`matrixAccounts` is meant to be the agent's full account list, but the
hive-internal `main` account was outside it: the nix module emitted only
the extras and `hive-matrix-daemon` prepended a `main` it synthesized
from the per-agent paths, with the option schema forbidding the name
outright.
nix/agent-modules/matrix.nix now declares `main` itself, as an ordinary
entry under `matrix.enable`, from the state-dir paths the module already
used for its token path-watcher (now a shared `stateDir` binding) plus
`matrix.url`. The whole set, `main` included, is serialized to
HIVE_MATRIX_ACCOUNTS.
accounts::configured therefore synthesizes `main` only when the parsed
list carries none, and otherwise takes the declared one verbatim —
hoisting it to index 0, since the daemon reads index 0 as the primary
and nix serializes an attrset, so `main` sorts wherever its key falls.
Declared xor synthesized: an agent whose harness predates this entry
keeps working, a current one gets its own, and there is no arrangement
where `main` is duplicated or missing.
The reserved-name assertion is replaced rather than dropped: the name
must now be legal (the module uses it), but `main`'s tokenFile stays
pinned to `<state>/matrix-token`, since hive-c0re provisions the
hive-internal token there and nowhere else — a retarget would evaluate
fine and then never restore. The other two fields are mkDefault and free
to override.
Refs #4475
c74249f371