inheritDefaultEnv is not honored on IsolationSession or WSLc

[theelliotm]

Relevant area(s)

Windows

Brief description of your issue

#1153 gave LXC, Bubblewrap, and Seatbelt the schema-0.9 process.inheritDefaultEnv contract that #1120 shipped for the Windows ProcessContainer tiers. IsolationSession and WSLc were left out and still flatten the four states into two.

The contract the other backends now honor:

process.env	inheritDefaultEnv	Result
omitted	—	the backend default
[]	—	empty
["FOO=bar"]	false (default)	verbatim
["FOO=bar"]	true	layered over the default; a caller entry wins

IsolationSession (src/backends/isolation_session/common/src/process_options.rs:179-187) fetches proc_options.Environment() and inserts into it, so it behaves as permanently inheritDefaultEnv: true. A caller who asks for a verbatim environment — which is the default — silently gets the session''s full default environment merged in. IMap::Clear() is available for the replace case.

WSLc (src/backends/wslc/common/src/wsl_container_runner.rs:1490, src/backends/wslc/common/src/container_steps.rs:404) guards the SDK call with if !effective_env.is_empty(), flattening omitted and [] together. Whether WslcSetProcessSettingsEnvVariables replaces or augments the image environment is undocumented — wslcsdk.h:343 has no comment — so that needs to be established first. If it augments, Explicit may not be honorable and should be rejected rather than silently downgraded.

Both backends currently use ExecutionRequest::env_entries(), whose doc comment now names them as the remaining callers.

Steps to reproduce

1. Build with --features isolation_session.
2. Run a 0.9.0-alpha config against containment: "isolationsession" with process.env set to ["FOO=bar"] and no inheritDefaultEnv.
3. Have the command print its full environment.

Expected behavior

Only FOO is present — the environment is used verbatim, as it is on every other backend at 0.9.

Actual behavior

FOO is present alongside the isolation session''s entire default environment.