diff --git a/src/ghidra/GhidraClient.ts b/src/ghidra/GhidraClient.ts
index 5442586c8..375a4f064 100644
--- a/src/ghidra/GhidraClient.ts
+++ b/src/ghidra/GhidraClient.ts
@@ -1,6 +1,5 @@
 import { randomBytes, randomUUID } from "node:crypto";
 import type { Socket } from "node:net";
-import { tmpdir } from "node:os";
 
 import { AnalysisError } from "../domain/analysisErrorBase.js";
 import type { JsonValue } from "../domain/jsonValue.js";
@@ -47,9 +46,10 @@ import {
 } from "./GhidraTransport.js";
 import { GhidraWire } from "./GhidraClientWire.js";
 import { completeGhidraStartupHandshake } from "./GhidraClientStartup.js";
+import { ghidraSessionRoot } from "./GhidraSessionRoot.js";
 
 const SHUTDOWN_TIMEOUT_MS = 10_000;
-const SESSION_ROOT = tmpdir();
+const SESSION_ROOT = ghidraSessionRoot();
 
 export type {
   GhidraClientOptions,
diff --git a/src/ghidra/GhidraSessionRoot.test.ts b/src/ghidra/GhidraSessionRoot.test.ts
new file mode 100644
index 000000000..bc5369dd3
--- /dev/null
+++ b/src/ghidra/GhidraSessionRoot.test.ts
@@ -0,0 +1,61 @@
+import { join, sep } from "node:path";
+import { describe, expect, it } from "vitest";
+
+import { ghidraSessionRoot } from "./GhidraSessionRoot.js";
+
+const hasDotPrefixElement = (directory: string): boolean =>
+  directory.split(sep).some((element) => element.startsWith("."));
+
+const POSIX = process.platform !== "win32";
+const posixFallback = join(sep, "tmp");
+const posixBase = (...segments: string[]) => join(sep, ...segments);
+
+describe("ghidraSessionRoot", () => {
+  it("keeps an inherited base that Ghidra accepts", () => {
+    const base = posixBase("var", "tmp", "rea-run");
+    expect(ghidraSessionRoot({ base, fallback: posixFallback })).toBe(base);
+  });
+
+  it("keeps a base whose elements only contain an interior dot", () => {
+    const base = posixBase("opt", "rea.run", "session");
+    expect(ghidraSessionRoot({ base, fallback: posixFallback })).toBe(base);
+  });
+
+  it("relocates a dot-prefixed base to the supplied dot-free fallback", () => {
+    const base = posixBase("home", "operator", ".cache", "scratch");
+    expect(ghidraSessionRoot({ base, fallback: posixFallback })).toBe(
+      posixFallback,
+    );
+  });
+
+  it("relocates a base that is itself a hidden directory", () => {
+    const base = posixBase("home", "operator", ".tmp");
+    expect(ghidraSessionRoot({ base, fallback: posixBase("var", "tmp") })).toBe(
+      posixBase("var", "tmp"),
+    );
+  });
+
+  it("ignores a fallback that is itself dotted", () => {
+    const base = posixBase("home", "operator", ".cache", "scratch");
+    expect(
+      ghidraSessionRoot({
+        base,
+        fallback: posixBase("home", "operator", ".tmp"),
+      }),
+    ).toBe(posixBase("home", "operator"));
+  });
+
+  it("never returns a path with a dot-prefixed element", () => {
+    const directory = ghidraSessionRoot({
+      base: posixBase("home", "operator", ".cache", "scratch"),
+      fallback: posixBase("home", "operator", ".cache"),
+    });
+    expect(hasDotPrefixElement(directory)).toBe(false);
+  });
+
+  it.skipIf(!POSIX)("prefers the platform temp directory by default", () => {
+    expect(
+      ghidraSessionRoot({ base: posixBase("home", "operator", ".cache") }),
+    ).toBe(posixBase("tmp"));
+  });
+});
diff --git a/src/ghidra/GhidraSessionRoot.ts b/src/ghidra/GhidraSessionRoot.ts
new file mode 100644
index 000000000..82c88c0bf
--- /dev/null
+++ b/src/ghidra/GhidraSessionRoot.ts
@@ -0,0 +1,55 @@
+import { dirname, isAbsolute, resolve, sep } from "node:path";
+import { tmpdir } from "node:os";
+
+/** Session roots may not contain a dot-prefixed path element. */
+const hasDotPrefixElement = (directory: string): boolean =>
+  resolve(directory)
+    .split(sep)
+    .some((element) => element.startsWith("."));
+
+/** Nearest ancestor of `directory`, inclusive, that has no dot-prefixed element. */
+const nearestSafeAncestor = (directory: string): string | undefined => {
+  let current = resolve(directory);
+  for (;;) {
+    if (!hasDotPrefixElement(current)) return current;
+    const parent = dirname(current);
+    if (parent === current) return undefined;
+    current = parent;
+  }
+};
+
+/** Coordinates accepted by {@link ghidraSessionRoot}. */
+export interface GhidraSessionRootOptions {
+  /** Inherited base directory, normally `os.tmpdir()`. */
+  readonly base?: string;
+  /** Platform-specific dot-free fallback directory passed to `mkdtemp`. */
+  readonly fallback?: string;
+  /** Platform override used by deterministic boundary tests. */
+  readonly platform?: NodeJS.Platform;
+}
+
+/**
+ * Select a session root usable as the parent of a Ghidra project path.
+ *
+ * Ghidra validates every project path element with `NamingUtilities.checkName`
+ * and aborts the headless analyzer on any element that starts with `.`, so an
+ * inherited `TMPDIR` such as `~/.cache/<tool>` fails every Ghidra operation
+ * with a generic analysis failure. Prefer the inherited base when it is usable,
+ * then a dot-free platform temp directory, then the nearest dot-free ancestor.
+ */
+export const ghidraSessionRoot = (
+  options: GhidraSessionRootOptions = {},
+): string => {
+  const base = resolve(options.base ?? tmpdir());
+  if (!hasDotPrefixElement(base)) return base;
+  const platform = options.platform ?? process.platform;
+  const fallback =
+    options.fallback ?? (platform === "win32" ? undefined : "/tmp");
+  if (
+    fallback !== undefined &&
+    isAbsolute(fallback) &&
+    !hasDotPrefixElement(fallback)
+  )
+    return resolve(fallback);
+  return nearestSafeAncestor(base) ?? base;
+};