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Entropyk/_bmad-output/implementation-artifacts/6-4-webassembly-compilation.md

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Story 6.4: WebAssembly Compilation

Status: in-progress

Story

As a web developer (Charlie), I want WebAssembly compilation support with TabularBackend as default, So that I can run thermodynamic simulations directly in the browser without server-side dependencies.

Acceptance Criteria

  1. Given a web application with the WASM module imported When creating a cycle and calling solve() Then it executes successfully in Chrome/Edge/Firefox And results are JSON-serializable for JavaScript consumption

  2. Given the WASM build configuration When compiling with wasm-pack build Then it defaults to TabularBackend (CoolProp unavailable in WASM) And pre-loaded fluid tables (R134a, R410A, etc.) are embedded

  3. Given a simple refrigeration cycle in WASM When measuring cycle solve time Then convergence completes in < 100ms (NFR2) And deterministic behavior matches native builds (NFR5)

  4. Given the compiled WASM package When publishing to npm Then package is installable via npm install @entropyk/wasm And TypeScript type definitions are included

  5. Given browser error conditions (invalid inputs, non-convergence) When an error occurs Then JavaScript exceptions are thrown (not panics) And error messages are human-readable

Tasks / Subtasks

  • Task 1: Create WASM bindings crate structure (AC: #1, #2)

    • Create bindings/wasm/Cargo.toml with wasm-bindgen dependencies
    • Create bindings/wasm/src/lib.rs with module initialization
    • Add bindings/wasm to workspace members in root Cargo.toml
    • Configure crate-type = ["cdylib"] for WASM target

  • Task 2: Implement WASM type wrappers (AC: #1)

    • Create bindings/wasm/src/types.rs - wrapper types for Pressure, Temperature, Enthalpy, MassFlow
    • Create bindings/wasm/src/errors.rs - JsError mapping from ThermoError
    • Implement #[wasm_bindgen] for all public types with JSON serialization

  • Task 3: Implement WASM component bindings (AC: #1)

    • Create bindings/wasm/src/components.rs - wrappers for Compressor, Condenser, Evaporator, etc.
    • Expose component constructors with JavaScript-friendly APIs
    • Implement JSON serialization for component states

  • Task 4: Implement WASM solver bindings (AC: #1, #3)

    • Create bindings/wasm/src/solver.rs - System and solver wrappers
    • Expose NewtonConfig, PicardConfig, FallbackConfig
    • Implement ConvergedState with JSON output
    • Add performance timing helpers for benchmarking

  • Task 5: Configure TabularBackend as default (AC: #2)

    • Create bindings/wasm/src/backend.rs - WASM-specific backend initialization
    • Embed fluid table data (R134a.json) using include_str!
    • Implement lazy-loading for additional fluid tables
    • Document fluid table embedding process for custom fluids

  • Task 6: Add panic hook and error handling (AC: #5)

    • Add console_error_panic_hook dependency
    • Configure panic hook in lib.rs initialization
    • Map all ThermoError variants to descriptive JsError messages

  • Task 7: Create npm package configuration (AC: #4)

    • Create bindings/wasm/package.json with npm metadata
    • Create bindings/wasm/README.md with usage examples
    • Configure wasm-pack for --target web and --target nodejs
    • Generate TypeScript type definitions

  • Task 8: Write WASM tests and examples (AC: #1, #3)

    • Create bindings/wasm/tests/simple_cycle.js - basic cycle test
    • Create bindings/wasm/examples/browser/ - HTML/JS demo
    • Add performance benchmark test (< 100ms verification)
    • Add determinism test (compare vs native)

Dev Notes

Architecture Compliance

  • Crate Location: bindings/wasm/ (follows existing bindings/python/ and bindings/c/ patterns)
  • Naming: Crate name entropyk-wasm, lib name via [lib] in Cargo.toml
  • Dependencies: Reuse internal crates (entropyk, entropyk-core, entropyk-components, entropyk-solver, entropyk-fluids)
  • Error Handling: Map errors to JsError - NEVER panic in WASM
  • Observability: Use tracing-wasm for browser console logging (never println!)

Critical: TabularBackend is REQUIRED

CoolProp C++ cannot compile to WASM. The WASM build MUST use TabularBackend with embedded fluid tables.

Project Structure Notes

  • Follow the exact pattern from bindings/python/src/lib.rs for module organization
  • Type wrappers mirror Python's types.rs pattern but with #[wasm_bindgen] instead of #[pyclass]
  • Component wrappers mirror Python's components.rs pattern
  • Solver wrappers mirror Python's solver.rs pattern

References

  • [Source: _bmad-output/planning-artifacts/epics.md#L1102-L1119] - Story 6.4 acceptance criteria
  • [Source: _bmad-output/planning-artifacts/architecture.md#L711-L715] - WASM binding structure
  • [Source: _bmad-output/planning-artifacts/architecture.md#L41-L44] - Technical stack (wasm-bindgen)
  • [Source: bindings/python/Cargo.toml] - Reference binding structure
  • [Source: crates/fluids/src/tabular_backend.rs] - TabularBackend implementation
  • [Source: crates/fluids/data/r134a.json] - Embedded fluid table

Dev Agent Record

Agent Model Used

zai-coding-plan/glm-5

Debug Log References

  • Initial compilation errors with wasm-bindgen builder pattern (fixed by using setters instead of returning &mut Self)
  • ThermoError import location issue (in entropyk crate, not entropyk-core)
  • System generic parameter removed (not needed in current API)
  • SolverStrategy enum variants (NewtonRaphson, SequentialSubstitution) - no Fallback variant
  • FallbackSolver::default_solver() instead of ::default()

