implements PLN-0008

discussion/index.ndjson

@@ -1,9 +1,9 @@
-{"type":"meta","next_id":{"DSC":9,"AGD":9,"DEC":7,"PLN":8,"LSN":24,"CLSN":1}}
+{"type":"meta","next_id":{"DSC":9,"AGD":9,"DEC":7,"PLN":9,"LSN":24,"CLSN":1}}
 {"type":"discussion","id":"DSC-0001","status":"done","ticket":"studio-docs-import","title":"Import docs/studio into discussion-framework artifacts","created_at":"2026-03-26","updated_at":"2026-03-26","tags":["studio","migration","discussion-framework","docs-import"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0001","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0001-assets-workspace-execution-wave-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0002","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0002-bank-composition-editor-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0003","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0003-mental-model-asset-mutations-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0004","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0004-mental-model-assets-workspace-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0005","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0005-mental-model-studio-events-and-components-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0006","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0006-mental-model-studio-shell-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0007","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0007-pack-wizard-shell-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0008","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0008-project-scoped-state-and-activity-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0016","file":"discussion/lessons/DSC-0001-studio-docs-import/LSN-0016-studio-docs-import-pattern.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"}]}
 {"type":"discussion","id":"DSC-0002","status":"open","ticket":"palette-management-in-studio","title":"Palette Management in Studio","created_at":"2026-03-26","updated_at":"2026-03-26","tags":["studio","legacy-import","palette-management","tile-bank","packer-boundary"],"agendas":[{"id":"AGD-0002","file":"AGD-0002-palette-management-in-studio.md","status":"open","created_at":"2026-03-26","updated_at":"2026-03-26"}],"decisions":[],"plans":[],"lessons":[]}
 {"type":"discussion","id":"DSC-0003","status":"done","ticket":"packer-docs-import","title":"Import docs/packer into discussion-framework artifacts","created_at":"2026-03-26","updated_at":"2026-03-26","tags":["packer","migration","discussion-framework","docs-import"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0009","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0009-mental-model-packer-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0010","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0010-asset-identity-and-runtime-contract-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0011","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0011-foundations-workspace-runtime-and-build-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0012","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0012-runtime-ownership-and-studio-boundary-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0013","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0013-metadata-convergence-and-runtime-sink-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0014","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0014-pack-wizard-summary-validation-and-pack-execution-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0015","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0015-tile-bank-packing-contract-legacy.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"},{"id":"LSN-0017","file":"discussion/lessons/DSC-0003-packer-docs-import/LSN-0017-packer-docs-import-pattern.md","status":"done","created_at":"2026-03-26","updated_at":"2026-03-26"}]}
 {"type":"discussion","id":"DSC-0004","status":"open","ticket":"tilemap-and-metatile-runtime-binary-layout","title":"Tilemap and Metatile Runtime Binary Layout","created_at":"2026-03-26","updated_at":"2026-03-26","tags":["packer","legacy-import","tilemap","metatile","runtime-layout"],"agendas":[{"id":"AGD-0004","file":"AGD-0004-tilemap-and-metatile-runtime-binary-layout.md","status":"open","created_at":"2026-03-26","updated_at":"2026-03-26"}],"decisions":[],"plans":[],"lessons":[]}
 {"type":"discussion","id":"DSC-0005","status":"open","ticket":"variable-tile-bank-palette-serialization","title":"Variable Tile Bank Palette Serialization","created_at":"2026-03-26","updated_at":"2026-03-26","tags":["packer","legacy-import","tile-bank","palette-serialization","versioning"],"agendas":[{"id":"AGD-0005","file":"AGD-0005-variable-tile-bank-palette-serialization.md","status":"open","created_at":"2026-03-26","updated_at":"2026-03-26"}],"decisions":[],"plans":[],"lessons":[]}
-{"type":"discussion","id":"DSC-0006","status":"open","ticket":"pbs-game-facing-asset-refs-and-call-result-discard","title":"PBS Game-Facing Asset References and Ignored Call Result Lowering","created_at":"2026-03-27","updated_at":"2026-03-27","tags":["compiler","pbs","ergonomics","lowering","runtime","asset-identity","expression-statements"],"agendas":[{"id":"AGD-0006","file":"AGD-0006-pbs-game-facing-asset-refs-and-call-result-discard.md","status":"accepted","created_at":"2026-03-27","updated_at":"2026-03-27"}],"decisions":[{"id":"DEC-0005","file":"DEC-0005-pbs-asset-address-surface-and-be-lowering.md","status":"accepted","created_at":"2026-03-27","updated_at":"2026-03-27","ref_agenda":"AGD-0006"},{"id":"DEC-0006","file":"DEC-0006-pbs-ignored-values-lowering-and-warning.md","status":"accepted","created_at":"2026-03-27","updated_at":"2026-03-27","ref_agenda":"AGD-0006"}],"plans":[{"id":"PLN-0005","file":"PLN-0005-pbs-asset-address-surface-spec-propagation.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27","ref_decisions":["DEC-0005"]},{"id":"PLN-0006","file":"PLN-0006-pbs-asset-address-surface-implementation.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27","ref_decisions":["DEC-0005"]},{"id":"PLN-0007","file":"PLN-0007-pbs-ignored-values-warning-implementation.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27","ref_decisions":["DEC-0006"]}],"lessons":[]}
+{"type":"discussion","id":"DSC-0006","status":"open","ticket":"pbs-game-facing-asset-refs-and-call-result-discard","title":"PBS Game-Facing Asset References and Ignored Call Result Lowering","created_at":"2026-03-27","updated_at":"2026-03-27","tags":["compiler","pbs","ergonomics","lowering","runtime","asset-identity","expression-statements"],"agendas":[{"id":"AGD-0006","file":"AGD-0006-pbs-game-facing-asset-refs-and-call-result-discard.md","status":"accepted","created_at":"2026-03-27","updated_at":"2026-03-27"}],"decisions":[{"id":"DEC-0005","file":"DEC-0005-pbs-asset-address-surface-and-be-lowering.md","status":"accepted","created_at":"2026-03-27","updated_at":"2026-03-27","ref_agenda":"AGD-0006"},{"id":"DEC-0006","file":"DEC-0006-pbs-ignored-values-lowering-and-warning.md","status":"accepted","created_at":"2026-03-27","updated_at":"2026-03-27","ref_agenda":"AGD-0006"}],"plans":[{"id":"PLN-0005","file":"PLN-0005-pbs-asset-address-surface-spec-propagation.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27","ref_decisions":["DEC-0005"]},{"id":"PLN-0006","file":"PLN-0006-pbs-asset-address-surface-implementation.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27","ref_decisions":["DEC-0005"]},{"id":"PLN-0007","file":"PLN-0007-pbs-ignored-values-warning-implementation.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27","ref_decisions":["DEC-0006"]},{"id":"PLN-0008","file":"PLN-0008-pbs-assetlowering-host-metadata-and-callsite-rewrite.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27","ref_decisions":["DEC-0005"]}],"lessons":[]}
 {"type":"discussion","id":"DSC-0007","status":"done","ticket":"pbs-learn-to-discussion-lessons-migration","title":"Migrate PBS Learn Documents into Discussion Lessons","created_at":"2026-03-27","updated_at":"2026-03-27","tags":["compiler","pbs","migration","discussion-framework","lessons","learn-prune"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0018","file":"discussion/lessons/DSC-0007-pbs-learn-to-discussion-lessons-migration/LSN-0018-pbs-ast-and-parser-contract-legacy.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27"},{"id":"LSN-0019","file":"discussion/lessons/DSC-0007-pbs-learn-to-discussion-lessons-migration/LSN-0019-pbs-name-resolution-and-linking-legacy.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27"},{"id":"LSN-0020","file":"discussion/lessons/DSC-0007-pbs-learn-to-discussion-lessons-migration/LSN-0020-pbs-runtime-values-identity-memory-boundaries-legacy.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27"},{"id":"LSN-0021","file":"discussion/lessons/DSC-0007-pbs-learn-to-discussion-lessons-migration/LSN-0021-pbs-diagnostics-and-conformance-governance-legacy.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27"},{"id":"LSN-0022","file":"discussion/lessons/DSC-0007-pbs-learn-to-discussion-lessons-migration/LSN-0022-pbs-globals-lifecycle-and-published-entrypoint-legacy.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27"}]}
 {"type":"discussion","id":"DSC-0008","status":"done","ticket":"pbs-low-level-asset-manager-surface","title":"PBS Low-Level Asset Manager Surface for Runtime AssetManager","created_at":"2026-03-27","updated_at":"2026-03-27","tags":["compiler","pbs","runtime","asset-manager","host-abi","stdlib","asset"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0023","file":"discussion/lessons/DSC-0008-pbs-low-level-asset-manager-surface/LSN-0023-lowassets-runtime-aligned-sdk-surface.md","status":"done","created_at":"2026-03-27","updated_at":"2026-03-27"}]}

