Every one encoded something that had since changed, or depended on a package
this checkout does not have. Each was read against the code before being
touched, and two turned out to be real defects:

- ggml_rpc.available() returned the bare exception, so a model naming RPC
  servers refused with "No module named 'llama_cpp'" -- true, but naming
  neither the capability nor the fix. Every refusal now says both.
- building a BitsAndBytesConfig without bitsandbytes installed raised
  PackageNotFoundError from importlib.metadata. The IMPORT is guarded; only
  construction consults metadata, so a Vulkan-only or CPU install got a
  traceback naming neither the model nor the setting. Now reported as loudly
  as an unrecognised mode, because the consequence is the same: full precision.
  The 2-bit path already did this for optimum-quanto.

The rest were stale expectations:
- the broker protocol inverted (the client speaks first: one read, no separate
  ack), gained keepalive pings and an immediate `pending` frame, and renamed
  its stream envelopes to chunk/done. Added coverage for the status gate that
  suppresses `pending`, which nothing tested.
- /admin/api/status was removed in def78c18 and the front owns status now, so
  its on-the-way-out coercion had nothing left to coerce. Retargeted to the
  invariant that survives: entries are well formed when MADE.
- main()'s default boot became the front/engine split, so the app instance
  reaches uvicorn in the ENGINE path now.

And four were brittle rather than wrong, each failing for something it was not
testing: a 4000-character source window that stopped covering the raise when a
comment was added above it (now the function's own source); a hand-written
Config stand-in that broke on every new section the product read (now falls
back to the real defaults, per section); a generic `selectedId` used as a proxy
for "the pipeline UI is gone" that unrelated code then adopted; and a pool test
that needed pypdfium2 to exercise what a BUSY pool does.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014T3rZnLhydX9QqUcfBbqLu