diff --git a/src/domain/expressions/expression_evaluation_service_test.ts b/src/domain/expressions/expression_evaluation_service_test.ts
index c09337e4..d522972a 100644
--- a/src/domain/expressions/expression_evaluation_service_test.ts
+++ b/src/domain/expressions/expression_evaluation_service_test.ts
@@ -77,6 +77,19 @@ Deno.test("containsVaultExpression returns false for vault-like but not vault.ge
   assertEquals(containsVaultExpression("vault_get(foo)"), false);
 });
 
+Deno.test("containsVaultExpression returns true for quoted args with spaces", () => {
+  assertEquals(
+    containsVaultExpression('vault.get("infra", "Client ID")'),
+    true,
+  );
+  assertEquals(
+    containsVaultExpression(
+      'vault.get("infra", "Tailscale K8s Operator/Client ID")',
+    ),
+    true,
+  );
+});
+
 // ============================================================================
 // containsEnvExpression
 // ============================================================================
diff --git a/src/domain/expressions/model_resolver.ts b/src/domain/expressions/model_resolver.ts
index 2722a8a1..5b450ec0 100644
--- a/src/domain/expressions/model_resolver.ts
+++ b/src/domain/expressions/model_resolver.ts
@@ -825,10 +825,14 @@ export class ModelResolver {
     redactor?: SecretRedactor,
     secretBag?: VaultSecretBag,
   ): Promise<string> {
-    // Pattern to match vault.get(vaultName, secretKey) expressions
-    // Handles both quoted and unquoted arguments
+    // Pattern to match vault.get(vaultName, secretKey) expressions.
+    // Handles both quoted and unquoted arguments. Quoted arguments may
+    // contain spaces (e.g. vault.get("infra", "Client ID")).
+    // Each argument uses alternation:
+    //   (['"`])(.+?)\1  — quoted: any chars up to the matching close quote
+    //   ([^\s,)]+)      — unquoted: non-whitespace, non-comma, non-paren
     const vaultPattern =
-      /vault\.get\(\s*(['"`]?)([^'"`\s,]+)\1\s*,\s*(['"`]?)([^'"`\s,]+)\3\s*\)/g;
+      /vault\.get\(\s*(?:(['"`])(.+?)\1|([^\s,)]+))\s*,\s*(?:(['"`])(.+?)\4|([^\s,)]+))\s*\)/g;
 
     let resolvedValue = value;
     const matches = Array.from(value.matchAll(vaultPattern));
@@ -841,7 +845,11 @@ export class ModelResolver {
     const vaultService = await this.getVaultService();
 
     for (const match of matches) {
-      const [fullMatch, , vaultName, , secretKey] = match;
+      // Groups: [1]=quote1, [2]=quoted vault, [3]=unquoted vault,
+      //         [4]=quote2, [5]=quoted key,   [6]=unquoted key
+      const fullMatch = match[0];
+      const vaultName = match[2] ?? match[3];
+      const secretKey = match[5] ?? match[6];
       try {
         const secretValue = await vaultService.get(vaultName, secretKey);
         redactor?.addSecret(secretValue);
diff --git a/src/domain/vaults/vault_expression_test.ts b/src/domain/vaults/vault_expression_test.ts
index f6a5885f..720fc7e1 100644
--- a/src/domain/vaults/vault_expression_test.ts
+++ b/src/domain/vaults/vault_expression_test.ts
@@ -93,6 +93,18 @@ Deno.test("ModelResolver.resolveVaultExpressions", async (t) => {
     return new ModelResolver(definitionRepo, { vaultService });
   }
 
+  // Helper to create a ModelResolver with multiple named vaults
+  function createResolverWithNamedVaults(
+    vaults: Record<string, Record<string, string>>,
+  ): ModelResolver {
+    const vaultService = new VaultService();
+    for (const [name, secrets] of Object.entries(vaults)) {
+      vaultService.registerVault({ name, type: "mock", config: secrets });
+    }
+    const definitionRepo = new YamlDefinitionRepository(tempDir);
+    return new ModelResolver(definitionRepo, { vaultService });
+  }
+
   await t.step("should resolve basic vault expression", async () => {
     const resolver = createResolverWithMockVault({ "api-key": "secret123" });
     const result = await resolver.resolveVaultExpressions(
@@ -365,6 +377,88 @@ Deno.test("ModelResolver.resolveVaultExpressions", async (t) => {
     },
   );
 
+  // ========================================================================
+  // Spaces in quoted vault names and secret keys (#902)
+  // ========================================================================
+
+  await t.step(
+    "should resolve vault expression with spaces in double-quoted key",
+    async () => {
+      const resolver = createResolverWithMockVault({
+        "Client ID": "my-client-id",
+      });
+      const result = await resolver.resolveVaultExpressions(
+        'vault.get("test-vault", "Client ID")',
+      );
+      assertEquals(result, '"my-client-id"');
+    },
+  );
+
+  await t.step(
+    "should resolve vault expression with spaces in single-quoted key",
+    async () => {
+      const resolver = createResolverWithMockVault({
+        "Client Secret": "super-secret",
+      });
+      const result = await resolver.resolveVaultExpressions(
+        "vault.get('test-vault', 'Client Secret')",
+      );
+      assertEquals(result, '"super-secret"');
+    },
+  );
+
+  await t.step(
+    "should resolve vault expression with 1Password-style path containing spaces",
+    async () => {
+      const resolver = createResolverWithMockVault({
+        "Tailscale K8s Operator/Client ID": "ts-client-id-123",
+      });
+      const result = await resolver.resolveVaultExpressions(
+        'vault.get("test-vault", "Tailscale K8s Operator/Client ID")',
+      );
+      assertEquals(result, '"ts-client-id-123"');
+    },
+  );
+
+  await t.step(
+    "should resolve vault expression with spaces in quoted vault name",
+    async () => {
+      const resolver = createResolverWithNamedVaults({
+        "my infra vault": { "api-key": "infra-key-456" },
+      });
+      const result = await resolver.resolveVaultExpressions(
+        'vault.get("my infra vault", "api-key")',
+      );
+      assertEquals(result, '"infra-key-456"');
+    },
+  );
+
+  await t.step(
+    "should resolve vault expression with spaces in both vault name and key",
+    async () => {
+      const resolver = createResolverWithNamedVaults({
+        "my infra vault": { "Client Secret": "both-spaces-val" },
+      });
+      const result = await resolver.resolveVaultExpressions(
+        'vault.get("my infra vault", "Client Secret")',
+      );
+      assertEquals(result, '"both-spaces-val"');
+    },
+  );
+
+  await t.step(
+    "should resolve mixed quoted vault name with unquoted key",
+    async () => {
+      const resolver = createResolverWithNamedVaults({
+        "my infra vault": { "api-key": "mixed-val" },
+      });
+      const result = await resolver.resolveVaultExpressions(
+        'vault.get("my infra vault", api-key)',
+      );
+      assertEquals(result, '"mixed-val"');
+    },
+  );
+
   // Cleanup
   await Deno.remove(tempDir, { recursive: true });
 });