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+# Microtables – TODO
+
+## 1. Keyboard Navigation & Table Bounds
+
+- [ ] **1.1 Decouple table size from keyboard movement**
+
+  Currently `press-enter-in-cell` uses `highest-row`/`highest-col` to decide where to move, coupling navigation to data extent. Intended design:
+  - `highest-row`/`highest-col` should include the cursor's current position
+  - `press-enter-in-cell` should only increment the position
+  - Add a dedicated event handler for Tab (native Tab is no longer sufficient)
+
+- [ ] **1.2 Add arrow-key navigation**
+
+  Implement `ArrowUp`, `ArrowDown`, `ArrowLeft`, `ArrowRight` handlers that move the cursor between cells, firing from `on-keyDown` (not `on-keyPress`). Navigation logic should live alongside Enter/Tab handling (1.1).
+
+- [ ] **1.3 Determine initial table size and scroll behaviour**
+
+  `maxrow = 20` and `maxcol = "G"` are hardcoded. Decide whether the grid grows as the cursor reaches the edge or stays fixed with a scroll container. A fixed viewport with overflow scroll is likely right for the quick-calculation use case.
+
+- [ ] **1.4 Movement within a range selection**
+
+  When a range is selected, Enter/Tab/arrow keys should cycle within the selection rather than the full table. Depends on the selection model (see section 5).
+
+---
+
+## 2. Formula Evaluation Engine
+
+- [ ] **2.1 Support lowercase cell references**
+
+  `parse-variables` already uppercases symbol names, but confirm end-to-end that typing `=a1 + b2` in a cell evaluates correctly.
+
+- [ ] **2.2 Clarify dirty-forward-reference error semantics**
+
+  `gather-variables-and-evaluate-cell` returns `:error` when forward references are dirty, but the intended semantics vs. `:insufficient-data` are not fully specified. Clarify and document the distinction.
+
+- [ ] **2.3 Verify `evaluate-all` handles cycles correctly**
+
+  `evaluate-all` calls `evaluate-from-cell` which runs `find-cycle`, so cycles should be caught at initialization. Confirm this is sufficient and clean up the open question.
+
+- [ ] **2.4 Handle multiple cells modified simultaneously**
+
+  The model processes one cell change at a time. A batch-update path will be needed for paste operations or future server sync.
+
+- [ ] **2.5 Consider incremental diff for back-reference updates**
+
+  `denotify-references` + `notify-references` wipe and re-add all back-references on every edit. Diffing old vs. new `:refs` and updating only the delta may help at scale.
+
+- [ ] **2.6 Consider memoizing `find-cycle`**
+
+  Evaluate whether a dynamic memoization strategy with cache invalidation on data change is worth the complexity.
+
+---
+
+## 3. Tests
+
+- [ ] **3.1 Unit tests for formula evaluation**
+
+  Cover the core evaluation engine with unit tests:
+  - Basic arithmetic formulas
+  - Cell references and chained references
+  - Range functions (`sum`, `average`, etc.)
+  - Cycle detection
+  - Error propagation (`:calc-error`, `:cycle-error`, `:insufficient-data`)
+  - Lowercase cell references (see 2.1)
+  - Edge cases: empty cells in ranges, self-references, deeply nested dependencies
+
+- [ ] **3.2 Integration tests for state transitions**
+
+  Test re-frame event handlers end-to-end through the db:
+  - Editing a cell and verifying downstream re-evaluation
+  - Entering and leaving a cell
+  - Reference graph updates when a formula changes
+
+- [ ] **3.3 End-to-end tests**
+
+  Browser-level tests covering full user flows:
+  - Data entry and formula results visible in cells
+  - Keyboard navigation
+  - Range selection operations (once implemented)
+  - Touch interactions (once implemented)
+
+---
+
+## 4. Formula Autocomplete
+
+- [ ] **4.1 Show available math functions after `=` is typed**
+
+  When a cell value begins with `=`, display a dropdown of available math.js functions. Filter the list as the user continues typing. Selecting an item inserts the function name with a placeholder for arguments.
+
+- [ ] **4.2 Cell and range reference autocomplete**
+
+  As the user types a column letter that could start a cell reference (e.g. `A`), suggest cell addresses that contain data. For ranges, trigger suggestions when `:` follows a cell reference.
+
+- [ ] **4.3 Argument hint tooltip**
+
+  Inside a function call, show a tooltip indicating expected arguments and their types (e.g. `sum(value1, value2, ...)`).
+
+---
+
+## 5. Selection & Highlight Mode
+
+- [ ] **5.1 Implement the selection data model**
+
+  The `:selection` key in `:position` is always `nil`. Implement `{:start {:col "A" :row 1} :end {:col "C" :row 3}}` as the selection shape. Set on shift+arrow or click-drag; clear on unmodified navigation.
+
+- [ ] **5.2 Wire up highlight rendering for selected cells**
+
+  `highlight-cells` in `subs.cljs` already sets `:view :highlighted` on cells within a selection range, but the `::table-data` subscription never calls it when `:selection` is non-nil. Connect the two so selected cells receive the `highlighted` CSS class.
