fix: isolate detached command context from parent cancellation

[mason5052]

Description of the Change

Problem

Detached terminal commands (detach=true) inherit the parent context. When the parent context is canceled (e.g., agent delegation timeout after ~2.5 minutes), the detached goroutine's ctx.Done() fires in getExecResult and kills the background command, even though the command has its own timeout (300-1200 seconds).

This makes agent delegation effectively unusable for commands that take more than ~2.5 minutes (which is most penetration testing tasks like nmap scans).

Closes #176

Solution

Use context.WithoutCancel(ctx) (Go 1.21+) for the detached goroutine. This:

• Preserves context values (tracing spans, logrus fields, observability data)
• Prevents parent cancellation from propagating to the background command
• Keeps the command's own timeout working (context.WithTimeout in getExecResult)

Non-detached commands are unchanged -- they still use the original ctx and respect parent cancellation as before.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Areas Affected

• Core Services (Backend API)

Testing and Verification

Test Configuration

• PentAGI Version: master
• Go Version: 1.24

Test Steps

1. Confirmed context.WithoutCancel is available in Go 1.24 (introduced in Go 1.21)
2. Verified non-detached path (last line of ExecCommand) still uses original ctx
3. Verified detached goroutine now uses isolated context with own timeout
4. Confirmed context values (observability, logging via t.tlp.PutMsg) are preserved through WithoutCancel
5. Verified getExecResult's defer cancel() still prevents goroutine leak

Security Considerations

No security impact. The change only affects context propagation for background commands. Commands still terminate when their own timeout expires.

Checklist

• My code follows the project's coding standards
• All new and existing tests pass
• I have run go fmt and go vet
• Security implications considered
• Changes are backward compatible

[Copilot]

Pull request overview

Fixes detached terminal commands (detach=true) being prematurely canceled when the parent context is canceled (e.g., agent delegation timeout), by isolating the detached goroutine’s context from parent cancellation while preserving context values.

Changes:

• Create a detached context via context.WithoutCancel(ctx) for background execution.
• Use the detached context when waiting for exec results in the detached goroutine.

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[Copilot]

The new detached execution behavior (using context.WithoutCancel) isn’t covered by tests. Since other tools in this package have unit tests, consider adding a terminal ExecCommand test that cancels the parent ctx and asserts the detached goroutine continues (e.g., via a mock dockerClient that would otherwise abort when ctx.Done() closes), while the command still stops on its own timeout.

[mason5052]

Valid suggestion. However, writing a meaningful test for this requires mocking the Docker client (ContainerExecCreate, ContainerExecAttach, etc.) and verifying goroutine behavior under cancellation -- which is fairly involved and would require test infrastructure that does not exist yet in this package. For a 2-line bugfix that uses an idiomatic Go pattern (context.WithoutCancel), I think the current verification (manual code review + go vet + build) is proportionate. Happy to add tests in a follow-up PR if the maintainers prefer.