safety(arch): RFC #46 architecture shift — std-only interpreter, kiln-builtins, Meld lowering

[avrabe]

Summary

Major architectural update following Bytecode Alliance RFC #46 ("Lowering components to core modules"):

Architecture Changes

• Delete obsolete COMPONENT_MODEL_IMPLEMENTATION_PLAN.md (Kiln no longer implements full CM runtime)
• Create docs/architecture/rfc46-toolchain-architecture.md documenting the new toolchain flow
• Update CLAUDE.md with post-RFC build(deps): bump wast from 228.0.0 to 229.0.0 #46 architecture section

STPA Updates

• H-4 sub-hazards (canonical ABI): marked delegated-to-meld
• H-7 (async): marked deferred (not in P2)
• H-13 (NEW): Meld-fused module ABI mismatch
• UCAs: CM operations scoped (delegated/reduced/deferred)
• UCA-BI-1 (NEW): Builtin wrong return type
• Loss scenarios LS-RF46-1, LS-RF46-2 for Meld/Synth integration

STPA-SEC Updates

• SH-3: Updated for kiln-builtins (not interpreter) no_std scope
• SH-7 (NEW): Synth↔kiln-builtins ABI mismatch
• SH-8 (NEW): Capability escalation through Meld fusion
• V-7, V-8: Vulnerability mappings with mitigations

Cross-Toolchain

• XH-1, XH-3: Updated for build-time Meld lowering
• XH-6 (NEW): Meld fusion format versioning
• XH-7 (NEW): kiln-builtins ABI stability
• CTRL-MELD, CTRL-SYNTH, PROC-BUILTINS, PROC-GALE added to control structure

Requirements

• SR-4 through SR-11: Status delegated to Meld
• SR-BUILTIN-ABI, SR-MELD-COMPAT (NEW)
• FR-BUILTINS, FR-MELD-INTEGRATION, FR-FILEPATH-MAP (NEW)
• AC-BUILTINS, AD-RFC46, AD-STD-ONLY-INTERP (NEW)

Implements: H-13, SR-BUILTIN-ABI

🤖 Generated with Claude Code

[github-actions]

🔍 Build Diagnostics Report

Summary

Metric	Base Branch	This PR	Change
Errors	0	0	0
Warnings	2	2	0

🎯 Impact Analysis

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• 0 files you modified

Cascading Issues (Your Changes Breaking Other Files)

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Note: "Cascading issues" are errors in files you didn't modify, caused by your changes (e.g., breaking API changes, dependency issues).

✅ No Issues Detected

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🔧 To reproduce locally:

# Install cargo-kiln
cargo install --path cargo-kiln

# Analyze your changes
cargo-kiln build --output json --filter-severity error
cargo-kiln check --output json --filter-severity warning