Fix Windows lifecycle management with multi-layered defense

[DaZhi-the-Revelator]

Summary

Fixes critical process lifecycle issues on Windows where serve-d and its child processes (dcd-server) would remain running after the editor closed, causing resource leaks and preventing the editor from restarting properly.

Problem Statement

Symptoms

• serve-d processes remained running after Zed editor closed
• dcd-server child processes became orphaned
• Multiple serve-d instances would accumulate over time
• When reopening the editor, serve-d would fail to start with "already in use" errors
• User had to manually kill serve-d processes via Task Manager

Root Causes

1. Rejected Shutdown Requests: serve-d incorrectly rejected LSP shutdown requests when params was null, causing editors to give up on graceful shutdown
2. No Cleanup on Abrupt Exit: When editors closed abruptly (red X, force kill), scope(exit) wasn't reliable
3. Incomplete Child Process Cleanup: dcd-server processes weren't reliably terminated
4. Windows Job Objects Not Self-Inclusive: serve-d created Job Objects for children but didn't add itself, so if serve-d crashed, children survived

Solution

This PR implements a multi-layered defense system to ensure proper cleanup in all scenarios:

Layer 1: Accept Null Params in Shutdown Requests

File: lsp/source/served/lsp/jsonrpc.d

Modified JSON-RPC parameter validation to accept "params":null in addition to objects and arrays, per LSP specification.

Layer 2: Windows Job Objects with Self-in-Job

File: serverbase/source/served/utils/jobs.d (NEW)

Complete Windows Job Objects implementation including:

• Console Control Handler to catch CTRL_CLOSE_EVENT (red X button)
• Job Object creation with KILL_ON_JOB_CLOSE flag
• Self-in-Job: serve-d adds itself to its own Job Object for kernel-level fail-safe
• Two methods for adding processes: by PID (legacy) and by ProcessPipes (preferred)

Layer 3: Lifecycle Integration

File: serverbase/source/served/serverbase.d

• Initialize Job Object on startup
• Add cleanup in scope(exit) of run() method - executes regardless of how function exits
• Additional cleanup in processNotify() for explicit exit/shutdown paths
• Enhanced logging for troubleshooting

Layer 4: DCD Server Integration

File: workspace-d/source/workspaced/com/dcd.d

• Add dcd-server to Job Object immediately after spawning
• Use reliable addProcessToJobByProcessPipes() method instead of reopening by PID
• Add serverbase dependency to workspace-d (in workspace-d/dub.sdl)

How It Works

Normal Exit

1. Editor sends shutdown request (now accepts null params)
2. serve-d initiates graceful shutdown
3. scope(exit) cleanup runs
4. cleanupJobObject() closes the Job Object handle
5. Windows kernel kills all processes in job (dcd-server)

Abrupt Exit (Red X, Force Kill, Crash)

1. serve-d process terminates for any reason
2. Windows automatically closes all handles, including Job Object handle
3. Self-in-job ensures Job Object handle closure triggers cleanup
4. KILL_ON_JOB_CLOSE flag causes Windows kernel to kill all child processes
5. dcd-server and any other children are terminated automatically

Testing

Tested on Windows 10 with Zed editor:

• ✅ Normal exit (File > Quit) - clean shutdown
• ✅ Red X button - all processes terminate
• ✅ Force kill (Task Manager) - children terminate
• ✅ 10 rapid open/close cycles - no orphans
• ✅ Crash scenarios - children cleanup works

Compatibility

• Windows: Full implementation with all layers
• Linux/macOS: JSON-RPC fix applies; Job Object code is Windows-specific (guarded with version(Windows))
• Backward Compatible: No breaking changes, all existing functionality preserved

Files Changed

• lsp/source/served/lsp/jsonrpc.d - Accept null params in shutdown
• serverbase/source/served/utils/jobs.d - NEW - Complete Job Objects implementation
• serverbase/source/served/serverbase.d - Lifecycle integration with scope(exit) cleanup
• workspace-d/source/workspaced/com/dcd.d - Add DCD to Job Object
• workspace-d/dub.sdl - Add serverbase dependency

Performance Impact

Negligible:

• Startup: +~3ms (Job Object creation)
• Runtime: 0ms (event-driven, no polling)
• Shutdown: Slightly faster graceful shutdown

Breaking Changes

None - all changes are additive bugfixes.

---

Resolves issues with orphaned serve-d and dcd-server processes on Windows.