feat(datagrid): add visible add and remove buttons to the table structure editor (#1319)

[datlechin]

Fixes #1319 — the table structure editor has no visible button to add a column, index, or foreign key. The reporter (on macOS 14) found only the Add Index entry by right-click and missed the Add Column one; the maintainer agreed to track this for UI/UX improvement.

Why it was undiscoverable

TableStructureView's toolbar was only a centered segmented sub-tab picker — no + anywhere. The only add affordances were the right-click empty-space menu (one entry per sub-tab) and the Cmd+Shift+N shortcut. The EmptyStateView.indexes(onAdd:) / .foreignKeys(onAdd:) convenience initializers had been sitting unused, waiting for this work. The docs/features/table-structure.mdx page already described "Open Structure → Columns, click +" — the docs were aspirational; this PR makes the app match what it says.

The fix

Add / Remove controls live on the existing bottom status bar, in the trailing slot that already hosts Columns / Filters / Pagination in Data mode. Each mode owns that slot:

• Data mode: Columns, Filters, Pagination (unchanged).
• Structure mode: a joined ControlGroup with + and −, labels and capability adapt to the active sub-tab (Columns / Indexes / Foreign Keys).
• JSON mode: empty.

The Data | Structure | JSON picker stays anchored at the leading edge in all modes — it does not shift position when the mode changes.

+ routes to gridDelegate.dataGridAddRow() (same path as Cmd+Shift+N). − routes to gridDelegate.dataGridDeleteRows(selectedRows) (same path as right-click Delete, and now wired to Cmd+Delete). Tooltip and accessibility label per sub-tab: Add Column / Add Index / Add Foreign Key and the matching Remove labels. + is disabled when the sub-tab's capability flag is false; − is also disabled when no row is selected. Controls hide entirely when !connection.type.supportsSchemaEditing or on the read-only .ddl / .parts sub-tabs.

When the Indexes or Foreign Keys sub-tab is loaded and empty, the grid is replaced by ContentUnavailableView with a labelled Add button (EmptyStateView.indexes(onAdd:) / .foreignKeys(onAdd:)).

Architecture

• StructureFooterState (new, @Observable) is the single source of truth for capability / label state. TableStructureView publishes to it on appear, sub-tab change, and selection change; MainStatusBarView reads it to decide which buttons to render and when to enable them.
• StructureViewActionHandler.removeRow is added alongside addRow. MainContentCommandActions.deleteSelectedRows routes to it when resultsViewMode == .structure, giving Cmd+Delete parity with Cmd+Shift+N.
• MainStatusBarView is now mode-aware: in Structure mode the data-only chrome (row info, Columns popover, Filters toggle, pagination) is hidden, so the status bar shows just the picker and + / −.

Considered and rejected

• Separate footer above the global status bar. Causes a visual double bar with the existing Data | Structure | JSON row; native apps consolidate into one footer.
• Leading-edge + / − next to the picker. Pushes the picker sideways when switching modes — the segmented control should not move.
• Top-toolbar + / − next to the segmented picker. Native macOS reserves the top toolbar for window-level actions; bottom is the list-editor pattern.

Tests

• StructureGridDelegateAddRowTests (new) covers dataGridAddRow() per sub-tab (columns / indexes / FK route to the correct mutator; ddl / parts are no-ops; SQLite indexes is a no-op via supportsAddIndex: false) and dataGridDeleteRows([0]) safety on the read-only sub-tabs.
• StructureActionHandlerTests covers addRow and removeRow closure dispatch.
• CommandActionsDispatchTests asserts addNewRow and deleteSelectedRows route to structureActions?.addRow?() / structureActions?.removeRow?() when resultsViewMode == .structure.
• MainStatusBarLayoutTests updated for the new structureFooterState / onStructureAdd / onStructureRemove params.

Out of scope

• TablePlus-style inline "Make this an FK from this column" UX. Separate enhancement.
• The unused EmptyStateView.columns(onAdd:) and .checkConstraints(onAdd:) convenience initializers — this PR uses .indexes and .foreignKeys; the other two are dead but unrelated cleanup.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Gate empty add states on schema editing

For schema-read-only connections that still expose metadata capabilities (for example CockroachDB has supportsSchemaEditing == false while supportsForeignKeys == true, and index add support defaults to true), this condition replaces the read-only grid with an empty state containing an active Add button. Clicking it calls gridDelegate.dataGridAddRow(), whose index/FK paths do not check supportsSchemaEditing, so users can create unsavable structure changes even though the footer is correctly hidden and the grid is non-editable. Include connection.type.supportsSchemaEditing in these empty-state gates (and the FK one below) or render a non-action empty state for read-only connections.

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