[IsolationSession] State-aware E2E reads the real-exec malformed_id envelope from stdout after #1308 moved it to stderr #1324

Relevant area(s)

Windows

Brief description of your issue

The nightly windows-prerelease-isolation-session, x64, isolation-session job fails on a single assertion (69/70 passed):

[malformed_id (every id-consuming phase rejects an undecodable id)]
  FAIL: exec (real): error.code is 'malformed_id' (got '<no envelope>')

This is a stale test assertion, not a product defect. PR #1308 ("[WSLC] Stop state-aware exec failures from corrupting the output they report on") deliberately moved non-dry-run exec error envelopes from stdout to stderr, and updated the documented contract accordingly. It added a Parse-StderrEnvelope helper to the IsolationSession harness but applied it to only one of the two affected call sites.

The runtime is behaving exactly as documented in docs/state-aware-lifecycle/mxc-state-aware-sandbox-api.md:770:

tests/scripts/run_isolation_session_state_aware_tests.ps1:576 still reads the envelope from stdout for the real (non-dry-run) exec phase, so it sees <no envelope> and fails.

Evidence of the incomplete port — conversions applied in #1308 per harness:

Regression window is exact:

The IsolationSession backend suite runs only in Validation.Tests.Scheduled.yml — it requires the 1es-mxc-e2e-win-prerelease-isolationsesh-x64 self-hosted image and is not part of PR validation, which is why #1308 merged green.

Steps to reproduce

1. On a host with IsolationSession support, build the executor and run:

   tests/scripts/run_isolation_session_state_aware_tests.ps1
   

2. Observe the test group malformed_id (every id-consuming phase rejects an undecodable id).

The underlying invocation is a state-aware exec carrying a structurally invalid id:

{ "phase": "exec",
  "sandboxId": "iso:not-a-valid-payload",
  "process": { "commandLine": "cmd.exe /c echo unreachable" } }

Expected behavior

The harness should read the real exec error envelope from stderr, matching the contract documented at mxc-state-aware-sandbox-api.md:770 and the routing in src/core/wxc/src/main.rs (finalize_state_aware_outcome -> StateAwareExit::ExecError).

Only the real exec iteration of the loop is affected. start, stop, and deprovision are non-exec phases and correctly keep their envelope on stdout; exec --dry-run also correctly keeps it on stdout, and both are already passing.

Actual behavior

tests/scripts/run_isolation_session_state_aware_tests.ps1:576 parses stdout for all four phases:

$r = Invoke-StateAware -Request $req
Assert-True ($r.ExitCode -ne 0) "$phase (real): exit code is non-zero"
$envObj = Parse-Envelope -Stdout $r.Stdout          # <-- stderr for real exec
$code = if ($envObj) { $envObj.error.code } else { '<no envelope>' }
Assert-True ($code -eq 'malformed_id') "$phase (real): error.code is 'malformed_id' (got '$code')"

For the real exec iteration stdout is empty (the workload never ran — correctly refused at the validation hook), the envelope is on stderr, and the assertion reports <no envelope>. The suite throws at scripts/ci/run_backend_validation_tests.ps1:363 and fails the job.

Notes

• Parse-StderrEnvelope already exists in this harness (line 316); the fix is to use it for the exec iteration only.
• Worth auditing the remaining Parse-Envelope -Stdout sites in this harness for any other real-exec error path missed by the same port.
• Behavior is correct — the exec never ran, exited non-zero, and emitted a well-formed malformed_id envelope. Only the channel the test reads is wrong.