refactor: address low-priority review follow-ups

- daemon-client RPC error path: stringify any non-null data.code instead
  of only forwarding strings. Preserves numeric codes from hypothetical
  future proxies/servers; for first-party daemon today this is a no-op
  since handlers already emit strings.
- errors.ts: expand AppErrorCode comment to call out the exhaustiveness
  tradeoff of the '(string & {})' widening for SDK consumers.

Author: thymikee

src/daemon-client.ts

@@ -977,7 +977,7 @@ async function sendHttpRequest(
               reject(
                 new AppError(
                   toAppErrorCode(
-                    typeof data.code === 'string' ? data.code : undefined,
+                    data.code != null ? String(data.code) : undefined,
                     'COMMAND_FAILED',
                   ),
                   String(data.message ?? parsed.error.message ?? 'Daemon RPC request failed'),

src/utils/errors.ts

@@ -15,8 +15,11 @@ export type KnownAppErrorCode =
   | 'AMBIGUOUS_MATCH'
   | 'UNKNOWN';
 
-// Accepts any string so wire codes from the daemon are preserved verbatim; the
-// `(string & {})` form keeps IDE autocomplete of the known codes.
+// Intentionally widened with `(string & {})` so daemon-originated codes pass
+// through verbatim without requiring the SDK union to be updated first. Known
+// codes still autocomplete in IDEs. Tradeoff: `switch (err.code)` is no longer
+// exhaustive by construction — SDK consumers handling unknown codes should
+// include a default branch.
 export type AppErrorCode = KnownAppErrorCode | (string & {});
 
 export function toAppErrorCode(