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/block_postfix_catch.md

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+# Block‑Postfix Catch Language Design (Draft)
+
+Goal
+- Make exception boundaries explicit by attaching `catch`/`cleanup` to standalone blocks.
+
+Design
+- Syntax: `{ body } catch (e) { handler } [cleanup { … }]` and `{ body } cleanup { … }`.
+- Policy: single catch (branch inside the catch); scope limited to the same block; no implicit propagation.
+- Static check (MVP): direct `throw` in a standalone block requires an immediate postfix `catch`.
+
+Implementation Notes
+- Parser (gated): normalize postfix to `ASTNode::TryCatch`.
+- Bridge(Result‑mode): ThrowCtx routes nested `throw` to the single catch; merge with PHI‑off.
+- Friendly errors: disallow top‑level leading `catch`/`cleanup`, and attaching to structural if/loop blocks.
+
+References
+- Parser: `src/parser/statements.rs`
+- Smokes: `src/tests/parser_block_postfix_{catch,errors}.rs`
+
+Open Questions
+- Multiple catch with type hierarchy; effects typing for static checks; formatter support.