ fake: "ignore-term" }), ...readFixtureLines("text.jsonl"), HOLD]);
+	assert.equal(getLastEvent(events).type, "done");
+	await assertCleanedUp(getOnlyCall(calls));
+	assert.equal(getOnlyCall(calls).child.signalCode, "SIGKILL");
+});
+
+test("a synchronous spawn failure removes both temp directories and the bridge", async () => {
+	let resources: { cwd: string; privateDir: string; url: string } | undefined;
+	const stream = createClaudeCodeStreamFunction((args, options) => {
+		const config = JSON.parse(readFileSync(getFlagValue(args, "--mcp-config"), "utf8"));
+		resources = { cwd: options.cwd, privateDir: dirname(getFlagValue(args, "--mcp-config")), url: config.mcpServers.learnharness.url };
+		throw new Error("synthetic spawn failure");
+	});
+	const events = await collectEvents(stream(getModel(), normalizeContext({ messages: [HI] })));
+	assert.match(getErrorMessage(events) ?? "", /failed to start/);
+	assert.ok(resources);
+	assert.equal(existsSync(resources.cwd), false);
+	assert.equal(existsSync(resources.privateDir), false);
+	await assert.rejects(fetch(resources.url));
+});
+
+test("a malformed JSON event shape fails the turn rather than escaping the readline handler", async (t) => {
+	const { events, calls } = await runScenario(t, [JSON.stringify({ type: "assistant", error: "bad", message: { content: [null] } }), HOLD]);
+	assert.match(getErrorMessage(events) ?? "", /malformed stream output/);
+	await assertCleanedUp(getOnlyCall(calls));
+});
+
+test("a mismatched MCP identity cannot admit a streamed call", async (t) => {
+	const read: ToolUse = { id: "toolu_intent", name: "read", arguments: { path: "a" } };
+	const { runClaude, calls } = createFakeRun(t, [...toToolUseMessage([read]), callTool({ ...read, id: "toolu_someone_else" })]);
+	const events = await collectEvents(createClaudeCodeStreamFunction(runClaude)(getModel(), normalizeContext({ messages: [HI], tools: [READ_TOOL] })));
+	assert.equal(events.some((event) => event.type === "toolcall_end"), false);
+	assert.match(getErrorMessage(events) ?? "", /does not match its streamed tool intent/);
+	await assertCleanedUp(getOnlyCall(calls));
+});
+
+for (const change of ["model", "effort", "system prompt", "tool schema", "tool description", "history"] as const) {
+	test(`a changed ${change} prevents reuse of a held process`, async (t) => {
+		const read: ToolUse = { id: `toolu_reuse_${change}`, name: "read", arguments: { path: "a" } };
+		const waiting = createFakeRun(t, [...toToolUseMessage([read]), callTool(read), REPLY]);
+		const fresh = createFakeRun(t, readFixtureLines("text.jsonl"));
+		const stream = createClaudeCodeStreamFunction((args, options) => (waiting.calls.length === 0 ? waiting : fresh).runClaude(args, options));
+		const message = await runTurn(stream, [HI]);
+		const messages = [change === "history" ? { ...HI, content: "replacement history after compaction" } : HI, message, toToolResult(read, "A")];
+		const context = normalizeContext({
+			systemPrompt: change === "system prompt" ? "Changed tutor instructions" : "You are a tutor.",
+			messages,
+			tools: [{ ...READ_TOOL,
+				...(change === "tool schema" ? { parameters: { type: "object", properties: { path: { type: "string" } } } } : {}),
+				...(change === "tool description" ? { description: "Changed description" } : {}),
+			}],
+		});
+		const model = change === "model" ? CLAUDE_CODE_MODELS[1]! : getModel();
+		const events = await collectEvents(stream(model, context, change === "effort" ? { reasoning: "high" } : undefined));
+		assert.equal(getLastEvent(events).type, "done");
+		assert.equal(fresh.calls.length, 1, "must start a fresh CLI rather than silently use stale configuration");
+		await assertCleanedUp(getOnlyCall(waiting.calls));
+	});
+}
+
+for (const sharedIdentity of [false, true]) test(`two concurrent stream owners keep separate processes${sharedIdentity ? " even with identical call IDs and arguments" : ""}`, async (t) => {
 	const readOne: ToolUse = { id: "toolu_concurrent_one", name: "read", arguments: { path: "one" } };
-	const readTwo: ToolUse = { id: "toolu_concurrent_two", name: "read", arguments: { path: "two" } };
+	const readTwo: ToolUse = sharedIdentity ? { ...readOne } : { id: "toolu_concurrent_two", name: "read", arguments: { path: "two" } };
 	const one = createFakeRun(t, [...toToolUseMessage([readOne]), callTool(readOne), REPLY]);
 	const two = createFakeRun(t, [...toToolUseMessage([readTwo]), callTool(readTwo), REPLY]);
 
