feat(client): T-1132 standalone Atlas companion shell + make atlas (D-254 SS3)

New atlas_standalone scene/script: attach-or-spawn boot (one REAL
connect_to_sim attempt at SR_PORT-or-9876 — a separate throwaway TCP
probe was proven by live run to kill a pre-accept-loop server via
broken handshake pipe; never abandon a connected socket), else spawn
--port 0 via new ServerProcess.start_with_pipe + LISTENING:{port}
stdout parse, retry against the resolved port. Reader role wired end
to end: protocol.encode_startup_message optional role param (empty
omits the wire key — byte-identical for all existing callers),
sim_bridge.connection_role suppresses the post-handshake
RequestAllSettings auto-send, hud_groups skips AutoPause/AutoResume
sends for readers (all three would otherwise burn Reader violation
strikes per the T-1130 matrix — endorsed by Oscar).

Generic implant host per D-254 SS3: the shell instantiates ALL
registered implant apps; implant_app_manifest gains
available_in_companion (opt-out, default true) and
implant_registry.instantiate_all a standalone filter param (default
preserves hud.gd behavior byte-identically). Boot order is
instantiate_all THEN open_app (reverse renders a permanently black
window — app_changed fires with no listener; matches hud.gd's order).
Owned-server lifecycle: _exit_tree stops a spawned child, attached
servers survive companion close. Known engine limitation documented:
raw SIGTERM bypasses all Godot notifications and orphans a spawned
server; WM close paths verified clean.

Live-verified: spawn-mode (301 systems rendered from systems.db over
the wire), attach-mode, two simultaneous readers, clean shutdown with
zero orphan processes. 14 new gdUnit tests (port/LISTENING parsing).

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

Makefile

@@ -1,6 +1,6 @@
 GODOT := $(shell command -v godot4 2>/dev/null || command -v godot 2>/dev/null)
 
-.PHONY: help setup build client server game stop test test-tooling lint lint-python setup-venv ci ci-client ci-server clean \
+.PHONY: help setup build client server game atlas stop test test-tooling lint lint-python setup-venv ci ci-client ci-server clean \
        decisions-sync decisions-active decisions-validate \
        validate-content check-fact-ids setup-hooks install-hooks \
        audit deny atlas-verify economy-db regen-db check-systems-db \
@@ -26,6 +26,7 @@ help:
 	@echo "  make setup-venv     Create .venv and install Python tooling deps"
 	@echo "  make build          Build client and server"
 	@echo "  make game           Build and run the full game (server + client)"
+	@echo "  make atlas          Standalone Atlas companion app — attach or spawn, read-only (D-254)"
 	@echo "  make stop           Stop any running server instance"
 	@echo "  make client         Run the Godot client (test mode)"
 	@echo "  make server         Run the Rust simulation server"
@@ -150,6 +151,20 @@ game: stop build
 	@SR_LIVE=1 $(GODOT) --path client
 	@$(MAKE) stop
 
+# D-254/T-1132: standalone Atlas companion app. Unlike `game`, no orchestration
+# here — atlas_standalone.gd owns its own attach-or-spawn decision and child
+# server lifecycle internally (D-254 §1/§3), so this target is just "build,
+# then launch the standalone scene". build-server ensures the debug binary
+# exists for spawn-mode (atlas_standalone.gd resolves it at
+# server/target/debug/settled-reach-server, the same path the E2E test files
+# use); build-client ensures imports are current. SR_LIVE=1 is required —
+# without it SimBridge boots in test mode (instant fake CONNECTED, no network
+# at all), which would make the companion open the Atlas against a dynamic
+# test-harness snapshot instead of the real systems.db world via the wire.
+atlas: build-server build-client
+	@test -n "$(GODOT)" || { echo "Godot not found. Run 'make setup' first."; exit 1; }
+	@SR_LIVE=1 $(GODOT) --path client scenes/atlas_standalone.tscn
+
 stop:
 	@lsof -ti :9876 | xargs -r kill 2>/dev/null || true
 	@echo "Stopped any running server on port 9876"

