Add IPC envelope and tool messages to proto

Implemented-By: Laguna S 2.1 (OpenCode)

crates/proto/tests/fixtures/wire/error.json

@@ -0,0 +1 @@
+{"v":1,"id":0,"final":true,"msg":{"kind":"error","body":{"code":"bad_version","detail":"expected 1"}}}

crates/proto/tests/fixtures/wire/tool_request.json

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+{"v":1,"id":7,"final":true,"msg":{"kind":"tool_request","body":{"session":"mm-thread-42","call":3,"tool":"read_file","arguments":"{\"path\":\"/etc/hosts\"}"}}}

crates/proto/tests/fixtures/wire/tool_response_denied.json

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+{"v":1,"id":9,"final":true,"msg":{"kind":"tool_response","body":{"status":"denied","reason":"taint_too_high"}}}

crates/proto/tests/fixtures/wire/tool_response_failed.json

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+{"v":1,"id":8,"final":true,"msg":{"kind":"tool_response","body":{"status":"failed","message":"exit status 2"}}}

crates/proto/tests/fixtures/wire/tool_response_pending.json

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+{"v":1,"id":7,"final":false,"msg":{"kind":"tool_response","body":{"status":"pending_approval","approval":"ap-0001","expires":"2026-09-17T08:35:00.000Z"}}}

crates/proto/tests/fixtures/wire/tool_response_result.json

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+{"v":1,"id":7,"final":true,"msg":{"kind":"tool_response","body":{"status":"result","content":"127.0.0.1 localhost\n","class":"private","untrusted":true,"truncated":false}}}