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.
Lint: eslint --fix over the merge-crossed projection/command files (arrow
parens, trailing commas, unnecessary assertions), Extract<> replaces the
keyof-map & string intersections no-redundant-type-constituents rejects,
the fold-adapter's merge loop drops its non-null assertions for a
bounds-carrying cursor, one JSDoc line wrapped under max-len (api-catalog
regenerated). Snapshots: the four TUI goldens re-recorded for the merged
event-count shift (the durable command lifecycle adds one event to the
seeded diagnostics log). The headless advanced-toolchain snapshot passes
on CI and fails locally in this sandbox both with and without these
changes (30s child timeout — environment-bound, tracked in the ledger).