client/scenes/atlas_standalone.tscn

@@ -0,0 +1,20 @@
+[gd_scene load_steps=2 format=3 uid="uid://atlas_standalone_sr"]
+
+[ext_resource type="Script" path="res://scripts/atlas_standalone.gd" id="1_standalone"]
+
+; D-254: standalone Atlas companion app entry scene (`make atlas`). Bare Control
+; root, full-rect anchored exactly like hud.gd's AppsContainer (ui/hud.tscn) —
+; ImplantRegistry.instantiate_all(self) parents every hosted app directly under
+; this node, so it needs the same full-viewport layout a normal implant app
+; expects from its parent. No gameplay layer, no HUD status panel, no camera —
+; the boot sequence (atlas_standalone.gd) is the entire content of this scene.
+
+[node name="AtlasStandalone" type="Control"]
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+mouse_filter = 0
+script = ExtResource("1_standalone")

client/scripts/atlas_standalone.gd

@@ -0,0 +1,269 @@
+extends Control
+## Standalone Atlas companion app entry point (D-254, T-1132, `make atlas`).
+##
+## Boots the SAME implant scene tree used in-game, skipping the player
+## entirely — no character, no main.tscn, no gameplay HUD. Auto-attaches to
+## an already-running game (read-only) or spawns its own server against the
+## real systems.db world (no --test-mode). Modeled on visual_capture.gd's
+## live-mode boot shape (D-254 §3), but a real scene script (normal _ready()),
+## not a SceneTree-extending offscreen test harness.
+##
+## D-254 §3 amendment (2026-07-17, generic implant host): this scene hosts
+## EVERY registered implant app (ImplantRegistry.instantiate_all(self, true) —
+## the standalone=true filter drops apps whose manifest sets
+## available_in_companion=false), fronting the Atlas (implant/map) as the
+## default open app. Future implant apps extend the companion with zero
+## changes here.
+##
+## Boot sequence (_ready → _boot, deferred so the node is in-tree first):
+##   1. Discovery/attach: SimBridge.connect_to_sim() against SR_PORT-or-9876,
+##      polled for up to ATTACH_CONNECT_TIMEOUT_S. On CONNECTED, attach
+##      succeeded — skip straight to step 4. On ERROR (nothing listening),
+##      fall through to spawn (own child server, --port 0, parse
+##      LISTENING:{port} from stdout — server_process.gd's start_with_pipe(),
+##      never --test-mode: real systems.db world), then repeat the connect
+##      against the newly-resolved port.
+##
+##      NOT a separate throwaway TCP probe-then-reconnect (an earlier version
+##      of this script had one, and a live run surfaced why that design is
+##      actively harmful against today's server: main.rs's FIRST connection is
+##      still a single blocking listener.accept() (server/src/main.rs, D-254
+##      §2/T-1130's own comment there) — a probe that connects, sees
+##      STATUS_CONNECTED, and disconnects has just consumed that one accept()
+##      slot and abandoned it mid-handshake. The server's very next line,
+##      bridge.send_handshake(), then hits "Broken pipe" writing to the dead
+##      probe socket and the WHOLE SERVER PROCESS EXITS (main.rs's
+##      .unwrap_or_else(|e| { ...; std::process::exit(1) }) on that call) —
+##      confirmed by a live repro against a real already-running server: the
+##      probe's own attach check killed the very server session it was
+##      checking on, and the companion's own real connection attempt right
+##      after then failed too, since there was nothing left to connect to.
+##      The fix: never abandon a connection that reached STATUS_CONNECTED.
+##      SimBridge.connect_to_sim() IS that one safe connection attempt (it
+##      already TCP-retries internally, see MAX_CONNECT_RETRIES/
+##      CONNECT_RETRY_INTERVAL in sim_bridge.gd) — this script drives it
+##      directly instead of pre-flighting with a disposable socket.
+##   2. Configure SimBridge for the resolved port; connection_role = "Reader"
+##      (D-254 §2) so the StartupMessage carries role: Reader.
+##   3. connect_to_sim(); poll SimBridge.state until CONNECTED (or ERROR).
+##   4. HudGroups.open_app("implant/map") — the default front app.
+##   5. ImplantRegistry.instantiate_all(self, true) populates every
+##      available_in_companion app.
+##   6. Intercept HudGroups.app_changed: when the Atlas's own KEY_M/KEY_ESCAPE
+##      handling (atlas_app.gd) calls HudGroups.close_app() from the "reach"
+##      screen, this scene re-opens implant/map instead of falling into a
+##      nonexistent gameplay layer (D-254 §3 recommended option (a) — does not
+##      touch atlas_app.gd).
+
+const DEFAULT_PORT: int = 9876
+## D-254 §1 names ~500ms for the attach check; SimBridge's own internal TCP
+## retry loop (MAX_CONNECT_RETRIES=20 * CONNECT_RETRY_INTERVAL=0.1s, sim_bridge.gd)
+## is ~2s end-to-end before it reports ConnectionState.ERROR. Since this
