feat(joinir): Phase 30.x jsonir v0 snapshot tests

Implement JSON snapshot testing for JoinIR regression detection.

Implementation:
- tests/fixtures/joinir/v0_*.jsonir: 6 snapshot fixtures for minimal JoinIR cases
- src/tests/joinir_json_min.rs: Added 6 snapshot comparison tests

Fixtures:
- v0_skip_ws_min.jsonir (1338 bytes)
- v0_funcscanner_trim_min.jsonir (4484 bytes)
- v0_funcscanner_append_defs_min.jsonir (988 bytes)
- v0_stage1_usingresolver_min.jsonir (987 bytes)
- v0_stageb_body_min.jsonir (1074 bytes)
- v0_stageb_funcscanner_min.jsonir (962 bytes)

Usage:
  # Run snapshot tests
  NYASH_JOINIR_SNAPSHOT_TEST=1 cargo test --release joinir_json_v0_

  # Regenerate fixtures (after intentional changes)
  NYASH_JOINIR_SNAPSHOT_TEST=1 NYASH_JOINIR_SNAPSHOT_GENERATE=1 cargo test --release joinir_json_v0_

Purpose:
- Fix current JoinIR shape as v0 baseline (pre-generic state)
- Detect unintended regressions during genericization
- Allow intentional fixture updates when design changes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/fixtures/joinir/v0_funcscanner_append_defs_min.jsonir

@@ -0,0 +1 @@
+{"version":0,"entry":0,"functions":[{"id":0,"name":"append_defs_entry","params":[9000,9001,9002],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"const","dst":9010,"value_type":"integer","value":0}},{"type":"call","func":1,"args":[9000,9001,9002,9010],"k_next":null,"dst":null}]},{"id":1,"name":"loop_step","params":[10000,10001,10002,10003],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"compare","dst":10010,"op":"ge","lhs":10003,"rhs":10002}},{"type":"jump","cont":0,"args":[],"cond":10010},{"type":"compute","op":{"kind":"boxcall","dst":10011,"box":"ArrayBox","method":"get","args":[10001,10003]}},{"type":"compute","op":{"kind":"boxcall","dst":null,"box":"ArrayBox","method":"push","args":[10000,10011]}},{"type":"compute","op":{"kind":"const","dst":10013,"value_type":"integer","value":1}},{"type":"compute","op":{"kind":"binop","dst":10012,"op":"add","lhs":10003,"rhs":10013}},{"type":"call","func":1,"args":[10000,10001,10002,10012],"k_next":null,"dst":null}]}]}

