design(agent-harness): define Software Factory A2A/Postman integration boundary

[i9wa4]

Summary

Define the integration boundary between the dotfiles-managed Software Factory
agent harness and the tmux-a2a-postman daemon repository.

The current harness contract is installed from config/tmux-a2a-postman/postman.md.
It defines roles, review routing, command approval, public-write gates, and the
future-only diplomat role. The daemon repository owns delivery, mailbox,
status, routing, and persistence behavior. The repositories need one explicit
contract for how those two ownership domains evolve together.

Why a new issue

No open issue in this repository matched Software Factory, A2A, or
postman in an open-and-closed duplicate search on 2026-07-26. Closed #95 is
a historical Go rewrite architecture for the daemon itself; #101 covers
inbox/context paths; #139 covers bounded approval-lane policy; #171 and #179
cover migration/compaction of role-contract documentation. None defines the
current cross-repository Software Factory integration contract.

This conclusion is based on the issue inventory and current checked-in
harness sources. It is not a claim that no unrecorded discussion exists.

Scope

• State the ownership boundary between this repository and i9wa4/tmux-a2a-postman.
• Define versioning/compatibility expectations for the role template,
  skill_path catalog, message metadata, status projections, and command
  approval surfaces consumed by the harness.
• Define lifecycle handoff rules for task intake, durable task artifacts,
  worker execution, guardian/critic review, human-gated public writes, and
  completion reporting.
• Define failure and observability semantics: queued versus processed delivery,
  timed-out daemon-submit requests, late responses, stale input requests, and
  when an agent must report transport uncertainty rather than retry.
• Define the boundary for command approval: it is an audited decision lane,
  not sandboxing or a substitute for human approval of public/production
  writes.
• Define the future diplomat boundary: cross-session authorization remains
  disabled until the daemon-side feature and an approved protocol contract
  exist.

Dependencies and boundaries

• i9wa4/dotfiles owns harness policy and installed role-template sources,
  including config/tmux-a2a-postman/postman.md and agent-harness skills.
• i9wa4/tmux-a2a-postman owns the Go daemon/CLI, delivery semantics,
  storage, status projection, and runtime behavior.
• This issue must not prescribe a daemon implementation or change daemon
  runtime/configuration. Such work belongs in i9wa4/tmux-a2a-postman after
  its own issue, design, and review gates.
• Coordinate with daemon-side cross-session/diplomat, command-approval, and
  daemon-submit reliability work before relying on those capabilities in the
  harness.

Acceptance criteria

• A source-of-truth table names each contract surface, its owning
  repository, its consumer, and its compatibility/release expectation.
• The task-to-completion lifecycle names the required evidence and the
  human-public-write boundary without duplicating daemon implementation
  detail.
• Delivery-state vocabulary distinguishes queued, processed, timeout,
  pending, and late response, including safe retry/escalation behavior.
• Command approval and sandbox/human-approval responsibilities are
  separated explicitly.
• The diplomat/cross-session feature is documented as disabled by default
  until a daemon-side protocol and verification gate are approved.
• Proposed changes, if any, identify only dotfiles-owned sources and list
  the corresponding daemon-side dependency or stable issue URL.
• Review includes maintainability and security evidence for both ownership
  boundaries before implementation work starts.

Non-goals

• Changing tmux-a2a-postman source, daemon runtime, routing configuration,
  or production state.
• Implementing cross-session relay behavior.
• Bypassing explicit human approval for public GitHub writes.
• Reopening the historical daemon rewrite scope in postman: Architecture Design Specification (Go Full Rewrite) #95.