+## script drives connect_to_sim() directly (no separate pre-probe — see the
+## header note above), the real wait for "nothing is listening" is bounded by
+## SimBridge's own retry budget, not this constant; ATTACH_CONNECT_TIMEOUT_S
+## is a slightly-generous outer deadline (SimBridge's ~2s + one frame margin)
+## so this script's own poll loop can never out-wait SimBridge's, not a
+## separate tunable that changes the actual ECONNREFUSED-detection speed.
+const ATTACH_CONNECT_TIMEOUT_S: float = 2.5
+const CONNECT_POLL_TIMEOUT_S: float = 10.0
+const SPAWN_READY_TIMEOUT_S: float = 15.0
+const WINDOW_TITLE: String = "The Settled Reach — Atlas"
+const FRONT_APP: String = "implant/map"
+
+## T-1134 seam: spawn-mode seed is the server's own default (SimRng default
+## seed=0, server/src/main.rs) — no seed picker in v1. Leaving this constant
+## (rather than inlining "no seed sent") makes the future seam obvious: T-1134
+## replaces this with a startup screen that sets SimBridge.world_seed_override
+## (or equivalent) before _boot() reaches step 2. StartupMessage.world_seed is
+## ALWAYS sent (server/src/bridge/types.rs: field is not optional on the wire)
+## — GameState.world_seed's own default (0) is what ships until T-1134 adds a
+## picker; this constant exists purely as the documented seam marker.
+const SPAWN_MODE_SEED_IS_SERVER_DEFAULT: bool = true
+
+var _server_process: Variant = null  # ServerProcess — owned here for spawn-mode only
+var _resolved_port: int = DEFAULT_PORT
+var _spawned: bool = false  # true once this scene has spawned its own server
+
+
+func _ready() -> void:
+	DisplayServer.window_set_title(WINDOW_TITLE)
+	HudGroups.app_changed.connect(_on_hud_app_changed)
+	_boot.call_deferred()
+
+
+func _exit_tree() -> void:
+	_stop_spawned_server()
+
+
+## D-254 §3 step 6 (recommended option (a)): the Atlas's own close handling
+## (atlas_app.gd _handle_key, KEY_M/KEY_ESCAPE from "reach") calls
+## HudGroups.close_app() unconditionally — it has no notion of "there is no
+## gameplay layer to fall back to". This intercepts that transition and
+## re-opens the Atlas immediately, so from the player's perspective M/Escape
+## on the top-level Atlas screen is a no-op in the companion (there is nothing
+## else to show). atlas_app.gd is never modified.
+func _on_hud_app_changed(app_path: String, mode: int) -> void:
+	if app_path == FRONT_APP and mode == HudGroups.Mode.GAMEPLAY:
+		HudGroups.open_app(FRONT_APP)
+
+
+func _boot() -> void:
+	_resolved_port = _attach_port()
+	SimBridge.server_path = ""  # atlas_standalone owns any child process, not SimBridge
+	SimBridge.server_port = _resolved_port
+	SimBridge.connection_role = "Reader"  # D-254 §2
+
+	# Attempt the ONE real attach connection — never a disposable pre-probe
+	# (see the class doc header for why: an earlier probe-then-reconnect design
+	# killed the server it was checking on). connect_to_sim() TCP-retries
+	# internally for ~2s (sim_bridge.gd) before reporting ERROR.
+	if SimBridge.state == SimBridge.ConnectionState.DISCONNECTED:
+		SimBridge.connect_to_sim()
+	var attached := await _wait_for_connected(ATTACH_CONNECT_TIMEOUT_S)
+
+	if not attached:
+		# Nothing answered on the attach port — fall through to spawn. The
+		# failed attempt above must be fully torn down before spawning: a
+		# leftover ERROR-state _bridge/_server would otherwise confuse the
+		# fresh connect_to_sim() call below (disconnect_from_sim() resets
+		# SimBridge to DISCONNECTED, which is connect_to_sim()'s required
+		# entry state — see the DISCONNECTED guard above and in main.gd).
+		SimBridge.disconnect_from_sim()
+		var spawn_ok := await _spawn_server()
+		if not spawn_ok:
+			push_error("atlas_standalone: failed to spawn server — cannot continue")
+			get_tree().quit(1)
+			return
+
+		SimBridge.server_port = _resolved_port  # _spawn_server() updated _resolved_port
+		SimBridge.connection_role = "Reader"
+		SimBridge.connect_to_sim()
+		attached = await _wait_for_connected(CONNECT_POLL_TIMEOUT_S)
+		if not attached:
+			push_error("atlas_standalone: connection to spawned server failed or timed out")
+			get_tree().quit(1)
+			return
+
+	# Re-apply the title here, not just in _ready(): confirmed by direct repro
+	# that Godot's un-exported debug-run window manager sets the title to
+	# "{config/name} (DEBUG)" on a LATER frame than _ready() (window-visible/
+	# focus timing, not measured precisely) — an early-only window_set_title()
+	# call loses that race and the window silently reverts to the project
+	# default. By the time the connection completes (at minimum one full TCP
+	# round-trip, often a spawn+handshake), that race has long resolved.
+	DisplayServer.window_set_title(WINDOW_TITLE)
+
+	# instantiate_all() MUST run before open_app(): ImplantApp._ready()
+	# (client/ui/implant/implant_app.gd) is what connects HudGroups.app_changed
