docs+runner+parser: SSOT+AST using finalized (legacy text inlining removed); provider verify reads nyash.toml; preflight warn hook; method-body guard removed; CURRENT_TASK updated for next JSON work

docs/reference/architecture/phi-and-ssa.md

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+# PHI and SSA in Nyash
+
+Overview
+- Nyash lowers high-level control flow (If/Loop/Match) to MIR and backends that rely on SSA form.
+- We prioritize IR hygiene and observability while keeping runtime cost at zero.
+
+Design points
+- PHI hygiene: no empty PHIs; PHIs at block head only.
+- JoinResult hint: when both branches assign the same variable, we emit a MIR hint for diagnostics.
+- Loop carriers: loops may expose a carrier observation (≤ N variables, where N is unconstrained by design; smokes emphasize common cases).
+
+Normalization
+- If: may optionally wrap into LoopForm under a conservative gate (dev only). Semantics remain unchanged.
+- Match: scrutinee evaluated once, guard fused; normalized to nested If‑chain in macro/core pass.
+
+Testing
+- LLVM smokes: fixed small cases ensure no empty PHIs and head placement.
+- MIR smokes: trace `scope|join|loop` to validate shaping without peeking into IR details.
+
+Roadmap
+- Remove text-level sanitization once finalize‑PHI is trustworthy across Loop/If/Match.
+- Expand goldens to cover nested joins and multi‑carrier loops while keeping CI light.
+