Track client operations and show inline progress

docs/product/frontend-operations.md

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+# Frontend operation registry
+
+Harbor tracks active browser mutations by operation key instead of one global `busy` flag:
+
+- `connection`: start, stop and restart;
+- `serverApply`: apply the selected server;
+- `subscriptionImport`, `subscriptionRefresh`, `subscriptionDelete`;
+- `gatewayAuto`: change the active route preference.
+
+Each entry is `{ status: "running", startedAt }`. A repeated operation key receives the same in-flight Promise, so a double click sends one request. A conflicting key resolves to `false` without starting its action. The symmetric conflict matrix lives in `src/web/state/operations.js`.
+
+The registry only disables controls that can mutate the same domain state. Copy actions, instruction navigation and local tabs remain available during subscription refresh. Progress is announced with `role="status"`; the structured error from TASK-004 remains `role="alert"` after failure.
+
+Subscription URL validation uses a latest-request runner. Starting a new validation aborts the previous signal and ignores its result even if the underlying request resolves late.
+
+The registry is local transport/UI state. It does not replace backend `snapshot.operation`, change revisions or persist data. Rollback is frontend-only. A `diagnostics` key is intentionally deferred until TASK-016 adds a diagnostics operation to run.