# Bounded state and composition (beta) `SemanticDeclaration.composition` is optional. Its profile is `urn:publisle:composition:beta`; existing package, document, block, artifact and ABI versions do not change. Changed declarations receive a new sealed contract digest. The closed wire shape is published in `contracts/schemas/semantics.json`. `parseComposition` and `validateSemantics` validate declarations during preparation. Unsupported profiles/operations fail explicitly; archival source remains intact. ## State and compatible snapshots Fields reference stable semantic input/state/output IDs and the same fixed JSON Pointer as their entity. Only finite numbers, safe integers, bounded strings and booleans are supported in this initial profile. Numeric bounds and finite enums are optional; strings are limited to 4096 Unicode scalar values, matching JSON Schema length semantics. Invalid Unicode is rejected. Objects, datasets, ephemeral requests, pointer positions and service handles are not writable state. Hosts can keep those separately without putting them in canonical source. - Authored configuration stays untouched. Compiled sessions retain a frozen scalar baseline; no full payload or schema is copied into the reader. - Named authored presets contain bounded, validated writable field values. Selection applies the preset's partial patch atomically; unlisted fields retain their current values. Presets are compiled constants, never reader-editable. - Each placement creates independent session state. `reset()` restores all fields to the authored baseline, not the most recently selected preset. - `shareable: true` is permitted only on writable fields. Other session fields are transient and never exported. They reset to authored values on restore. - `snapshot()` emits `profile: "urn:publisle:snapshot:beta"`, `documentDigest`, `contractDigest`, `blockId` and exactly the shareable `state` fields. Export and restore reject snapshots exceeding 16 KiB of UTF-8 JSON. Restore rejects stale identities, missing/extra fields, wrong types, bounds and accessors before any mutation. No automatic migration, fallback revision or silent truncation. Snapshot transport is a host responsibility: URL encoding, storage, authentication, strict duplicate-key/Unicode JSON parsing and optional compression are not owned by the document. The generated object API expects plain JSON data, not hostile Proxy objects or services. It does not ship the general JSON/schema parser to readers. Snapshot profiles identify compatibility without introducing a beta version counter. `createSnapshotSchema(validatedProfile, target)` in `@publisle/contracts` exports a closed Draft 2020-12 schema with those exact revision constants and shareable field constraints for independent backend validators. `validateSnapshot(value, schema)` adds the 16 KiB policy check at the offline tooling boundary; it is not reader code. ## Meaning versus execution Abstractions are parameter-control, plot, series, table, state-diagram, image-annotation, scene-entity and narrative-action. They reference entities with compatible kinds. Relations have IDs and typed endpoints: dependency, containment, series-axis, action-state and narrative-preset. Dependencies **do not compute** anything. Hosts may implement equivalent accessible views, not identical pixels. Allowlisted operations have stable action IDs: | Operation | Deterministic behavior | | ------------ | ----------------------------------------------------------------------------- | | assign | Validate a host-provided scalar, then replace one writable field | | preset | Apply one validated named partial patch | | transition | Require the exact `from` value, then write `to`; both belong to a finite enum | | view binding | Return a fresh frozen map of declared view IDs to current field values | There is no expression language, arithmetic, shader execution, graph evaluation, callback source or scientific simulation. Invalid actions do not mutate state. Observations associate preset/output IDs with authored explanation. Optional assertions declare typed expected values, nonnegative tolerance and producer/evidence provenance. Semantic export retains them as **not executed**, not verified results. Scientific verification requires separate evidence and implementation. ## Compile once, bind per placement `compileComposition` is exported by `@publisle/adapter-core` (build-time entry, **not** `/publication-runtime`). Supply verified, host-approved instances containing `blockId`, contract body `contractDigest`, normalized data and semantic declarations, plus the digest of the exact canonical document and declared port connections. The compiler checks structure/behavior but does not resolve or authenticate contracts; use the pinned preparation/resolution workflow first. It returns a direct ES module exporting `createPlacement()`. Bundle it as an approved host module alongside actual island implementations. Native/artifact hosts can provide the placement handle as an out-of-band service; no source import string authorizes execution. The module includes only referenced state checks, action handlers, views and direct port assignments. It contains no profile, relationship graph, schema evaluator, registry, Ajv, compiler or source AST. Merely importing the build-time API into a reader is unsupported. No Three.js or diagram engine is added to Publisle. Each placement exposes `session(blockId)`, `observe(blockId, hostListener)`, `batch(commands)` and idempotent `dispose()`. Observers receive frozen view values and an AbortSignal; they are approved host functions, never canonical callbacks. Use `batch` for connected changes. Direct session actions/restore are local; submit an assignment batch after restore when connected propagation is desired. ## Ports, ordering and failure rules Ports have stable IDs, input/output direction and a field whose declared scalar type defines the port type. Inputs require writable fields. Connections name exact block/port IDs. An input with `presetSelection: true` requires a finite string enum of declared preset IDs; it applies the receiving block's validated preset and then writes the selector field. This exchanges named presets without callbacks or routing. Missing references, duplicate edges, mismatched types and **all cycles**, including self-links, are rejected. Bounds/enums are checked by receiving handlers: an incompatible value isolates that edge rather than corrupting state. Commands are captured when submitted and executed in submission order. Within a batch, invalid commands are reported and valid commands continue. Propagation runs once after the commands, using final source values. Blocks are topologically ordered with UTF-16 lexical ID tie-breaking; outgoing edges use JCS lexical order. Multiple writes to one input are last-writer-wins in that explicit order. Each successful receiving block propagates downstream. Failed edges do not prevent other edges. There is no implicit global mutable state. Changed host views are notified in that same block order after propagation. Throws and rejected promises become returned errors; they do not poison subsequent batches. An observer times out after one second. Disposal aborts pending observation waits, rejects queued work, clears listeners and invalidates session access. Host code must honor cancellation for its own effects; arbitrary functions cannot be forcibly terminated or sandboxed. Observer timeouts do not roll back already committed state. Do not await a nested batch from an observer: the queue is serialized. Limits: 64 KiB per profile, 128 entries per collection, 128 blocks, 256 connections, 128 commands per batch, and 128-character IDs. Each operation is a bounded direct assignment or patch. Hosts separately impose input/request budgets and approve code. ## Executable evidence `contracts/fixtures/composition.json` provides a shared positive declaration; negative unit fixtures cover malformed profiles, IDs, bindings, types, presets, relationships, stale/oversized snapshots and unsupported cycles. Sealed-contract tests verify provenance and tamper rejection. Reader tests exercise actual production bundling and Chromium: two related islands, presets/reset/snapshots, asynchronous failure isolation, repeated placements and useful no-JavaScript authored fallback. `tools/composition/demo.ts` is the host-owned accessible reference demo builder. Its isolated production module inventory contains only the generated host entry; the fixture budget is under 5 KiB gzip. This is a bounded fixture budget, not a universal performance or visual/scientific equivalence claim.