discussion/workflow/plans/PLN-0008-pbs-assetlowering-host-metadata-and-callsite-rewrite.md

@@ -0,0 +1,196 @@
+---
+id: PLN-0008
+ticket: pbs-game-facing-asset-refs-and-call-result-discard
+title: Implement Mandatory AssetLowering Host Metadata and Backend Callsite Rewrite
+status: done
+created: 2026-03-27
+completed: 2026-03-27
+tags: [compiler, pbs, implementation, assetlowering, host-metadata, backend-lowering, correction]
+---
+
+## Objective
+
+Complete the missing normative part of `DEC-0005` by implementing mandatory host-backed `AssetLowering` metadata and using it to rewrite `Addressable` arguments into runtime-facing `asset_id` at backend callsite lowering time.
+
+## Background
+
+`DEC-0005` did not only require:
+
+- `FESurfaceContext = List<Addressable(address, asset_id)>`,
+- symbolic `assets...` semantics,
+- and backend ownership of final validation.
+
+It also normatively locked a second requirement:
+
+- asset-aware lowering metadata must live on the host-backed declaration surface;
+- the backend must use that metadata to identify which host parameter is asset-facing;
+- and host-backed lowering must rewrite the `Addressable` argument to operational `asset_id` before the final `LowAssets` path.
+
+`PLN-0006` implemented the symbolic surface and direct symbolic-to-`asset_id` expression lowering, but it did not implement:
+
+- reserved attribute `[AssetLowering(param = N)]`,
+- reserved-metadata propagation for host bindings,
+- host-signature validation for asset-lowered parameters,
+- or host-callsite rewriting driven by parameter metadata.
+
+This plan exists to correct that gap without reinterpreting `DEC-0005`.
+
+## Scope
+
+### Included
+- Add `AssetLowering(param = N)` as a PBS reserved attribute on host-backed signatures.
+- Validate the attribute shape and its admissible target surface.
+- Extend backend host-binding metadata to carry asset-lowering parameter information.
+- Rewrite host call lowering so asset-facing parameters consume symbolic `Addressable` values and lower them to `asset_id` according to host metadata.
+- Align tests and specs so the normative path is explicit and covered.
+- Correct any now-misleading tests or implementation shortcuts introduced by `PLN-0006`.
+
+### Excluded
+- Redesign of `DEC-0005`.
+- Changes to the `LowAssets` ABI already fixed by `DEC-0004`.
+- Generalization to non-asset metadata families beyond the exact `AssetLowering` rule.
+- Runtime-dynamic asset lookup exceptions.
+
+## Execution Steps
+
+### Step 1 - Add Reserved Attribute Surface For AssetLowering
+
+**What:**
+Introduce `[AssetLowering(param = N)]` as a normative reserved attribute on host-backed callable surfaces.
+
+**How:**
+Extend the PBS reserved attribute extractor and declaration validation so:
+
+- `AssetLowering` is recognized as reserved metadata;
+- it is admitted only on supported host-backed callable declarations;
+- `param` is mandatory and must be a valid zero-based parameter index;
+- the targeted parameter must match the `Addressable` author-facing contract required by `DEC-0005`;
+- duplicate or malformed declarations fail deterministically.
+
+**File(s):**
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsReservedMetadataExtractor.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/semantics/PbsDeclarationSemanticsValidator.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/semantics/PbsSemanticsErrors.java`
+- tests under `prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/`
+
+### Step 2 - Propagate AssetLowering Through Reserved Metadata
+
+**What:**
+Make host binding metadata carry the asset-lowering contract instead of relying on implicit expression-level lowering.
+
+**How:**
+Extend `IRReservedMetadata.HostMethodBinding` or the equivalent host-binding metadata shape so each binding can expose:
+
+- whether asset lowering is required;
+- which parameter index is asset-facing.
+
+Update metadata construction, merging, indexing, and any downstream readers so the information survives all backend-facing frontend phases.
+
+**File(s):**
+- `prometeu-compiler/prometeu-frontend-api/src/main/java/p/studio/compiler/models/IRReservedMetadata.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsReservedMetadataExtractor.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/PbsExecutableLoweringModels.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/PbsExecutableMetadataIndexFactory.java`
+- metadata conformance tests under `prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/`
+
+### Step 3 - Rewrite Host Calls Using AssetLowering Metadata
+
+**What:**
+Move final `Addressable -> asset_id` host-argument rewriting into the backend-owned host call path mandated by `DEC-0005`.
+
+**How:**
+Update executable lowering so:
+
+- host callsites inspect `AssetLowering(param = N)` metadata from the resolved host binding;
+- the backend validates that the selected argument is a terminal backend-known `Addressable`;
+- the selected argument is lowered to operational `asset_id`;
