A claude agent with useApiKey gets ANTHROPIC_API_KEY through
backendEnvironmentFile, but only the harness unit loaded that file;
hive-subagent-daemon loaded it for ACP agents alone. The daemon's nested
claude inherits the daemon's environment (hive-claude adds to it, never
clears it), and an api-key agent has no OAuth session in ~/.claude, so
its claude subagents started with no credentials.
hive-subagent-daemon now loads backendEnvironmentFile when the agent is
ACP (unchanged) or has useApiKey set. Module-eval covers the api-key
claude arm; the existing claude arm (file set, useApiKey unset) still
asserts no EnvironmentFile.
Closes#5088
a5448c81c4