Add exploration notes on NASA's spacewasm project

SPACEWASM_EXPLORATION.md

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+# SpaceWASM Exploration Notes
+
+Notes from looking into NASA's [spacewasm](https://github.com/nasa/spacewasm) project.
+
+## What it is
+
+SpaceWASM is a WebAssembly interpreter purpose-built for spacecraft flight
+software, designed to run WASM binaries in resource-constrained flight
+environments where general-purpose interpreters aren't practical.
+
+It has two main pieces:
+
+- **Decoder/Validator** — processes WASM binaries in streaming chunks rather
+  than requiring a single contiguous block, keeping peak memory usage low.
+  Produces an optimized intermediate representation in a single validation
+  pass.
+- **Interpreter** — executes the decoded IR, managing linear memory and
+  interfacing with embedded host functions.
+
+## Notable design choices
+
+- **Deterministic memory management** — fixed-size memory pages, no
+  mid-allocation deallocation, matching typical flight-software constraints.
+- **Hard resource limits** — e.g. 256 modules max, 255-parameter functions
+  max, configurable stack depths.
+- **Minimal unsafe Rust** — unsafe code confined to custom allocation
+  structures.
+- **Test coverage** — unit tests, WASM spec-suite integration tests, and
+  fuzzing infrastructure.
+
+## Open questions
+
+- No public documentation ties SpaceWASM directly to F Prime; this is
+  exploratory only.
+- Worth revisiting if/when there's a concrete use case for running dynamic,
+  sandboxed code aboard an F Prime-based mission.