+- non-asset-facing arguments are lowered normally;
+- the final emitted host call matches the already accepted `LowAssets` runtime path.
+
+This step must remove reliance on the current shortcut where symbolic asset references are lowered generically without host-parameter ownership.
+
+**File(s):**
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/PbsExecutableBodyLowerer.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/PbsExecutableCallsiteEmitter.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/PbsExecutableLoweringContext.java`
+- related lowering metadata/index files
+- targeted lowering tests under `prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/`
+
+### Step 4 - Realign Symbolic Expression Lowering With The Host-Metadata Contract
+
+**What:**
+Correct the partial implementation from `PLN-0006` so symbolic asset expressions support the normative host-metadata path instead of bypassing it.
+
+**How:**
+Review the current direct lowering of `assets...` expressions and keep only the behavior that remains valid under `DEC-0005`.
+
+At minimum:
+
+- standalone symbolic `Addressable` semantics must remain correct;
+- host-backed `AssetLowering` callsites must no longer depend on an implicit generic shortcut;
+- tests that previously “passed” through direct expression lowering must be updated to assert the host-metadata path explicitly.
+
+If any `PLN-0006` behavior contradicts `DEC-0005`, correct the code and the tests rather than preserving the shortcut.
+
+**File(s):**
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/semantics/`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsFrontendCompilerTest.java`
+- `prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/services/PBSFrontendPhaseServiceTest.java`
+
+### Step 5 - Propagate And Pin The Contract In Specs And Tests
+
+**What:**
+Ensure the normative wording and regression coverage now match the corrected implementation.
+
+**How:**
+Update specs and tests so they explicitly cover:
+
+- `AssetLowering(param = N)` as mandatory host-backed metadata for asset-aware lowering;
+- the backend-owned rewrite from symbolic `Addressable` to operational `asset_id`;
+- rejection of malformed attribute usage and invalid parameter targeting;
+- a representative `LowAssets`-aligned host call path using the metadata-bearing surface.
+
+**File(s):**
+- `docs/specs/compiler-languages/pbs/4. Static Semantics Specification.md`
+- `docs/specs/compiler-languages/pbs/12. Diagnostics Specification.md`
+- `docs/specs/compiler-languages/pbs/13. Lowering IRBackend Specification.md`
+- `docs/specs/compiler/20. IRBackend to IRVM Lowering Specification.md`
+- targeted PBS frontend/compiler tests
+
+## Test Requirements
+
+### Unit Tests
+- Reserved-attribute tests for valid and invalid `AssetLowering(param = N)` usage.
+- Metadata tests proving host bindings preserve the asset-lowering parameter index.
+- Negative tests for duplicate, malformed, or out-of-range `AssetLowering` declarations.
+
+### Integration Tests
+- End-to-end PBS frontend compilation tests where a host-backed asset API uses `Addressable` plus `[AssetLowering(param = N)]`.
+- Lowering tests proving the backend rewrites the marked argument to `asset_id` before the final host call.
+- Regression tests proving `LowAssets`-aligned callsites still lower correctly after removing the shortcut path.
+
+### Manual Verification
+- Inspect extracted reserved metadata and verify `AssetLowering` is carried on the host binding.
+- Inspect lowered instruction streams for an asset-aware host call and verify the asset-facing argument becomes `asset_id`.
+- Confirm malformed host metadata fails with deterministic source-facing diagnostics.
+
+## Acceptance Criteria
+
+- [ ] PBS supports `[AssetLowering(param = N)]` as a validated reserved attribute on the correct host-backed surface.
+- [ ] Host binding metadata preserves the asset-lowering parameter contract through backend lowering preparation.
+- [ ] Backend host-call lowering uses the metadata to rewrite the selected `Addressable` argument into runtime-facing `asset_id`.
+- [ ] The final asset-aware host path remains aligned with `LowAssets` and no longer depends on a generic shortcut that bypasses host metadata.
+- [ ] Tests and specs explicitly cover the normative `AssetLowering` path from `DEC-0005`.
+
+## Dependencies
+
+- `DEC-0005-pbs-asset-address-surface-and-be-lowering`
+- `DEC-0004` low-level `LowAssets` contract
+- existing `PLN-0006` implementation as the correction baseline
+
+## Risks
+
+- The current direct symbolic lowering path may overlap with the normative host-metadata path and require careful removal or restriction.
+- Extending host metadata may require synchronized updates across multiple compiler layers, increasing the chance of partial propagation if done carelessly.
+- If tests keep asserting the shortcut path instead of the normative path, the repository may regress into the same discrepancy again.

