feat: make the radiator report its own internal state

v1.1.0 loaded cleanly and still did nothing, so the NetworkValue rewrite
was not the whole story. Rather than keep guessing at which link in the
chain is dead, add indicator icons bound to the internal signals.

An indicator draws while its toggle is off, so one glance at a radiator
now separates the cases that were previously indistinguishable:

  wrench absent   -> the AddBase never merged; nothing in the mod runs
  thermal missile -> no thermal-ammo signal arriving
  resource        -> no hold signal arriving from a battery

Tests check that every added indicator binds to a component that exists
and to a sprite that exists in the indicators atlas.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011oLWY1G6S8U35bi2FxVWni

README.md

@@ -136,6 +136,25 @@ An auto-idled radiator shows the same "powered off" indicator icon as a manually
 switched-off one, and stops emitting its steam plume. That icon appearing on a
 radiator you did *not* switch off is the mod working.
 
+## Reading the diagnostic icons
+
+The radiator reports its own internal state through indicator icons. An icon is
+drawn while its toggle is **off**, so:
+
+| Icon on a radiator | Meaning |
+|---|---|
+| 🔧 wrench (`MissingComponent`) | **Always expected.** Its absence means the mod's components never merged onto the part, and nothing else in the mod is running. |
+| thermal missile | No thermal-ammo signal is reaching this radiator — no launcher on its heat network is set to Thermal Canister Missiles. |
+| resource | No hold signal is reaching this radiator — no thermal battery on its network is asking it to hold. |
+| power-off | The radiator is idle: either you switched it off, or the automation idled it. |
+
+A correctly working setup, on a ship with a thermal launcher and a battery below
+the vent ceiling, shows **the wrench alone**.
+
+These make the failure legible rather than guessable: wrench missing points at
+the patch mechanism, either other icon points at the specific signal that is
+dead.
+
 ## Status
 
 Validated against game data version 0.30.4c, and confirmed to load cleanly

components/radiator_auto.rules

@@ -83,3 +83,14 @@ AutoPowerToggle
 	Toggles = [ PowerToggle, AutoRad_VentAllowed ]
 	Mode = All
 }
+
+// Diagnostic anchor. An indicator icon shows while its toggle is OFF, so an
+// icon bound to this one is visible whenever these components were merged onto
+// the part at all. If that icon is absent, the AddBase in mod.rules did not
+// take effect and nothing else in this file is running either -- which is the
+// single most useful thing to be able to tell apart from a dead signal.
+AutoRad_AlwaysOff
+{
+	Type = StaticToggle
+	ToggleOn = false
+}

mod.rules

@@ -16,7 +16,7 @@
 
 ID = ganter.auto_radiator
 Name = "Auto Radiator"
-Version = 1.1.0
+Version = 1.2.0
 CompatibleGameVersions = ["0.30.4c", "0.30.4"]
 ModifiesGameplay = true
 Author = "Tobias Ganter"
@@ -118,4 +118,49 @@ Actions
 			Toggle = AutoPowerToggle
 		}
 	}
+
+	// --- Diagnostic indicators -------------------------------------------
+	//
+	// An indicator icon is drawn while its toggle is OFF. These three make the
+	// radiator report its own internal state, so a radiator that is not
+	// behaving can be read directly instead of guessed at:
+	//
+	//   wrench icon      always visible -> these components merged onto the part
+	//                    absent        -> the AddBase did not take effect
+	//   thermal missile  visible       -> no thermal-ammo signal is arriving
+	//   resource icon    visible       -> no hold signal is arriving from a battery
+	//
+	// A working setup on a ship with a thermal launcher and a battery below the
+	// vent ceiling shows the wrench alone.
+	{
+		Action = AddMany
+		AddTo = "<ships/terran/radiator/radiator.rules>/Part/Components/Indicators/Indicators"
+		ManyToAdd
+		[
+			{
+				Toggle = AutoRad_AlwaysOff
+				AtlasSprite
+				{
+					File = &/INDICATORS/MissingComponent
+					Size = [1, 1]
+				}
+			}
+			{
+				Toggle = AutoRad_ThermalAmmoInUse
+				AtlasSprite
+				{
+					File = &/INDICATORS/NoThermalMissiles
+					Size = [1, 1]
+				}
+			}
+			{
+				Toggle = AutoRad_IsHolding
+				AtlasSprite
+				{
+					File = &/INDICATORS/NoResource
+					Size = [1, 1]
+				}
+			}
+		]
+	}
 ]

tests/test_mod.py

@@ -365,7 +365,50 @@ def test_no_name_collisions_with_vanilla():
 
 
 # ---------------------------------------------------------------------------
-# 7. The mod manifest must declare the fields Cosmoteer requires.
+# 7. Added indicators must bind to a real toggle and a real atlas sprite.
+# ---------------------------------------------------------------------------
+
+def test_added_indicators_are_valid():
+    mod = rules_parser.parse_file(os.path.join(MOD_ROOT, "mod.rules"))
+    radiator_components = resolve("<ships/terran/radiator/radiator.rules>/Part/Components")
+    added = rules_parser.parse_file(os.path.join(MOD_ROOT, "components", "radiator_auto.rules"))
+    known = set(added.order) | set(radiator_components.order if radiator_components else [])
+
+    atlas = vanilla("gui/game/indicators/indicators.rules")
+    check(atlas is not None, "cannot read the indicators atlas")
+
+    for action in iter_actions(mod):
+        kind = action.get("Action")
+        add_to = action.get("AddTo")
+        if not kind or kind.value != "AddMany" or add_to is None:
+            continue
+        if "Indicators" not in add_to.value:
+            continue
+        entries = action.get("ManyToAdd")
+        check(entries is not None, "indicator AddMany has no ManyToAdd list")
+        if entries is None:
+            continue
+        for key in entries.order:
+            entry = entries.children[key]
+            toggle = entry.get("Toggle")
+            check(toggle is not None, "an added indicator has no Toggle")
+            if toggle is not None:
+                check(
+                    toggle.value.strip() in known,
+                    f"added indicator binds to unknown component '{toggle.value.strip()}'",
+                )
+            sprite = entry.get("AtlasSprite/File")
+            check(sprite is not None, "an added indicator has no AtlasSprite/File")
+            if sprite is not None and atlas is not None:
+                name = sprite.value.strip().rsplit("/", 1)[-1]
+                check(
+                    name in atlas.children,
+                    f"added indicator uses unknown atlas sprite '{name}'",
+                )
+
+
+# ---------------------------------------------------------------------------
+# 8. The mod manifest must declare the fields Cosmoteer requires.
 # ---------------------------------------------------------------------------
 
 def test_manifest_is_well_formed():