diff --git a/sdk/src/query/phase-uat-passed.test.ts b/sdk/src/query/phase-uat-passed.test.ts
index ac368b5c6..af7fef583 100644
--- a/sdk/src/query/phase-uat-passed.test.ts
+++ b/sdk/src/query/phase-uat-passed.test.ts
@@ -6,7 +6,7 @@ import { describe, it, expect, beforeEach, afterEach } from 'vitest';
 import { mkdtemp, writeFile, mkdir, rm } from 'node:fs/promises';
 import { join } from 'node:path';
 import { tmpdir } from 'node:os';
-import { isPhaseUatPassed, REASON_CODE } from './phase-uat-passed.js';
+import { isPhaseUatPassed, REASON_CODE, PhaseUatPassedError, ERROR_CODE } from './phase-uat-passed.js';
 
 const UAT_PASS_CONTENT = `---
 status: complete
@@ -306,6 +306,18 @@ result: pass
     }
   });
 
+  it("throws PhaseUatPassedError with PROJECT_DIR_MISSING code when projectDir does not exist", async () => {
+    const missingPath = `/nonexistent/path/that/should/never/be/real-${Date.now()}`;
+    let thrown: unknown;
+    try {
+      await isPhaseUatPassed(missingPath, '5');
+    } catch (e) {
+      thrown = e;
+    }
+    expect(thrown).toBeInstanceOf(PhaseUatPassedError);
+    expect((thrown as PhaseUatPassedError).code).toBe(ERROR_CODE.PROJECT_DIR_MISSING);
+  });
+
   it("emits NO_ITEMS_EXTRACTED reason when UAT file has no parseable items, orphans, or placeholders", async () => {
     const localTmp = await mkdtemp(join(tmpdir(), 'gsd-uat-c14-'));
     try {
diff --git a/sdk/src/query/phase-uat-passed.ts b/sdk/src/query/phase-uat-passed.ts
index 381236c13..6474c39ac 100644
--- a/sdk/src/query/phase-uat-passed.ts
+++ b/sdk/src/query/phase-uat-passed.ts
@@ -5,11 +5,12 @@
  * Non-pass items (result not literally 'pass') emit a typed NON_PASS_RESULT reason.
  */
 
-import { readFile, readdir } from 'node:fs/promises';
+import { readFile, readdir, stat } from 'node:fs/promises';
 import { join, relative } from 'node:path';
 import { resolvePhaseDir } from './phase-list-queries.js';
 import { extractFrontmatter } from './frontmatter.js';
 import { parseVerificationFrontmatterItems } from './uat.js';
+import { GSDError, ErrorClassification } from '../errors.js';
 
 export const REASON_CODE = Object.freeze({
   NON_PASS_RESULT: 'non_pass_result',
@@ -24,6 +25,17 @@ export const REASON_CODE = Object.freeze({
 
 export type ReasonCode = typeof REASON_CODE[keyof typeof REASON_CODE];
 
+export const ERROR_CODE = Object.freeze({
+  PROJECT_DIR_MISSING: 'project_dir_missing',
+} as const);
+export type ErrorCode = typeof ERROR_CODE[keyof typeof ERROR_CODE];
+
+export class PhaseUatPassedError extends GSDError {
+  constructor(message: string, public readonly code: ErrorCode) {
+    super(message, ErrorClassification.Validation);
+  }
+}
+
 export type UatReason = {
   code: ReasonCode;
   file?: string;
@@ -115,6 +127,18 @@ export async function isPhaseUatPassed(
   reasonsHuman: string[];
   items: Record<string, unknown>[];
 }> {
+  try {
+    await stat(projectDir);
+  } catch (err: unknown) {
+    if ((err as NodeJS.ErrnoException).code === 'ENOENT') {
+      throw new PhaseUatPassedError(
+        `projectDir does not exist: ${projectDir}`,
+        ERROR_CODE.PROJECT_DIR_MISSING,
+      );
+    }
+    throw err;
+  }
+
   const dir = await resolvePhaseDir(phase, projectDir, workstream);
   if (!dir) {
     return {