docs/specs/compiler-languages/pbs/12. Diagnostics Specification.md

@@ -207,6 +207,13 @@ At minimum, the PBS diagnostics baseline must cover:
    - a stable warning when a materialized value is produced and then ignored,
    - and no warning for unit-like expression statements.
 
+Reserved-attribute diagnostics for host-backed asset lowering must also cover:
+
+- duplicate `AssetLowering` declarations on the same host signature,
+- missing or malformed `AssetLowering(param = N)` arguments,
+- out-of-range `AssetLowering.param` indexes,
+- and `AssetLowering` targets whose selected parameter is not statically typed as `Addressable`.
+
 At minimum, host-admission diagnostics must cover missing or malformed host capability metadata and unknown or undeclared capability names.
 
 Only backend-originated failures that remain source-attributable and user-actionable belong to the PBS-facing diagnostics contract.

docs/specs/compiler-languages/pbs/13. Lowering IRBackend Specification.md

@@ -185,6 +185,7 @@ When available at this boundary, declared host ABI shape (`arg_slots`, `ret_slot
 When a host-backed callsite also depends on backend-owned symbolic asset lowering:
 
 - the frontend boundary MUST preserve which callsite argument is asset-facing;
+- for PBS v1 this asset-facing designation is carried by reserved host metadata `[AssetLowering(param = N)]`;
 - the preserved symbolic operand MUST remain attributable to a backend-provided `Addressable` identity;
 - backend stages MUST be able to rewrite that symbolic operand into runtime-facing `asset_id` before the final low-level host path is emitted.
 

docs/specs/compiler-languages/pbs/4. Static Semantics Specification.md

@@ -80,14 +80,19 @@ Rules:
 - Attributes are not first-class values and are not reflectable in v1 core.
 - Attributes do not automatically survive into runtime or bytecode artifacts.
 - An attribute affects runtime artifacts only when another specification defines an explicit lowering for its semantic effect.
-- In v1 core, the normative reserved attributes are `Host`, `Capability`, `BuiltinType`, `BuiltinConst`, `IntrinsicCall`, `Init`, `Frame`, and `InitAllowed`.
+- In v1 core, the normative reserved attributes are `Host`, `Capability`, `AssetLowering`, `BuiltinType`, `BuiltinConst`, `IntrinsicCall`, `Init`, `Frame`, and `InitAllowed`.
 - `Host` is valid only on a host method signature declared directly inside a reserved stdlib/interface-module `declare host` body.
 - `Capability` is valid only on a host method signature declared directly inside a reserved stdlib/interface-module `declare host` body.
+- `AssetLowering` is valid only on a host method signature declared directly inside a reserved stdlib/interface-module `declare host` body.
 - `Init` is valid only on a top-level userland `fn` declaration with lifecycle-admissible signature.
 - `Frame` is valid only on a top-level userland `fn` declaration with lifecycle-admissible signature.
 - `InitAllowed` is valid only on a host method signature declared directly inside a reserved stdlib/interface-module `declare host` body.
 - `Host` is invalid on ordinary user-authored modules, top-level `fn`, struct methods, service methods, callbacks, contracts, and constants.
 - `Host` metadata is consumed by the compiler during host-binding lowering.
+- `AssetLowering` MUST declare exactly the named argument `param`.
+- `AssetLowering.param` MUST be a zero-based integer literal that names a valid host parameter position.
+- The parameter targeted by `AssetLowering.param` MUST be statically typed as `Addressable`.
+- `AssetLowering` metadata is consumed by backend-owned host-call lowering to rewrite the targeted symbolic `Addressable` operand into runtime-facing `asset_id`.
 - The `Host` attribute syntax itself is not exported as runtime metadata; instead, its canonical identity participates in PBX host-binding emission as defined by the Host ABI Binding specification.
 - `BuiltinType` is valid only on a reserved top-level `declare builtin type` declaration.
 - `BuiltinConst` is valid only on a reserved top-level `declare const` declaration that omits an initializer.

docs/specs/compiler-languages/pbs/6.2. Host ABI Binding and Loader Resolution Specification.md

@@ -143,7 +143,8 @@ For example, the PBS-facing declaration:
 declare host LowAssets {
   [Host(module = "asset", name = "load", version = 1)]
   [Capability(name = "asset")]
-  fn load(asset_id: int, slot: int) -> (status: int, loading_handle: int);
+  [AssetLowering(param = 0)]
+  fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
 }
 ```
 
@@ -155,6 +156,8 @@ maps to the canonical runtime identity:
 
 The loader MUST NOT derive runtime identity from the source owner spelling `LowAssets`.
 
+At the PBS-facing declaration layer, `AssetLowering(param = 0)` marks the author-facing `Addressable` parameter as the backend-owned symbolic operand that must be rewritten to operational `asset_id` before the final low-level host path is emitted.
+
 ## 7. PBX Host Binding Section
 
 ### 7.1 Temporary section contract

docs/specs/compiler-languages/pbs/8. Stdlib Environment Packaging and Loading Specification.md

@@ -214,7 +214,8 @@ or:
 declare host LowAssets {
   [Host(module = "asset", name = "load", version = 1)]
   [Capability(name = "asset")]
-  fn load(asset_id: int, slot: int) -> (status: int, loading_handle: int);
+  [AssetLowering(param = 0)]
+  fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
 }
 ```
 
