Phase 201 introduces JoinValueSpace to prevent ValueId collisions between
Pattern 2 frontend (alloc_join_value) and JoinIR lowering (alloc_value).
ValueId Space Layout:
- PHI Reserved (0-99): For LoopHeader PHI dst
- Param Region (100-999): For ConditionEnv, CarrierInfo, CapturedEnv
- Local Region (1000+): For Const, BinOp, etc. in pattern lowerers
Changes:
- Add join_value_space.rs with JoinValueSpace struct (10 tests)
- Add ConditionEnvBuilder v2 API using JoinValueSpace
- Wire Pattern 2 frontend to use JoinValueSpace for param allocation
Note: E2E tests fail until Task 201-5 wires lowerers to alloc_local()
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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