+	# -> _internal_app_changed, which is the ONLY thing that flips an app's
+	# `visible` flag and fires on_open(). open_app() first would emit
+	# app_changed while the Atlas doesn't exist as a node yet — no listener,
+	# no visibility, a permanently blank window (found via a live run: the
+	# window opened, connected, and instantiated both apps correctly, but
+	# rendered solid black — the exact fingerprint of this ordering bug).
+	# hud.gd's own _ready() establishes the same order for the in-game case
+	# (instantiate_all is unconditional there; open_app only ever happens
+	# later, from player input).
+	ImplantRegistry.instantiate_all(self, true)  # standalone=true: available_in_companion filter
+	HudGroups.open_app(FRONT_APP)
+
+
+## Pure function: SR_PORT env override, else DEFAULT_PORT. Matches the
+## SR_PORT two-tier discovery visual_capture.gd/locomotion_sandbox.gd already
+## use (D-254 §1) — same env var, same fallback. This is the port the ONE
+## attach connect_to_sim() call targets (see _boot()) — no separate probe.
+static func _attach_port(port_env: String = "") -> int:
+	var env := port_env if not port_env.is_empty() else OS.get_environment("SR_PORT")
+	if env.is_empty():
+		return DEFAULT_PORT
+	if not env.is_valid_int():
+		push_warning("atlas_standalone: SR_PORT='%s' is not a valid int — using default" % env)
+		return DEFAULT_PORT
+	return int(env)
+
+
+## D-254 §1/§3: spawn-mode lifecycle — tests/run-visual's --port 0 +
+## LISTENING:{port} precedent, WITHOUT --test-mode (real systems.db world,
+## not Gauntlet fixtures). Ownership: this scene owns the ServerProcess
+## instance directly (not SimBridge's built-in spawn path, which has no
+## stdout access and therefore can't resolve an OS-assigned port) — the same
+## OS.kill/NOTIFICATION_PREDELETE safety net server_process.gd already
+## implements, reused via start_with_pipe() (added for this ticket; start()'s
+## existing OS.create_process contract is untouched for its three existing
+## callers). Returns true once LISTENING:{port} is parsed and _resolved_port
+## is updated; false on spawn failure or timeout (server never printed the
+## signal within SPAWN_READY_TIMEOUT_S).
+func _spawn_server() -> bool:
+	var server_path := _server_binary_path()
+	if not FileAccess.file_exists(server_path):
+		push_error("atlas_standalone: server binary not found at %s (run `make build-server`)" % server_path)
+		return false
+
+	var SP := load("res://scripts/protocol/server_process.gd")
+	_server_process = SP.new()
+	var pid: int = _server_process.start_with_pipe(server_path, ["--port", "0"])
+	if pid <= 0:
+		return false
+	_spawned = true
+
+	var elapsed := 0.0
+	var frame_budget := 1.0 / 60.0
+	while elapsed < SPAWN_READY_TIMEOUT_S:
+		if not _server_process.is_alive():
+			push_error("atlas_standalone: spawned server died before printing LISTENING signal")
+			return false
+		var line: String = _server_process.read_stdout_line()
+		if not line.is_empty():
+			var parsed := _parse_listening_line(line)
+			if parsed >= 0:
+				_resolved_port = parsed
+				return true
+		await get_tree().process_frame
+		elapsed += frame_budget
+
+	push_error("atlas_standalone: no LISTENING signal from spawned server after %.1fs" % SPAWN_READY_TIMEOUT_S)
+	return false
+
+
+## Pure function: parse "LISTENING:{port}" -> port, or -1 if the line doesn't
+## match (main.rs's exact signal format — server/src/main.rs, "LISTENING
+## signal to stdout"). Split out from _spawn_server()'s polling loop so the
+## parse itself is unit-testable without a live process.
+static func _parse_listening_line(line: String) -> int:
+	var stripped := line.strip_edges()
+	if not stripped.begins_with("LISTENING:"):
+		return -1
+	var port_str := stripped.substr("LISTENING:".length())
+	if not port_str.is_valid_int():
+		return -1
+	return int(port_str)
+
+
+## Wall-clock poll of SimBridge.state until CONNECTED or ERROR (same
+## ConnectionState enum/shape as visual_capture.gd's live-mode wait, per
+## D-254 §3 step 3 — minus the fixed-frame settle budget a screenshot capture
+## needs but a real window does not).
+func _wait_for_connected(timeout_s: float) -> bool:
+	var elapsed := 0.0
+	var frame_budget := 1.0 / 60.0
+	while elapsed < timeout_s:
+		if SimBridge.state == SimBridge.ConnectionState.CONNECTED:
+			return true
+		if SimBridge.state == SimBridge.ConnectionState.ERROR:
+			return false
+		await get_tree().process_frame
+		elapsed += frame_budget
+	return false
+
+
+func _server_binary_path() -> String:
+	var project_dir := ProjectSettings.globalize_path("res://")
+	return project_dir.path_join("../server/target/debug/settled-reach-server")
+
+
+func _stop_spawned_server() -> void:
+	if _spawned and _server_process != null:
+		_server_process.stop()
+	_server_process = null
+	_spawned = false

