fix(abgen): never adopt an orphaned server; reap the child on crash (Windows)

With the fixed default port an abgen orphaned by a crashed session owns the
endpoint the next session expects; the health check accepted any listener, so
a stale server (old version, other workspace's realm) was silently adopted
while our own child died on bind. StartAsync now verifies our child is alive
after the health check and fails fast otherwise. On Windows (player and
editor) every child is additionally assigned to a kill-on-close Job Object,
so the kernel reaps it when the explorer dies for any reason — crash included.
macOS keeps cooperative teardown; a parent-pid watchdog in abgen is the
upstream complement.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: dalkia

docs/abgen-sidecar.md

@@ -58,6 +58,16 @@ uses `CreateProcessW` with `CREATE_NO_WINDOW`, macOS/Linux the `DclProcesses` na
 `kill(pid, 0)`), not the managed `Exited` event. Only the editor keeps the managed `Process`
 path (with drained stdout/stderr pipes).
 
+**Orphan protection**: teardown is cooperative (Dispose kills the child), so a hard crash of the
+explorer used to leave the server running — and with the fixed default port an orphan *owns* the
+endpoint the next session expects. Two defenses: on Windows (player and editor) every child is
+assigned to a kill-on-close Job Object, so the kernel reaps it when the explorer dies for any
+reason; and `StartAsync` refuses to adopt a foreign listener — after the health check passes it
+verifies our own child is still alive, and if the port is answered by anything else (orphan from a
+crashed macOS session, unrelated process) it fails fast with an explicit milestone instead of
+silently serving stale bundles. macOS has no job-object equivalent; a parent-pid watchdog in abgen
+is the tracked upstream complement.
+
 Measured (Linux x86_64, CPU encoder): cold whole-entity JIT 0.8s (2-GLB scene) / 5.3s (24-GLB,
 12MB); warm disk-cache hits <1ms; server RSS ~16MB idle, 130–435MB peak during converts. v0.16.0's
 per-file parallelization cut cold whole-scene conversion by ~30 s on an M-series Mac against a real
@@ -83,13 +93,30 @@ failure). First run therefore enters the world with bundles already served; outs
 LSD + `--local-ab` the task is pre-completed and boot is unaffected. The wait is absorbed under
 the splash screen, before the authentication screen.
 
+**Clean fallback when the sidecar can't be had**: the readiness task resolves to a bool — false
+when the server never came up — and `MainSceneLoader` then drops the optimized-assets override
+(`DecentralandUrlsSource.ClearOptimizedAssetsOverride`, which also evicts the flag-dependent URL
+cache) before any optimized-asset request has resolved. The whole session — scene bundles,
+wearables, emotes, LODs, and the registry-composed profile/entities endpoints — falls back to the
+production hosts exactly as if `--local-ab` had not been passed, instead of hitting the dead
+loopback port and recovering per request. A server that turns healthy and dies later keeps the
+override (bundles JIT per request; supervision restarts it up to 3×).
+
 ## Visibility
 
 The scene dev console's AB tab mirrors `/progress/{entity}` live: the summary shows the server's
 authoritative `converted/total` counter, per-file rows show whatever the 500 ms poll catches
 (backfilled to the full census when the manifest lands), and milestone rows mark every lifecycle
 moment — download progress, installed, warm-up started, READY in Ns, already-warm, server-side
-failures (manifest exitCode), sidecar failed. The sidebar AB button pulses while conversion runs
+failures (manifest exitCode), sidecar failed. Content-edit reconversions are mirrored too: the LSD
+reload path (`LocalSceneDevelopmentController`, which already receives the preview server's edit
+message — including the changed model's path) raises a consumable signal on
+`AbgenConversionMetrics`; the sidecar's session-long watcher (`WatchReconversionsAsync`) consumes it
+and re-runs the manifest lane, which coalesces with (or triggers) the server's rebuild — the panel
+flips back to converting, names the edited file, tracks the rebuild and settles to READY with a
+"reconverted in Ns" milestone, accurate even when the rebuild outpaces the progress poll (texture
+edits arrive as unnamed whole-scene updates — sdk-commands only names `.glb/.gltf` changes).
+The sidebar AB button pulses while conversion runs
 and stays lit after unseen failures. The panel **opens itself** when long-running work starts
 (consumable open-request on `AbgenConversionMetrics`, consumed by `DebugMenuController`) and
 **closes itself** a few seconds after a clean READY — any failure keeps it open, and a manual