Completion Notes List

  • Created complete WASM bindings crate structure following Python/C binding patterns
  • Implemented type wrappers (Pressure, Temperature, Enthalpy, MassFlow) with JSON serialization
  • Created stub component bindings (full integration requires additional component API work)
  • Implemented solver bindings using SolverStrategy and FallbackSolver
  • Configured TabularBackend with embedded R134a table
  • Added console_error_panic_hook for browser error handling
  • Created npm package.json and README for distribution
  • Added browser example and Node.js test file

File List

  • bindings/wasm/Cargo.toml
  • bindings/wasm/src/lib.rs
  • bindings/wasm/src/types.rs
  • bindings/wasm/src/errors.rs
  • bindings/wasm/src/components.rs
  • bindings/wasm/src/solver.rs
  • bindings/wasm/src/backend.rs
  • bindings/wasm/package.json
  • bindings/wasm/README.md
  • bindings/wasm/tests/simple_cycle.js
  • bindings/wasm/examples/browser/index.html
  • Cargo.toml (updated workspace members)

Review Findings

  • [Review][Decision→Patch] Component bindings are non-functional stubs — constructors hardcode R410A, dummy port state. Resolved (1a): completed component bindings with proper fluid-param constructors, Result returns, and input validation.

  • [Review][Decision→Patch] Only R134a fluid table embedded — spec AC#2 says "R134a, R410A, etc." Resolved (2a): created global backend infrastructure with lazy init. Additional tables (R410A, R32) require generation from TabularBackend tool — only R134a data file exists.

  • [Review][Decision→Patch] TypeScript type definitions not included — AC#4. Resolved (3b): documented TypeScript generation workflow in README. Types are auto-generated by wasm-pack build.

  • [Review][Decision→Patch] Missing tracing-wasm dependency. Resolved (4a): added tracing + tracing-wasm to Cargo.toml.

  • [Review][Patch] load_fluid_table is a no-op — fixed: validates table, warns about registration limitation. [backend.rs]

  • [Review][Patch] get_node_result fabricates placeholder data — fixed: uses FluidBackend::full_state() to compute real ThermoState from P and h. [solver.rs]

  • [Review][Patch] solve() ignores WasmFallbackConfig — fixed: wraps real FallbackConfig, passes to FallbackSolver::new(config). [solver.rs]

  • [Review][Patch] timeout_ms silently discarded — fixed: removed no-op, replaced with actual FallbackConfig fields (set_fallback_enabled, set_return_to_newton_threshold, set_max_fallback_switches). [solver.rs]

  • [Review][Patch] Component constructors panic on .unwrap() — fixed: all constructors return Result<T, JsValue> with descriptive errors. [components.rs]

  • [Review][Patch] add_edge no bounds validation — fixed: checks node indices against node_count() before creating NodeIndex. [solver.rs]

  • [Review][Patch] get_node_result no bounds checking — fixed: validates p_idx/h_idx against state.len(). [solver.rs]

  • [Review][Patch] README examples mismatch actual API — fixed: all examples rewritten with correct constructor signatures. [README.md]

  • [Review][Patch] No UA validation on Condenser/Evaporator — fixed: rejects NaN, infinity, zero, and negative values. [components.rs]

  • [Review][Patch] WasmPipe::new panics on invalid geometry — fixed: validates length/diameter, returns Result. [components.rs]

  • [Review][Patch] toJson uses wrong serializer — fixed: replaced serde_wasm_bindgen with serde_json::to_string(). Removed serde-wasm-bindgen dependency. [types.rs]

  • [Review][Patch] WasmConvergedState loses metadata — fixed: added status field with ConvergenceStatus mapping (Converged/TimedOut/ControlSaturation). [solver.rs, types.rs]

  • [Review][Patch] errors.rs is dead code — fixed: expanded with thermo_error_to_js() that maps all ThermoError variants to descriptive messages. [errors.rs]

  • [Review][Patch] WasmComponent::name() always returns "Component" — fixed: stores component type name in WasmComponent wrapper. [components.rs]

  • [Review][Patch] No physical validation on type constructors — fixed: WasmPressure rejects negative/NaN, WasmTemperature rejects negative/NaN, all types reject NaN. Constructors return Result. [types.rs]

  • [Review][Patch] set_relaxation_factor no bounds — fixed: clamps to (0, 1] with tracing warning. [solver.rs]

  • [Review][Patch] WasmSystem::Default uses expect — fixed: removed Default impl for WasmSystem. Users must use new() which returns Result. [solver.rs]

  • [Review][Defer] No performance benchmark/timing helpers — Task 4 (AC#3) requires < 100ms convergence verification. No automated benchmark exists. Deferred: feature not implemented, not a bug in current code.

  • [Review][Defer] No determinism test — Task 8 requires "compare vs native" determinism test. No test exists. Deferred: feature not implemented.

  • [Review][Defer] Test file simple_cycle.js cannot run without manual wasm-pack build — no CI target or npm pretest hook. Deferred: needs CI/build setup.

  • [Review][Defer] into_component() consumes self — prevents configure-then-add workflow from JS. Deferred: design choice, not a bug.

  • [Review][Defer] list_available_fluids creates fresh backend on every call — re-parses embedded R134a JSON each time. Deferred: minor perf, not a correctness issue.

  • [Review][Defer] Missing tracing-wasm integration — no logging infrastructure in WASM crate beyond console_error_panic_hook. Deferred alongside Decision item.

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