client/scripts/autoloads/hud_groups.gd

@@ -60,7 +60,20 @@ func _ready() -> void:
 ## send_named_action (protocol-level, not bound to an InputMapper.Action
 ## keybind) — the same mechanism as RequestBookmarkCatalog — since occlusion
 ## is a UI-state transition, not a physical input.
+## D-254 §2: skipped for Reader connections (atlas_standalone.gd's companion
+## app) — this travels through the same Vec<PlayerInput> pipeline as
+## MoveNorth/Interact, which the Reader permission matrix marks "no". A
+## Reader has no character and no pausable gameplay session of its own (the
+## standalone scene calls HudGroups.open_app() as its normal boot step, not a
+## player occluding their own gameplay), so there is nothing meaningful to
+## pause — sending it anyway would just be dropped as a role violation on
+## every single companion boot (confirmed via a live run against a real
+## server: "Reader connection ... sent 1 disallowed PlayerInput(s) — dropped
+## (strike 1/3)" fired from this exact call site the first time the companion
+## opened the Atlas fullscreen).
 func _on_gameplay_occluded_auto_pause(occluded: bool) -> void:
+	if SimBridge.connection_role == "Reader":
+		return
 	if occluded:
 		SimBridge.send_named_action("AutoPause")
 	else:

client/scripts/autoloads/sim_bridge.gd

@@ -25,6 +25,11 @@ var test_mode: bool = OS.get_environment("SR_LIVE") != "1"  # SR_LIVE=1 connects
 var harness = null  # Test simulation (D-020: game logic lives outside production client)
 var server_port: int = 9876  # Default matches server's default bind address
 var server_path: String = ""  # Path to server binary — set before connect_to_sim()
+# D-254 §2/§3: ConnectionRole wire value for the next StartupMessage — "" (default)
+# omits the "role" key (server defaults to Player, byte-identical to pre-D-254
+# behavior). atlas_standalone.gd sets this to "Reader" before connect_to_sim();
+# every existing caller (main.gd, locomotion_sandbox.gd, tests) leaves it unset.
+var connection_role: String = ""
 
 var _last_snapshot: Variant = null  # Most recent decoded snapshot (consumed by poll_snapshot)
 var _outbound_buffer: Array[Dictionary] = []  # Raw inputs awaiting batch encode + transport
@@ -283,8 +288,10 @@ func _process(delta: float) -> void:  # gdlint:disable=max-returns
 
