Zambo This document specifies AER-1, a small vocabulary for recording one AI agent tool call as a portable, independently checkable execution receipt. A receipt identifies the execution, records when it happened, preserves the canonical bytes used for the output commitment, names the tool and caller scope, carries a provenance class, and resolves at a stable public URL. The format separates what the system observed from claims about the outside world, and it separates provenance (who ran or reported the action) from the record itself. A reference implementation is deployed, and its receipts are publicly verifiable without an account or token. The specification covers workflow receipts, which bind an ordered sequence of step receipts to a single goal with a Merkle root over the step sequence, and hash-chained job timelines for tamper-evident sequencing of executions. This revision closes honesty and precision gaps: it adds the workflow-receipt truncation limit (new Section 8.4), normatively specifies the external anchor format and its verification procedure (rewritten Section 10, new Section 10.1), fixes a RECOMMENDED/MUST contradiction in Section 8.1, makes the Section 6 verification step testable, and documents replay, low-entropy, empty-record, and size-limit considerations. It changes no receipt field, digest construction, or existing verification rule. The -13 revision fixes a malformed sentence in the Abstract, three incorrect section cross-references, stale Table of Contents page numbers, a skipped footer page number, misaligned table rows, and chain version-string updates, and records two reported interoperability examples in Implementation Status; it changes no receipt field, digest construction, or verification rule. The -14 revision adds tamper-evident metadata binding (new Section 3.1; conditional metadata_hash for schema 0.4 and later), disambiguates the anchor receipt_id (Table 4), corrects the self-anchoring witnessing claim (Section 10), makes the Section 8.3 display rule a SHOULD with a byte-testable MUST, narrows the provenance attestation wording (Section 5), states the binding non-transfer rule normatively (new Section 10.2), pins anchored_digest to bare hex (Table 4), corrects the vector corpus counts, and adds normative disclosure of missing issuer authentication. It changes no existing receipt field, digest construction, or verification rule for schema 0.3 and earlier. The -15 revision narrows the Implementation Status wording for the reported interoperability examples at the implementer's request; it changes no receipt field, digest construction, or verification rule. The -16 revision documents the live workflow tools API (new Sections 8.5, 8.6, 8.7): the workflow_close tool, workflow metadata in step receipts, and the workflow view API. It changes no receipt field, digest construction, or existing verification rule. The -17 revision documents the recommended execution_context member (new Section 3.2): an optional, non-core structure for recording source and version context such as the model name and version behind a tool call and the identity of the source system acted upon. It changes no existing receipt field, digest construction, or verification rule. The -18 revision repairs the reference apparatus (normative references to RFC 3339, RFC 8259, RFC 4122, and RFC 4648, and the previously missing RFC 7942 entry), pins two parser edge cases (duplicate JSON member names and leap-second timestamps are rejected), names the Unicode normalization behavior in Section 4 with a computed vector pair, adopts the unknown- versus-not-applicable convention for optional members, adds optional members for readback outcomes, per-field provenance, negative records, reversal state, method descriptors, and payment references, completes the execution_context member set (model and environment digests), adds the optional input_hash commitment (Section 3.3), permits SCITT and RFC 3161 anchors under Section 10, states the clock-trust and equivocation limits in Section 13, and rewrites Section 15 to position the specification against adjacent work. It changes no receipt field, digest construction, or verification outcome for any receipt well-formed under the -17 rules. The -19 revision aligns the workflow tool and workflow view descriptions in Sections 8.5 and 8.7 with the normative Merkle construction in Section 8.1: both descriptions named step output hashes as the root's leaf input where Section 8.1 specifies step receipt identifiers. An implementer report identified the divergence. It changes no construction, receipt field, digest, or verification outcome.