@@ -228,8 +229,8 @@ Rules:
 - stdlib line `1` MUST expose the low-level asset interface module at `@sdk:asset`,
 - that module MUST declare `LowAssets`,
 - that module MUST use runtime module `asset` and capability `asset`,
-- that module MUST use the runtime-aligned signatures:
+- that module MUST use the runtime-aligned signatures and reserved lowering metadata:
-  - `load(asset_id: int, slot: int) -> (status: int, loading_handle: int)`
+  - `load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int)` together with `[AssetLowering(param = 0)]`
   - `status(loading_handle: int) -> int`
   - `commit(loading_handle: int) -> int`
   - `cancel(loading_handle: int) -> int`

docs/specs/compiler/20. IRBackend to IRVM Lowering Specification.md

@@ -150,6 +150,8 @@ Before bytecode emission, backend must run structural pre-verification on lowere
 7. and structural validity of host/intrinsic call forms.
 8. and structural validity of backend-owned symbolic-to-operational rewrites such as `Addressable -> asset_id`.
 
+For PBS host-backed asset calls in v1, this validation includes the rewrite selected by preserved host metadata such as `[AssetLowering(param = N)]`.
+
 This pre-verification does not replace runtime verifier authority.
 
 ## 11. Deterministic Rejection Policy

prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsReservedMetadataExtractor.java

@@ -15,6 +15,7 @@ public final class PbsReservedMetadataExtractor {
     private static final String ATTR_BUILTIN_TYPE = "BuiltinType";
     private static final String ATTR_INTRINSIC_CALL = "IntrinsicCall";
     private static final String ATTR_BUILTIN_CONST = "BuiltinConst";
+    private static final String ATTR_ASSET_LOWERING = "AssetLowering";
 
     public IRReservedMetadata extract(
             final PbsAst.File ast,
@@ -68,6 +69,7 @@ public final class PbsReservedMetadataExtractor {
             final var capability = capabilityAttribute
                     .flatMap(attr -> stringArgument(attr, "name"))
                     .orElse("");
+            final var assetLoweringAttribute = firstAttributeNamed(signature.attributes(), ATTR_ASSET_LOWERING);
             hostMethodBindings.add(new IRReservedMetadata.HostMethodBinding(
                     hostDecl.name(),
                     signature.name(),
@@ -78,6 +80,9 @@ public final class PbsReservedMetadataExtractor {
                         case INFERRED_UNIT, EXPLICIT_UNIT -> 0;
                         case PLAIN, RESULT -> 1;
                     },
+                    assetLoweringAttribute.isPresent()
+                            ? safeToInteger(longArgument(assetLoweringAttribute.get(), "param").orElse(-1L))
+                            : null,
                     capabilityAttribute.isPresent(),
                     capability,
                     signature.span()));
@@ -261,4 +266,11 @@ public final class PbsReservedMetadataExtractor {
         }
         return ReadOnlyList.wrap(required.stream().toList());
     }
+
+    private Integer safeToInteger(final long value) {
+        if (value < Integer.MIN_VALUE || value > Integer.MAX_VALUE) {
+            return null;
+        }
+        return (int) value;
+    }
 }

prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/PbsExecutableBodyLowerer.java

@@ -415,10 +415,28 @@ final class PbsExecutableBodyLowerer {
             final PbsAst.CallExpr callExpr,
             final PbsExecutableLoweringContext context) {
         lowerCallsiteReceiver(callExpr.callee(), context);
-        lowerExpressionList(callExpr.arguments(), context);
+        lowerCallArguments(callExpr, context);
         callsiteEmitter.emitCallsite(callExpr, context);
     }
 
+    private void lowerCallArguments(
+            final PbsAst.CallExpr callExpr,
+            final PbsExecutableLoweringContext context) {
+        final var hostBinding = callsiteEmitter.resolveUniqueHostBinding(callExpr, context);
+        if (hostBinding == null || hostBinding.assetLoweringParam() == null) {
+            lowerExpressionList(callExpr.arguments(), context);
+            return;
+        }
+        for (int i = 0; i < callExpr.arguments().size(); i++) {
+            final var argument = callExpr.arguments().get(i);
+            if (i == hostBinding.assetLoweringParam()) {
+                lowerAssetFacingArgument(argument, hostBinding, context);
+                continue;
+            }
+            lowerExpression(argument, context);
+        }
+    }
+
     private void lowerExpressionList(
             final ReadOnlyList<PbsAst.Expression> expressions,
             final PbsExecutableLoweringContext context) {
@@ -461,6 +479,26 @@ final class PbsExecutableBodyLowerer {
         lowerExpression(memberExpr.receiver(), context);
     }
 
+    private void lowerAssetFacingArgument(
+            final PbsAst.Expression expression,
+            final p.studio.compiler.models.IRReservedMetadata.HostMethodBinding hostBinding,
+            final PbsExecutableLoweringContext context) {
+        final var assetReference = flattenAssetReference(expression);
+        if (assetReference == null) {
+            lowerExpression(expression, context);
+            return;
+        }
+        final var assetId = context.resolveAssetId(assetReference);
+        if (assetId == null) {
+            reportUnsupportedLowering(
+                    "asset-facing host parameter does not resolve in backend-owned surface: " + assetReference,
+                    expression.span(),
+                    context);
+            return;
+        }
+        emitPushI32(assetId, expression.span(), context);
+    }
+
     private void lowerIfExpression(
             final PbsAst.IfExpr ifExpr,
             final PbsExecutableLoweringContext context) {

prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/lowering/PbsExecutableCallsiteEmitter.java

