Durable inbox: multi-machine recipes, honest sync limits, and notice signal paths #10

Goal

Make durable inbox usable across machines and agent sessions without turning the local core into a network service.

This is the near-term "more usable, not local-only forever" step that needs no daemon, accounts, or remote listener in core.

Context

• Local durable inbox (V5) + delivery notices (0.7.0) are shipped: pack → send → notice → pull/import → ack → status.
• Claude Code cross-session messaging validates multi-session coordination, but is Claude-only plain text. 3Notch owns the portable packet bus; vendor messengers carry the signal, not the archive.
• README already lists cross-machine transport recipes and honest sync guarantees as wanted help.

Scope

Docs / recipes

• Opinionated recipes for pointing two stores at one mailbox root via Tailscale, Syncthing, iCloud, git, scp/rsync (what works, what fails, permission model).
• Explicit honest limits: no distributed locks, no guaranteed delivery across sync products, SHA-256 is integrity not authorship, local: is a label not identity.
• Clear guidance that anyone with FS access to the mailbox root can read/change it until encryption/signing land (see related issues).

Agent / notice signal paths

• Document forwarding the plain-text delivery notice through:
  • Claude Code cross-session messaging (SendMessage)
  • Slack / email / GitHub comments / any text channel
• Agent prompt / onboard wording: notice is signal only; receiver still runs 3Notch under its own permissions.
• Optional small examples of "sender posts notice → receiver pulls by delivery_id".

Out of scope here

• Encryption, signing, remote HTTP transport, network listeners, hosted relay (tracked separately).
• Unblocking private/seed packets on the shared mailbox (intentionally blocked).

Acceptance ideas

• Guide (or README section) with at least two multi-machine recipes and failure modes.
• Honest-limits section cross-linked from durable-inbox + security story.
• Notice signal-path section naming Claude messaging as one channel among many.
• Prompt/onboard text updated if recipes change agent behavior expectations.

Related

• Depends on nothing blocked; builds on shipped inbox + notices.
• Soft prerequisite for smoother adoption of encryption and remote transport.