The route a new session starts from was frozen into the gateway's
composition entry, so switching models in a conversation reached only that
conversation and every later session went back to the shipped default.
The gateway now owns an `api-gateway` settings section: the entry is the
base layer and the user document layers over it, so `session.selectModel`
records an accepted switch as the default for the next session. The write
is wholesale rather than a merge — switching to a model with no reasoning
effort has to clear a stored one — and a storage failure is reported
without undoing the switch, which already applies to its own session.
`targetFor` now resolves its tiers on every read instead of seeding once:
an explicit selection, else the session's own logged request header, else
the live default. That is what keeps a session that has run a turn deriving
its route from its log forever after, while a session still blank — New
Session reuses one rather than minting another — starts from a default
saved after it was created.
The rename impl narrows on SessionTitleInvalidError: only an
empty-normalizing title maps to title-invalid (its message renders verbatim
in the rename dialog alert), while liveness/disposal races fall to internal;
the absent-service message trims to one presentable sentence. rpc-schemas
gains the title-invalid accept/missing-details lines; cosmetic ordering
(type-only import comment, tsconfig reference, schema import order) restored.
New unary method in RpcMethodMap with the title-invalid error code; the impl
resolves the agent (cold sessions resume first) and delegates to
ctx.sessionTitle.rename, returning the normalized title plus its event seq so
clients settle the title projection cell ahead of the push frame. session.fork
stays on the reserved-seam list.
