[SaladDay]

Hosted Sessions now stream the pinned agent.session.environment.pending and agent.session.environment.ready events, which the ledger listed as a known gap.

• An openai_hosted Environment journals pending in the transaction that starts its initialization and ready in the one that completes it. Each transition is a conditional update, so retries, a preparation-cache hit and a Core restart never repeat an event. self_hosted Environments emit neither. Connected, disconnected and failed are unchanged.
• The ledger moves the remaining differences to their sections: ready is not re-emitted before each later Turn as one official Session did, hosted Environments still emit connected/disconnected, and when the official service emits pending is unverified.

Checks: go test ./internal/sessions, go vet ./... (services/core), go test ./tests/integration/ ./internal/api/ -run 'Initialization|EnvironmentInputActivity|CreationStream|HostedEnvironment|Event|Stream|Hosted|Environment|Turn' against PostgreSQL.

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