 		# Send startup message with world_seed and character appearance (#175, D-010/D-029, #718).
 		# Server blocks waiting for this before entering the tick loop.
+		# D-254 §2: connection_role threads "Reader" for the standalone companion;
+		# every other caller leaves it "" (omitted key, decodes as Player).
 		var startup_bytes := Protocol.encode_startup_message(
-			GameState.world_seed, GameState.character_visual_descriptor
+			GameState.world_seed, GameState.character_visual_descriptor, connection_role
 		)
 		if startup_bytes.size() > 0:
 			var send_err: int = _bridge.send_message(startup_bytes)
@@ -307,6 +314,13 @@ func _process(delta: float) -> void:  # gdlint:disable=max-returns
 		_set_state(ConnectionState.CONNECTED)
 		# #646: Request full settings dump on connect — hydrates GameState.ai_enhanced_dialogue_enabled
 		# from server SQLite so the client reflects the authoritative persisted state (D-138).
+		# D-254 §2: this travels as a Vec<PlayerInput> entry (same pipeline as
+		# MoveNorth/Interact), which the permission matrix marks "no" for Reader —
+		# a Reader has no settings to hydrate (no character, no per-player state),
+		# so skip the send rather than have the server log-and-drop it on every
+		# companion connection once role enforcement lands server-side.
+		if connection_role == "Reader":
+			return
 		(
 			_outbound_buffer
 			. append(

client/scripts/protocol/protocol.gd

@@ -639,14 +639,22 @@ static func _decode_enum_variant(raw) -> Dictionary:
 ## Sent by the client immediately after handshake validation.
 ## Server reads this to initialize SimRng (D-010, D-029).
 ## character_visual: optional CharacterVisualDescriptor — included as "character_visual_descriptor" dict.
+## role: D-254 §2 ConnectionRole wire value — "" (default, every caller before
+## D-254) omits the "role" key entirely, matching server StartupMessage::role's
+## #[serde(default)] and decoding as ConnectionRole::Player — byte-identical to
+## pre-D-254 output. atlas_standalone.gd is the one caller that passes "Reader"
+## (unit enum variant, bare string per this file's header wire-format note —
+## same encoding as PlayerAction unit variants like "MoveNorth").
 static func encode_startup_message(
-	world_seed: int, character_visual: Variant = null
+	world_seed: int, character_visual: Variant = null, role: String = ""
 ) -> PackedByteArray:
 	var msg := {
 		"world_seed": world_seed,
 	}
 	if character_visual != null and character_visual.has_method("to_dict"):
 		msg["character_visual_descriptor"] = character_visual.to_dict()
+	if not role.is_empty():
+		msg["role"] = role
 	var result = _mp().encode(msg)
 	if result.status != null:
 		push_error("Protocol: startup message encode failed: %s" % result.status)

client/scripts/protocol/server_process.gd

@@ -2,6 +2,9 @@ class_name ServerProcess
 ## Manages the Rust simulation server as a subprocess (D-020).
 
 var _pid: int = -1
+## Populated only by start_with_pipe() — the stdout FileAccess handle used to
+## read the LISTENING:{port} signal (D-254 §1/§3). Null after plain start().
+var _stdio: FileAccess = null
 
 
 ## Start the server process. Returns the PID, or -1 on failure.
@@ -19,6 +22,43 @@ func start(server_path: String, args: Array = []) -> int:
 	return _pid
 
 
+## Start the server process with its stdout piped back to this process
+## (D-254 §1/§3: the companion app's --port 0 spawn-mode, which needs to read
+## the LISTENING:{port} signal main.rs prints — see server/src/main.rs). Unlike
+## start()/OS.create_process, this uses OS.execute_with_pipe, which does not
+## block (the shell precedent, tests/run-visual, achieves the same read via a
+## redirected log file + `grep` from a wrapper script; this is the Godot-native
+## equivalent for a caller with no shell wrapper). Returns the PID, or -1 on
+## failure. Call read_stdout_line() from a per-frame poll to drain the pipe.
+func start_with_pipe(server_path: String, args: Array = []) -> int:
+	if _pid > 0 and is_alive():
+		push_warning("ServerProcess: server already running (pid %d)" % _pid)
+		return _pid
+	if not FileAccess.file_exists(server_path):
+		push_error("ServerProcess: server binary not found at %s" % server_path)
+		return -1
+	var result: Dictionary = OS.execute_with_pipe(server_path, args)
+	if not result.has("pid") or int(result.get("pid", -1)) <= 0:
+		push_error("ServerProcess: failed to start server (pipe) at %s" % server_path)
+		return -1
+	_pid = int(result["pid"])
+	_stdio = result.get("stdio", null)
+	return _pid
+
+
+## Non-blocking read of one line from the piped server's stdout, or "" if no
+## complete line is buffered yet (FileAccess.get_line() on a pipe never
+## blocks — it returns immediately with whatever is currently available).
+## Only meaningful after start_with_pipe(); returns "" if _stdio was never set
+## (plain start()) or the process has exited (stream at EOF).
+func read_stdout_line() -> String:
+	if _stdio == null:
+		return ""
+	if _stdio.get_error() != OK:
+		return ""
+	return _stdio.get_line()
+
+
 ## Check if the server process is still running.
 ## NOTE: OS.is_process_running() doesn't distinguish starting/healthy/zombie.
 ## TODO: Add health check (e.g. TCP readiness probe) when server supports it.

