fix(runtime): erase pi tool array type safely

src/main/worker/runtime/index.ts

@@ -1,10 +1,10 @@
-import type { Agent, AgentMessage, AgentTool } from "@mariozechner/pi-agent-core";
+import type { Agent, AgentMessage } from "@mariozechner/pi-agent-core";
 import { resolveModel, resolveExtraStreamHeaders } from "../../model-resolver";
 import type { RunStatus } from "@shared/types";
 import type { ChildMessage, RunJob } from "./helpers";
 import { applyEnvOverrides, buildRedactor } from "./helpers";
 import { createCodingTools } from "@mariozechner/pi-coding-agent";
-import { createPiAgent, resolveThinkingLevel } from "./pi-agent-factory";
+import { createPiAgent, resolveThinkingLevel, type ErasedAgentTool } from "./pi-agent-factory";
 import type { WorkerRpcClient } from "../entry/rpc";
 import { createHireAgentTool, HIRE_AGENT_TOOL_NAME } from "./internal-tools/hire-agent-tool";
 import { createFileApprovalTool, FILE_APPROVAL_TOOL_NAME } from "./internal-tools/file-approval-tool";
@@ -149,20 +149,14 @@ export class WorkerRunner {
 
         const cwd = job.workspacePath ?? process.cwd();
         const codingTools = createCodingTools(cwd);
-        // pi's `AgentTool<TSchema>` is generic over the concrete TypeBox
-        // schema; two tools with different schemas cannot share a single
-        // `AgentTool<TSchema>[]` without widening to the base shape. The
-        // internal-tool factories return properly-typed instances; we
-        // widen via unknown only at the array boundary so each execute
-        // signature stays type-checked at definition time.
-        const internalTools: AgentTool[] = [];
+        const internalTools: ErasedAgentTool[] = [];
         for (const toolName of job.internalTools ?? []) {
           switch (toolName) {
             case HIRE_AGENT_TOOL_NAME:
-              internalTools.push(createHireAgentTool(rpc, job.runId) as unknown as AgentTool);
+              internalTools.push(createHireAgentTool(rpc, job.runId));
               break;
             case FILE_APPROVAL_TOOL_NAME:
-              internalTools.push(createFileApprovalTool(rpc, job.runId) as unknown as AgentTool);
+              internalTools.push(createFileApprovalTool(rpc, job.runId));
               break;
             default: {
               // Exhaustiveness guard: a new entry in the `internalTools`
@@ -173,7 +167,7 @@ export class WorkerRunner {
             }
           }
         }
-        const tools = [...codingTools, ...internalTools] as never;
+        const tools: ErasedAgentTool[] = [...codingTools, ...internalTools];
 
         const agent = createPiAgent({
           runId: job.runId,

src/main/worker/runtime/pi-agent-factory.ts

@@ -16,6 +16,7 @@
 import {
   Agent,
   type AgentMessage,
+  type AgentState,
   type ThinkingLevel,
 } from "@mariozechner/pi-agent-core";
 import type { Api, Model } from "@mariozechner/pi-ai";
@@ -27,16 +28,14 @@ import { safeStreamSimple } from "./pi-safe-stream";
 // graph so any drift in pi-agent-core hook shapes breaks the build here.
 import "./pi-hook-contract";
 
+export type ErasedAgentTool = AgentState["tools"][number];
+
 export interface PiAgentFactoryInput {
   runId: string;
   taskSessionId: string;
   systemPrompt: string;
   model: Model<Api>;
-  // `never` preserves the pre-C4 contract where the caller owns tool
-  // typing (pi-coding-agent's union is too wide to mirror here and C4
-  // adds local internal tools with their own TSchema). The caller casts
-  // a concrete tools array at the `createPiAgent` site.
-  tools: never;
+  tools: ErasedAgentTool[];
   priorMessages: AgentMessage[];
   thinkingLevel: ThinkingLevel;
   apiKey: string;

tests/unit/pi-agent-factory.test.ts

@@ -1,3 +1,5 @@
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
 import type { Model } from "@mariozechner/pi-ai";
 import { describe, expect, it } from "vitest";
 import { createPiAgent } from "../../src/main/worker/runtime/pi-agent-factory";
@@ -25,7 +27,7 @@ describe("pi agent factory", () => {
       taskSessionId: "session_1",
       systemPrompt: "You are an engineer.",
       model: createModel(),
-      tools: [] as never,
+      tools: [],
       priorMessages: [],
       thinkingLevel: "off",
       apiKey: "test-key",
@@ -39,4 +41,14 @@ describe("pi agent factory", () => {
 
     expect(agent.toolExecution).toBe("sequential");
   });
+
+  it("keeps worker tool arrays on the erased pi tool contract", () => {
+    const runnerSource = readFileSync(join(process.cwd(), "src/main/worker/runtime/index.ts"), "utf8");
+    const factorySource = readFileSync(join(process.cwd(), "src/main/worker/runtime/pi-agent-factory.ts"), "utf8");
+
+    expect(runnerSource).not.toContain("as unknown as AgentTool");
+    expect(runnerSource).not.toContain("as never");
+    expect(factorySource).not.toContain("tools: never");
+    expect(factorySource).toContain('type ErasedAgentTool = AgentState["tools"][number]');
+  });
 });