Track and clean up detached port-forward processes across envrc and eval workflows #330

Summary

Make detached port-forward lifecycle handling consistent across --envrc and --eval workflows.

Requested by @mclasmeier during review of PR #329.

Verified behavior

At PR #329's base revision (257fffb9faff7e349280e8a3d960a1dc39968538), the deployer reads ROXIE_PORT_FORWARD_PID, retains the PID returned by StartDetached, exports it to the envrc file, and uses it during teardown.

However, configureCentralEndpoint starts a new detached forwarder and overwrites the previously tracked PID without stopping the previous process. This replacement-cleanup gap predates PR #329.

PR #329 adds a separate gap in roxie shell --eval: it discards the PID returned by StartDetached, and printExports does not export ROXIE_PORT_FORWARD_PID. The current shell can therefore retain a stale PID or have no PID for the new forwarder.

Required changes

• Retain and export the PID of the detached forwarder created by roxie shell --eval.
• Define consistent replacement handling for an existing tracked forwarder in both workflows.
• After the replacement forwarder is ready, stop the previously tracked forwarder before replacing its tracked PID.
• Preserve the existing forwarder and its tracking if replacement startup fails.
• Ensure teardown can stop the currently tracked detached forwarder.
• Handle absent, invalid, or already-exited tracked PIDs without failing the workflow. Account for stale PID safety.

Affected areas

• cmd/shell.go: detached startup in eval mode.
• cmd/subshell.go: environment exports.
• internal/deployer/deploy_via_operator.go: detached startup and PID replacement.
• internal/deployer/deployer.go: PID import, envrc export, and teardown.
• internal/portforward/portforward.go: detached process lifecycle.
• tests/e2e/basic_test.go: existing envrc port-forward coverage.

Acceptance criteria

• Both envrc and eval output identify the newly created detached forwarder with ROXIE_PORT_FORWARD_PID.
• Repeated setup with a previously tracked forwarder does not leave that forwarder untracked and running after successful replacement.
• Failed replacement does not stop the previous working forwarder.
• Teardown stops the currently tracked forwarder.
• Regression coverage includes PID export, successful replacement, failed replacement, and stale or missing PID handling.

References

• PR: Implement --eval as alternative to sub-shell mode and envrc #329
• Review discussion: Implement --eval as alternative to sub-shell mode and envrc #329 (comment)