Make the libvirt trace compact: libvirt API names, one error field, terse test output

The first live run showed the trace working but noisy: testr printed
ts/level/msg and the per-run constants on every line, the error text
appeared twice, host appeared twice on image-cache lines, and the Go
method name was less useful than the libvirt function it maps to.

The tracer now logs rpc=virDomainLookupByName (go-libvirt's names are the
public API names without the vir prefix), error plus libvirtError (code
name) and libvirtCode, and image.go stops re-adding host. The integration
test replaces testr with a compact logr sink: time, logger name, the rpc
as headline, then fields, with provider/host/name omitted since the first
line of the run states them. Docs and execution log updated.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/plans-executions/2026-09-10-0805-kvm-libvirt-tracing.md

@@ -55,3 +55,46 @@ Worth noting: the live run (`make test-integration-kvm` against beelink)
 had not happened when this was written; it is what Step 7 of the KVM
 provider plan is waiting on, and its output is the acceptance test for
 this feature. Expected shape is in the plan's Verification section.
+
+## Revision after the first live run — less noise, libvirt names
+
+The first live run on beelink showed the trace working but hard to read:
+`testr` printed `"ts"`, `"level"`, `"msg"` and the three per-run
+constants on every line, the error text appeared twice (`error` and
+`libvirtMessage`), `host` appeared twice on image-cache lines (the
+logger already carried it), and `method=DomainLookupByName` was
+go-libvirt's name rather than something to look up in libvirt's docs.
+The user asked for "less verbose but more informative". Changes:
+
+- The tracer's headline field is now `rpc=virDomainLookupByName`: the
+  public libvirt API function, which go-libvirt's method names are
+  exactly minus the `vir` prefix (they come from the same
+  `remote_protocol.x`). Not gRPC, for the record: libvirt's own
+  XDR-based RPC over the forwarded unix socket.
+- Errors are one `error` field plus `libvirtError=ErrNoDomain` and
+  `libvirtCode=42`; `libvirtMessage` is gone from both the tracer and
+  `logAPIError`, since it is the error text.
+- `image.go` no longer adds `host` to lines whose logger has it.
+- The integration test replaces `testr` with a small `compactSink`
+  (`logr.LogSink` plus `GetCallStackHelper`, so `t.Log` still
+  attributes lines to `trace.go`): `HH:MM:SS.mmm libvirt
+  virDomainCreate domain=… duration=… error=… libvirtError=…`. The
+  `rpc` value becomes the headline, `provider`/`host`/`name` are
+  dropped (the run's first `t.Log` line states them), and values with
+  spaces are quoted. Production zap output is unchanged apart from the
+  field renames; structured logs are meant to repeat context.
+
+Previewed by driving the sink through the fake provider with an
+injected `DomainCreate` failure (a throwaway integration-tagged test,
+not committed):
+
+```
+trace.go:55: 09:04:33.165 libvirt virDomainLookupByName domain=proxy-abc123def456ghij duration=4µs error="Domain not found: …" libvirtError=ErrNoDomain libvirtCode=42
+trace.go:55: 09:04:33.165 libvirt virStorageVolUpload pool=default volume=proxy-abc123def456ghij-seed.iso offset=0 length=0 duration=71µs
+kvm.go:262:  09:04:33.165 kvm seed volume uploaded volume=proxy-abc123def456ghij-seed.iso bytes=45056
+trace.go:55: 09:04:33.165 libvirt virDomainCreate domain=proxy-abc123def456ghij duration=0s error="internal error: process exited…" libvirtError=ErrResourceBusy libvirtCode=87
+```
+
+Worth noting: `length=0` on `virStorageVolUpload` is what the provider
+passes (libvirt reads to EOF); the following `seed volume uploaded`
+line has the byte count.