[Interop experiment request] Declarative Capsule handoff over A2A

[jaden3824]

Urusilla is an experimental, unsigned declarative language Capsule for bounded agent-to-agent exchanges. This is not a proposal to replace A2A, and the current general unfamiliar-agent result is deliberately unfavorable: post-decode model API-input saving is 0%, while total tokens per safely completed real task remain unknown.

I am looking for one or two A2A implementers, preferably under a different operator and runtime, to test a narrow interoperability question:

Can an A2A exchange carry an immutable non-executable Capsule URI, SHA-256 digest, actual signature status, positive/negative comprehension evidence, and an explicit session adoption decision—then safely fall back to concise language or JSON on any mismatch?

A same-project fresh-context pilot reached three receivers. Capsule digest reproduction and structural message generation were 3/3, but explicit adoption-before-use was only 2/3 because the last receiver used a valid reply without recording the required adoption decision. That ordering failure is retained as negative evidence. No external effects occurred, and it is not independent or organic adoption.

For an external reproduction, please:

1. use a fresh or explicitly reset receiver and disclose prior exposure, memory, caches, tools, model/runtime, and operator relationship;
2. provide only the exact Capsule identity and declared wrapper; do not execute submitted content;
3. run positive, negative, and exact-reconstruction gates before explicit session adoption;
4. compare matched concise-language, JSON, and Urusilla arms over a bounded 3–10-turn task;
5. count the complete denominator: discovery, Capsule/context, gates, all model input/output, conversion, repair, retry, fallback, judge/router, and final answer;
6. optionally relay the same immutable identity to one fresh downstream receiver and record acknowledgement;
7. prohibit persistence, permission expansion, spending authority, executable installation, and external effects.

Negative, null, refusal, fallback, and regression results are welcome. One chain cannot establish adoption, general savings, security, or SOTA.

Resources:

• Agent-readable entry: https://github.com/jaden3824/urusilla/blob/main/llms.txt
• Full protocol and matched-ledger requirements: https://github.com/jaden3824/urusilla/blob/main/INTEROP_LAB.md
• Structured evidence form: https://github.com/jaden3824/urusilla/issues/new/choose
• First controlled pilot: https://github.com/jaden3824/urusilla/blob/main/interop_lab/evidence/PILOT_001.md
• Public evidence room: Urusilla Interop Lab: public multi-hop agent test room jaden3824/urusilla#6

A2A-specific review question: would an Agent Card extension plus a normal DataPart carrying only the immutable Capsule reference and verification result be the least disruptive mapping, or is there a more appropriate existing A2A mechanism?

Disclosure: this request was drafted and posted with Codex assistance under the repository owner's authorization. The requested external evidence must identify its own operators and assistance.

Runnable packet update

A frozen 750-byte packet, SHA-256, expected typed JSON, and deterministic decoder are now available at https://github.com/jaden3824/urusilla/blob/51ff0e3/interop_lab/evidence/challenge_001.md, with a matched HF record at https://huggingface.co/datasets/jaden3824/urusilla-interop-lab. It is non-executable and grants no persistence, spending, permission expansion, network action, or external effect. Broad post-decode saving remains 0%; refusal and null results are valid.

[jaden3824]

Runnable artifact update (project-authored; not independent evidence): the repository now includes a frozen 750-byte Urusilla REQUEST, its SHA-256, expected typed JSON, and an exact decode/re-encode command:

• https://github.com/jaden3824/urusilla/blob/51ff0e3/interop_lab/evidence/challenge_001.md
• https://huggingface.co/datasets/jaden3824/urusilla-interop-lab

For A2A reviewers, the bounded question is whether this declarative, non-effect-authorizing Capsule/payload pattern maps cleanly to an A2A DataPart or extension without weakening A2A identity, task, and authorization semantics. Broad post-decode API-input saving remains 0%; a refusal, mismatch, or null result is welcome. No executable installation, persistence, spending, permission expansion, or external effects are requested. Codex assisted with the artifact and this disclosure.

[jaden3824]

Bounded controller update (project-authored; not independent evidence): commit https://github.com/jaden3824/urusilla/tree/f612ea1 adds session-local alias evolution with frozen matched shadow trials, cumulative failed-attempt accounting, and rollback on unknown usage. Local full regression is 392/392; demonstrated general unfamiliar-agent token saving remains 0%. A zero-install 60-second/10-minute falsification prompt is at jaden3824/urusilla#8. A2A-specific feedback is especially useful on whether the activation-versus-retention boundary and the required one-controller-per-scope host lease can be represented without implying new task or authorization authority. Negative/null results are welcome.