Add the Windows Sandbox state-aware lifecycle + host daemon (Phase 2)

[MGudgin]

Note

Stacked on #577 (which is stacked on #576). This PR's base is
user/gudge/wsb-phase1-one-shot, so the diff shows only the Phase 2 commit.
Merge order: #576 -> #577 -> this PR. GitHub auto-retargets the base to main
as each parent merges and its branch is deleted.

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• This pull request is related to an issue.
• If this PR changes build commands, project architecture, or key conventions, I have updated .github/copilot-instructions.md.

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Summary

Phase 2 of the Windows Sandbox rewrite stack: add the state-aware lifecycle
(provision -> start -> exec* -> stop -> deprovision) for Windows Sandbox on top
of the Phase 1 one-shot rewrite, holding a single live VM across separate
wxc-exec phase processes behind a persistent detached host-side daemon. The SDK
follows in Phase 3.

Details

• windows_sandbox_lifecycle: re-enables state_aware.rs -- the
  StatefulSandboxBackend impl on WindowsSandboxRunner. provision validates +
  snapshots the filesystem policy and mints wsb:<token>; start spawns the
  detached daemon (which boots the VM and holds the guest control connection);
  exec relays a script over the held connection; stop/deprovision tear down.
  A process-global named mutex serialises start/stop/deprovision; the single host
  VM slot is enforced.
• Daemon rewrite (wxc_windows_sandbox_daemon): control_server.rs serves a
  nonce-authenticated localhost line protocol (PING/STOP/EXEC), each
  connection on its own task so a long exec can't block a STOP. Auth nonce via
  stdin; sandbox token via --token. Re-added to the workspace members (dropped
  in Phase 1); the legacy pipe_server/sandbox_vm/tcp_bridge/rendezvous
  modules are deleted (rendezvous now lives in the lifecycle crate).
• wxc dispatch: run_state_aware routes the wsb: prefix to
  WindowsSandboxRunner with the same --experimental gate as one-shot;
  state_aware_dispatch learns the wsb -> WindowsSandbox prefix mapping.
• Docs: the full dual-mode rewrites land here with the behavior they describe --
  windows-sandbox.md/windows-sandbox-reference.md, schema.md (dual-mode
  backend row + state-aware envelope section), the state-aware API doc, and
  copilot-instructions.md. While touching schema.md I reconciled its version
  table to the canonical schemas/schema-version.json (>=0.4, <=0.8; stable
  0.7.0-alpha; state-aware 0.6.0-alpha) -- the rewrite had left it at the pre-0.8
  <=0.7.
• Tests: adds run_windows_sandbox_state_aware_tests.ps1 (state-aware E2E).

Tests

• cargo check --workspace --all-targets, cargo clippy --workspace --all-targets -- -D warnings, and cargo fmt --all -- --check: clean.
• cargo test: windows_sandbox_lifecycle 157 (incl. the state-aware suite),
  wxc_windows_sandbox_daemon 23, wxc_common 364 (incl. the new wsb resolver
  test), wxc 13 -- all passed.
• node scripts/versioning/check-schema-versions.js: green.

Related Issues

• docs: reconcile docs/schema.md supported-version table with schema-version.json #565 (schema.md version-table reconciliation, partially addressed here)

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