Add test case for multiple indexes on the same realm (#11080)

A test case for https://github.com/astral-sh/uv/pull/11074 (and related
issues)

crates/uv/tests/it/lock.rs

@@ -8305,6 +8305,56 @@ fn lock_env_credentials() -> Result<()> {
     Ok(())
 }
 
+/// Test solving for packages that are pinned to separate indexes in the same realm.
+/// This requires the credentials to be cached at the URL-level instead of the realm-level, or
+/// credentials for one index will be used for both indexes and the request will fail.
+#[test]
+fn lock_multiple_indexes_same_realm_different_credentials() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "foo"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig", "anyio"]
+
+        [tool.uv.sources]
+        iniconfig = { index = "internal-proxy-heron" }
+        anyio = { index = "internal-proxy-eagle" }
+
+        [[tool.uv.index]]
+        name = "internal-proxy-heron"
+        url = "https://pypi-proxy.fly.dev/basic-auth-heron/simple"
+
+        [[tool.uv.index]]
+        name = "internal-proxy-eagle"
+        url = "https://pypi-proxy.fly.dev/basic-auth-eagle/simple"
+        "#,
+    )?;
+
+    // Provide credentials via environment variables.
+    uv_snapshot!(context.filters(), context.lock()
+        .env(EnvVars::index_username("INTERNAL_PROXY_HERON"), "public")
+        .env(EnvVars::index_password("INTERNAL_PROXY_HERON"), "heron")
+        .env(EnvVars::index_username("INTERNAL_PROXY_EAGLE"), "public")
+        .env(EnvVars::index_password("INTERNAL_PROXY_EAGLE"), "eagle"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: Missing version constraint (e.g., a lower bound) for `iniconfig`
+    warning: Missing version constraint (e.g., a lower bound) for `anyio`
+    error: Failed to fetch: `https://pypi-proxy.fly.dev/basic-auth-heron/files/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl.metadata`
+      Caused by: HTTP status client error (401 Unauthorized) for url (https://pypi-proxy.fly.dev/basic-auth-heron/files/packages/ef/a6/62565a6e1cf69e10f5727360368e451d4b7f58beeac6173dc9db836a5b46/iniconfig-2.0.0-py3-none-any.whl.metadata)
+    "###);
+
+    Ok(())
+}
+
 /// Resolve against an index that uses relative links.
 #[test]
 fn lock_relative_index() -> Result<()> {