diff --git a/apps/desktop/src/main/__tests__/context-budget-policy.test.ts b/apps/desktop/src/main/__tests__/context-budget-policy.test.ts
index ee1e069728..6a880f37d4 100644
--- a/apps/desktop/src/main/__tests__/context-budget-policy.test.ts
+++ b/apps/desktop/src/main/__tests__/context-budget-policy.test.ts
@@ -146,3 +146,84 @@ describe('desktop activeToolResultPrune policy', () => {
     assert.equal(policy?.maxHistoryEstimatedTokens, 128_000 - 4096);
   });
 });
+
+const STALE_PRUNE_ENV_KEYS = [
+  'MAKA_CONTEXT_BUDGET',
+  'MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE',
+  'MAKA_CONTEXT_STALE_TOOL_RESULT_MAX_TOKENS',
+  'MAKA_CONTEXT_STALE_TOOL_RESULT_MIN_RECENT_TURNS',
+  'MAKA_CONTEXT_MIN_RECENT_TURNS',
+] as const;
+
+describe('desktop staleToolResultPrune policy', () => {
+  const savedStaleEnv: Record<string, string | undefined> = {};
+
+  beforeEach(() => {
+    for (const key of STALE_PRUNE_ENV_KEYS) {
+      savedStaleEnv[key] = process.env[key];
+      delete process.env[key];
+    }
+  });
+
+  afterEach(() => {
+    for (const key of STALE_PRUNE_ENV_KEYS) {
+      if (savedStaleEnv[key] === undefined) delete process.env[key];
+      else process.env[key] = savedStaleEnv[key];
+    }
+  });
+
+  test('is enabled by default with the measured 2048-token threshold', () => {
+    const policy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(policy?.staleToolResultPrune?.enabled, true);
+    assert.equal(policy?.staleToolResultPrune?.maxResultEstimatedTokens, 2048);
+    assert.equal(policy?.staleToolResultPrune?.minRecentTurnsFull, 2);
+  });
+
+  test('can be disabled with explicit false', () => {
+    process.env.MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE = 'false';
+    const policy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(policy?.staleToolResultPrune, undefined);
+  });
+
+  test('can be disabled with explicit off', () => {
+    process.env.MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE = 'off';
+    const policy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(policy?.staleToolResultPrune, undefined);
+  });
+
+  test('accepts standard truthy values as enabled', () => {
+    process.env.MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE = 'true';
+    const policy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(policy?.staleToolResultPrune?.enabled, true);
+  });
+
+  test('rejects malformed boolean values instead of silently disabling', () => {
+    process.env.MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE = 'maybe';
+    assert.throws(
+      () => buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' }),
+      /MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE must be a boolean/,
+    );
+  });
+
+  test('respects max result estimated tokens env', () => {
+    process.env.MAKA_CONTEXT_STALE_TOOL_RESULT_MAX_TOKENS = '4096';
+    const policy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(policy?.staleToolResultPrune?.maxResultEstimatedTokens, 4096);
+  });
+
+  test('respects min recent turns full env with MAKA_CONTEXT_MIN_RECENT_TURNS fallback', () => {
+    process.env.MAKA_CONTEXT_MIN_RECENT_TURNS = '3';
+    const fallbackPolicy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(fallbackPolicy?.staleToolResultPrune?.minRecentTurnsFull, 3);
+
+    process.env.MAKA_CONTEXT_STALE_TOOL_RESULT_MIN_RECENT_TURNS = '5';
+    const explicitPolicy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(explicitPolicy?.staleToolResultPrune?.minRecentTurnsFull, 5);
+  });
+
+  test('MAKA_CONTEXT_BUDGET=off disables the whole policy including staleToolResultPrune', () => {
+    process.env.MAKA_CONTEXT_BUDGET = 'off';
+    const policy = buildDefaultContextBudgetPolicy(openaiConnection(), { name: 'desktop-default-history-budget' });
+    assert.equal(policy, undefined);
+  });
+});
diff --git a/packages/headless/src/__tests__/harbor-cell.test.ts b/packages/headless/src/__tests__/harbor-cell.test.ts
index dd0976dc89..072ddc0b65 100644
--- a/packages/headless/src/__tests__/harbor-cell.test.ts
+++ b/packages/headless/src/__tests__/harbor-cell.test.ts
@@ -1430,7 +1430,7 @@ describe('runHarborCell', () => {
   });
 
   test('Harbor context budget env treats explicit false-like booleans as disabled', () => {
-    // stale and archive default off; activeToolResultPrune defaults on, so disabling
+    // archive retrieval defaults off; stale and active prune default on, so disabling
     // stale/archive alone still leaves an enabled activeToolResultPrune policy.
     assert.deepEqual(
       buildHarborCellContextBudgetBackendOptions({ MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE: 'false' }).contextBudget?.activeToolResultPrune,
@@ -1471,14 +1471,49 @@ describe('runHarborCell', () => {
   });
 
