Third and last of #2860's agent-facing URL fallbacks. The operator's
ruling was "any special casing is done on the nix side - same binaries,
no hard coded fallback", so the default is deleted rather than replaced.
Every layer guessed the same wrong thing, and each guess was only ever
correct for a process sharing the host netns:
- nix/agent-modules/matrix.nix: matrixUrlDefault = localhost:8008, both
as the option's default and as a sentinel the daemon unit compared
against to decide whether to write HIVE_MATRIX_URL. Now nullOr str,
default null, the guard is != null, and the doc says what forge.url's
already says: null means "no matrix", not "guess one".
- nix/host-modules/hive-c0re/environment.nix: forwarded
http://127.0.0.1:<port> when no gatewayHost was set. hive-c0re shares
the host netns so it reads as harmless, but the value is handed to
agents, which do not -- there it names the agent itself. Now forwarded
only when there is a gateway vhost to name, matching the guard
HIVE_MATRIX_PUBLIC_URL already uses twelve lines below.
- hive-matrix-mcp: paths::DEFAULT_HOMESERVER was the same address
compiled in, so dropping the nix defaults alone would have left the
daemon dialling loopback inside the agent's own netns -- the very bug,
one layer down. homeserver_url() is now Option, and an account with no
homeserver is skipped with a log, exactly as one with no token is.
discover_token_accounts already refused to guess for the same reason.
Two comments taught the assumption back to the next reader ("shared host
netns means every agent container resolves localhost to the same
machine"); both now say which side of the netns boundary they describe.
MATRIX_HTTP keeps its value -- hive-c0re really does share the host
netns -- but no longer claims agents do.
Gated with nix eval against the extended agent-base config, as a pair:
with no url set the daemon unit carries no HIVE_MATRIX_URL, and with one
set it carries exactly that. Either check alone passes on a broken guard.
