fix(builder): re-enable Preview after patient-column changes

[matthewpeterkort]

Why

Changing a patient column while Preview was in flight left the old preview request loading. The toolbar derives its busy state from that request, so Preview could remain disabled after the column command completed. Stale preview recovery could also resume after the edit and start more work.

Changing the row limit exposed a related overlap bug in the shared mutation hook. Settlement of the aborted preview cleared its single loading boolean while the replacement preview was still active.

Scope

• Own and abort the active preview request when commands or Explorer selection invalidate it.
• Use a preview generation to prevent stale responses, errors, and recovery work from mutating current Builder state.
• Preserve current-preview retry and receipt-recovery behavior.
• Track concurrent mutation loading by pending request count so older settlements cannot clear a newer request's busy state.
• Add regression coverage for the original race, deferred catalog recovery, successful re-preview, legitimate disabled states, and overlapping row-limit previews.

Blast Radius

Preview request ownership remains local to Explorer Builder. The shared mutation hook now reports aggregate loading across concurrent calls, which is the intended contract for all mutation consumers. Preview eligibility rules, compile ownership, and command serialization remain intact.

Verification

• npm test in ui: 19 files passed, 98 tests passed
• npm run build in ui: production package and demo builds passed
• Built Loom demo patient-column race: the edit aborted the stale request, Preview re-enabled, and no alert appeared
• Built Loom demo row-limit race: changing 25 to 50 aborted the first preview, Preview stayed disabled while the replacement ran, then enabled after it completed
• Sol medium final review: no remaining correctness blocker

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-03T18:43:31.168485Z	f742742	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: f742742098

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[chatgpt-codex-connector]

Keep loading state tied to the replacement preview

When a user changes the row limit while a preview is in flight, the enabled selector calls preview(limit) and reaches this abort immediately before starting the replacement request. The custom useMutation uses one boolean and sets it to false whenever any invocation settles (react.tsx lines 141–146), so the aborted request's asynchronous rejection clears previewStatus.isLoading after the replacement has set it to true. The toolbar therefore becomes enabled while the new preview is still running, recreating the incorrect busy state and allowing additional edits or previews; track loading by request identity/count, or disable limit changes while busy.

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