   test('Harbor active tool result prune can be disabled with explicit off', () => {
-    assert.equal(
-      buildHarborCellContextBudgetBackendOptions({ MAKA_CONTEXT_ACTIVE_TOOL_RESULT_PRUNE: 'off' }).contextBudget,
-      undefined,
-    );
-    assert.equal(
-      buildHarborCellContextBudgetPolicySnapshot({ MAKA_CONTEXT_ACTIVE_TOOL_RESULT_PRUNE: 'off' }),
-      undefined,
-    );
+    const options = buildHarborCellContextBudgetBackendOptions({ MAKA_CONTEXT_ACTIVE_TOOL_RESULT_PRUNE: 'off' });
+    assert.equal(options.contextBudget?.activeToolResultPrune, undefined);
+    assert.deepEqual(options.contextBudget?.staleToolResultPrune, { enabled: true, minRecentTurnsFull: 2 });
+  });
+
+  test('Harbor stale tool result prune is enabled by default without any env', () => {
+    const backend = buildHarborCellContextBudgetBackendOptions({});
+    // minRecentTurnsFull is set explicitly so the runtime protection window
+    // matches the policy snapshot and desktop default instead of the runtime's
+    // internal ?? 1 fallback.
+    assert.deepEqual(backend.contextBudget?.staleToolResultPrune, { enabled: true, minRecentTurnsFull: 2 });
+
+    const snapshot = buildHarborCellContextBudgetPolicySnapshot({});
+    assert.equal(snapshot?.enabled, true);
+    assert.equal(snapshot?.staleToolResultPrune?.enabled, true);
+    assert.equal(snapshot?.staleToolResultPrune?.maxResultEstimatedTokens, 2048);
+    assert.equal(snapshot?.staleToolResultPrune?.minRecentTurnsFull, 2);
+  });
+
+  test('Harbor stale tool result prune can be disabled with explicit off', () => {
+    const options = buildHarborCellContextBudgetBackendOptions({ MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE: 'off' });
+    assert.equal(options.contextBudget?.staleToolResultPrune, undefined);
+    assert.deepEqual(options.contextBudget?.activeToolResultPrune, { enabled: true });
+  });
+
+  test('Harbor stale tool result prune min recent turns falls back to MAKA_CONTEXT_MIN_RECENT_TURNS', () => {
+    const fallback = buildHarborCellContextBudgetBackendOptions({ MAKA_CONTEXT_MIN_RECENT_TURNS: '3' });
+    assert.equal(fallback.contextBudget?.staleToolResultPrune?.minRecentTurnsFull, 3);
+
+    const explicit = buildHarborCellContextBudgetBackendOptions({
+      MAKA_CONTEXT_MIN_RECENT_TURNS: '3',
+      MAKA_CONTEXT_STALE_TOOL_RESULT_MIN_RECENT_TURNS: '5',
+    });
+    assert.equal(explicit.contextBudget?.staleToolResultPrune?.minRecentTurnsFull, 5);
+  });
+
+  test('Harbor context budget is empty when both default-on prunes are explicitly off', () => {
+    const env = {
+      MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE: 'off',
+      MAKA_CONTEXT_ACTIVE_TOOL_RESULT_PRUNE: 'off',
+    };
+    assert.equal(buildHarborCellContextBudgetBackendOptions({ ...env }).contextBudget, undefined);
+    assert.equal(buildHarborCellContextBudgetPolicySnapshot({ ...env }), undefined);
   });
 
   test('Harbor parses semantic compact policy for headless runs', () => {
diff --git a/packages/headless/src/harbor-cell.ts b/packages/headless/src/harbor-cell.ts
index 4809c3b51e..6c453b1c1d 100644
--- a/packages/headless/src/harbor-cell.ts
+++ b/packages/headless/src/harbor-cell.ts
@@ -704,7 +704,7 @@ export function buildHarborCellContextBudgetBackendOptions(
     env.MAKA_HARBOR_CONTEXT_STALE_TOOL_RESULT_PRUNE ??
     env.MAKA_TOOL_RESULT_PRUNE,
     'MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE',
-  ) ?? false;
+  ) ?? true;
   const activePruneEnabled = booleanEnv(
     env.MAKA_CONTEXT_ACTIVE_TOOL_RESULT_PRUNE ??
     env.MAKA_HARBOR_CONTEXT_ACTIVE_TOOL_RESULT_PRUNE ??
@@ -760,7 +760,9 @@ export function buildHarborCellContextBudgetBackendOptions(
     contextBudget.staleToolResultPrune = {
       enabled: true,
       ...(maxResultEstimatedTokens !== undefined ? { maxResultEstimatedTokens } : {}),
-      ...(minRecentTurnsFull !== undefined ? { minRecentTurnsFull } : {}),
+      // Explicit so the runtime protection window matches the policy snapshot
+      // and desktop default (2) instead of the runtime's internal ?? 1 fallback.
+      minRecentTurnsFull: minRecentTurnsFull ?? minRecentTurns ?? 2,
     };
   }
 
diff --git a/packages/runtime/src/context-budget-policy.ts b/packages/runtime/src/context-budget-policy.ts
index b20b454cb4..ade6ab165a 100644
--- a/packages/runtime/src/context-budget-policy.ts
+++ b/packages/runtime/src/context-budget-policy.ts
@@ -95,7 +95,11 @@ export function buildManualCompactLookupPolicy(
 function buildStaleToolResultPrunePolicy(
   env: Record<string, string | undefined>,
 ): NonNullable<ContextBudgetPolicy['staleToolResultPrune']> | undefined {
-  if (env.MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE !== 'on') return undefined;
+  const enabled = parseOptionalBoolean(
+    env.MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE,
+    'MAKA_CONTEXT_STALE_TOOL_RESULT_PRUNE',
+  );
+  if (enabled === false) return undefined;
   return {
     enabled: true,
     maxResultEstimatedTokens: parsePositiveInt(