**English** | [简体中文](adapter-contracts.zh-CN.md)

# Adapter capability contracts

These are discovery contracts. No implementation is bundled.

| Capability | Required input | Required receipt | Honest absence behavior |
|---|---|---|---|
| `agent.registry.read` | role/capability query, policy scope | candidates plus source revision | produce a packet for manual delivery; do not invent a recipient |
| `agent.spawn` | recipient ID and validated `bounded_subagent` packet | dispatch ID, recipient ID, timestamp, requested/effective mode | mark packet `undelivered` |
| `agent.task.create` | recipient ID and validated `independent_task` packet | dispatch ID, separately resumable task/thread ID, recipient ID, timestamp, authoritative workspace receipt | leave `undelivered`, or explicitly degrade only when the packet allows it and continuity is not required |
| `agent.message` | live dispatch ID and follow-up packet | message ID and timestamp | state that no follow-up mechanism was available |
| `workspace.authoritative.resolve` | stable root ID and task context | resolved real path plus resolution evidence | require a parent-supplied root and verify it from the parent filesystem; never substitute the current cwd |
| `collaboration.log.append` | structured event with redacted refs | exit code zero, event ID, append position/version | omit shared append; do not claim atomic logging |
| `agent.inbox.deliver` | recipient ID and directed message | delivery ID and destination ref | keep a copyable message and mark it undelivered |

Adapters may map these contracts to a specific Harness, but must not:

- promote optional capabilities to bundled features;
- alter safety or routing policy;
- expose secret values in packets or receipts;
- report `sent`, `spawned`, `followed_up`, or `appended` without provider evidence.

Provider-specific metadata belongs under a namespaced receipt field and must
not replace the required evidence. Validate neutral packet and receipt fields
against [`../contracts/`](../contracts/).

For a v1.3 durable chain, the validated handoff packet supplies `handoff_id`
and its persistence contract supplies `contract_id`. The dispatch adapter adds
its real `dispatch_id`. Every downstream return, closure receipt, and parent
verification repeats all three IDs. Reject a receipt when any ID belongs to a
different task, even when its fields and artifact paths otherwise look valid.
IDs are correlation labels, so each required target also carries a fresh
dispatcher-issued `evidence_nonce`. The adapter or parent combines it with the
real `dispatch_id` to produce the target's `evidence_anchor`. The file,
provider event, or board proposal must carry that anchor; the parent derives
it again from the saved dispatch receipt and contract instead of trusting
child-supplied labels alone.

Represent honest non-delivery with the `undelivered` branch in
`dispatch-receipt.schema.json`; it requires a reason and forbids invented
dispatch/task IDs or provider receipts.

`agent.task.create` means an independently identifiable, resumable task or
thread. A nested child that can only return to its parent does not satisfy this
contract. An adapter may report a degradation receipt only when it contains
both modes and a concrete reason.

Persistence does not choose the adapter. A `bounded_subagent` packet may carry
a required persistence contract and complete all four durable targets through
`agent.spawn`; that still remains bounded. Only a real, separately resumable
task/thread receipt from `agent.task.create` establishes `independent_task`.

For `independent_task`, compare the adapter's workspace receipt with the
persistence contract field by field: root ID, normalized resolved path, and
resolution evidence. Also compare a v1.3 return's declared mode with the
dispatch receipt's effective mode. A correct ID set does not excuse either
mismatch.

The selected log provider owns its atomicity guarantee. A thrown error, timeout,
missing receipt, malformed receipt, or nonzero exit means append failure. Do not
manufacture an event ID after failure.

The central board is not an append adapter. Configure one writer (normally the
parent/coordinator); children send proposals through their return packet. The
single writer serializes updates and re-reads the board after every merge.

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> Both language editions are maintained in sync. If they ever diverge, the **English edition** is authoritative — please open an [issue](https://github.com/LucioLiu/handoff-protocol/issues) if you spot one.