feat: pinned tabs

[mathuo]

Adds a PinnedTabs module: pin a tab so it stays put — pinned tabs render before all unpinned tabs in their group, never overflow into the dropdown, resist reorder across the pin boundary, and (optionally) render on their own row. Modelled on VS Code / Chrome pinned tabs.

Additive and removable: every core seam defaults to a no-op, so a component built without the module is byte-identical to today, and the module is dormant unless pinnedTabs.enabled is set.

Capabilities

• Ordering — pinned tabs sort to the front ([pinned][unpinned]), stable pin order, active panel preserved across the reorder.
• Overflow — pinned tabs are excluded from the … overflow dropdown (pure Set.has predicate; unpinned tabs overflow as before).
• Reorder guard — a drag cannot land a tab on the wrong side of the pin boundary. Cross-boundary drag is clamped by default (togglePinOnCrossBoundaryDrag: false, Chrome-style); set it true for the VS-Code flip.
• Serialization — pinned state round-trips through toJSON/fromJSON (GroupviewPanelState.pinned, emitted only when true; old layouts load unpinned).
• Rendering — a pinned tab keeps its title plus an injected pin glyph and loses its close button (protected from a stray close; close via context menu / keyboard / unpin). compact: true opts into icon-only.
• Second row — mode: 'separate-row' mounts a pinned row above the main strip; the header grows and content reflows; the row collapses when nothing is pinned.
• Context menu — a built-in 'pin' tab-menu item renders "Pin tab"/"Unpin tab".

Public API

```ts
// options
interface DockviewOptions { pinnedTabs?: PinnedTabsOptions; }
interface PinnedTabsOptions {
enabled?: boolean; // master switch (dormant until set)
mode?: 'inline' | 'separate-row'; // default 'inline'
compact?: boolean; // default false (labelled + glyph)
togglePinOnCrossBoundaryDrag?: boolean; // default false (clamp)
contextMenuItem?: boolean;
}

// panel api
panel.api.isPinned: boolean
panel.api.setPinned(pinned: boolean): void
panel.api.onDidChangePinned: Event<{ isPinned: boolean }>

// component api
dockview.api.onDidPanelPinnedChange: Event<{ panel, isPinned }>
```

Core seams (all no-op by default → removable)

• panel.api.isPinned/setPinned/onDidChangePinned + component onDidPanelPinnedChange; pinned state lives on the panel (mirrors title), mutated through a gated DockviewComponent.setPanelPinned.
• Tabs.setOverflowExclude(fn), TabsContainer.setDropIndexResolver/resolveDropIndex, TabsContainer.setPinnedRow(el) — exposed on IHeader.
• GroupviewPanelState.pinned serialization; built-in 'pin' context-menu token.

Testing

• Unit (jsdom): ordering math, reorder-guard clamp/flip matrix, overflow-exclusion seam, serialization round-trip, class/glyph application, second-row DOM, context-menu item. Auto-generated removability test passes.
• e2e (real browser): separate-row grows the header + reflows content (jsdom can't see layout — this caught a real CSS specificity bug), compact hides the title, the pin glyph is actually visible, the close button is hidden, and pinned tabs stay out of the overflow dropdown.
• Green: dockview-core 1107, dockview-modules 236, e2e 30; format + lint clean.

Deferred follow-ups

• Cross-row drag-and-drop and custom tab renderers in the separate row (the row shows the title today).
• "Sticky-to-the-left" pinned tabs on horizontal scroll (currently flex-shrink: 0 + dropdown-exclusion).
• A dedicated pinned section in the overflow dropdown when pinned tabs alone exceed the strip.
• Auto-injecting the context-menu item (dockview's menu is app-callback-driven; the 'pin' token is opt-in via getTabContextMenuItems).

🤖 Generated with Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
88.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud