Add a remote source to the inspector entity tree (#26014)

# Objective

Part of #23013.

The inspector can only look at the world it runs in. To inspect a
running game from a separate app, it needs to read another world over
the Bevy Remote Protocol.

# Solution

Remote entities live in their own `World`, the `RemoteWorld`, spawned at
their remote ids. This is @Zeophlite design and it replaces the proxy
entities and id map from earlier revisions. The entity tree and details
panel just read whichever world `world_to_inspect` hands them, so no
local hook, observer or system ever sees remote data.

- polls read `Name`, `ChildOf` and the label defining components, and a
fuller poll with `has` runs when unseen entities show up and every 10
seconds, so internal entities like observers and systems stay hidden
- only `Name` and `ChildOf` are inserted for now, a child whose parent
isn't mirrored yet shows as a root until the parent appears
- polls run off the main thread with one in flight at a time, and the
tree only resyncs when something changed
- the remote world is rebuilt on reconnect, on source change, on a
failed connection, and when a remote id goes back a generation, which
means the remote app restarted
- selecting a remote entity shows only its name and hierarchy for now,
component values come in the follow-up PR

`World::spawn_at` only accepts an index's current generation and there's
no public way to set one, so `spawn_at_remote_id` steps the generation
up by spawning and despawning without freeing, and reserves every index
up to the remote one so the allocator never hands those out. A small
`bevy_ecs` follow-up adding a public way to move an unspawned index to a
given generation, and to reserve an index in the allocator, would let us
replace that function with a single call.

# AI disclosure

This is the first part of the remote inspection that already works in
Jackdaw. I had AI rebuild it on top of what has merged since, review it
for edge cases and run it end to end against the server example, then
went through the changes myself. The biggest change from the original is
that remote components are no longer inserted into the local world.
After review, this moved to Zeophlite's separate world design, which AI
reworked from his WIP branch, tested end to end against the server
example, and I reviewed.

# Showcase


https://github.com/user-attachments/assets/396987b0-a9b6-4bbe-b28e-e1d79d92c959

---------

Co-authored-by: Daniel Skates <zeophlite@gmail.com>

Author: jbuehler23

Cargo.toml

@@ -4883,6 +4883,18 @@ description = "Inspects the app's own world with the bevy_inspector entity tree
 category = "Dev tools"
 wasm = true
 
+[[example]]
+name = "remote_inspector"
+path = "examples/inspector/remote_inspector.rs"
+doc-scrape-examples = true
+required-features = ["bevy_inspector", "bevy_remote_client"]
+
+[package.metadata.example.remote_inspector]
+name = "Remote Inspector"
+description = "Inspects a separate running app with the bevy_inspector panels over the Bevy Remote Protocol"
+category = "Dev tools"
+wasm = false
+
 [[example]]
 name = "2d_top_down_camera"
 path = "examples/camera/2d_top_down_camera.rs"

_release-content/release-notes/inspection.md

@@ -1,7 +1,7 @@
 ---
 title: Entity inspection tools
 authors: ["@jbuehler23", "@alice-i-cecile", "@Nilirad", "@Zeophlite"]
-pull_requests: [25818, 25822, 25823, 25824, 25826, 25837, 25845, 25866, 25883, 25884, 25885, 25923]
+pull_requests: [25818, 25822, 25823, 25824, 25826, 25837, 25845, 25866, 25883, 25884, 25885, 25923, 26014]
 ---
 