diff --git a/tests/claude-code-tool-bridge.test.ts b/tests/claude-code-tool-bridge.test.ts
index 3d18881..9b44dfb 100644
--- a/tests/claude-code-tool-bridge.test.ts
+++ b/tests/claude-code-tool-bridge.test.ts
@@ -107,13 +107,13 @@ test("tools/call stays pending until resolved and returns its text and image con
 	t.after(() => client.close());
 
 	let settled = false;
-	const pending = client.callTool({ name: "read", arguments: { path: "notes.md" } }).finally(() => {
+	const pending = client.callTool({ name: "read", arguments: { path: "notes.md" }, _meta: { "claudecode/toolUseId": "call-1" } }).finally(() => {
 		settled = true;
 	});
 
 	const [call] = await bridge.waitForToolCalls(1);
 	assert.ok(call);
-	assert.deepEqual(call, { name: "read", arguments: { path: "notes.md" } });
+	assert.deepEqual(call, { id: "call-1", name: "read", arguments: { path: "notes.md" } });
 	assert.deepEqual(bridge.getPendingToolCalls(), [call]);
 
 	await new Promise((resolve) => setTimeout(resolve, 20));
@@ -147,15 +147,15 @@ test("waitForToolCalls resolves once that many calls are pending, in arrival ord
 		waited = true;
 	});
 
-	void client.callTool({ name: "read", arguments: { path: "a.md" } }).catch(() => {});
+	void client.callTool({ name: "read", arguments: { path: "a.md" }, _meta: { "claudecode/toolUseId": "call-1" } }).catch(() => {});
 	await new Promise((resolve) => setTimeout(resolve, 20));
 	assert.equal(waited, false);
 
-	void client.callTool({ name: "screenshot", arguments: {} }).catch(() => {});
+	void client.callTool({ name: "screenshot", arguments: {}, _meta: { "claudecode/toolUseId": "call-2" } }).catch(() => {});
 
 	assert.deepEqual(await waiting, [
-		{ name: "read", arguments: { path: "a.md" } },
-		{ name: "screenshot", arguments: {} },
+		{ id: "call-1", name: "read", arguments: { path: "a.md" } },
+		{ id: "call-2", name: "screenshot", arguments: {} },
 	]);
 });
 
@@ -165,7 +165,7 @@ test("isError result becomes MCP isError true", async (t) => {
 	const client = await connectClient(bridge);
 	t.after(() => client.close());
 
-	const pending = client.callTool({ name: "read", arguments: { path: "missing.md" } });
+	const pending = client.callTool({ name: "read", arguments: { path: "missing.md" }, _meta: { "claudecode/toolUseId": "call-1" } });
 	const [call] = await bridge.waitForToolCalls(1);
 	assert.ok(call);
 
@@ -180,7 +180,7 @@ test("close fails pending calls and frees the port", async () => {
 	const bridge = await createToolBridge([READ_TOOL]);
 	const port = Number(new URL(getServerConfig(bridge).url).port);
 	const client = await connectClient(bridge);
-	const pending = client.callTool({ name: "read", arguments: { path: "notes.md" } });
+	const pending = client.callTool({ name: "read", arguments: { path: "notes.md" }, _meta: { "claudecode/toolUseId": "call-1" } });
 	await bridge.waitForToolCalls(1);
 
 	await bridge.close();
@@ -219,6 +219,25 @@ test('mcpConfig is {"mcpServers":{"learnharness":{"type":"http","url":...,"heade
 	assert.match(server.headers.Authorization, /^Bearer [0-9a-f]{64}$/);
 });
 
