refactor(desktop): make AppShell a renderer composition root

[chihumyum]

Problem

The previous AppShell governance work improved file-level separation, but
AppShell remains the default owner of renderer state, environment IO,
subscriptions, feature lifecycles, and prop assembly.

After the Workbar extraction, app-shell.tsx is still 3,230 lines with
105 imports and 21 direct window.maka references. The wider
app-shell* / use-app-shell* family contains 30 files and 8,942 lines.

This is not a line-count target. The problem is ownership and dependency
direction.

Desired boundary

AppShell may own:

• root providers and error boundaries;
• top-level location and frame composition;
• composition of feature public APIs;
• explicit cross-feature intent wiring.

AppShell must not own:

• feature reducers or persistence;
• feature-specific subscriptions or environment IO;
• transcript, submission, Goal, Workbar, or dynamic-resource lifecycles;
• tool-specific view-model construction.

Proposed direction

Use the Workbar model / controller / ui / ports / desktop adapter / testing boundary as the reference for the remaining renderer slices.

• Extract Workbar ownership into a feature slice (refactor(desktop): extract Workbar as a feature slice #3444)
• Establish shell regions and dependency guardrails
• Extract Goals (refactor(desktop): extract goals as a feature slice #3531)
• Extract Module Hub ownership
• Establish Session catalog authority
• Extract Session Navigation
• Extract Task Entry / Workspace
• Establish the Conversation host
• Move Conversation runtime behind services
• Isolate Session controls
• Move Task submission out of AppShell
• Remove the remaining legacy shell ownership

Invariants

No product, visual, IPC, storage-schema, copy, or shortcut changes.
Composer mount semantics, bootstrap behavior, streaming isolation,
Session-switch races, and Workbar resource lifecycles must remain compatible.

Non-goals

• No new global state library or service locator
• No IPC redesign
• No packages/ui extraction
• No mechanical movement of every large renderer file into features/

[chihumyum]

I’m currently working on this issue

If anyone would like to take one of the remaining items, please comment with the scope you’re interested in so we can coordinate and avoid overlapping work.

Contributions are very welcome.

[chihumyum]

I’m taking the Goals slice next.

Scope: move Goal state and subscriptions, arm/pause/resume/clear lifecycle, dialog ownership, and Goal view-model assembly behind a feature boundary with a Desktop adapter, test fakes, and boundary coverage. AppShell will only provide the active Session context and consume the feature host/commands/selectors surface.

This will preserve the current product behavior, IPC contracts, copy, shortcuts, and Session-switch semantics. I’ll keep the broader shell-region/guardrail checklist item separate unless this change genuinely completes it.