Adds LB-pool-by-shared-name without introducing a new resource. The
existing `Llm.name` stays globally unique; a new optional `poolName`
column declares membership in a pool. Multiple Llms sharing a non-null
`poolName` stack into one load-balanced pool that the chat dispatcher
expands at request time.
Effective pool key = `poolName ?? name`. Solo rows (poolName=null) are
addressable as a "pool of 1" via their own name, so existing single-Llm
agents and YAMLs keep working unchanged. A solo row whose name happens
to match an explicit poolName joins the same pool — by design — so an
operator can transparently promote an existing Llm to pool seed.
Dispatcher (chat.service): prepareContext now resolves a randomly-
shuffled list of viable pool candidates (status != inactive) once per
turn. runOneInference and streamInference iterate the list on
transport-level failure (network, virtual publisher disconnect) until
one succeeds or the list is exhausted. Streaming failover only covers
"failed before first chunk" — once we've yielded text, we're committed
to that backend. Auth/4xx errors surfaced as result.status are NOT
retried; siblings with the same key/model would fail identically.
When the agent's pinned Llm is itself inactive but a sibling pool
member is up, dispatch transparently uses the sibling — that's the
whole point. When every member is inactive, prepareContext throws a
clear "No active Llm in pool '<key>' (pinned: <name>)" error rather
than letting the dispatcher's "exhausted" branch surface it.
Tests:
- 5 new chat-service tests for pool dispatch / failover / pinned-down /
all-inactive (chat-service.test.ts).
- 7 new db schema tests for the column, the unique-name invariant, the
fallback-to-name semantics, and the solo-name-joins-explicit-pool
edge case (llm-pool-schema.test.ts).
- mcpd 865/865 (was 860; +5), db pool-schema 7/7, no regressions.
Stage 2 (next): HTTP route /api/v1/llms/<name>/members + aggregate pool
stats on the existing single-Llm route, CLI POOL column + describe
block + --pool-name flag, yaml round-trip.
