diff --git a/src/resources/extensions/gsd/paths.ts b/src/resources/extensions/gsd/paths.ts
index c41ee596e..601e7e1d9 100644
--- a/src/resources/extensions/gsd/paths.ts
+++ b/src/resources/extensions/gsd/paths.ts
@@ -9,9 +9,40 @@
  * via prefix matching, so existing projects work without migration.
  */
 
-import { readdirSync, existsSync } from "node:fs";
+import { readdirSync, existsSync, Dirent } from "node:fs";
 import { join } from "node:path";
 
+// ─── Directory Listing Cache ──────────────────────────────────────────────────
+
+const dirEntryCache = new Map<string, Dirent[]>();
+const dirListCache = new Map<string, string[]>();
+
+function cachedReaddirWithTypes(dirPath: string): Dirent[] {
+  const cached = dirEntryCache.get(dirPath);
+  if (cached) return cached;
+  const entries = readdirSync(dirPath, { withFileTypes: true });
+  dirEntryCache.set(dirPath, entries);
+  return entries;
+}
+
+function cachedReaddir(dirPath: string): string[] {
+  const cached = dirListCache.get(dirPath);
+  if (cached) return cached;
+  const entries = readdirSync(dirPath);
+  dirListCache.set(dirPath, entries);
+  return entries;
+}
+
+/**
+ * Clear the directory listing cache.
+ * Call after milestone transitions, file creation in planning directories,
+ * or at the start/end of a dispatch cycle.
+ */
+export function clearPathCache(): void {
+  dirEntryCache.clear();
+  dirListCache.clear();
+}
+
 // ─── Name Builders ─────────────────────────────────────────────────────────
 
 /**
@@ -58,7 +89,7 @@ export function buildTaskFileName(taskId: string, suffix: string): string {
 export function resolveDir(parentDir: string, idPrefix: string): string | null {
   if (!existsSync(parentDir)) return null;
   try {
-    const entries = readdirSync(parentDir, { withFileTypes: true });
+    const entries = cachedReaddirWithTypes(parentDir);
     // Exact match first (current convention: bare ID)
     const exact = entries.find(e => e.isDirectory() && e.name === idPrefix);
     if (exact) return exact.name;
@@ -83,7 +114,7 @@ export function resolveFile(dir: string, idPrefix: string, suffix: string): stri
   if (!existsSync(dir)) return null;
   const target = `${idPrefix}-${suffix}.md`.toUpperCase();
   try {
-    const entries = readdirSync(dir);
+    const entries = cachedReaddir(dir);
     // Direct match: ID-SUFFIX.md
     const direct = entries.find(e => e.toUpperCase() === target);
     if (direct) return direct;
@@ -113,7 +144,7 @@ export function resolveTaskFiles(tasksDir: string, suffix: string): string[] {
     const currentPattern = new RegExp(`^T\\d+-${suffix}\\.md$`, "i");
     // Legacy convention: T01-INSTALL-PACKAGES-PLAN.md
     const legacyPattern = new RegExp(`^T\\d+-.*-${suffix}\\.md$`, "i");
-    return readdirSync(tasksDir)
+    return cachedReaddir(tasksDir)
       .filter(f => currentPattern.test(f) || legacyPattern.test(f))
       .sort();
   } catch {
diff --git a/src/resources/extensions/gsd/tests/complete-milestone.test.ts b/src/resources/extensions/gsd/tests/complete-milestone.test.ts
index cdb286792..0055cb862 100644
--- a/src/resources/extensions/gsd/tests/complete-milestone.test.ts
+++ b/src/resources/extensions/gsd/tests/complete-milestone.test.ts
@@ -3,6 +3,7 @@ import { join, dirname } from "node:path";
 import { tmpdir } from "node:os";
 import { fileURLToPath } from "node:url";
 import { createTestContext } from './test-helpers.ts';
+import { clearPathCache } from '../paths.ts';
 
 // loadPrompt reads from ~/.gsd/agent/extensions/gsd/prompts/ (main checkout).
 // In a worktree the file may not exist there yet, so we resolve prompts
@@ -179,6 +180,7 @@ async function main(): Promise<void> {
 
       // Now add the summary and verify it transitions to complete
       writeMilestoneSummary(base, "M001", "# M001 Summary\n\nDone.");
+      clearPathCache();
       const stateAfter = await deriveState(base);
       assertEq(stateAfter.phase, "complete", "deriveState returns complete after summary exists");
       assertEq(stateAfter.registry[0]?.status, "complete", "registry shows complete status");
diff --git a/src/resources/extensions/gsd/tests/draft-promotion.test.ts b/src/resources/extensions/gsd/tests/draft-promotion.test.ts
index 0fb7160cd..1037d9809 100644
--- a/src/resources/extensions/gsd/tests/draft-promotion.test.ts
+++ b/src/resources/extensions/gsd/tests/draft-promotion.test.ts
@@ -3,7 +3,7 @@ import { join } from "node:path";
 import { tmpdir } from "node:os";
 
 import { deriveState } from "../state.js";
-import { resolveMilestoneFile } from "../paths.js";
+import { resolveMilestoneFile, clearPathCache } from "../paths.js";
 
 let passed = 0;
 let failed = 0;
@@ -40,6 +40,7 @@ assert(
 const contextPath = join(gsd, "milestones", "M001", "M001-CONTEXT.md");
 writeFileSync(contextPath, "# M001: Full Context\n\nDeep discussion output.\n");
 
