232 lines
7.0 KiB
Markdown
232 lines
7.0 KiB
Markdown
# Build Artifacts and Deterministic Packing Specification
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Status: Draft
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Scope: Runtime-facing artifacts and deterministic build behavior
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Purpose: Define how the packer emits `assets.pa` and companion artifacts.
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## Authority and Precedence
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This specification consolidates the initial packer agenda and decision wave into normative form.
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Runtime-side reading semantics remain upstream in:
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- `../runtime/docs/runtime/specs/13-cartridge.md`
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- `../runtime/docs/runtime/specs/15-asset-management.md`
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## Core Rules
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1. `assets.pa` is the authoritative runtime-facing artifact.
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2. Companion JSON files do not replace the internal header as the runtime contract.
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3. The global asset table order is deterministic by increasing `asset_id`.
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4. The runtime-facing `asset_id` is the same stable `asset_id` allocated by the packer registry.
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## `assets.pa` Structure
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Baseline structure:
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```text
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[fixed binary prelude]
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[canonical JSON header]
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[binary payload region]
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```
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### Prelude Fields
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The baseline prelude includes:
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- `magic`
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- `schema_version`
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- `header_len`
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- `payload_offset`
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- `flags`
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- `reserved`
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Rules:
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- `flags` and `reserved` exist from day 1;
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- `flags = 0` unless later specified otherwise;
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- `reserved = 0` unless later specified otherwise;
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- `header_checksum` is not part of the baseline envelope contract.
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## Canonical JSON Header
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The header is serialized canonically.
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Rules:
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- UTF-8 encoding;
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- no extra whitespace;
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- object keys sorted lexicographically;
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- arrays preserve declared order;
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- canonicalization applies recursively;
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- runtime-facing header values in v1 must avoid floating-point numbers.
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## Header Contents
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The header carries:
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- `asset_table`
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- `preload`
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### Asset Table
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`asset_table` is emitted as a deterministically ordered list of asset entries.
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Rules:
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- one entry per included asset in the current build set;
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- no secondary runtime-only identity layer;
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- no synthetic dense reindexing layer;
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- `asset_name` remains present as logical/API-facing metadata.
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### Asset Entry Metadata Convergence
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Each emitted asset entry has one runtime metadata sink: `AssetEntry.metadata`.
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Rules:
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- packer materialization must normalize all runtime-consumable metadata-producing sources into `asset_table[].metadata`;
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- equivalent declaration/build inputs must produce equivalent normalized metadata;
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- metadata key collisions across independent sources must fail build unless the family/format spec declares an explicit merge rule;
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- normalization behavior must be testable and covered by conformance-oriented tests.
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Baseline normalized metadata segmentation:
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- `output.metadata` materializes at the metadata root;
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- `output.codec_configuration` materializes under `metadata.codec`;
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- `output.pipeline` materializes under `metadata.pipeline`;
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- format-specific runtime-required fields may remain directly readable at the metadata root when the runtime consumer requires them there.
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### Preload
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Preload is emitted deterministically from per-asset declaration.
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Rules:
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- assets with `preload.enabled = false` do not appear in emitted preload data;
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- assets with `preload.enabled = true` do appear;
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- preload ordering is deterministic by increasing `asset_id`.
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## Companion Artifacts
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The baseline companion artifacts are:
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- `build/asset_table.json`
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- `build/preload.json`
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- `build/asset_table_metadata.json`
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Rules:
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- `build/asset_table.json` mirrors `header.asset_table` 1:1;
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- `build/preload.json` mirrors `header.preload` 1:1;
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- `build/asset_table_metadata.json` is tooling-only;
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- richer tooling data must not be added to the 1:1 mirror files.
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## Alignment and Offsets
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Alignment exists only when explicitly required by spec.
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Rules:
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- there is no implicit baseline alignment beyond envelope and format requirements;
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- any required alignment must be normative and visible;
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- emitted offsets are always relative to the payload region, never the start of the full file.
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Offset ambiguity guardrail:
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- `asset_table[].offset`/`asset_table[].size` describe payload slicing inside `assets.pa`;
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- internal pipeline indexing data (for example per-sample ranges for audio banks) must live under `asset_table[].metadata`;
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- internal indexing fields must not be interpreted as payload slicing fields.
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## Format-Specific Baseline: `TILES/indexed_v1`
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The first-wave producer contract for `TILES/indexed_v1` is fixed and runtime-aligned.
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### Tile Selection and Identity
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Rules:
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- only selected artifacts participate in the emitted tile bank;
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- `1 artifact = 1 tile` in v1;
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- artifacts are normalized by ascending `artifacts[*].index`;
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- emitted `tile_id` equals the normalized artifact index;
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- duplicate or gapped artifact indices are build-blocking structural failures.
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### Emitted Sheet Shape
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Rules:
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- the emitted tile-bank sheet is always `256 x 256` in v1;
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- tile placement within that emitted sheet is row-major;
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- runtime `width` and `height` for the bank entry therefore refer to the full emitted sheet, not one individual artifact;
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- resulting per-bank capacities are:
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- `tile_size = 8` -> `1024` tiles
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- `tile_size = 16` -> `256` tiles
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- `tile_size = 32` -> `64` tiles
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- capacity overflow is a build-blocking structural failure.
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### Payload Layout
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Rules:
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- the serialized payload for `TILES/indexed_v1` is:
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1. one packed `u4` pixel plane for the full emitted sheet;
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2. one palette block of `64 * 16 * 2 = 2048` bytes;
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- packed pixel bytes must be emitted by the packer, not inferred later by the runtime;
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- the palette block is serialized as `RGB565` `u16` values;
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- palette bytes must be emitted in little-endian order;
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- payload interpretation must not depend on incidental per-artifact boundaries.
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### Runtime Entry Derivation
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Rules:
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- emitted tile-bank entries use:
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- `bank_type = TILES`
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- `codec = NONE`
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- tile-bank v1 metadata must expose at least:
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- `tile_size`
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- `width`
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- `height`
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- `palette_count`
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- tile-bank v1 requires `palette_count = 64`;
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- tile-bank v1 size formulas are:
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- `size = ceil(width * height / 2) + 2048`
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- `decoded_size = (width * height) + 2048`
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### Palette Contract
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Rules:
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- bank palettes are declared under `output.pipeline.palettes`;
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- each palette declaration uses the shape `{ "index": <int>, "palette": { ... } }`;
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- palette ordering is ascending numeric `index`, never raw array position;
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- palette ids in the emitted tile bank are the normalized declared palette indices;
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- any tile in the bank may be rendered with any palette in the bank at runtime;
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- palette selection is a runtime draw concern, not a tile-payload embedding concern.
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## Determinism
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Equivalent build inputs must produce equivalent outputs.
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Rules:
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- no filesystem iteration dependence;
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- no hidden defaults that affect output;
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- no usage-based hot-first packing in the baseline contract;
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- determinism is preferred over speculative physical-layout optimization.
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## Non-Goals
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- per-format payload internals for every output family
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- future locality optimization policy
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- cartridge-level integrity/signature strategy
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## Exit Criteria
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This specification is complete enough when:
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- runtime-facing artifact authority is explicit;
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- companion artifacts are bounded;
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- emitted ordering and header behavior are deterministic.
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