tests/fixtures/joinir/v0_funcscanner_trim_min.jsonir

@@ -0,0 +1 @@
+{"version":0,"entry":0,"functions":[{"id":0,"name":"trim_main","params":[5000],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"const","dst":5005,"value_type":"string","value":""}},{"type":"compute","op":{"kind":"binop","dst":5001,"op":"add","lhs":5005,"rhs":5000}},{"type":"compute","op":{"kind":"boxcall","dst":5002,"box":"StringBox","method":"length","args":[5001]}},{"type":"compute","op":{"kind":"const","dst":5006,"value_type":"integer","value":0}},{"type":"call","func":2,"args":[5001,5006,5002],"k_next":null,"dst":5003},{"type":"compute","op":{"kind":"binop","dst":5004,"op":"add","lhs":5002,"rhs":5006}},{"type":"call","func":1,"args":[5001,5003,5004],"k_next":null,"dst":null}]},{"id":1,"name":"loop_step","params":[6000,6001,6002],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"compare","dst":6003,"op":"gt","lhs":6002,"rhs":6001}},{"type":"compute","op":{"kind":"const","dst":6019,"value_type":"bool","value":false}},{"type":"compute","op":{"kind":"boxcall","dst":6004,"box":"StringBox","method":"substring","args":[6000,6001,6002]}},{"type":"compute","op":{"kind":"compare","dst":6020,"op":"eq","lhs":6003,"rhs":6019}},{"type":"jump","cont":0,"args":[6004],"cond":6020},{"type":"compute","op":{"kind":"const","dst":6005,"value_type":"integer","value":1}},{"type":"compute","op":{"kind":"binop","dst":6006,"op":"sub","lhs":6002,"rhs":6005}},{"type":"compute","op":{"kind":"boxcall","dst":6007,"box":"StringBox","method":"substring","args":[6000,6006,6002]}},{"type":"compute","op":{"kind":"const","dst":6012,"value_type":"string","value":" "}},{"type":"compute","op":{"kind":"compare","dst":6008,"op":"eq","lhs":6007,"rhs":6012}},{"type":"compute","op":{"kind":"const","dst":6013,"value_type":"string","value":"\\t"}},{"type":"compute","op":{"kind":"compare","dst":6009,"op":"eq","lhs":6007,"rhs":6013}},{"type":"compute","op":{"kind":"const","dst":6014,"value_type":"string","value":"\\n"}},{"type":"compute","op":{"kind":"compare","dst":6010,"op":"eq","lhs":6007,"rhs":6014}},{"type":"compute","op":{"kind":"const","dst":6015,"value_type":"string","value":"\\r"}},{"type":"compute","op":{"kind":"compare","dst":6011,"op":"eq","lhs":6007,"rhs":6015}},{"type":"compute","op":{"kind":"binop","dst":6016,"op":"or","lhs":6008,"rhs":6009}},{"type":"compute","op":{"kind":"binop","dst":6017,"op":"or","lhs":6016,"rhs":6010}},{"type":"compute","op":{"kind":"binop","dst":6018,"op":"or","lhs":6017,"rhs":6011}},{"type":"compute","op":{"kind":"compare","dst":6021,"op":"eq","lhs":6018,"rhs":6019}},{"type":"jump","cont":1,"args":[6004],"cond":6021},{"type":"compute","op":{"kind":"binop","dst":6022,"op":"sub","lhs":6002,"rhs":6005}},{"type":"call","func":1,"args":[6000,6001,6022],"k_next":null,"dst":null}]},{"id":2,"name":"skip_leading","params":[7000,7001,7002],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"compare","dst":7003,"op":"ge","lhs":7001,"rhs":7002}},{"type":"jump","cont":2,"args":[7001],"cond":7003},{"type":"compute","op":{"kind":"const","dst":7004,"value_type":"integer","value":1}},{"type":"compute","op":{"kind":"binop","dst":7005,"op":"add","lhs":7001,"rhs":7004}},{"type":"compute","op":{"kind":"boxcall","dst":7006,"box":"StringBox","method":"substring","args":[7000,7001,7005]}},{"type":"compute","op":{"kind":"const","dst":7011,"value_type":"string","value":" "}},{"type":"compute","op":{"kind":"compare","dst":7007,"op":"eq","lhs":7006,"rhs":7011}},{"type":"compute","op":{"kind":"const","dst":7012,"value_type":"string","value":"\\t"}},{"type":"compute","op":{"kind":"compare","dst":7008,"op":"eq","lhs":7006,"rhs":7012}},{"type":"compute","op":{"kind":"const","dst":7013,"value_type":"string","value":"\\n"}},{"type":"compute","op":{"kind":"compare","dst":7009,"op":"eq","lhs":7006,"rhs":7013}},{"type":"compute","op":{"kind":"const","dst":7014,"value_type":"string","value":"\\r"}},{"type":"compute","op":{"kind":"compare","dst":7010,"op":"eq","lhs":7006,"rhs":7014}},{"type":"compute","op":{"kind":"binop","dst":7015,"op":"or","lhs":7007,"rhs":7008}},{"type":"compute","op":{"kind":"binop","dst":7016,"op":"or","lhs":7015,"rhs":7009}},{"type":"compute","op":{"kind":"binop","dst":7017,"op":"or","lhs":7016,"rhs":7010}},{"type":"compute","op":{"kind":"const","dst":7018,"value_type":"bool","value":false}},{"type":"compute","op":{"kind":"compare","dst":7019,"op":"eq","lhs":7017,"rhs":7018}},{"type":"jump","cont":3,"args":[7001],"cond":7019},{"type":"call","func":2,"args":[7000,7005,7002],"k_next":null,"dst":null}]}]}

tests/fixtures/joinir/v0_skip_ws_min.jsonir

@@ -0,0 +1 @@
+{"version":0,"entry":0,"functions":[{"id":0,"name":"skip","params":[3000],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"const","dst":3001,"value_type":"integer","value":0}},{"type":"compute","op":{"kind":"boxcall","dst":3002,"box":"StringBox","method":"length","args":[3000]}},{"type":"call","func":1,"args":[3000,3001,3002],"k_next":null,"dst":null}]},{"id":1,"name":"loop_step","params":[4000,4001,4002],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"compare","dst":4003,"op":"ge","lhs":4001,"rhs":4002}},{"type":"jump","cont":0,"args":[4001],"cond":4003},{"type":"compute","op":{"kind":"const","dst":4007,"value_type":"integer","value":1}},{"type":"compute","op":{"kind":"binop","dst":4006,"op":"add","lhs":4001,"rhs":4007}},{"type":"compute","op":{"kind":"boxcall","dst":4004,"box":"StringBox","method":"substring","args":[4000,4001,4006]}},{"type":"compute","op":{"kind":"const","dst":4010,"value_type":"string","value":" "}},{"type":"compute","op":{"kind":"compare","dst":4005,"op":"eq","lhs":4004,"rhs":4010}},{"type":"compute","op":{"kind":"const","dst":4011,"value_type":"bool","value":false}},{"type":"compute","op":{"kind":"compare","dst":4012,"op":"eq","lhs":4005,"rhs":4011}},{"type":"jump","cont":1,"args":[4001],"cond":4012},{"type":"call","func":1,"args":[4000,4006,4002],"k_next":null,"dst":null}]}]}

