diff --git a/src/main/credentials/credential-store.ts b/src/main/credentials/credential-store.ts
index 9a88c1ea..19db1a7d 100644
--- a/src/main/credentials/credential-store.ts
+++ b/src/main/credentials/credential-store.ts
@@ -1,12 +1,39 @@
 import type { AppDatabase } from "@main/database";
 import type { CredentialBackend, CredentialKind } from "@main/database/credentials";
 import type { CredentialStatus } from "@main/database/credentials";
-import type { CredentialSummary } from "@shared/contracts/schemas-credentials";
+import { credentialPayloadSchema, type CredentialSummary } from "@shared/contracts/schemas-credentials";
+import { z } from "zod";
+import { UpstreamError } from "../errors/index.js";
 import type { StoredCredentialPayload } from "./types";
 
 const HINT_SUFFIX_LEN = 4;
 const HINT_PREFIX_LEN = 6;
 
+const oauthCredentialPayloadSchema = z.object({
+  refresh: z.string().min(1),
+  access: z.string().min(1),
+  expires: z.number().finite(),
+}).passthrough();
+
+const storedCredentialPayloadSchema = z.union([
+  credentialPayloadSchema,
+  z.object({ kind: z.literal("oauth"), value: oauthCredentialPayloadSchema }),
+]);
+
+export class CredentialStoreReadError extends UpstreamError {
+  readonly connectorId: string;
+
+  constructor(connectorId: string, message: string) {
+    super({
+      code: "CREDENTIAL_INVALID",
+      message,
+      context: { connectorId },
+    });
+    this.name = "CredentialStoreReadError";
+    this.connectorId = connectorId;
+  }
+}
+
 function maskApiKey(value: string): string {
   if (value.length <= HINT_PREFIX_LEN + HINT_SUFFIX_LEN) {
     return `${value.slice(0, 2)}...`;
@@ -48,6 +75,36 @@ export interface CredentialStoreDeps {
   db: AppDatabase;
 }
 
+function formatCredentialPayloadError(error: z.ZodError): string {
+  return error.issues
+    .map((issue) => {
+      const path = issue.path.length > 0 ? issue.path.join(".") : "payload";
+      return `${path}: ${issue.message}`;
+    })
+    .join("; ");
+}
+
+function parseStoredCredentialPayload(
+  connectorId: string,
+  kind: CredentialKind,
+  json: string,
+): StoredCredentialPayload {
+  let value: unknown;
+  try {
+    value = JSON.parse(json);
+  } catch {
+    throw new CredentialStoreReadError(connectorId, "Stored credential payload is not valid JSON.");
+  }
+  const parsed = storedCredentialPayloadSchema.safeParse({ kind, value });
+  if (!parsed.success) {
+    throw new CredentialStoreReadError(
+      connectorId,
+      `Stored credential payload failed schema validation: ${formatCredentialPayloadError(parsed.error)}`,
+    );
+  }
+  return parsed.data as StoredCredentialPayload;
+}
+
 export class CredentialStore {
   constructor(private readonly deps: CredentialStoreDeps) {}
 
@@ -99,8 +156,7 @@ export class CredentialStore {
       row.backend,
       Buffer.isBuffer(row.ciphertext) ? row.ciphertext : Buffer.from(row.ciphertext),
     );
-    const value = JSON.parse(json);
-    return { kind: row.kind, value } as StoredCredentialPayload;
+    return parseStoredCredentialPayload(connectorId, row.kind, json);
   }
 
   remove(connectorId: string): void {
diff --git a/tests/unit/credential-resolver.test.ts b/tests/unit/credential-resolver.test.ts
index d07ac68f..c01cf990 100644
--- a/tests/unit/credential-resolver.test.ts
+++ b/tests/unit/credential-resolver.test.ts
@@ -4,6 +4,7 @@ import { join } from "node:path";
 import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
 import { AppDatabase } from "../../src/main/database";
 import { CredentialStore } from "../../src/main/credentials/credential-store";
+import { CredentialStoreReadError } from "../../src/main/credentials/credential-store";
 import { CredentialResolver, CredentialError } from "../../src/main/credentials/credential-resolver";
 import { AppError } from "../../src/main/errors";
 
@@ -136,7 +137,7 @@ describe("CredentialResolver", () => {
       thrown = error;
     }
 
-    expect(thrown).toBeInstanceOf(CredentialError);
+    expect(thrown).toBeInstanceOf(CredentialStoreReadError);
     expect(thrown).toMatchObject({
       kind: "upstream",
       code: "CREDENTIAL_INVALID",
@@ -198,7 +199,7 @@ describe("CredentialResolver", () => {
       thrown = error;
     }
 
-    expect(thrown).toBeInstanceOf(CredentialError);
+    expect(thrown).toBeInstanceOf(CredentialStoreReadError);
     expect(thrown).toMatchObject({
       kind: "upstream",
       code: "CREDENTIAL_INVALID",
diff --git a/tests/unit/credential-store.test.ts b/tests/unit/credential-store.test.ts
index 85ac3670..b8f6e931 100644
--- a/tests/unit/credential-store.test.ts
+++ b/tests/unit/credential-store.test.ts
@@ -3,7 +3,7 @@ import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
 import { AppDatabase } from "../../src/main/database";
-import { CredentialStore } from "../../src/main/credentials/credential-store";
+import { CredentialStore, CredentialStoreReadError } from "../../src/main/credentials/credential-store";
 
 beforeAll(() => {
   // SecretVault throws unless safeStorage is available or this gate is set.
@@ -62,6 +62,78 @@ describe("CredentialStore", () => {
     }
   });
 
+  it("round-trips an oauth credential through the read schema", () => {
+    store.save("claude-pro", {
+      kind: "oauth",
+      value: {
+        refresh: "refresh-token",
+        access: "access-token",
+        expires: Date.now() + 60_000,
+        domain: "anthropic.com",
+      },
+    });
+
+    const decrypted = store.read("claude-pro");
+    expect(decrypted?.kind).toBe("oauth");
+    if (decrypted?.kind === "oauth") {
+      expect(decrypted.value.refresh).toBe("refresh-token");
+      expect(decrypted.value.access).toBe("access-token");
+      expect(decrypted.value.domain).toBe("anthropic.com");
+    }
+  });
+
+  it("rejects stored credentials whose decrypted payload does not match the row kind", () => {
+    const encrypted = db.vault.encrypt(JSON.stringify({ source: "literal", value: "sk-test-abcdefghij" }));
+    db.core.credentials.upsert({
+      connectorId: "amazon-bedrock",
+      kind: "aws",
+      backend: encrypted.backend,
+      ciphertext: encrypted.payload,
+      displayHint: "bad",
+      status: "active",
+    });
+
+    let thrown: unknown;
+    try {
+      store.read("amazon-bedrock");
+    } catch (error) {
+      thrown = error;
+    }
+
+    expect(thrown).toBeInstanceOf(CredentialStoreReadError);
+    expect(thrown).toMatchObject({
+      code: "CREDENTIAL_INVALID",
+      context: { connectorId: "amazon-bedrock" },
+    });
+    expect(thrown).toHaveProperty("message", expect.stringContaining("failed schema validation"));
+  });
+
+  it("rejects stored credentials whose ciphertext is not valid JSON", () => {
+    const encrypted = db.vault.encrypt("{not-json");
+    db.core.credentials.upsert({
+      connectorId: "anthropic",
+      kind: "api_key",
+      backend: encrypted.backend,
+      ciphertext: encrypted.payload,
+      displayHint: "bad",
+      status: "active",
+    });
+
+    let thrown: unknown;
+    try {
+      store.read("anthropic");
+    } catch (error) {
+      thrown = error;
+    }
+
+    expect(thrown).toBeInstanceOf(CredentialStoreReadError);
+    expect(thrown).toMatchObject({
+      code: "CREDENTIAL_INVALID",
+      context: { connectorId: "anthropic" },
+    });
+    expect(thrown).toHaveProperty("message", "Stored credential payload is not valid JSON.");
+  });
+
   it("removes a credential", () => {
     store.save("openai", { kind: "api_key", value: { source: "literal", value: "sk-test-abcdefghij" } });
     expect(store.list().some((row) => row.connectorId === "openai")).toBe(true);