stage3: unify to cleanup; MIR return-defer; docs+smokes updated; LLVM(harness): finalize_phis ownership, ret.py simplified, uses-predeclare; cleanup return override green; method-postfix cleanup return WIP (PHI head)

docs/papers/result_mode_exceptions.md

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+# Structured Exceptions via Result‑Mode (Draft)
+
+Problem
+- Language exceptions are hard to implement portably (unwinding, landing pads) and complicate SSA/CFG.
+
+Contribution (Nyash)
+- Express try/catch/cleanup with Result‑mode lowering (no MIR Throw/Catch): structured blocks and jumps.
+- Thread‑local ThrowCtx to aggregate nested `throw` to a single catch.
+- PHI‑Off: merge variables via edge‑copy; harness synthesizes PHIs.
+- Block‑Postfix Catch syntax: `{ body } catch (e) { … } [cleanup { … }]` with single‑catch policy.
+
+Method
+- Parser (gated): accept try/throw + postfix catch, normalize to `ASTNode::TryCatch`.
+- Bridge: set ThrowCtx on try entry; route `throw` to catch BB; bind catch param via incoming.
+- Cleanup: always runs; merge at exit with PHI‑off rules.
+
+Code References
+- Parser: `src/parser/statements.rs`
+- Bridge lowering: `src/runner/json_v0_bridge/lowering/{try_catch.rs, throw_ctx.rs}`
+- Smokes: `tools/test/smoke/bridge/try_result_mode.sh`
+
+Evaluation Plan
+- Semantic parity: PyVM vs. harness binaries on representative cases.
+- Control‑flow complexity: nested if/loop + cleanup; ensure merges are stable.
+
+Reproduce
+- `bash tools/test/smoke/bridge/try_result_mode.sh`