fix(mobile): split-view inspectors stop re-registering on every render#21973

Problem

In split view, a screen that shows a workspace inspector (thread Files/Git, file screen) deactivates and re-registers it on almost every render. Each re-registration writes { render, active: true } into layout state, so the whole workspace layout re-renders again while a turn streams.

There are two causes:

1. useRegisterWorkspaceInspector: #21133 passed an inline callback to useFocusEffect, and that callback calls a useEffectEvent function. An effect event changes identity on every render, so the compiled callback changes on every render too. useFocusEffect re-runs when its callback changes, which means a deactivate and a register on every render. Effect events are only meant to be called from inside effects, not used as an identity anything depends on. This was the re-register half of the loop in #21866. #21867 stopped the context churn, which ended the crash, but not this.
2. ThreadFileScreen: relativePath came from a plain call, normalizeRoutePath(params.path). The compiler can't tell that its result is never mutated, so it treats it as live while it's passed to later functions, and that range crosses several hook calls. The compiler prunes any scope that spans a hook, so one pruned block took 24 values with it, renderInspector among them. A new renderInspector meant a new inspector renderer on every render, and the hook's [wrappedRender] effect re-registered each time.

Change

• The hook subscribes to the screen's focus and blur events in a plain useEffect keyed on [navigation], and calls the effect event only inside those listeners. Nothing depends on the effect event's identity anymore. Unmount cleanup moved into the same effect. I didn't use useIsFocused, because react-native-screens freezes blurred screens, so a screen that has to re-render to notice a blur would leak its pane.
• useThreadFilesWorkspace now resolves relativePath along with the rest of the route's workspace. A hook's return value is frozen, so nothing spans the later hooks, and the compiler caches renderInspector without any manual memo.

There's no useMemo, useCallback, or stable-callback useState/useRef. The hook still re-registers when the inspector's content changes, because that's how the pane gets new content.

Scope and approval

This is a small, focused fix for a regression from #21133, and it finishes the loop fix from #21866 / #21867. It touches only the registration hook and the file screen. It changes no behavior and no UI.

Validation

Compiler output (repo babel config, the same setup as reactCompilerCoverage.test.ts):

Nothing new bails out in either file. The registration effect's dependency array is now just [navigation]. useThreadFilesWorkspace keeps the 1 pruned block it already has on main.

Registration counts (jsdom). I compiled the real hook source with the React Compiler, mounted it under a workspace host and a mock navigation object, and rendered the registering screen 20 times:

Blur, a render while blurred, refocus, and unmount behave the same on both: blur deactivates once, nothing registers while blurred, and refocus registers once. These harness numbers replace the earlier iPad simulator counts, which were measured on the previous version of this fix.

Checks:

• reactCompilerCoverage.test.ts passes (894 tests).
• vp run typecheck in apps/mobile passes.
• vp lint on both files reports the same 3 warnings as main.

ThreadRouteScreen's own inspector renderer still changes whenever the thread does. That's a separate cause, and this PR doesn't change it.

Claude Opus 5.5 via Claude Code in T3 Code