Function maybe_reuse_editor_pane 

pub(super) async fn maybe_reuse_editor_pane(
    state: &AppState,
    caller_block_id: &str,
    file: &str,
    connection: &str,
) -> Result<Option<PaneOpenResult>, String>

If the calling agent (identified by its own block id, caller_block_id) already has an Editor pane open in its own tab, push file into that pane as a new tab instead of creating another Editor pane. Returns Ok(None) when there’s no existing Editor pane to reuse (or the caller’s tab can’t be resolved) — the normal create-new-block path handles that case unchanged.

Known, accepted limitation: does not apply layout focus. An earlier version of this function resolved the reused block’s layout leaf id and dispatched Command::SetFocusedNode — reagent (PR #2404) confirmed the leaf-id resolution itself was correct, then found a deeper problem: the frontend’s onBackendUpdate (frontend/layout/lib/layoutPersistence.ts) only re-derives focusedNodeId at initial model construction or via a pendingBackendActions-driven tree action — a bare focusednodeid MuxObj push to an ALREADY-MOUNTED LayoutModel (confirmed by reading the function directly: no branch reads muxObj.focusednodeid outside those two triggers) is silently never applied to the live treeState. Making that work would mean changing onBackendUpdate’s reactivity — shared code this file’s own comments show has deliberately been kept narrow/non-reactive before (see the dangling-leaf-prune history right above it) — a real, separate piece of work, not a one-line fix. Shipping a backend dispatch that compiles and passes a reducer-internal test but has no visible frontend effect would be worse than not attempting it: it would look done without being done. The reused pane’s new tab still becomes its own active tab via openFile(); only the cross-pane layout-focus indicator is unaffected, same as before this feature existed.