Systems 5: the game location, item icons and index status tell through signals

[Pelotrio]

Fifth PR of docs/SYSTEMS.md, stacked on #115: the owners that still told through their own listener lists tell through signals, so the pages PR can make every page follow signals only.

Finish line

Behavior	Test
Followers of the game location hear its connection, process and playing once each, in the order they happen; what the game told before its connection was established is heard as told then	GameStateTest.followersHearEachChangeOnce, GameStateTest.whatTheGameToldBeforeItsConnectionWasEstablishedCounts
Views are told of new item icons once, on the Swing thread, and not when the same snapshot comes again	ItemIconServiceTest.viewsAreToldOnceOnTheSwingThreadOnlyWhenTheSnapshotChanged
Each index status is heard as it is published	RuntimeIndexServiceTest, LocalIndexTest, RuntimeIndexRecoveryTest
A closed search popup stops following the index and ignores a status told before it closed	SearchEverywherePopupTest.disposedPopupUnsubscribesAndIgnoresQueuedRuntimeStatus
No listener list is left for these three	SystemsRulesTest (their exceptions are gone)

What changes

• GameLocation has three signals, connectionChanged, processChanged and playingChanged, instead of addListener(Consumer<Change>) and the Change enum. They fire where the changes fired before, in the same order. Followers read the location for what changed: ConfigChanges, ChangePipeline, Reloads, GamePacks, WorldReading, the configuration pages and the Project tree.
• ItemIconService has a changed signal, fired on the Swing thread after a newer snapshot was adopted, instead of its listener list. The adoption guard has its own lock object.
• RuntimeIndexService has a statusChanged signal instead of addStatusListener and removeStatusListener. The status is set and told under the lifecycle lock, so a follower reads the status that was told. CompanionApplication and the search popup read the current status once when they start following.
• docs/SYSTEMS.md: this PR comes before the pages, which can only follow signals; the order table is renumbered. The remaining exceptions in SystemsRulesTest name the PRs that remove them.

Left as it is

The debugger's session events, notifications, script runs, search matches and control events keep their listeners. They carry events, not state, as SystemsRulesTest lists them.

:companion:test passes (1642).

🤖 Generated with Claude Code

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-30T14:03:59.784037Z	8be04c2	New commits

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