diff --git a/packages/app/tests/hooks/session-backup-gist.test.ts b/packages/app/tests/hooks/session-backup-gist.test.ts
new file mode 100644
index 0000000..dce5aa2
--- /dev/null
+++ b/packages/app/tests/hooks/session-backup-gist.test.ts
@@ -0,0 +1,74 @@
+// CHANGE: add regression coverage for session backup tmp filtering
+// WHY: session snapshots must ignore transient tmp directories while preserving persistent files
+// REF: issue-198
+// PURITY: SHELL (tests filesystem traversal against committed backup script)
+
+import { describe, expect, it } from "@effect/vitest"
+import { Effect } from "effect"
+import fs from "node:fs"
+import path from "node:path"
+
+import sessionBackupGist from "../../../../scripts/session-backup-gist.js"
+
+const { collectSessionFiles, shouldIgnoreSessionPath } = sessionBackupGist
+const tmpDirPrefix = path.join(process.cwd(), ".tmp-session-backup-gist-")
+
+const withTempDir = Effect.acquireRelease(
+  Effect.sync(() => fs.mkdtempSync(tmpDirPrefix)),
+  (tmpDir) =>
+    Effect.sync(() => {
+      fs.rmSync(tmpDir, { recursive: true, force: true })
+    })
+)
+
+describe("session-backup-gist tmp filtering", () => {
+  it.effect("ignores tmp directories while keeping persistent session files", () =>
+    Effect.scoped(
+      Effect.gen(function*(_) {
+        const tmpDir = yield* _(withTempDir)
+        const codexDir = path.join(tmpDir, ".codex")
+        const claudeDir = path.join(tmpDir, ".claude")
+
+        yield* _(
+          Effect.sync(() => {
+            fs.mkdirSync(path.join(codexDir, "tmp", "run"), { recursive: true })
+            fs.mkdirSync(path.join(codexDir, "memory"), { recursive: true })
+            fs.mkdirSync(path.join(claudeDir, "tmp"), { recursive: true })
+            fs.mkdirSync(path.join(claudeDir, "profiles"), { recursive: true })
+
+            fs.writeFileSync(path.join(codexDir, "tmp", "run", ".lock"), "lock")
+            fs.writeFileSync(path.join(codexDir, "history.jsonl"), "{\"event\":1}\n")
+            fs.writeFileSync(path.join(codexDir, "memory", "notes.md"), "# notes\n")
+            fs.writeFileSync(path.join(claudeDir, "tmp", "session.lock"), "lock")
+            fs.writeFileSync(path.join(claudeDir, "profiles", "default.json"), "{}\n")
+          })
+        )
+
+        const files = [
+          ...collectSessionFiles(codexDir, ".codex", false),
+          ...collectSessionFiles(claudeDir, ".claude", false)
+        ]
+        const logicalNames = files
+          .map((file) => file.logicalName)
+          .toSorted((left, right) => left.localeCompare(right))
+
+        yield* _(
+          Effect.sync(() => {
+            expect(logicalNames).toContain(".codex/history.jsonl")
+            expect(logicalNames).toContain(".codex/memory/notes.md")
+            expect(logicalNames).toContain(".claude/profiles/default.json")
+            expect(logicalNames.some((name) => name.split("/").includes("tmp"))).toBe(false)
+          })
+        )
+      })
+    ))
+
+  it.effect("marks tmp paths for exclusion", () =>
+    Effect.sync(() => {
+      expect(shouldIgnoreSessionPath("tmp")).toBe(true)
+      expect(shouldIgnoreSessionPath("tmp/run/.lock")).toBe(true)
+      expect(shouldIgnoreSessionPath("memory/tmp/run/.lock")).toBe(true)
+      expect(shouldIgnoreSessionPath("history.jsonl")).toBe(false)
+      expect(shouldIgnoreSessionPath("memory/notes.md")).toBe(false)
+    }))
+})
diff --git a/scripts/session-backup-gist.d.ts b/scripts/session-backup-gist.d.ts
new file mode 100644
index 0000000..84322d8
--- /dev/null
+++ b/scripts/session-backup-gist.d.ts
@@ -0,0 +1,22 @@
+export type SessionBackupFile = {
+  readonly logicalName: string
+  readonly sourcePath: string
+  readonly size: number
+}
+
+export declare const collectSessionFiles: (
+  dirPath: string,
+  baseName: string,
+  verbose: boolean
+) => ReadonlyArray<SessionBackupFile>
+
+export declare const shouldIgnoreSessionPath: (
+  relativePath: string
+) => boolean
+
+declare const sessionBackupGist: {
+  readonly collectSessionFiles: typeof collectSessionFiles
+  readonly shouldIgnoreSessionPath: typeof shouldIgnoreSessionPath
+}
+
+export default sessionBackupGist
diff --git a/scripts/session-backup-gist.js b/scripts/session-backup-gist.js
index 89c13f1..cd9a34f 100644
--- a/scripts/session-backup-gist.js
+++ b/scripts/session-backup-gist.js
@@ -43,6 +43,14 @@ const {
 const SESSION_DIR_NAMES = [".codex", ".claude", ".qwen", ".gemini"];
 const SESSION_WALK_IGNORE_DIR_NAMES = new Set([".git", "node_modules", "tmp"]);
 
+const toLogicalRelativePath = (relativePath) =>
+  relativePath.split(path.sep).join(path.posix.sep);
+
+const shouldIgnoreSessionPath = (relativePath) => {
+  const logicalPath = toLogicalRelativePath(relativePath);
+  return logicalPath === "tmp" || logicalPath.startsWith("tmp/") || logicalPath.includes("/tmp/");
+};
+
 const isPathWithinParent = (targetPath, parentPath) => {
   const relative = path.relative(parentPath, targetPath);
   return relative === "" || (!relative.startsWith("..") && !path.isAbsolute(relative));
@@ -365,6 +373,12 @@ const collectSessionFiles = (dirPath, baseName, verbose) => {
     for (const entry of entries) {
       const fullPath = path.join(currentPath, entry.name);
       const relPath = relativePath ? `${relativePath}/${entry.name}` : entry.name;
+      const logicalRelPath = toLogicalRelativePath(relPath);
+
+      if (shouldIgnoreSessionPath(logicalRelPath)) {
+        log(verbose, `Skipping tmp path: ${path.posix.join(baseName, logicalRelPath)}`);
+        continue;
+      }
 
       if (entry.isDirectory()) {
         if (SESSION_WALK_IGNORE_DIR_NAMES.has(entry.name)) {
@@ -374,7 +388,7 @@ const collectSessionFiles = (dirPath, baseName, verbose) => {
       } else if (entry.isFile()) {
         try {
           const stats = fs.statSync(fullPath);
-          const logicalName = path.posix.join(baseName, relPath.split(path.sep).join(path.posix.sep));
+          const logicalName = path.posix.join(baseName, logicalRelPath);
           files.push({
             logicalName,
             sourcePath: fullPath,
@@ -662,4 +676,11 @@ const main = () => {
   }
 };
 
-main();
+if (require.main === module) {
+  main();
+}
+
+module.exports = {
+  collectSessionFiles,
+  shouldIgnoreSessionPath,
+};