@@ -16,6 +16,23 @@ import java.util.Map;
 import static p.studio.compiler.pbs.lowering.PbsExecutableLoweringModels.*;
 
 final class PbsExecutableCallsiteEmitter {
+    IRReservedMetadata.HostMethodBinding resolveUniqueHostBinding(
+            final PbsAst.CallExpr callExpr,
+            final PbsExecutableLoweringContext context) {
+        final var calleeIdentity = resolveCalleeIdentity(callExpr.callee(), context.nameTable());
+        if (calleeIdentity == null) {
+            return null;
+        }
+        final var candidates = resolveCallsiteCandidates(callExpr, calleeIdentity, context);
+        if (!candidates.callableCandidates().isEmpty() || !candidates.intrinsicCandidates().isEmpty()) {
+            return null;
+        }
+        if (candidates.hostCandidates().size() != 1) {
+            return null;
+        }
+        return candidates.hostCandidates().getFirst();
+    }
+
     int returnSlotsOf(
             final PbsAst.CallExpr callExpr,
             final PbsExecutableLoweringContext context) {

prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/semantics/PbsDeclarationSemanticsValidator.java

@@ -18,6 +18,7 @@ public final class PbsDeclarationSemanticsValidator {
     private static final String ATTR_BUILTIN_CONST = "BuiltinConst";
     private static final String ATTR_INTRINSIC_CALL = "IntrinsicCall";
     private static final String ATTR_INIT_ALLOWED = "InitAllowed";
+    private static final String ATTR_ASSET_LOWERING = "AssetLowering";
 
     private static final Set<String> RESERVED_ATTRIBUTES = Set.of(
             ATTR_HOST,
@@ -25,7 +26,8 @@ public final class PbsDeclarationSemanticsValidator {
             ATTR_BUILTIN_TYPE,
             ATTR_BUILTIN_CONST,
             ATTR_INTRINSIC_CALL,
-            ATTR_INIT_ALLOWED);
+            ATTR_INIT_ALLOWED,
+            ATTR_ASSET_LOWERING);
 
     private final NameTable nameTable;
     private final PbsConstSemanticsValidator constSemanticsValidator = new PbsConstSemanticsValidator();
@@ -403,13 +405,15 @@ public final class PbsDeclarationSemanticsValidator {
             final DiagnosticSink diagnostics) {
         final var hostAttributes = attributesNamed(signature.attributes(), ATTR_HOST);
         final var initAllowedAttributes = attributesNamed(signature.attributes(), ATTR_INIT_ALLOWED);
+        final var assetLoweringAttributes = attributesNamed(signature.attributes(), ATTR_ASSET_LOWERING);
         for (final var attribute : signature.attributes()) {
             if (!isReservedAttribute(attribute.name())) {
                 continue;
             }
             if (ATTR_HOST.equals(attribute.name())
                     || ATTR_CAPABILITY.equals(attribute.name())
-                    || ATTR_INIT_ALLOWED.equals(attribute.name())) {
+                    || ATTR_INIT_ALLOWED.equals(attribute.name())
+                    || ATTR_ASSET_LOWERING.equals(attribute.name())) {
                 continue;
             }
             reportInvalidReservedAttributeTarget(
@@ -438,10 +442,19 @@ public final class PbsDeclarationSemanticsValidator {
             }
         }
 
+        if (assetLoweringAttributes.size() > 1) {
+            for (int i = 1; i < assetLoweringAttributes.size(); i++) {
+                reportDuplicateReservedAttribute(assetLoweringAttributes.get(i), ATTR_ASSET_LOWERING, diagnostics);
+            }
+        }
+
         validateHostAttributeShape(hostAttributes.getFirst(), diagnostics);
         if (!initAllowedAttributes.isEmpty()) {
             validateInitAllowedAttributeShape(initAllowedAttributes.getFirst(), diagnostics);
         }
+        if (!assetLoweringAttributes.isEmpty()) {
+            validateAssetLoweringAttributeShape(assetLoweringAttributes.getFirst(), signature, diagnostics);
+        }
     }
 
     private void validateBuiltinTypeAttribute(
@@ -587,6 +600,39 @@ public final class PbsDeclarationSemanticsValidator {
         }
     }
 
+    private void validateAssetLoweringAttributeShape(
+            final PbsAst.Attribute attribute,
+            final PbsAst.FunctionSignature signature,
+            final DiagnosticSink diagnostics) {
+        final var args = validateNamedArguments(attribute, Set.of("param"), Set.of(), diagnostics);
+        if (args == null) {
+            return;
+        }
+        validateRequiredIntArgument(attribute, args, "param", false, diagnostics);
+        final var value = args.get("param");
+        if (!(value instanceof PbsAst.AttributeIntValue intValue)) {
+            return;
+        }
+        final var paramIndex = intValue.value();
+        if (paramIndex < 0 || paramIndex >= signature.parameters().size()) {
+            p.studio.compiler.source.diagnostics.Diagnostics.error(diagnostics,
+                    PbsSemanticsErrors.E_SEM_MALFORMED_RESERVED_ATTRIBUTE.name(),
+                    "AssetLowering param index %d is out of range for host signature '%s'".formatted(paramIndex, signature.name()),
+                    attribute.span());
+            return;
+        }
+        final var parameter = signature.parameters().get((int) paramIndex);
+        final var parameterType = unwrapGroup(parameter.typeRef());
+        if (parameterType == null
+                || parameterType.kind() != PbsAst.TypeRefKind.SIMPLE
+                || !"Addressable".equals(parameterType.name())) {
+            p.studio.compiler.source.diagnostics.Diagnostics.error(diagnostics,
+                    PbsSemanticsErrors.E_SEM_MALFORMED_RESERVED_ATTRIBUTE.name(),
+                    "AssetLowering target parameter '%s' must have Addressable type".formatted(parameter.name()),
+                    attribute.span());
+        }
+    }
+
     private Map<String, PbsAst.AttributeValue> validateNamedArguments(
             final PbsAst.Attribute attribute,
             final Set<String> requiredNames,
@@ -690,6 +736,13 @@ public final class PbsDeclarationSemanticsValidator {
         return trimmed.isEmpty();
     }
 
