prometeu-studio/docs/pbs/agendas/12.4. IR and Lowering Workshop 4 - Builtins, Host Bindings, and Artifact Invariants.md

PBS IR and Lowering Workshop 4

Status: Active

Purpose

Run the fourth focused discussion for 12. IR and Lowering Specification.md on the backend-facing edges:

• builtin projections,
• builtin constants,
• intrinsic member calls,
• host-binding emission,
• and artifact invariants required before verifier or loader stages.

Why This Slice Last

This slice should come last because it depends on the general lowering contract plus the special ownership rules around VM-owned versus host-backed behavior.

Proposed Meeting Order

1. Reconfirm already-settled builtin and host-binding facts.
2. Close lowering obligations for builtin projections and constants.
3. Close lowering obligations for intrinsic member calls.
4. Close host-binding emission obligations.
5. Close pre-verifier and pre-loader artifact invariants.

Decisions To Produce

1. Builtin lowering obligations beyond already-settled metadata consumption.
2. Host-binding emission obligations before loader resolution.
3. The artifact invariants required before verifier/loader stages.
4. The exact boundary between 12, 15, and 19.

Candidate Decisions

1. Builtin Projections Stay VM-Owned Through Lowering

Candidate direction:

• builtin projection access lowers through VM-owned operations only,
• and never through host-binding tables or host syscall paths.

Rationale:

• This is already settled; 12 needs only to make the preserved obligation explicit.

2. Builtin Constants Lower Through Materialization, Not Constant Folding Semantics

Candidate direction:

• builtin constants lower through their VM-owned materialization path,
• not through ordinary user-authored compile-time constant evaluation.

Rationale:

• This keeps builtin shells distinct from ordinary declare const.

3. Host-Binding Emission Must Be Explicit Before 15

Candidate direction:

• lowering must produce canonical host-binding entries,
• deduplicate them by canonical identity,
• and emit host-backed callsites in the pre-load form already fixed elsewhere.

Rationale:

• This is the bridge between bound source and artifact mapping.

4. 12 Defines Artifact Invariants, 15 Defines Encoding

Candidate direction:

• 12 states what must be true of the emitted artifact boundary,
• 15 states exactly how those facts appear in PBX and bytecode form,
• 19 states what must be verified.

Rationale:

• This keeps the three backend-facing specs from overlapping.

Questions To Resolve In The Room

1. Does 12 need any abstract instruction vocabulary for builtins and host calls?
2. Which invariants belong to lowering rather than to verification?
3. How much ordering and dedup detail should 12 restate versus reference from other specs?
4. Should intrinsic lowering be specified as abstract op families or only semantic obligations?
5. What exact artifact guarantees must 13 eventually assert?

Expected Outputs

1. a decision record for builtin lowering obligations,
2. a decision record for host-binding emission obligations,
3. and an artifact-invariants checklist spanning 12, 15, and 19.

Explicit Deferrals

• exact bytecode instruction encodings,
• exact PBX section layout,
• and verifier algorithm details.

Inputs

• docs/pbs/specs/6.1. Intrinsics and Builtin Types Specification.md
• docs/pbs/specs/6.2. Host ABI Binding and Loader Resolution Specification.md
• docs/pbs/specs/12. IR and Lowering Specification.md
• docs/pbs/specs/15. Bytecode and PBX Mapping Specification.md
• docs/pbs/specs/19. Verification and Safety Checks Specification.md
• docs/pbs/agendas/12. IR and Lowering Agenda.md
• docs/pbs/agendas/12.3. IR and Lowering Workshop 3 - Callables, Services, Contracts, and Callbacks.md