tests/fixtures/joinir/v0_stage1_usingresolver_min.jsonir

@@ -0,0 +1 @@
+{"version":0,"entry":0,"functions":[{"id":0,"name":"resolve_entries","params":[7000,7001,7002,7003,7004],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"const","dst":7010,"value_type":"integer","value":0}},{"type":"call","func":1,"args":[7000,7001,7002,7003,7004,7010],"k_next":null,"dst":null}]},{"id":1,"name":"loop_step","params":[8000,8001,8002,8003,8004,8005],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"compare","dst":8010,"op":"ge","lhs":8005,"rhs":8001}},{"type":"jump","cont":0,"args":[8004],"cond":8010},{"type":"compute","op":{"kind":"boxcall","dst":8011,"box":"ArrayBox","method":"get","args":[8000,8005]}},{"type":"compute","op":{"kind":"const","dst":8013,"value_type":"integer","value":1}},{"type":"compute","op":{"kind":"binop","dst":8012,"op":"add","lhs":8005,"rhs":8013}},{"type":"compute","op":{"kind":"binop","dst":8014,"op":"or","lhs":8004,"rhs":8011}},{"type":"call","func":1,"args":[8000,8001,8002,8003,8014,8012],"k_next":null,"dst":null}]}]}

tests/fixtures/joinir/v0_stageb_body_min.jsonir

@@ -0,0 +1 @@
+{"version":0,"entry":0,"functions":[{"id":0,"name":"build_body_src","params":[11000,11001],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"boxcall","dst":11002,"box":"StringBox","method":"length","args":[11000]}},{"type":"compute","op":{"kind":"const","dst":11003,"value_type":"integer","value":0}},{"type":"compute","op":{"kind":"const","dst":11004,"value_type":"integer","value":0}},{"type":"call","func":1,"args":[11000,11001,11002,11004,11003],"k_next":null,"dst":null}]},{"id":1,"name":"loop_step","params":[12000,12001,12002,12003,12004],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"compare","dst":12010,"op":"ge","lhs":12004,"rhs":12002}},{"type":"jump","cont":0,"args":[12003],"cond":12010},{"type":"compute","op":{"kind":"const","dst":12011,"value_type":"integer","value":1}},{"type":"compute","op":{"kind":"binop","dst":12012,"op":"add","lhs":12004,"rhs":12011}},{"type":"compute","op":{"kind":"binop","dst":12013,"op":"add","lhs":12003,"rhs":12011}},{"type":"call","func":1,"args":[12000,12001,12002,12013,12012],"k_next":null,"dst":null}]}]}

tests/fixtures/joinir/v0_stageb_funcscanner_min.jsonir

@@ -0,0 +1 @@
+{"version":0,"entry":0,"functions":[{"id":0,"name":"scan_all_boxes","params":[13000],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"boxcall","dst":13001,"box":"StringBox","method":"length","args":[13000]}},{"type":"compute","op":{"kind":"const","dst":13002,"value_type":"integer","value":0}},{"type":"compute","op":{"kind":"const","dst":13003,"value_type":"integer","value":0}},{"type":"call","func":1,"args":[13000,13001,13002,13003],"k_next":null,"dst":null}]},{"id":1,"name":"loop_step","params":[14000,14001,14002,14003],"exit_cont":null,"body":[{"type":"compute","op":{"kind":"compare","dst":14010,"op":"ge","lhs":14003,"rhs":14001}},{"type":"jump","cont":0,"args":[14002],"cond":14010},{"type":"compute","op":{"kind":"const","dst":14011,"value_type":"integer","value":1}},{"type":"compute","op":{"kind":"binop","dst":14012,"op":"add","lhs":14003,"rhs":14011}},{"type":"call","func":1,"args":[14000,14001,14002,14012],"k_next":null,"dst":null}]}]}