+    private PbsAst.TypeRef unwrapGroup(final PbsAst.TypeRef typeRef) {
+        if (typeRef == null || typeRef.kind() != PbsAst.TypeRefKind.GROUP) {
+            return typeRef;
+        }
+        return unwrapGroup(typeRef.inner());
+    }
+
     private List<PbsAst.Attribute> attributesNamed(
             final ReadOnlyList<PbsAst.Attribute> attributes,
             final String name) {

prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/resources/stdlib/1/sdk/asset/main.pbs

@@ -1,7 +1,8 @@
 declare host LowAssets {
   [Host(module = "asset", name = "load", version = 1)]
   [Capability(name = "asset")]
-  fn load(asset_id: int, slot: int) -> (status: int, loading_handle: int);
+  [AssetLowering(param = 0)]
+  fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
 
   [Host(module = "asset", name = "status", version = 1)]
   [Capability(name = "asset")]

prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsFrontendCompilerTest.java

@@ -9,12 +9,18 @@ import p.studio.compiler.models.IRGlobalVisibility;
 import p.studio.compiler.models.IRSyntheticCallableKind;
 import p.studio.compiler.models.SourceKind;
 import p.studio.compiler.pbs.lexer.LexErrors;
+import p.studio.compiler.pbs.lexer.PbsLexer;
+import p.studio.compiler.pbs.parser.PbsParser;
 import p.studio.compiler.pbs.semantics.PbsSemanticsErrors;
 import p.studio.compiler.source.diagnostics.DiagnosticPhase;
 import p.studio.compiler.source.diagnostics.DiagnosticSink;
 import p.studio.compiler.source.identifiers.FileId;
+import p.studio.compiler.source.identifiers.ModuleId;
+import p.studio.compiler.source.tables.NameTable;
 import p.studio.utilities.structures.ReadOnlyList;
 
+import java.util.Map;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -433,7 +439,8 @@ class PbsFrontendCompilerTest {
                 declare host LowAssets {
                   [Host(module = "asset", name = "load", version = 1)]
                   [Capability(name = "asset")]
-                  fn load(asset_id: int, slot: int) -> (status: int, loading_handle: int);
+                  [AssetLowering(param = 0)]
+                  fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
 
                   [Host(module = "asset", name = "status", version = 1)]
                   [Capability(name = "asset")]
@@ -462,7 +469,8 @@ class PbsFrontendCompilerTest {
                 .anyMatch(h -> h.ownerName().equals("LowAssets")
                         && h.abiModule().equals("asset")
                         && h.abiMethod().equals("load")
-                        && h.abiVersion() == 1));
+                        && h.abiVersion() == 1
+                        && java.util.Objects.equals(h.assetLoweringParam(), 0)));
     }
 
     @Test
@@ -493,6 +501,61 @@ class PbsFrontendCompilerTest {
                         && "37".equals(i.label())));
     }
 
+    @Test
+    void shouldRewriteAssetLoweringHostParameterToAssetId() {
+        final var interfaceSource = """
+                declare host LowAssets {
+                  [Host(module = "asset", name = "load", version = 1)]
+                  [Capability(name = "asset")]
+                  [AssetLowering(param = 0)]
+                  fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
+                }
+                """;
+        final var source = """
+                fn boot() -> (status: int, loading_handle: int) {
+                  return LowAssets.load(assets.ui.panel, 2);
+                }
+                """;
+
+        final var diagnostics = DiagnosticSink.empty();
+        final var compiler = new PbsFrontendCompiler();
+        final var interfaceBackend = compiler.compileFile(new FileId(16), interfaceSource, diagnostics, SourceKind.SDK_INTERFACE);
+        final var sourceFileId = new FileId(17);
+        final var sourceTokens = PbsLexer.lex(source, sourceFileId, diagnostics);
+        final var sourceAst = PbsParser.parse(sourceTokens, sourceFileId, diagnostics);
+        final var interfaceTokens = PbsLexer.lex(interfaceSource, new FileId(18), diagnostics);
+        final var interfaceAst = PbsParser.parse(interfaceTokens, new FileId(18), diagnostics, PbsParser.ParseMode.INTERFACE_MODULE);
+        final var fileBackend = compiler.compileParsedFile(
+                sourceFileId,
+                sourceAst,
+                diagnostics,
+                SourceKind.PROJECT,
+                ModuleId.none(),
+                ReadOnlyList.empty(),
+                HostAdmissionContext.permissiveDefault(),
+                new FESurfaceContext(ReadOnlyList.from(new Addressable("assets.ui.panel", 55))),
+                new NameTable(),
+                interfaceAst.topDecls(),
+                ReadOnlyList.empty(),
+                ReadOnlyList.empty(),
+                interfaceBackend.reservedMetadata(),
+                Map.of());
+
+        assertEquals(0, diagnostics.errorCount(), diagnostics.stream().map(d -> d.getCode() + ":" + d.getMessage()).toList().toString());
+        final var executableBoot = fileBackend.executableFunctions().stream()
+                .filter(fn -> fn.callableName().equals("boot"))
+                .findFirst()
+                .orElseThrow();
+        assertTrue(executableBoot.instructions().stream().anyMatch(i ->
+                i.kind() == p.studio.compiler.models.IRBackendExecutableFunction.InstructionKind.PUSH_I32
+                        && "55".equals(i.label())));
+        assertTrue(executableBoot.instructions().stream().anyMatch(i ->
+                i.kind() == p.studio.compiler.models.IRBackendExecutableFunction.InstructionKind.CALL_HOST
+                        && i.hostCall() != null
+                        && "asset".equals(i.hostCall().module())
+                        && "load".equals(i.hostCall().name())));
+    }
+
     @Test
     void shouldRejectUnresolvedBackendOwnedAssetReference() {
         final var source = """

prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsGateUSdkInterfaceConformanceTest.java

@@ -332,7 +332,8 @@ class PbsGateUSdkInterfaceConformanceTest {
                 declare host LowAssets {
                   [Host(module = "asset", name = "load", version = 1)]
                   [Capability(name = "asset")]
-                  fn load(asset_id: int, slot: int) -> (status: int, loading_handle: int);
+                  [AssetLowering(param = 0)]
+                  fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
 
                   [Host(module = "asset", name = "status", version = 1)]
                   [Capability(name = "asset")]
@@ -361,8 +362,9 @@ class PbsGateUSdkInterfaceConformanceTest {
         assertEquals("asset", backend.reservedMetadata().requiredCapabilities().getFirst());
         assertTrue(backend.reservedMetadata().hostMethodBindings().stream()
                 .anyMatch(h -> h.ownerName().equals("LowAssets")
+                        && java.util.Objects.equals(h.assetLoweringParam(), 0)
                         && h.abiModule().equals("asset")
-                        && h.abiMethod().equals("cancel")
+                        && h.abiMethod().equals("load")
                         && h.abiVersion() == 1));
     }
 

prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/semantics/PbsInterfaceModuleSemanticsTest.java

@@ -126,7 +126,8 @@ class PbsInterfaceModuleSemanticsTest {
                 declare host LowAssets {
                   [Host(module = "asset", name = "load", version = 1)]
                   [Capability(name = "asset")]
-                  fn load(asset_id: int, slot: int) -> (status: int, loading_handle: int);
+                  [AssetLowering(param = 0)]
+                  fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
 
                   [Host(module = "asset", name = "status", version = 1)]
                   [Capability(name = "asset")]
@@ -140,6 +141,24 @@ class PbsInterfaceModuleSemanticsTest {
         assertTrue(diagnostics.isEmpty(), diagnostics.stream().map(d -> d.getCode() + ":" + d.getMessage()).toList().toString());
     }
 
+    @Test
+    void shouldRejectMalformedAssetLoweringOnHostSurface() {
+        final var source = """
+                declare host LowAssets {
+                  [Host(module = "asset", name = "load", version = 1)]
+                  [Capability(name = "asset")]
+                  [AssetLowering(param = 1)]
+                  fn load(addressable: Addressable) -> int;
+                }
+                """;
+        final var diagnostics = DiagnosticSink.empty();
+
+        new PbsFrontendCompiler().compileFile(new FileId(5), source, diagnostics, SourceKind.SDK_INTERFACE);
+
+        assertTrue(diagnostics.stream().anyMatch(d ->
+                d.getCode().equals(PbsSemanticsErrors.E_SEM_MALFORMED_RESERVED_ATTRIBUTE.name())));
+    }
+
     @Test
     void shouldRejectBuiltinFieldWithNonAdmissibleLayoutType() {
         final var source = """

prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/stdlib/InterfaceModuleLoaderTest.java

@@ -69,7 +69,8 @@ class InterfaceModuleLoaderTest {
                         declare host LowAssets {
                           [Host(module = "asset", name = "load", version = 1)]
                           [Capability(name = "asset")]
-                          fn load(asset_id: int, slot: int) -> (status: int, loading_handle: int);
+                          [AssetLowering(param = 0)]
+                          fn load(addressable: Addressable, slot: int) -> (status: int, loading_handle: int);
                         }
                         """))),
                 "pub host LowAssets;");

prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/services/PBSFrontendPhaseServiceTest.java

@@ -950,7 +950,8 @@ class PBSFrontendPhaseServiceTest {
         assertTrue(irBackend.getReservedMetadata().hostMethodBindings().stream()
                 .anyMatch(h -> h.ownerName().equals("LowAssets")
                         && h.sourceMethodName().equals("load")
-                        && h.abiModule().equals("asset")));
+                        && h.abiModule().equals("asset")
+                        && java.util.Objects.equals(h.assetLoweringParam(), 0)));
     }
 
     @Test

prometeu-compiler/prometeu-frontend-api/src/main/java/p/studio/compiler/models/IRReservedMetadata.java

@@ -33,6 +33,7 @@ public record IRReservedMetadata(
             String abiMethod,
             long abiVersion,
             int retSlots,
+            Integer assetLoweringParam,
             boolean capabilityDeclared,
             String requiredCapability,
             Span span) {
@@ -44,6 +45,9 @@ public record IRReservedMetadata(
             if (retSlots < 0) {
                 throw new IllegalArgumentException("host retSlots must be non-negative");
             }
+            if (assetLoweringParam != null && assetLoweringParam < 0) {
+                throw new IllegalArgumentException("assetLoweringParam must be non-negative");
+            }
             requiredCapability = requiredCapability == null ? "" : requiredCapability;
             span = Objects.requireNonNull(span, "span");
         }