 `bevy_dev_tools::inspection` is gaining a backend for inspecting worlds, entities, components, and resources.
@@ -18,3 +18,4 @@ This note will be completed once the rest of the series lands.
 - Added serde support and structured values to the inspection types (#25866)
 - Added `world.inspect*`, `world.summarize` and `registry.component_metadata` to the Bevy Remote Protocol (#25883)
 - Added the `bevy_inspector` crate with a local entity tree and an editable details panel (#25884, #25885, #25923)
+- Added a remote source to `bevy_inspector`, showing the entity tree of a separate running app over the Bevy Remote Protocol (#26014)

crates/bevy_inspector/Cargo.toml

@@ -26,6 +26,15 @@ bevy_ui = { path = "../bevy_ui", version = "0.20.0-dev" }
 bevy_ui_widgets = { path = "../bevy_ui_widgets", version = "0.20.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.20.0-dev" }
 bevy_window = { path = "../bevy_window", version = "0.20.0-dev" }
+bevy_remote = { path = "../bevy_remote", version = "0.20.0-dev", default-features = false, features = [
+  "client",
+  "http",
+], optional = true }
+bevy_tasks = { path = "../bevy_tasks", version = "0.20.0-dev", optional = true }
+
+# other
+serde = { version = "1", optional = true }
+serde_json = { version = "1.0.140", optional = true }
 
 [dev-dependencies]
 bevy_camera = { path = "../bevy_camera", version = "0.20.0-dev" }
@@ -36,6 +45,14 @@ bevy_math = { path = "../bevy_math", version = "0.20.0-dev" }
 
 [features]
 default = []
+# Inspect a separate running app over the Bevy Remote Protocol
+remote = [
+  "dep:bevy_remote",
+  "dep:bevy_tasks",
+  "dep:serde",
+  "dep:serde_json",
+  "bevy_ecs/serialize",
+]
 
 [lints]
 workspace = true

crates/bevy_inspector/src/details_panel.rs

@@ -205,13 +205,13 @@ struct FieldWidget {
 
 /// A component of the inspected entity, with its fields flattened into rows.
 #[derive(Debug, Clone)]
-struct ComponentDetails {
-    id: ComponentId,
+pub(crate) struct ComponentDetails {
+    pub(crate) id: ComponentId,
     /// The name shown in the group header, a [`ShortName`] of the component type.
-    name: String,
-    type_path: String,
-    memory: String,
-    fields: Vec<FieldEntry>,
+    pub(crate) name: String,
+    pub(crate) type_path: String,
+    pub(crate) memory: String,
+    pub(crate) fields: Vec<FieldEntry>,
 }
 
 /// The group spawned for one component, whether its fields were spawned, and the rows they were
@@ -835,8 +835,9 @@ pub fn sync_details_panel(world: &mut World) {
         return;
     };
 
-    let components = inspect_components(world, selection);
-    let empty = empty_state(world, selection, &components);
+    let inspected = crate::world_to_inspect(world);
+    let components = inspect_components(inspected, selection);
+    let empty = empty_state(inspected, selection, &components);
 
     let index = world.resource::<DetailsIndex>();
     if selection_changed || index.body != Some(body) || index.empty != empty {
@@ -855,7 +856,11 @@ fn find_body(world: &mut World) -> Option<Entity> {
         .next()
 }
 
-fn inspect_components(world: &World, selection: Option<Entity>) -> Vec<ComponentDetails> {
+/// The component groups of `selection` in the inspected `world`, sorted in display order.
+pub(crate) fn inspect_components(
+    world: &World,
+    selection: Option<Entity>,
+) -> Vec<ComponentDetails> {
     let Some(entity) = selection else {
         return Vec::new();
     };
@@ -916,6 +921,10 @@ fn inspect_components(world: &World, selection: Option<Entity>) -> Vec<Component
             }
         })
         .collect();
+    #[cfg(feature = "remote")]
+    if let Some(record) = world.component_id::<crate::remote::RemoteComponents>() {
+        components.retain(|component| component.id != record);
+    }
     components.sort_by(|left, right| (&left.name, left.id).cmp(&(&right.name, right.id)));
     components
 }
@@ -1684,7 +1693,7 @@ impl Walk {
 }
 
 /// The read-only caption form of a field value.
-fn read_only(value: FieldValue) -> FieldValue {
+pub(crate) fn read_only(value: FieldValue) -> FieldValue {
     FieldValue::Label(match value {
         FieldValue::Bool(value) => value.to_string(),
         FieldValue::Number(NumericValue::F32(value)) => value.to_string(),