Make an object a place a tab goes to

[pyricau]

Reworks navigation and information hierarchy in Shark Explorer: an object is a first class thing you go to, and everything the window draws follows from which object a tab is on.

The problem

The window kept where it was in two coordinates — which screen it was on, and a path the treemap had zoomed along — set from a dozen places. A click on a rectangle, a row of the object list, a field in the details panel and a step of the chain each set them slightly differently, so which panes agreed with each other depended on which of the four you had used.

A tab is one Place

Place (shark-explorer-core) is the whole of where a tab is: an object, the pile of smaller objects left out of one, the object list with its filter, the leaks, the starred. Every pane is a function of it — the map is laid out at place.viewRootObjectId, the chain walks up to a GC root from that object, the details panel summarises it, the tab is named after it. Place.of(cell) for a rectangle and Place.Object(id) everywhere else, through one open, so every way to an object is the same move.

The stored path could go because it was never independent: in a dominator tree the way down to an object is unique, so the map root is a function of the object. TreemapNavigation and ExplorerScreen are gone with it. The map is rooted at the object clicked rather than zoomed along a chain to it, so an object that dominates nothing draws as one rectangle of its own bytes — the honest answer to what it holds. How it is held is the chain pane's answer.

Tabs

Which tab a click means is the click's own answer, decided in OpenIn and nowhere else:

Gesture	What it does
Click	Goes there in the tab being read, like a link in a browser tab
Middle click, ⌘/Ctrl click	Opens a tab behind the one being read
Right click → Open in a new tab	Same, and it is what makes the other two findable
A button on the bar	Always opens a tab, in front

Two object lists filtered differently are two useful tabs, which is why the bar never reuses the tab of the same name. Every tab closes, the last one included — a window with no tab still holds the heap dump it spent seconds reading, and the bar is one click from a tab again. A tab's history is its own, so the back arrow never walks out of the tab you are reading. A tab is named class-plus-address, since a strip of a dozen instances of one class is only one you can pick out of if each tab says which instance it is.

The three panes are resizable against each other and each folds away to the button that unfolds it.

All objects is now Object list.

Roles, which is also what makes this testable

Three things in the window can say Whole heap dump at once — the button on the bar, the tab, and the top row of every chain — and they are three different moves. Role.Button on the bar, Role.Tab on the strip, and no role at all on a row that navigates, which is a link rather than a button. Correct for a screen reader, and what lets an assertion say which of the three it means.

Tests

Place and Tabs are plain immutable state in shark-explorer-core, unit tested (TabsTest, 14 cases). New TabStripTest covers the tab rules end to end in the UI; ObjectsScreenTest holds the object list tests moved out of ExplorerAppTest. 175 UI tests, check and detekt green.

Notes and docs updated in the same change: notes/decisions.md, notes/treemap-rendering.md, shark/shark-explorer/AGENTS.md and docs/shark-explorer.md.

No change log entry — Shark Explorer's Unreleased is still ✨ Initial release.