A credential's models or budget change without the key; a new provider or base URL needs it again (openvibe-contracts 0.73.0 -> 0.74.0, ai.credential-put@1 api_key optional after the first put). A key never follows a new endpoint on its own: 400 credential.key_required. test/credentials.test.js covers both. npm test passes.

ddiff --git a/package-lock.json b/package-lock.json
iindex 84007e3..aef230d 100644
---- a/package-lock.json
++++ b/package-lock.json
@@@ -13,7 +13,7 @@
          "better-sqlite3": "^11.10.0",
          "dotenv": "^16.4.7",
          "express": "^4.21.2",
--        "openvibe-contracts": "https://codeload.github.com/OpenVibers/OpenVibe.Contracts/tar.gz/refs/tags/v0.73.0",
++        "openvibe-contracts": "https://codeload.github.com/OpenVibers/OpenVibe.Contracts/tar.gz/refs/tags/v0.74.0",
          "openvibe-sdk": "https://codeload.github.com/OpenVibers/OpenVibe.SDK/tar.gz/refs/tags/v0.11.0",
          "openvibe-shared": "https://codeload.github.com/OpenVibers/OpenVibe.Shared/tar.gz/refs/tags/v1.22.0"
        },
@@@ -1395,9 +1395,9 @@
        }
      },
      "node_modules/openvibe-contracts": {
--      "version": "0.73.0",
--      "resolved": "https://codeload.github.com/OpenVibers/OpenVibe.Contracts/tar.gz/refs/tags/v0.73.0",
--      "integrity": "sha512-SPgU/Ys9TLa8K+++V38C3uK50hNXXUeSPrIyWBT9HdY7eOsE/dnNRZqQnuUzihHOK22aQI15bRBE7u944tW0WA==",
++      "version": "0.74.0",
++      "resolved": "https://codeload.github.com/OpenVibers/OpenVibe.Contracts/tar.gz/refs/tags/v0.74.0",
++      "integrity": "sha512-ZwlzNihXHXd/qEzBqzsmu5sPZLMS2LUcaX9f3eJcqFYMfhrXzqcmQYbRzLVxN8UvAgDTUiH9WIcTdblPmflNmA==",
        "license": "AGPL-3.0-only",
        "dependencies": {
          "ajv": "^8.17.1",
ddiff --git a/package.json b/package.json
iindex a6d3b49..bd4f6ea 100644
---- a/package.json
++++ b/package.json
@@@ -19,7 +19,7 @@
      "better-sqlite3": "^11.10.0",
      "dotenv": "^16.4.7",
      "express": "^4.21.2",
--    "openvibe-contracts": "https://codeload.github.com/OpenVibers/OpenVibe.Contracts/tar.gz/refs/tags/v0.73.0",
++    "openvibe-contracts": "https://codeload.github.com/OpenVibers/OpenVibe.Contracts/tar.gz/refs/tags/v0.74.0",
      "openvibe-sdk": "https://codeload.github.com/OpenVibers/OpenVibe.SDK/tar.gz/refs/tags/v0.11.0",
      "openvibe-shared": "https://codeload.github.com/OpenVibers/OpenVibe.Shared/tar.gz/refs/tags/v1.22.0"
    },
ddiff --git a/server/credentials.js b/server/credentials.js
iindex 3ea192a..2c70b31 100644
---- a/server/credentials.js
++++ b/server/credentials.js
@@@ -82,8 +82,13 @@ function createCredentials({ db, config, clock = { now: () => Date.now() } }) {
          const v = validate('ai.credential-put@1', body);
          if (!v.valid) throw new AiError(422, 'input.invalid', 'body does not match ai.credential-put@1', { errors: v.errors });
          const at = iso(clock.now());
--        const key = String(body.api_key);
          const prev = row(owner, subject);
++        // The stored key stays for a change of models or budget; a new provider or endpoint needs the key again.
++        const sameEndpoint = prev && prev.provider === body.provider && (prev.base_url || null) === (body.base_url || null);
++        if (body.api_key == null && !sameEndpoint) {
++            throw new AiError(400, 'credential.key_required', prev ? 'enter the key again to change the provider or its address' : 'api_key is required the first time');
++        }
++        const key = body.api_key != null ? String(body.api_key) : open(prev.key_enc, `${owner}|${subject}`);
          db.prepare(`INSERT INTO subject_credentials (owner, subject, provider, base_url, key_enc, key_hint, models, budget_usd_day, created_at, updated_at)
                      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
                      ON CONFLICT(owner, subject) DO UPDATE SET provider = excluded.provider, base_url = excluded.base_url, key_enc = excluded.key_enc,
ddiff --git a/test/credentials.test.js b/test/credentials.test.js
iindex f7298e9..e338c32 100644
---- a/test/credentials.test.js
++++ b/test/credentials.test.js
@@@ -42,6 +42,11 @@ t.test('store, read without the key, refuse other services', async () => {
      assert.ok(validate('ai.credential@1', r.body).valid, JSON.stringify(validate('ai.credential@1', r.body).errors));
      const row = h.db.prepare('SELECT key_enc FROM subject_credentials WHERE owner = ? AND subject = ?').get('live', DANA);
      assert.ok(row.key_enc.startsWith('v1:') && !row.key_enc.includes(API_KEY), 'encrypted at rest');
++    // A models change keeps the stored key; a new endpoint needs it again.
++    r = await request(h.base, 'PUT', `/api/v1/credentials/${DANA}`, { tok: live, body: { provider: 'openai', base_url: 'https://llm.example.com/v1', models: { chat: 'gpt-4o-mini', vision: 'gpt-4o' }, budget_usd_per_day: 0.003 } });
++    assert.deepStrictEqual([r.status, r.body.key_hint, r.body.models.vision], [200, '…WXYZ', 'gpt-4o']);
++    r = await request(h.base, 'PUT', `/api/v1/credentials/${DANA}`, { tok: live, body: { provider: 'openai', base_url: 'https://attacker.example/v1' } });
++    assert.deepStrictEqual([r.status, r.body.code], [400, 'credential.key_required']);
      r = await request(h.base, 'GET', `/api/v1/credentials/${DANA}`, { tok: tools });
      assert.strictEqual(r.status, 404, 'another service does not see it');
      // A row moved to another owner does not decrypt: the key is bound to owner and subject.