[SaladDay]

Official API alignment (ST-05): after a waiting Turn is cancelled (202), the official Session keeps requires_action until the Turn ends; Core switched to in_progress at once and journaled an interim agent.session.in_progress.

• The cancel request on a waiting Turn now only records the request; the Session keeps requires_action with its actions until the Turn ends, then turn.cancelled and agent.session.idle follow as before.
• Function results after the cancel are still rejected, and the executor gets no pending calls for a cancelling Turn. Unconfirmed cancels still fail after the existing cancel_unconfirmed bound.
• Docs (sessions-events.md, ledger line, + zh) updated.

Checks: go test ./internal/sessions ./internal/api ./internal/execution, ./tests/integration -run TestFunctionState against a test database, make sqlc-generate (no diff), go vet ./..., gofmt.

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