client/tests/test_atlas_standalone.gd

@@ -0,0 +1,138 @@
+class_name TestAtlasStandalone
+extends GdUnitTestSuite
+## Unit tests for atlas_standalone.gd (D-254, T-1132, `make atlas`).
+##
+## Scope: the pure, static decision-logic functions the boot script exposes
+## specifically for testability — port resolution (_attach_port) and the
+## LISTENING:{port} signal parse (_parse_listening_line). These are the two
+## places a wrong answer silently misroutes the whole attach-vs-spawn
+## decision, and both are extractable as pure functions with no network, no
+## process, no scene tree required.
+##
+## Deliberately NOT covered here (would require a live server / real window,
+## per the ticket's "VERIFY LIVE once" instruction rather than an automated
+## suite): the full _boot() sequence, the attach-then-fallback-to-spawn
+## control flow, the HudGroups close-interception behavior, and the
+## orphan-on-exit server lifecycle. Those were verified via a live make atlas
+## run (see the T-1132 report) — a unit test double for a live TCP server
+## fighting the exact same real server-restart-safety issue a live run would
+## catch is not a good trade for this ticket's scope.
+##
+## Loaded via load() inside method bodies, never at class top-level or in a
+## _ready()-equivalent — atlas_standalone.gd's own _ready() references the
+## HudGroups autoload directly, which the autoload parse-order rule
+## (CLAUDE.md) says must not be resolved before autoloads are live. Since
+## GdUnitTestSuite test methods run after the full scene tree (autoloads
+## included) has booted, a method-body load() is safe; an early _init()-time
+## load() (verified by hand while writing this suite) fails to compile with
+## "Identifier not found: HudGroups" — confirming why this matters here and
+## not just for autoload scripts themselves.
+const SCRIPT_PATH := "res://scripts/atlas_standalone.gd"
+
+
+func _script():
+	return load(SCRIPT_PATH)
+
+
+# =============================================================================
+# _attach_port — SR_PORT env override, else DEFAULT_PORT (D-254 §1's two-tier
+# discovery, matching visual_capture.gd/locomotion_sandbox.gd's existing
+# SR_PORT convention).
+# =============================================================================
+
+
+func test_attach_port_empty_env_returns_default() -> void:
+	var s = _script()
+	assert_that(s._attach_port("")).is_equal(9876)
+
+
+func test_attach_port_valid_env_returns_parsed_int() -> void:
+	var s = _script()
+	assert_that(s._attach_port("12345")).is_equal(12345)
+
+
+func test_attach_port_env_zero_is_valid() -> void:
+	# "0" is a syntactically valid int (even though a real caller would never
+	# set SR_PORT=0 for an attach target) — the function's job is parsing,
+	# not judging whether the resulting port is a sensible one to dial.
+	var s = _script()
+	assert_that(s._attach_port("0")).is_equal(0)
+
+
+func test_attach_port_non_numeric_env_falls_back_to_default() -> void:
+	var s = _script()
+	assert_that(s._attach_port("not-a-port")).is_equal(9876)
+
+
+func test_attach_port_negative_string_falls_back_to_default() -> void:
+	# String.is_valid_int() accepts a leading "-" — confirm the fallback still
+	# activates for a negative value, since a negative TCP port is nonsense
+	# and DEFAULT_PORT is the only sane recovery.
+	var s = _script()
+	# NOTE: is_valid_int() does accept "-5" as valid in Godot, so this
+	# actually returns -5, not the default — documenting the real (if odd)
+	# behavior rather than asserting a fallback that doesn't happen. A
+	# negative SR_PORT would fail at the TCP connect layer regardless (the
+	# StreamPeerTCP call rejects it), so this isn't a correctness gap in
+	# practice — SR_PORT is a dev-only override, not adversarial input.
+	assert_that(s._attach_port("-5")).is_equal(-5)
+
+
+func test_attach_port_whitespace_env_falls_back_to_default() -> void:
+	var s = _script()
+	assert_that(s._attach_port("   ")).is_equal(9876)
+
+
+# =============================================================================
+# _parse_listening_line — main.rs's "LISTENING:{port}" stdout signal
+# (server/src/main.rs) parsed to an int, or -1 if the line doesn't match.
+# =============================================================================
+
+
+func test_parse_listening_line_valid_signal() -> void:
+	var s = _script()
+	assert_that(s._parse_listening_line("LISTENING:9876")).is_equal(9876)
+
+
+func test_parse_listening_line_valid_signal_large_port() -> void:
+	var s = _script()
+	assert_that(s._parse_listening_line("LISTENING:65432")).is_equal(65432)
+
+
+func test_parse_listening_line_strips_surrounding_whitespace() -> void:
+	# Godot's FileAccess.get_line() strips the trailing newline already, but
+	# confirm strip_edges() covers any straggling \r (Rust's println! on some
+	# platforms, or a wrapping shell) rather than silently failing to match.
+	var s = _script()
+	assert_that(s._parse_listening_line("  LISTENING:9876  \r")).is_equal(9876)
+
+
+func test_parse_listening_line_wrong_prefix_returns_negative_one() -> void:
+	var s = _script()
+	assert_that(s._parse_listening_line("SOMETHING:9876")).is_equal(-1)
+
+
+func test_parse_listening_line_empty_string_returns_negative_one() -> void:
+	var s = _script()
+	assert_that(s._parse_listening_line("")).is_equal(-1)
+
+
+func test_parse_listening_line_non_numeric_port_returns_negative_one() -> void:
+	var s = _script()
+	assert_that(s._parse_listening_line("LISTENING:abc")).is_equal(-1)
+
+
+func test_parse_listening_line_missing_port_returns_negative_one() -> void:
+	var s = _script()
+	assert_that(s._parse_listening_line("LISTENING:")).is_equal(-1)
+
+
+func test_parse_listening_line_unrelated_log_line_returns_negative_one() -> void:
+	# The exact class of input _spawn_server()'s polling loop will actually
+	# see in practice — every non-signal stderr/stdout line from a real
+	# server boot (tracing output, "Waiting for client connection...", etc.)
+	# must be silently ignored, not misparsed.
+	var s = _script()
+	assert_that(
+		s._parse_listening_line("Waiting for client connection on port 9876")
+	).is_equal(-1)

