[Host Foundation] Define the shell input contract for product identity, bundled content, builtins, and policy

[ogyrec-o]

Summary

Define the canonical contract between concrete product/app shells and the generic host foundation.

The shell must provide inputs and policy. The host foundation must own canonical load-plan construction. Concrete shells must not each invent their own resolver semantics.

Problem

Freven's long-term architecture is:

• shared core
• generic host foundation
• concrete app shells

But the exact input boundary between "shell" and "host foundation" needs to be explicit before more packaging/product profiles are added.

Without this, product shells can drift into custom resolution behavior, hardcoded Vanilla assumptions, or duplicate load-plan truth.

Target model

Shells own:

• app identity / branding / executable identity
• default entry flow
• bundled experiences / payload
• builtin registry provider
• packaging / distribution layout
• player-facing boot behavior
• instance/save/config namespace
• whether extra mods / overlays are allowed
• local trust / transport / mod policy envelope

Host foundation owns:

• canonical experience resolution
• canonical mod resolution
• canonical load-plan construction
• activation derivation
• common host/runtime wiring
• shared validation of shell-provided inputs

Core/runtime owns:

• lower-level runtime activation semantics
• guest/native/external/builtin attach semantics
• transport/runtime behavior below the host foundation

Requirements

Define a stable shell input structure/model that can express:

• product identity
• default experience id
• experience roots / visible experience universe
• builtin mod registry provider
• mod roots / overlay roots
• unsafe native mod policy
• external process mod policy
• optional client-local policy envelope
• packaging/profile identity
• instance namespace expectations

Non-goals

• Do not fully implement every shell.
• Do not build the final launcher UI.
• Do not add custom resolver algorithms per shell.
• Do not make Vanilla mandatory in the contract.

Deliverables

• Architecture doc update.
• Proposed Rust-side/input model if implementation-ready.
• Clear statement that shells provide inputs/policy, while host foundation builds the canonical load plan.
• Follow-up implementation issue links where needed.