Full isolation still let get_runtime_dir() consume the ambient XDG_RUNTIME_DIR, so yams-daemon.status.json landed outside the temp root. Relocate XDG_RUNTIME_DIR (POSIX) and APPDATA/LOCALAPPDATA/USERPROFILE (Windows) under the run root, and scrub YAMS_EMBED_BACKEND, YAMS_PREFERRED_MODEL, YAMS_RERANKER_MODEL and YAMS_EMBED_DIM, which ConfigResolver ranks above TOML, so the generated config is deterministic. Apply the same to ingestion_e2e_bench and extend the isolation test with a decoy runtime dir and model overrides.
Signed-off-by: trvon <me@trevon.dev>
DaemonHarness only relocated state when isolateState/isolateConfig were set,
and even then left HOME, XDG_DATA_HOME, XDG_CACHE_HOME and ambient
YAMS_DAEMON_SOCKET_PATH/YAMS_STORAGE/YAMS_DATA_DIR visible to the daemon, so a
run could still resolve a developer's config, data and cache.
Add DaemonHarnessOptions::isolateEnvironment (and DaemonHarness::isolatedOptions())
which implies isolateState and isolateConfig, points HOME and every XDG base
directory at the run's temp root, and scrubs the ambient config/data/socket
variables for the daemon's lifetime, restoring them through ScopedEnvVar RAII.
The new Catch2 case exports a decoy config.toml (distinctive data_dir marker) and
decoy XDG/HOME/YAMS_* values, then asserts the daemon's config path, data dir and
every ambient path resolver stay under the temp root, the decoy is never read or
populated, and the ambient environment is restored after stop.
Signed-off-by: trvon <me@trevon.dev>
