docs: codify rejected runtime and MEL semantics

[eggplantiny]

Context

Derived from the 2026-04-25 and 2026-04-28 Claude Code usage review.

Some requested conveniences would make short-term agent driver work easier but would violate Manifesto's runtime, replay, or MEL analysis boundaries.

Current assessment

SPEC status: these directions should remain unsupported or explicitly rejected.

Desired outcome

Create an ADR or normative docs guardrail that codifies rejected semantics so future agent/tooling work does not re-open them accidentally.

Rejected directions to document:

• Reconstructing canonical snapshots from projected user-facing snapshots.
• Using subscribe() as a live in-flight phase monitor.
• Merging state event and telemetry event channels.
• Runtime-default self-dispatch suppression.
• Calling live external effects during deterministic replay and calling that replay deterministic.
• Promoting Host projection/shadow state to source of truth.
• Allowing non-trivial arbitrary unions beyond literal-only and nullable-compatible cases.
• Expanding MEL into a broad TypeScript-like language with optional chaining, computed keys, rest, or array spread.

Acceptance criteria

• Guardrail references current runtime/MEL source-of-truth docs.
• Each rejected direction has a brief rationale tied to determinism, explainability, replayability, or analysis boundaries.
• Allowed alternatives are named where they exist, such as getCanonicalSnapshot(), getWorldSnapshot(worldId), telemetry on(...), recorded effect receipts, or helper-layer filtering.
• The document does not redefine core semantics beyond codifying these boundaries.