System overview

The shell composes services; it is not a render engine disguised as a window. The current implementation is WorkbenchWindow, but its widget layout is not the conceptual architecture.

Workbench shell
+-- ShaderWorkspace
|   +-- ShaderDocument(s) and DocumentSession(s)
|   +-- focused document
|   +-- TimeContext
|   `-- TimeTransport
+-- WorkspaceEditor and active-document Inspector
+-- live tool contributions
|   +-- RenderToySession  -> Scene/Post QRhi consumers
|   `-- ShaderToySession  -> fullscreen QRhi consumer
+-- in-process Slang
|   +-- module filesystem/search paths
|   +-- reflection and entry points
|   `-- generated target code
`-- rendering
    +-- RhiBackendPolicy
    +-- SlangRhiWidget / RenderPass
    `-- QRhi device resources and submission

Responsibilities and lifetimes

ShaderWorkspace lasts with the shell and owns open documents, editor sessions, focus, and shared evaluation objects. ShaderDocument owns authored source and the compiler/reflection products derived from that source. WorkspaceEditor only presents a focused document and preserves cheap view state.

A tool session lasts independently of which primary surface is visible. It owns bindings and entry-point choices, not documents or time. A contribution supplies a surface, status, and actions to the shell. Selecting a view changes presentation; it does not create or destroy the session.

Slang owns language semantics, module resolution, compilation, reflection, and backend code generation. Workbench owns editor state, dependency identity and invalidation, UI presentation, consumer bindings, and native execution. Qt/QRhi owns graphics API abstraction and resource lifecycle; C++ owns synchronization and stable native object lifetime. Python exposes these QObjects through Shiboken only.

End-to-end flow

authored Slang -> ShaderDocument -> SlangCompiler -> module resolution
    -> reflection + entry points -> DependencyGraph products
    -> tool-selected capabilities -> QShader bridge -> QRhi consumer

Changing a slider normally stops at uniform upload. Changing a module can restart compilation and pipeline work. These different paths are why identity, ownership, and dirty work are documented separately.

Implementation

Start at cpp/src/workbench/modes/render_toy/WorkbenchWindow.cpp for composition, not ownership rules. Follow ShaderWorkspace and ShaderDocument into the Slang layer, tool sessions into modes/, and GPU work into rendering/. See Native source layout for placement rules.