+
+- [ ] **5.3 Aggregate display for a selection**
+
+  When a numeric range is selected, display the sum and average in the UI (e.g. a status bar or floating chip). Offer to insert the result as a formula into a user-chosen cell.
+
+---
+
+## 6. Cell & Range Control Buttons
+
+When a cell or range is selected, show a compact set of floating action buttons positioned around the selection. Buttons must be large enough to tap comfortably on a phone screen. Implement in this order:
+
+- [ ] **6.1 Expand / contract selection** — drag handles or +/− buttons to resize the selection boundary
+- [ ] **6.2 Calculate** — show sum/average inline for numeric selections (ties into 5.3)
+- [ ] **6.3 Clear** — delete cell contents and re-evaluate dependents
+- [ ] **6.4 Copy** — copy selection to the clipboard
+- [ ] **6.5 Move** — designate a new top-left cell; handle destination conflicts
+- [ ] **6.6 Delete** — remove cells and displace neighbours inward
+- [ ] **6.7 Intelligent fill** — trigger pattern inference (see section 10)
+
+---
+
+## 7. Column & Row Aggregates
+
+*Under consideration.*
+
+- [ ] **7.1 Always-visible column totals row**
+
+  A pinned row below the table showing the sum (and possibly average) of each column, updating reactively. Show only for columns that contain numbers.
+
+- [ ] **7.2 Always-visible row totals column**
+
+  Equivalent pinned column to the right of the table for row aggregates.
+
+---
+
+## 8. UI & Control Panel
+
+- [ ] **8.1 Implement a compact, functional control panel**
+
+  The current left and bottom panel slots exist but contain only placeholder content. Replace with a small, well-designed panel surfacing the most useful controls. The panel should stay visually aligned with the table as it scrolls (likely `position: sticky` or a scroll event listener).
+
+- [ ] **8.2 Add a "Help" modal**
+
+  A small modal (triggered from the control panel) listing and explaining:
+  - Supported formula syntax
+  - Available math functions
+  - Keyboard shortcuts
+  - How cell references and ranges work
+
+- [ ] **8.3 Replace "About" with a popup modal**
+
+  Remove the current inline disclaimer text. Add an About button that opens a conventional modal with app info, version, and credits.
+
+- [ ] **8.4 Replace the logo**
+
+  The current `logo.svg` is a placeholder. Design and replace with a better mark.
+
+---
+
+## 9. Touch Support
+
+- [ ] **9.1 Make cells tap-friendly**
+
+  Ensure cells are large enough to tap accurately on mobile. Tap to select, double-tap or long-press to enter edit mode. The current `on-focus`/`on-blur` model may need adjustment for touch events.
+
+- [ ] **9.2 Touch-friendly range selection**
+
+  Implement tap-and-drag or tap-then-drag-handle selection. The floating control buttons (section 6) should be comfortably tappable.
+
+- [ ] **9.3 Responsive layout**
+
+  Adapt the layout to small screens: control panel sidebars should collapse by default on mobile; consider a bottom sheet instead of a side panel.
+
+- [ ] **9.4 Software keyboard handling**
+
+  On mobile, the software keyboard resizes the viewport and may conflict with cell navigation. Ensure formula entry and cell-to-cell movement work correctly with a software keyboard open.
+
+---
+
+## 10. Intelligent Fill
+
+*Longer-term.*
+
+- [ ] **10.1 Pattern inference from a selection**
+
+  When a user selects a range and triggers fill (via the control button in 6.7), infer the pattern (arithmetic sequence, geometric, repeated value, date sequence, etc.) and propose a continuation into adjacent empty cells.
+
+- [ ] **10.2 Fill preview and confirmation**
+
+  Show a preview of the proposed fill before committing, allowing the user to accept, adjust the inferred pattern, or cancel.
+
+---
+
+## 11. Data Persistence
+
+*Long-term consideration — not yet committed.*
+
+- [ ] **11.1 Local storage persistence**
+
+  Save the table to the browser's `localStorage` on change and restore on page load. Provides durable-but-local storage with no backend required.
+
+- [ ] **11.2 Server-side persistence**
+
+  Extend the Express server to store table data, with considerations for:
+  - Authentication / account model
+  - Paid vs. free tier
+  - Expiry / TTL on stored tables
+  - Conflict resolution for future collaboration
+
+- [ ] **11.3 Table sharing**
+
+  Allow a user to share a table with others via a link. Requires server-side persistence (11.2). Considerations:
+  - Read-only vs. editable share links
+  - Expiry / revocation of share links
+  - Real-time collaboration (multiple users editing simultaneously)
+
+---
+
+## 12. Code Refactoring
+
+- [ ] **12.1 Rewrite `create-all-references` to use `walk-modify-data`**
+
+  Both functions perform a `reduce-kv` double-walk over the data map. Eliminate the duplication by having `create-all-references` call `walk-modify-data`.