fix(ai): drop empty-string env values before merge so they can't clobber config keys (#1249)

Claude Code injects ANTHROPIC_API_KEY='' to neuter subprocess LLM calls; an
unconditional process.env spread let that empty string override a valid
config.json key, breaking every gateway op with NO_ANTHROPIC_API_KEY. Filter
'' / undefined before the merge; '0' and 'false' are preserved.

src/core/ai/build-gateway-config.ts

@@ -61,6 +61,18 @@ export function buildGatewayConfig(c: GBrainConfig): AIGatewayConfig {
     chat_model: c.chat_model,
     chat_fallback_chain: c.chat_fallback_chain,
     base_urls: { ...envBaseUrls, ...(c.provider_base_urls ?? {}) }, // config wins over env
-    env: { ...envFromConfig, ...process.env }, // process.env wins
+    // #1249: process.env still wins over the config-plane fallback, BUT only for
+    // keys that carry a real value. Claude Code (and some launchers) inject
+    // ANTHROPIC_API_KEY='' to neuter subprocess LLM calls; an unconditional
+    // `...process.env` lets that empty string clobber a valid config.json key, so
+    // every gateway op then throws NO_ANTHROPIC_API_KEY. Drop empty-string /
+    // undefined entries before the merge. Only '' and undefined are dropped —
+    // '0' and 'false' are legitimate values and survive.
+    env: {
+      ...envFromConfig,
+      ...Object.fromEntries(
+        Object.entries(process.env).filter(([, v]) => v !== undefined && v !== ''),
+      ),
+    },
   };
 }

test/ai/build-gateway-config.test.ts

@@ -85,3 +85,35 @@ describe('buildGatewayConfig env-baseURL passthrough', () => {
     );
   });
 });
+
+describe('buildGatewayConfig env empty-string clobber guard (#1249)', () => {
+  test('an empty-string process.env value does NOT clobber a valid config-plane key', async () => {
+    // Claude Code injects ANTHROPIC_API_KEY='' to neuter subprocess LLM calls.
+    await withEnv({ ANTHROPIC_API_KEY: '' }, async () => {
+      const cfg = buildGatewayConfig({
+        anthropic_api_key: 'sk-config-plane',
+      } as unknown as GBrainConfig);
+      expect(cfg.env.ANTHROPIC_API_KEY).toBe('sk-config-plane');
+    });
+  });
+
+  test('a real process.env value still wins over the config-plane fallback', async () => {
+    await withEnv({ ANTHROPIC_API_KEY: 'sk-env-plane' }, async () => {
+      const cfg = buildGatewayConfig({
+        anthropic_api_key: 'sk-config-plane',
+      } as unknown as GBrainConfig);
+      expect(cfg.env.ANTHROPIC_API_KEY).toBe('sk-env-plane');
+    });
+  });
+
+  test("legitimate falsy-but-present values ('0' / 'false') are preserved, not dropped", async () => {
+    await withEnv(
+      { GBRAIN_TEST_ZERO_VAL: '0', GBRAIN_TEST_FALSE_VAL: 'false' },
+      async () => {
+        const cfg = buildGatewayConfig(baseConfig);
+        expect(cfg.env.GBRAIN_TEST_ZERO_VAL).toBe('0');
+        expect(cfg.env.GBRAIN_TEST_FALSE_VAL).toBe('false');
+      },
+    );
+  });
+});