[PROVES EFT-3295 #1226] Abandon tests fail on main as it stands — do not merge

[jimmyp]

Purpose

The two abandon integration tests from #1226, plus only the empty stubs needed to make them compile and run. Behaviour-bearing code is left as no-ops:

• ScriptServiceV2.AbandonScriptAsync returns a status snapshot but never fires the abandon token.
• RunningScript has no abandon-token catch block; the script process keeps running until it exits naturally or the cancel kills it.
• The script-isolation mutex is NOT released on abandon.

The single real (non-stub) production change is the Hitman env-var check that makes the scenario reproducible: with TentacleDebugDisableProcessKill_UNSAFE_FOR_PRODUCTION set, cancel does not kill the script process, so the test reaches the abandon path instead of the cancel-just-killed-it path. Without that, the tests would not exercise the abandon contract at all.

Running the tests against this branch produces meaningful assertion failures that document the behaviour gap #1226 closes.

Test failures

Failed AbandonScript_WhenCancelFailsToKillProcess_ReturnsAbandonedExitCode(Listening,Latest,ScriptServiceV2) [33 s]
Error Message:
 System.Exception : Abandoned script did not reach Complete state within 30s

Failed AbandonScript_WhenCancelFailsToKillProcess_ReturnsAbandonedExitCode(Polling,Latest,ScriptServiceV2) [33 s]
Error Message:
 System.Exception : Abandoned script did not reach Complete state within 30s

Failed AbandonScript_ReleasesIsolationMutexEvenWhileProcessIsStillRunning(Listening,Latest,ScriptServiceV2) [2 m]
  (test hits IntegrationTestTimeout: the second FullIsolation script
   blocks waiting on a mutex the first script never released)

Failed AbandonScript_ReleasesIsolationMutexEvenWhileProcessIsStillRunning(Polling,Latest,ScriptServiceV2) [2 m]
  (test hits IntegrationTestTimeout: the second FullIsolation script
   blocks waiting on a mutex the first script never released)

Failed\!  - Failed: 4, Passed: 0, Skipped: 0, Total: 4

Files changed

File	What's in it
ClientScriptExecutionAbandon.cs	The two abandon integration tests (copied verbatim from #1226)
EnvironmentVariables.cs	Adds the TentacleDebugDisableProcessKill_UNSAFE_FOR_PRODUCTION constant
SilentProcessRunner.cs	Hitman.TryKillProcessAndChildrenRecursively early-returns when the env var is set, so the test can reproduce a "cancel can't kill" state
ScriptExitCodes.cs	Adds AbandonedExitCode = -48 (the value the test asserts on)
AbandonScriptCommandV2.cs	New contract DTO, no logic
IScriptServiceV2.cs / IAsyncClientScriptServiceV2.cs / IAsyncScriptServiceV2.cs	Adds the AbandonScript method signature to the three V2 interfaces so the contract compiles
ScriptServiceV2.cs	Server-side AbandonScriptAsync STUB: returns the current status snapshot WITHOUT firing any abandon token. This is the behaviour gap.
ITentacleClient.cs / TentacleClient.cs	Client-side AbandonScript method wired through the RPC executor; downstream is the no-op above
TentacleClientExtensionMethods.cs	Test-only helpers that let the test call tentacleClient.AbandonScript(scriptTicket, CT) etc. with a ScriptTicket instead of a CommandContext
ScriptServiceV2DecoratorBuilder.cs / TestDecoratorsAreCalledInTheCorrectOrder.cs	Test scaffolding extended to implement the new interface method (pass-through / NotImplementedException)

What's deliberately NOT here (and is on #1226):

• The abandon-token catch block in RunningScript that translates the token into AbandonedExitCode
• The workspace.Delete tolerance in ScriptServiceV2.CompleteScriptAsync
• The CapabilitiesServiceV2 advertisement of AbandonScriptV2
• The RunningScript.CreateAbandonable factories
• Test refactors and the SilentProcessRunner async migration

Not for merge

#1226 is the real PR with the real implementation. Close this one when #1226 lands.