fix: wire up three unreachable UI affordances

[vibhavkatre]

Follow-up to the cleanup audit (#24). That audit found code that exists and works but has no way to reach it from the UI — these read as bugs to a user, not as missing features, so this PR wires all three.

1. Mind-map cross-links could be created but never deleted

The overlay has a "Link to node" button and the node layer renders the links, but nothing ever called unlinkNodes. A cross-link could only be undone via undo history — and once the session moved on, not at all.

Cross-links are now selectable and removable (Delete/Backspace, or the × at the link's midpoint). An invisible 12px hit-line makes the 1.5px dotted line comfortably clickable, and the selected link turns blue.

Selection details that matter:

• A cross-link isn't a node, so it can't live in store.state.selection (which holds node ids). It gets its own slot, mindmapUi.selectedCrosslinkId.
• Node and link selection are mutually exclusive — selectNode() clears the link, and Delete only targets a link when no node is selected. Delete never has two plausible targets.
• Escape deselects; pressing empty canvas clears it, so the × never lingers.
• Clicking a link while "click a target node" is armed is ignored, so it can't steal the link-creation click.

2. Mind-map focus mode had no activator

Isolating one branch (dimming the rest to 12%) was fully implemented — MindMapNodeLayer already read mindmapUi.focusId — but nothing could turn it on. There's now a "Focus this branch" toggle in the contextual toolbar.

The way out is deliberately a separate always-visible pill at the top of the screen, not that toolbar button: the contextual toolbar only renders while a node is selected, so clicking empty canvas while focused would otherwise hide the only exit and strand the user in a dimmed map.

3. Palette tiles couldn't be dragged onto the canvas

The receiving side was always live — DiagramCanvas binds dragover/drop and onCanvasDrop places the shape at the drop point (or a two-endpoint line for connectors) — but no tile called startPaletteDrag, so nothing produced a payload and the gesture silently did nothing. All three tile groups (Recent, Shapes, Lines & connectors) are now draggable.

Two details:

• The popover closes on dragend, not dragstart — closing on dragstart unmounts the dragged element, which cancels the drag in some browsers.
• startPaletteDrag also arms draw mode, so releasing outside the canvas leaves the tool ready, matching what clicking the tile does.

DATA_TRANSFER_KEY is now exported so a test can pin the producer/consumer contract. That's the failure mode worth guarding: the halves live in different files, agree only on that string, and a mismatch makes the gesture a silent no-op — exactly the bug being fixed.

Note on the fourth item

The audit also flagged duplicate_diagram as unwired. On closer inspection that was a misclassification — Duplicate already works from the tile menu, implemented frontend-side via the list resource (TileGrid.duplicate), the same way trash and delete are. The backend endpoint is therefore superseded, not missing, and is removed in #26 alongside the others.

Testing

• 114 vitest pass (102 before — 12 new: 7 in stores/mindmapUi.test.js, 5 in composables/useShapeCreation.test.js)
• Tests cover selection exclusivity, Delete routing in both directions, cross-link removal as one undo step, focus always toggling off, and the drag payload contract
• One test documents an existing good behaviour the work surfaced: deleteSubtree already prunes cross-links touching a removed node, so deleting an endpoint leaves no dangling link
• yarn build clean

Not yet verified in a live browser — local Playwright driving is blocked on site credentials.

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

Both previously reported focus-state failures are fixed, and no blocking failure remains.

_{Reviews (5): Last reviewed commit: "fix(mindmap): clear the mind-map chrome ..." | Re-trigger Greptile}