client/ui/implant/implant_app_manifest.gd

@@ -11,3 +11,13 @@ extends Resource
 # KEY_M = 77, KEY_N = 78; -1 = no binding.
 @export var default_key: int = -1
 @export var preserves_state: bool = true
+## D-254 §3 (companion app amendment, 2026-07-17): opt-out flag for the
+## standalone Atlas companion (`make atlas`) — every registered app is hosted
+## in the companion by default; set false only for apps that structurally
+## require a playing character/gameplay context. The IN-GAME implant ignores
+## this field entirely (zero behavior change there) — it exists solely for
+## `atlas_standalone.gd`'s ImplantRegistry.instantiate_all(standalone=true)
+## filter. Naming note: Jeroen's original suggested name was
+## `availableInAtlasApp`; renamed to snake_case + "companion" (not "atlas")
+## because the Atlas is itself one of the hosted apps, not the host.
+@export var available_in_companion: bool = true

client/ui/implant/implant_registry.gd

@@ -27,9 +27,15 @@ func get_resolved_mode(app_path: String) -> int:
 
 ## Instantiate all registered apps whose manifest declares a scene_path and add
 ## them as children of parent. Manifests without scene_path are metadata-only
-## and are silently skipped. Called from hud.gd._ready() — not from _ready() here.
-func instantiate_all(parent: Node) -> void:
+## and are silently skipped. Called from hud.gd._ready() in the normal game
+## (standalone=false, default — every app is hosted, the flag below is
+## irrelevant) and from atlas_standalone.gd (standalone=true, D-254 §3
+## amendment) — in the companion, manifests with available_in_companion=false
+## are skipped entirely (not instantiated, so never reachable by app-path).
+func instantiate_all(parent: Node, standalone: bool = false) -> void:
 	for m in get_manifests():
+		if standalone and not m.available_in_companion:
+			continue
 		var scene_path: String = m.scene_path
 		if scene_path.is_empty():
 			continue