1 files changed, 51 insertions, 1 deletions
diff --git a/src/auth_manager.zig b/src/auth_manager.zig
index 5504807..e91339b 100644
--- a/src/auth_manager.zig
+++ b/src/auth_manager.zig
@@ -166,6 +166,31 @@ pub const AuthManager = struct {
     }
 };
 
+/// When an auth exchange returns only an origin/base host but the provider's
+/// configured base_url carries an API path segment (e.g. Anthropic providers
+/// configured as `.../v1`), preserve that path on the override. This keeps
+/// dynamic-host exchanges from accidentally dropping a required version prefix.
+fn mergeBaseUrlOverride(
+    arena: Allocator,
+    style: panto.APIStyle,
+    provider_base_url: []const u8,
+    override_base_url: ?[]const u8,
+) ![]const u8 {
+    const over = override_base_url orelse return provider_base_url;
+    if (style != .anthropic_messages) return over;
+
+    const prov_uri = std.Uri.parse(provider_base_url) catch return over;
+    const over_uri = std.Uri.parse(over) catch return over;
+    const prov_path = prov_uri.path.percent_encoded;
+    const over_path = over_uri.path.percent_encoded;
+
+    const prov_has_path = prov_path.len > 0 and !std.mem.eql(u8, prov_path, "/");
+    const over_has_path = over_path.len > 0 and !std.mem.eql(u8, over_path, "/");
+    if (!prov_has_path or over_has_path) return over;
+
+    return try std.fmt.allocPrint(arena, "{s}{s}", .{ over, prov_path });
+}
+
 /// Patch a resolved credential into the live provider config: set the bearer/
 /// key, override base_url when the credential supplies one, and merge the
 /// provider's static `extra_headers` with the auth-derived ones (into `arena`).
@@ -181,7 +206,7 @@ fn patchCredential(
     @memcpy(merged[0..prov.extra_headers.len], prov.extra_headers);
     @memcpy(merged[prov.extra_headers.len..], cred.extra_headers);
 
-    const base_url = cred.base_url_override orelse prov.base_url;
+    const base_url = try mergeBaseUrlOverride(arena, prov.style, prov.base_url, cred.base_url_override);
     switch (live.provider) {
         .openai_chat => |*c| {
             c.api_key = cred.api_key;
@@ -239,6 +264,31 @@ test "patchCredential: injects key, base_url override, merged headers" {
     try t.expectEqualStrings("chatgpt-account-id", live.provider.openai_chat.extra_headers[1].name);
 }
 
+test "patchCredential: anthropic preserves provider path on base_url override" {
+    var aa = std.heap.ArenaAllocator.init(t.allocator);
+    defer aa.deinit();
+    const arena = aa.allocator();
+
+    const prov: config_file.Provider = .{
+        .name = "copilot-anthropic",
+        .style = .anthropic_messages,
+        .base_url = "https://api.individual.githubcopilot.com/v1",
+        .auth_name = "github_copilot",
+    };
+    var live: panto.Config = .{ .provider = .{ .anthropic_messages = .{
+        .api_key = "",
+        .base_url = prov.base_url,
+        .model = "claude-sonnet-4-5",
+    } } };
+    const cred: panto.ResolvedCredential = .{
+        .api_key = "exchanged-token",
+        .base_url_override = "https://api.individual.githubcopilot.com",
+    };
+    try patchCredential(&live, &prov, cred, arena);
+
+    try t.expectEqualStrings("https://api.individual.githubcopilot.com/v1", live.provider.anthropic_messages.base_url);
+}
+
 test "resolveInto: api_key auth is a no-op" {
     const a = t.allocator;
     var env = std.process.Environ.Map.init(a);