Runtime Values, Identity, and Memory Boundaries

Original Problem

PBS needed a consistent user-visible runtime model for:

which values carry identity,
which values are copied payload,
where ownership changes at host boundaries,
what the collector is allowed to assume,
and which cost facts matter semantically.

Without that closure, later lowering and diagnostics would have to guess whether a construct implied allocation, aliasing, retention, or host-owned state.

Consolidated Decision

PBS keeps the runtime model intentionally small and explicit.

The stable rules are:

Scalars are copied values without user-visible identity.
Structs are identity-bearing reference values.
Services are canonical singleton identity-bearing values.
Host-backed resources are identity-bearing on the PBS side even when authority remains host-owned.
optional, result, and tuples are carriers; they do not create identity of their own.
Contract values do not create a second identity separate from the underlying value.
Host interaction is stack-only across the boundary.
The GC and reachability model must preserve identity-bearing values and retained callback contexts.
Cost visibility is semantic only where it changes reasoning:
- allocation-bearing versus non-allocation-bearing,
- retention-bearing versus non-retention-bearing,
- copy versus aliasing,
- host-boundary crossing,
- and trap possibility.

Final Model

The runtime contract is qualitative, not byte-accounting-driven.

PBS does not promise:

exact byte counts,
one exact heap layout,
or one exact collector schedule.

It does promise the semantic facts that maintenance tooling and humans need:

whether aliasing is preserved,
whether retention exists,
whether a construct may allocate,
and whether a boundary crossing is happening.

Practical Consequences

bind(context, fn_name) is the main retention-bearing primitive in the current surface.
Carrier constructs are not allocation-bearing by themselves.
Host memory authority remains on the host side even when PBS models the value as identity-bearing.
Lifetime-control surfaces beyond the current line remain future-profile work, not silently implied support.

Common Pitfalls

Treating carriers like optional or result as if they created fresh identity.
Assuming stack-only host crossing means host ownership disappears.
Confusing qualitative cost guarantees with exact runtime budgeting.
Treating future lifetime-control or concurrency surfaces as part of core-v1 by implication.

Source Decisions

Value Representation and Identity Decision.md
Host Memory Boundary Decision.md
GC and Reachability Decision.md
Allocation and Cost Visibility Decision.md
Lifetime Control and Future Profiles Decision.md
Dynamic Semantics - Execution Model Decision.md
Dynamic Semantics - Branch Selection Decision.md
Dynamic Semantics - Effect Surfaces Decision.md

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