refactor(codex): avoid sync context history reads (#75917)

extensions/codex/src/app-server/run-attempt.context-engine.test.ts

@@ -212,6 +212,7 @@ describe("runCodexAppServerAttempt context-engine lifecycle", () => {
     SessionManager.open(sessionFile).appendMessage(
       assistantMessage("existing context", Date.now()) as never,
     );
+    const openSpy = vi.spyOn(SessionManager, "open");
     const contextEngine = createContextEngine();
     const harness = createStartedThreadHarness();
     const params = createParams(sessionFile, workspaceDir);
@@ -265,6 +266,7 @@ describe("runCodexAppServerAttempt context-engine lifecycle", () => {
 
     await harness.completeTurn();
     await run;
+    expect(openSpy).not.toHaveBeenCalled();
   });
 
   it("calls afterTurn with the mirrored transcript and runs turn maintenance", async () => {

extensions/codex/src/app-server/run-attempt.ts

@@ -1,6 +1,5 @@
 import { createHash } from "node:crypto";
 import fs from "node:fs/promises";
-import { SessionManager } from "@mariozechner/pi-coding-agent";
 import {
   assembleHarnessContextEngine,
   bootstrapHarnessContextEngine,
@@ -401,9 +400,7 @@ export async function runCodexAppServerAttempt(
     },
   });
   const hadSessionFile = await fileExists(params.sessionFile);
-  const sessionManager = activeContextEngine ? SessionManager.open(params.sessionFile) : undefined;
-  let historyMessages =
-    (await readMirroredSessionHistoryMessages(params.sessionFile, sessionManager)) ?? [];
+  let historyMessages = (await readMirroredSessionHistoryMessages(params.sessionFile)) ?? [];
   const hookContext = {
     runId: params.runId,
     agentId: sessionAgentId,
@@ -421,7 +418,6 @@ export async function runCodexAppServerAttempt(
       sessionId: params.sessionId,
       sessionKey: sandboxSessionKey,
       sessionFile: params.sessionFile,
-      sessionManager,
       runtimeContext: buildHarnessContextEngineRuntimeContext({
         attempt: runtimeParams,
         workspaceDir: effectiveWorkspace,
@@ -1121,7 +1117,6 @@ export async function runCodexAppServerAttempt(
           promptCache: result.promptCache,
         }),
         runMaintenance: runHarnessContextEngineMaintenance,
-        sessionManager,
         warn: (message) => embeddedAgentLog.warn(message),
       });
     }
@@ -1557,9 +1552,8 @@ function readString(record: JsonObject, key: string): string | undefined {
 
 async function readMirroredSessionHistoryMessages(
   sessionFile: string,
-  sessionManager?: Pick<SessionManager, "buildSessionContext">,
 ): Promise<AgentMessage[] | undefined> {
-  const messages = await readCodexMirroredSessionHistoryMessages(sessionFile, sessionManager);
+  const messages = await readCodexMirroredSessionHistoryMessages(sessionFile);
   if (!messages) {
     embeddedAgentLog.warn("failed to read mirrored session history for codex harness hooks", {
       sessionFile,

extensions/codex/src/app-server/session-history.ts

@@ -1,5 +1,5 @@
 import fs from "node:fs/promises";
-import type { SessionEntry, SessionManager } from "@mariozechner/pi-coding-agent";
+import type { SessionEntry } from "@mariozechner/pi-coding-agent";
 import {
   buildSessionContext,
   migrateSessionEntries,
@@ -18,12 +18,8 @@ function isMissingFileError(error: unknown): boolean {
 
 export async function readCodexMirroredSessionHistoryMessages(
   sessionFile: string,
-  sessionManager?: Pick<SessionManager, "buildSessionContext">,
 ): Promise<AgentMessage[] | undefined> {
   try {
-    if (sessionManager) {
-      return sessionManager.buildSessionContext().messages;
-    }
     const raw = await fs.readFile(sessionFile, "utf-8");
     const entries = parseSessionEntries(raw);
     const firstEntry = entries[0] as { type?: unknown; id?: unknown } | undefined;

src/agents/harness/context-engine-lifecycle.ts

@@ -23,7 +23,7 @@ export async function bootstrapHarnessContextEngine(params: {
   sessionId: string;
   sessionKey?: string;
   sessionFile: string;
-  sessionManager: unknown;
+  sessionManager?: unknown;
   runtimeContext?: ContextEngineRuntimeContext;
   runMaintenance?: typeof runHarnessContextEngineMaintenance;
   warn: (message: string) => void;
@@ -101,7 +101,7 @@ export async function finalizeHarnessContextEngineTurn(params: {
   tokenBudget?: number;
   runtimeContext?: ContextEngineRuntimeContext;
   runMaintenance?: typeof runHarnessContextEngineMaintenance;
-  sessionManager: unknown;
+  sessionManager?: unknown;
   warn: (message: string) => void;
 }) {
   if (!params.contextEngine) {