+test("missing and reused Claude tool IDs are rejected rather than matched by arguments", async (t) => {
+	const failures: string[] = [];
+	const bridge = await createToolBridge([READ_TOOL], { onCall: () => {}, onError: (error) => failures.push(error.message) });
+	t.after(() => bridge.close());
+	const client = await connectClient(bridge);
+	t.after(() => client.close());
+	await assert.rejects(client.callTool({ name: "read", arguments: { path: "a" } }), /claudecode\/toolUseId/);
+	assert.deepEqual(bridge.getPendingToolCalls(), []);
+	const params = { name: "read", arguments: { path: "a" }, _meta: { "claudecode/toolUseId": "same-id" } };
+	const first = client.callTool(params);
+	const [call] = await bridge.waitForToolCalls(1);
+	assert.ok(call);
+	bridge.resolveToolCall(call, toolResult([{ type: "text", text: "first" }]));
+	await first;
+	await assert.rejects(client.callTool(params), /claudecode\/toolUseId/);
+	assert.deepEqual(bridge.getPendingToolCalls(), []);
+	assert.equal(failures.length, 2);
+});
+
 test("toolNameFromMcp strips the bridge prefix", () => {
 	assert.equal(toolNameFromMcp("mcp__learnharness__read"), "read");
 	assert.equal(toolNameFromMcp("read"), "read");
diff --git a/tests/fixtures/claude-code/fake-claude.mjs b/tests/fixtures/claude-code/fake-claude.mjs
index cb64d65..d1fef86 100644
--- a/tests/fixtures/claude-code/fake-claude.mjs
+++ b/tests/fixtures/claude-code/fake-claude.mjs
@@ -4,11 +4,15 @@
  * line. Lines with a "fake" key are directives instead of output:
  *   {"fake":"hold"}                          stay alive until killed, like the CLI waiting on a held MCP call
  *   {"fake":"exit","code":1,"stderr":"..."}  write stderr and exit with that code
- *   {"fake":"call","name":"read","arguments":{...}}  call that tool on the MCP bridge and wait for its result
+ *   {"fake":"call","id":"toolu_...","name":"read","arguments":{...}}  call the MCP bridge and wait for its result
+ *   {"fake":"start-call",...}                start the same request without waiting for its result
+ *   {"fake":"wait-for-message"}              pause until the test releases the child over IPC
+ *   {"fake":"ignore-term"}                   ignore SIGTERM to exercise kill escalation
  *   {"fake":"reply"}                         stream one assistant message whose text is every result so far, joined by " | "
  * FAKE_CLAUDE_STDIN, when set, receives the stdin it read.
  */
 import { readFileSync, writeFileSync } from "node:fs";
+import { once } from "node:events";
 
 import { Client } from "@modelcontextprotocol/sdk/client/index.js";
 import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";
@@ -49,10 +53,15 @@ if (process.env.FAKE_CLAUDE_STDIN) writeFileSync(process.env.FAKE_CLAUDE_STDIN,
 
 let bridge = null;
 const results = [];
+const pendingResults = [];
 const lines = readFileSync(process.env.FAKE_CLAUDE_SCENARIO, "utf8").split("\n").filter(Boolean);
 for (const line of lines) {
 	const directive = JSON.parse(line);
 
+	if (directive.fake === "wait-for-message") {
+		await once(process, "message");
+		continue;
+	}
 	if (directive.fake === "hold") {
 		setInterval(() => {}, HOLD_INTERVAL_MS);
 		break;
@@ -63,14 +72,28 @@ for (const line of lines) {
 		process.exit(directive.code);
 	}
 
-	if (directive.fake === "call") {
+	if (directive.fake === "ignore-term") {
+		process.on("SIGTERM", () => {});
+		continue;
+	}
+	if (directive.fake === "call" || directive.fake === "start-call") {
 		bridge ??= await connectBridge(mcpConfig);
-		const result = await bridge.callTool({ name: directive.name, arguments: directive.arguments });
-		results.push(result.content.map((block) => block.text).join(""));
+		const request = bridge.callTool({
+			name: directive.name,
+			arguments: directive.arguments,
+			...(directive.id !== undefined ? { _meta: { "claudecode/toolUseId": directive.id } } : {}),
+		});
+		if (directive.fake === "start-call") {
+			pendingResults.push(request);
+			void request.catch(() => {});
+		} else {
+			const result = await request;
+			results.push(result.content.map((block) => block.text).join(""));
+		}
 		continue;
-
 	}
 	if (directive.fake === "reply") {
+		for (const result of await Promise.all(pendingResults.splice(0))) results.push(result.content.map((block) => block.text).join(""));
 		await writeReply(results.join(" | "));
 		continue;
 	}
diff --git a/tests/send-to-user.test.ts b/tests/send-to-user.test.ts
index beaeae3..80109d4 100644
--- a/tests/send-to-user.test.ts
+++ b/tests/send-to-user.test.ts
@@ -88,6 +88,9 @@ describe("send_to_user model gate", () => {
 		["openrouter", "anthropic/claude-sonnet-5.5", true],
 		["amazon-bedrock", "us.anthropic.claude-opus-5-5-v1:0", true],
 		["fixture", "CLAUDE-fixture", true],
+		["claude-code", "opus", true],
+		["claude-code", "sonnet", true],
+		["claude-code", "haiku", true],
 		["openrouter", "z-ai/glm-5.3-flash", false],
 		["openai", "gpt-4o-mini", false],
 		["anthropic", "opaque-alias", false],