From ae0b110e444b26740a32083b273b07db4e05d13d Mon Sep 17 00:00:00 2001
From: Xinhua Gu <xinhua.gu@gmail.com>
Date: Mon, 16 Feb 2026 18:32:34 +0100
Subject: [PATCH] fix(security): set 0o600 on remaining session file write
 paths
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Follow-up to #18066 — three session file write sites were missed:

- auto-reply/reply/session.ts: forked session transcript header
- pi-embedded-runner/session-manager-init.ts: session file reset
- gateway/server-methods/sessions.ts: compacted transcript rewrite

All now use mode 0o600 consistent with transcript.ts and chat.ts.
---
 src/agents/pi-embedded-runner/session-manager-init.ts | 2 +-
 src/auto-reply/reply/session.ts                       | 5 ++++-
 src/gateway/server-methods/sessions.ts                | 5 ++++-
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/agents/pi-embedded-runner/session-manager-init.ts b/src/agents/pi-embedded-runner/session-manager-init.ts
index 95c699947..ef7957183 100644
--- a/src/agents/pi-embedded-runner/session-manager-init.ts
+++ b/src/agents/pi-embedded-runner/session-manager-init.ts
@@ -43,7 +43,7 @@ export async function prepareSessionManagerForRun(params: {
 
   if (params.hadSessionFile && header && !hasAssistant) {
     // Reset file so the first assistant flush includes header+user+assistant in order.
-    await fs.writeFile(params.sessionFile, "", "utf-8");
+    await fs.writeFile(params.sessionFile, "", { encoding: "utf-8", mode: 0o600 });
     sm.fileEntries = [header];
     sm.byId?.clear?.();
     sm.labelsById?.clear?.();
diff --git a/src/auto-reply/reply/session.ts b/src/auto-reply/reply/session.ts
index b73de9991..0a0594ddd 100644
--- a/src/auto-reply/reply/session.ts
+++ b/src/auto-reply/reply/session.ts
@@ -89,7 +89,10 @@ function forkSessionFromParent(params: {
       cwd: manager.getCwd(),
       parentSession: parentSessionFile,
     };
-    fs.writeFileSync(sessionFile, `${JSON.stringify(header)}\n`, "utf-8");
+    fs.writeFileSync(sessionFile, `${JSON.stringify(header)}\n`, {
+      encoding: "utf-8",
+      mode: 0o600,
+    });
     return { sessionId, sessionFile };
   } catch {
     return null;
diff --git a/src/gateway/server-methods/sessions.ts b/src/gateway/server-methods/sessions.ts
index eadbdef2b..91cdf7704 100644
--- a/src/gateway/server-methods/sessions.ts
+++ b/src/gateway/server-methods/sessions.ts
@@ -471,7 +471,10 @@ export const sessionsHandlers: GatewayRequestHandlers = {
 
     const archived = archiveFileOnDisk(filePath, "bak");
     const keptLines = lines.slice(-maxLines);
-    fs.writeFileSync(filePath, `${keptLines.join("\n")}\n`, "utf-8");
+    fs.writeFileSync(filePath, `${keptLines.join("\n")}\n`, {
+      encoding: "utf-8",
+      mode: 0o600,
+    });
 
     await updateSessionStore(storePath, (store) => {
       const entryKey = compactTarget.primaryKey;