+clearPathCache();
 const state2 = await deriveState(tmpBase);
 assert(
   state2.phase === "pre-planning",
@@ -65,6 +66,7 @@ assert(
 );
 
 // Step 4: After cleanup, state is still pre-planning (CONTEXT.md exists)
+clearPathCache();
 const state3 = await deriveState(tmpBase);
 assert(
   state3.phase === "pre-planning",
diff --git a/src/resources/extensions/gsd/tests/integration-mixed-milestones.test.ts b/src/resources/extensions/gsd/tests/integration-mixed-milestones.test.ts
index d5b761075..7e16581eb 100644
--- a/src/resources/extensions/gsd/tests/integration-mixed-milestones.test.ts
+++ b/src/resources/extensions/gsd/tests/integration-mixed-milestones.test.ts
@@ -23,6 +23,7 @@ import {
   parseSliceBranch,
   switchToMain,
 } from '../worktree.ts';
+import { clearPathCache } from '../paths.ts';
 import { createTestContext } from './test-helpers.ts';
 
 // ─── Assertion Helpers ────────────────────────────────────────────────────
@@ -437,6 +438,7 @@ Built the legacy feature successfully.
 `);
       run('git add .', base);
       run('git commit -m add-m001', base);
+      clearPathCache();
 
       // M001 (seq=1) < M001-abc123 (seq=1) — but M001 has incomplete S02
       // Since M001 seq=1 and M002-abc123 seq=2, blocker should reference M001/S02
@@ -459,6 +461,7 @@ Built the legacy feature successfully.
 `);
       run('git add .', base);
       run('git commit -m complete-m001', base);
+      clearPathCache();
 
       assertEq(
         getPriorSliceCompletionBlocker(base, 'main', 'plan-slice', 'M002-abc123/S01'),
diff --git a/src/resources/extensions/gsd/tests/unit-runtime.test.ts b/src/resources/extensions/gsd/tests/unit-runtime.test.ts
index b96439ede..64c7ee49a 100644
--- a/src/resources/extensions/gsd/tests/unit-runtime.test.ts
+++ b/src/resources/extensions/gsd/tests/unit-runtime.test.ts
@@ -8,6 +8,7 @@ import {
   readUnitRuntimeRecord,
   writeUnitRuntimeRecord,
 } from "../unit-runtime.ts";
+import { clearPathCache } from '../paths.ts';
 import { createTestContext } from './test-helpers.ts';
 
 const { assertEq, assertTrue, report } = createTestContext();
@@ -48,6 +49,7 @@ console.log("\n=== execute-task durability inspection ===");
     "utf-8",
   );
   writeFileSync(join(base, ".gsd", "STATE.md"), "## Next Action\nExecute T10 for S02: next thing\n", "utf-8");
+  clearPathCache();
 
   status = await inspectExecuteTaskDurability(base, "M100/S02/T09");
   assertEq(status!.summaryExists, true, "summary found after write");
@@ -128,6 +130,7 @@ console.log("\n=== must-haves: partially mentioned in summary ===");
   );
   writeFileSync(join(mhBase, ".gsd", "STATE.md"), "## Next Action\nExecute T02 for S02: next thing\n", "utf-8");
 
+  clearPathCache();
   const status = await inspectExecuteTaskDurability(mhBase, "M200/S02/T01");
   assertTrue(status !== null, "mh-partial: status exists");
   assertEq(status!.mustHaveCount, 3, "mh-partial: mustHaveCount is 3");
@@ -155,6 +158,7 @@ console.log("\n=== must-haves: no task plan file ===");
   );
   writeFileSync(join(mhBase, ".gsd", "STATE.md"), "## Next Action\nExecute T02 for S03: next thing\n", "utf-8");
 
+  clearPathCache();
   const status = await inspectExecuteTaskDurability(mhBase, "M200/S03/T01");
   assertTrue(status !== null, "mh-noplan: status exists");
   assertEq(status!.mustHaveCount, 0, "mh-noplan: mustHaveCount is 0 when no task plan");
@@ -179,6 +183,7 @@ console.log("\n=== must-haves: present but no summary file ===");
   );
   writeFileSync(join(mhBase, ".gsd", "STATE.md"), "## Next Action\nExecute T01 for S04: build parser\n", "utf-8");
 
+  clearPathCache();
   const status = await inspectExecuteTaskDurability(mhBase, "M200/S04/T01");
   assertTrue(status !== null, "mh-nosummary: status exists");
   assertEq(status!.mustHaveCount, 2, "mh-nosummary: mustHaveCount is 2");
@@ -210,6 +215,7 @@ console.log("\n=== must-haves: substring matching (no backtick tokens) ===");
   );
   writeFileSync(join(mhBase, ".gsd", "STATE.md"), "## Next Action\nExecute T02 for S05: next thing\n", "utf-8");
 
+  clearPathCache();
   const status = await inspectExecuteTaskDurability(mhBase, "M200/S05/T01");
   assertTrue(status !== null, "mh-substr: status exists");
   assertEq(status!.mustHaveCount, 3, "mh-substr: mustHaveCount is 3");