Platform differences between Windows and macOS (beyond the sandbox)

[lIang70]

Background

The Windows desktop build now compiles (Wails v2.15, wails build -platform windows/amd64). Besides the known sandbox difference (Windows runs under
sandboxlocal with no OS-level isolation like seatbelt/bwrap), the current
code has the following platform differences between Windows and macOS.
Recording them here for future alignment.

Differences

1. Interactive terminal sessions (PTY) unavailable

• flowcraft's sandbox/session_other.go (//go:build !unix) returns
  NotAvailable directly: Windows has no pty, process groups, or signal
  delivery.
• As a result, execd does not advertise the pty capability
  (internal/execd/server.go Capabilities); on Windows commands run through
  pipes only, with no TTY interactive sessions.
• Expectation: define an explicit degradation path in the short term; evaluate
  ConPTY later (suggested as a separate follow-up issue).

2. execd graceful shutdown degrades

• stop() in internal/execd/fork.go first sends SIGTERM and waits for a
  graceful exit; Windows os.Process.Signal only supports Kill, so SIGTERM is
  ignored and the child is force-killed after 3 seconds.
• Result: in-process session cleanup does not run (the socket is removed by
  the parent, so functionality is unaffected, but cleanup semantics differ
  from Unix).

3. Parent-death watchdog never fires

• watchParent in execd_main.go relies on Unix reparenting: after the parent
  dies, os.Getppid() changes. On Windows, Getppid reads ParentProcessID
  from the process entry, which does not change after the parent exits, so the
  watchdog never triggers.
• Result: after a parent crash, the execd child can leak (on Unix it exits on
  its own).
• Suggestion: use a Job Object on Windows, or poll for parent liveness, to
  replace this mechanism.

4. Desktop window chrome

• macOS: hidden inset title bar + traffic-light alignment + disabled scroll
  elasticity (mac_window_darwin.go).
• Windows: standard title bar (mac_window_other.go no-op). Cosmetic only; no
  functional impact.

5. Builtin plugin directory layout

• macOS: .app/Contents/Resources/plugins; Windows/Linux: plugins/ next to
  the executable (BuiltinPluginRoot in internal/plugins/runtime/runtime.go).

6. Plugin binary signing

• macOS ad-hoc codesigns plugin binaries (signAdHoc in
  internal/plugins/plugin.go); no-op on Windows.

7. Open file/directory command

• open (macOS) vs cmd /c start (Windows) (openCommand in
  internal/desktop/bindings.go).

8. Rendering engine

• macOS uses WKWebView (WebKit); Windows uses WebView2 (Chromium). Same React
  frontend, but minor differences in fonts, scrolling, and compatibility
  behavior.

9. Paths

• Data dir is ~/.opencraft on both (i.e. C:\Users\<user>\.opencraft on
  Windows).
• The execd socket lives under the user cache dir: ~/Library/Caches on
  macOS, %LocalAppData% on Windows.

10. Shell reported by execd

• internal/execd/server.go hardcodes "Shell": "/bin/sh", which is
  inaccurate on Windows. It is currently just an informational field (actual
  execution is decided by the agent), so impact is low; suggest returning
  cmd.exe / powershell.exe per platform.

Suggestions

• Add a Job Object or parent-liveness detection for execd on Windows to restore
  graceful shutdown and crash cleanup.
• Return the Shell field per platform.
• Evaluate ConPTY support for interactive sessions (suggested as a separate
  follow-up issue).

[lIang70]

Implemented on top of flowcraft core v0.2.2 (upgraded from v0.2.1 in #41). Final decision: on Windows, safety wins — the sandbox runs with OS-level write confinement, and interactive exec_session is disabled there.

• 1. Interactive sessions (Windows): the execd child (SandboxRunner) and the in-process local backend now use flowcraft's Windows sandbox backend with WithWriteConfinement() — children run under a restricted Low-integrity token and can only write inside the workspace/root plus configured writable paths, alongside job-object lifecycle/resource caps. flowcraft does not combine confinement with ConPTY yet, so exec_session is no longer registered on Windows and the pty capability is no longer advertised (noTTYRunner keeps the advertised surface honest and rejects TTY starts defensively). Non-interactive (pipe) sessions still work, including the sandbox diagnostics probe.
• 2. Graceful shutdown: stop() closes the client connection first so the child's Serve loop sees EOF and runs its in-process session cleanup. On Windows this replaces the ignored SIGTERM + 3s stall; sandboxed trees are additionally guaranteed dead via job KILL_ON_JOB_CLOSE.
• 3. Parent-death watchdog: watchParent is platform-specific. Windows waits on a handle to the parent process (OpenProcess + WaitForSingleObject) instead of relying on orphan reparenting, so the execd child no longer leaks after a parent crash.
• 10. Shell field: EnvironmentInfo reports cmd.exe on Windows and /bin/sh elsewhere.
• 4. Window chrome and 7. open command were already implemented (frameless custom title bar on Windows; cmd /c start opener).
• 5/8/9. Plugin layout, rendering engine, paths: intentional, documented platform conventions; no code change needed.
• 6. Plugin signing: still a no-op on Windows — ad-hoc codesigning is macOS-only. A real implementation needs external signing infrastructure (signtool + certificate); suggesting a separate follow-up issue.

Verified: darwin build/vet/full test suite pass; windows/amd64 and linux/amd64 cross-compile; windows vet passes.