[foxnne]

Part of fizzyedit/work#33

What changes

A plugin can replace the workbench's home page (logo, New File, Open Folder) by registering a surface with the keyword home (sdk.keywords.ide.home):

try host.registerSurface(.{ .id = "graphl.start", .title = "Start",
    .keywords = sdk.keywords.ide.home, .draw = drawStart });

While its one document pane is empty, the workbench declares a region named Home inside it (Workspace.drawHome: keywords = {"home"}, shows = .one, hide_when_empty). It draws the surface that region accepts, or its own page when there isn't one. Because the place exists only while nothing is open, a document opening puts the home away. So does a restored session landing a few frames after startup, and the last document closing brings it back. Graphl no longer has to retry revealSurface until the regions exist, or watch for the restore.

Design note

(a) A home keyword, and a Home place the workbench declares (chosen). This reuses the existing seams. Keywords say what a surface is. A plugin region decides where it goes and when it exists. Assignments choose between two: an app can call host.assignSurfaces("Home", &.{"graphl.start"}), the same list session restore and the picker write, and a user can choose in Settings › Layout. None of the shape's regions accept home (Fit.none against main), so a home surface never turns up as a tab in Main. The web build runs the same statically linked workbench.

(b) An app setting or AppInfo field naming the home surface id. The workbench would read it through a new EditorAPI member, which moves the fingerprint. It would also be a second way to say where a surface goes, beside keywords and assignments, and only an app could use it: a plugin couldn't offer a home page, and a user couldn't choose between two.

(a) is narrower and declarative. The boundary's shape doesn't move (test-sdk-version passes unchanged); the only addition is one keyword preset. The note is also on fizzyedit/work#33.

Also: Editor.fizzy_api_vtable is now pub, so the test can drive the workbench's own drawHome through a real Host.

SDK impact

• None
• Core-only or additive: reaches plugins at the next SDK release. It adds sdk.keywords.ide.home; a plugin on an older SDK can write &.{"home"}. The fingerprint did not move.
• Fingerprint moved: recorded in sdk/src/version.zig, sdk_version untouched, PR labelled sdk
• SDK release: bumps sdk_version, lists the sdk PRs since the last sdk-v* tag

Verified

• macOS: the new integration test workbench: a home surface shows while nothing is open, and a document puts it away drives the workbench's Workspace.drawHome inside a pane declared as Workspace.draw declares it. It checks that: with no home surface the place declines and the built-in page draws; a home surface draws once, in Home and not in Main; a restored pane listing a document that hasn't landed keeps the home, and the landing puts it away (drawn nowhere); the last document closing brings it back; and with two home surfaces the first shows until assignSurfaces("Home", …) picks the other. I broke one expectation once to confirm the test runs. Gates: check-fmt (only the existing backend/src/platform/win32_titlebar.zig, untouched here), zig build, test, test-integration (80/80 steps), check-web, test-sdk-version, check-tests-reached, and check-examples (example-app zig-0.17 + example-plugin main via EXAMPLES_DIR; the default zig-0.17 ref no longer exists for example-plugin, which ci: the example repos are checked at main again #598 fixes). I didn't run it in the live app: fizzy registers no home surface, so its page goes down the unchanged path.
• Windows:
• Linux: CI
• Web: check-web only

Follow-ups

• Shapes without the workbench (example-app's minimal, studio, endless) have no Home place. A shape that wants one declares a region that takes home itself.
• Graphl's start page: switch its keywords to sdk.keywords.ide.home and drop the startup retry and restore watch, once this reaches an SDK release.

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