fix(studio): dedupe repeated selection telemetry

[jrusso1020]

What

• Ignore repeated non-additive selections of the same DOM target instead of rewriting selection and timeline state.
• Emit studio:tab_switch only when the right-panel tab or visible inspector pane actually changes.
• Keep explicit same-target refreshes and flat-inspector Design/Layers restoration working.
• Move the useDomSelection type contract into a focused module so the hook remains within the repository's file-size limit.

Why

A single Studio installation repeatedly selected the same target and reopened the already-active Design tab. Each pass recreated selection state, republished it, and emitted another studio:tab_switch, producing millions of events for one PostHog distinct ID and triggering PostHog's high-volume-ID protection.

The redundant state churn also amplified studio:studio_selection_publish_failed when the local Studio selection endpoint was unavailable.

This is a product-side event loop. No PostHog project configuration change is required; person processing should remain enabled for these real installation-scoped events.

How

• Compare the current single selection and group against the incoming target before changing state.
• Preserve panel reveal behavior on repeated selection, while relying on the panel setter's same-state guard.
• Track right-panel transitions through refs so rapid repeated calls within one render batch emit once.
• Treat inspector-pane visibility as part of the transition, preserving the case where the umbrella tab is already design but the flat inspector currently shows Layers.
• Allow preserveGroup refreshes through so changed selection metadata is not hidden.

Test plan

• Unit tests added/updated
• Manual testing performed
• Documentation updated (not applicable; internal behavior)

Verified on current origin/main:

• 53/53 relevant Studio tests pass across selection, panel layout, timeline sync, and Studio test-hook coverage.
• Studio TypeScript typecheck passes.
• Oxfmt and Oxlint pass on all changed files.
• Fallow audit gate passes with no new issues.
• Repository pre-commit and commit-message hooks pass, including file-size and tracked-artifact gates.

Additional suite evidence: a prior full Studio run passed 4,467 tests and reported 11 load-sensitive failures in two unrelated test files; both files then passed independently (27/27).

[miguel-heygen]

Reviewed at exact head e746e41be66356db224f3d4916fd3667616f9b14.

Code audit: read all five changed files and enumerated every applyDomSelection, setRightPanelTab, and studio:tab_switch site. The same-target guard runs before selection/timeline state mutation, but still reveals the inspector; preserveGroup refreshes remain additive to metadata; Variables stays in place. The panel refs make same-render-batch calls compare against the latest requested tab/pane rather than stale React state, so a real flat-inspector Layers→Design reveal emits once while repeated calls emit zero.

Verification: full repository build passed. The five focused Studio files passed 53/53 tests; Studio typecheck, Oxfmt check, and Oxlint passed. All hosted exact-head checks are green.

Runtime — synthetic local Studio PR build: a fixture composition selected #headline through the documented window.__studioTest hook. The first selection produced one /api/projects/qa3498/selection PUT; 100 sequential same-target selections produced zero additional PUTs. With the flat inspector showing Layers, two repeated selections restored Design and still produced zero selection PUTs. No page errors were reported. This validates client selection/panel behavior only; no production data or PostHog project configuration was touched.

Non-blocking existing asymmetry: direct Design/Layers button changes go through setExclusiveRightInspectorPane and still do not emit tab_switch; this PR correctly dedupes and restores the setRightPanelTab path that caused the storm, but it does not make direct pane-click analytics complete.

Verdict: APPROVE
Reasoning: The state guard removes the high-volume loop without suppressing explicit refreshes or inspector restoration, and code, focused tests, hosted CI, and the live Studio witness agree.

— Magi