Per-Input Source-Obligation Accounting for Workflow Graphs, Including Machine-Composed Workflow Graphs: Stable Input Identities with Immutable Port Identifiers, Canonical Availability Normalization of Unavailable-Value Sentinels, Binding-Grounded Obligation Resolution, Execution Control from Obligation Status, and Declared-Versus-Actual Fulfilment Attestation with Expected-Attestation Reconciliation over an Immutable Input-Identity Ledger