refactor(native-sidecar): partition VM and event ownership

[NathanFlurry]

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[NathanFlurry]

Stack for rivet-dev/agentos

• #1899 refactor(native-sidecar): simplify VM lifecycle coordination
• #1890 test(agentos): remove the ACP prompt workaround
• #1891 fix(native-sidecar): broker output without blocking ingress
• #1889 fix(agentos-sidecar): route ACP progress concurrently
• #1892 refactor(native-sidecar): partition VM and event ownership 👈
• #1888 feat(runtime): bound concurrent protocol operations
• main

Get stack: forklift get 1892
Push local edits: forklift submit
Merge when ready: forklift merge 1892

_{change znmuvwzw}