chore: file the session-mailbox intents, the basics-plus-adapter principle and the messaging survey

.abcd/development/brief/06-delivery/03-out-of-scope.md

@@ -109,6 +109,8 @@ gate. That is what keeps "not hand-counted" true after the day it was written.
 - `itd-176` — Whatever ships says how hard anyone looked at it (Phase 7)
 - `itd-201` — every question abcd's agents put to a human is asked one at a time, in plain language, in the addressee's register, with options that widen
 - `itd-2609061543533170` — one verb sets up a managed repository's release-rendered site end to end: the site composition, the wrangler configuration, the render-then-deploy workflow, the environments it needs, and the worker itself where a credential is held
+- `itd-2609151838312703` — sessions on one machine or one local network leave each other messages in a shared mailbox abcd owns (the built-in basic; nothing leaves the local network)
+- `itd-2609151838327688` — an opt-in adapter to a local message broker brings push delivery and cross-machine reach to the session mailbox (sequenced after the mailbox)
 - `itd-2609151541116052` — every question an interview puts to a human shows the thing being decided before it asks, at every step (refines itd-201)
 - `itd-2609151658486398` — a release cut publishes the security advisories its fixes close, and closes those resolved as won't-fix (the publication step the 2026-08-27 advisory-handling pilot named as its target)
 - `itd-2609091014076309` — Session and agent worktrees live in a machine-scoped store (`~/.abcd/worktrees/<root-sha>/<name>/`) that abcd lists and reclaims, never beside the user's own projects (the rule is adr-2609091248200336; `builds_on` itd-118, whose worktree clause it supplies the store and the reclaim verb for)

.abcd/development/intents/drafts/itd-2609151838312703-sessions-on-one-machine-or-one-local-network-leave-each-othe.md

@@ -0,0 +1,50 @@
+---
+id: itd-2609151838312703
+slug: sessions-on-one-machine-or-one-local-network-leave-each-othe
+spec_id: null
+kind: null
+suggested_kind: null
+reclassification_history: []
+builds_on: []
+severity: minor
+impact: additive
+origin: researcher-authored
+production_mode: dictated-and-formatted
+---
+
+# Sessions on one machine or one local network leave each other messages in a shared mailbox abcd owns: a session under another account or on another machine writes a signed record into a shared directory, the recipient's prompt hook injects it and acknowledges it, and every message stays a readable record; no daemon, no dependency, nothing leaves the local network
+
+## Press Release
+
+> _Seeded from a quoted-text intent capture. Expand into the full press-release narrative before planning._
+
+## Why This Matters
+
+Sessions on one machine or one local network leave each other messages in a shared mailbox abcd owns: a session under another account or on another machine writes a signed record into a shared directory, the recipient's prompt hook injects it and acknowledges it, and every message stays a readable record; no daemon, no dependency, nothing leaves the local network
+
+## Mechanism
+
+> _Prompted (the claim-recording gradient): why the authors expect this to work, as a falsifiable "we expect X because Y" — not the outcome restated. Replace this line with the claim, or with the exact token `None stated.` alone on its line to record the claim as considered and declined._
+
+## Scope Conditions
+
+> _Required (the claim-recording gradient): the population, platform, scale, or assumptions this claim holds under, one per top-level bullet — `abcd intent plan` stamps each with a persistent identity. Replace this line with those bullets, or with the exact token `None stated.` alone on its line._
+
+## Acceptance Criteria
+
+> _Required (the itd-1 discipline): add at least one Given-When-Then bullet describing the verifiable bar for "shipped" before this draft can be planned._
+
+## Prior Art
+
+- [2026-09-15-agent-messaging-on-a-local-network](../../research/notes/2026-09-15-agent-messaging-on-a-local-network.md) — the survey this draft rests on: a Maildir-shaped shared-directory mailbox ranked first as the built-in basic under the local-only bound.
+- [basics-built-in-adapters-bring-power](../../principles/basics-built-in-adapters-bring-power.md) — the stance that makes this the basic half; the broker adapter is itd-2609151838327688.
+- The prompt-router hook (`abcd hook prompt-router`, itd-20's loader) — the injection path the mailbox reuses; no second hook.
+- The hand protocol of 2026-09-15: two sessions under two accounts passing dated notes through one shared markdown file; this draft removes its two failure modes (colliding appends, no acknowledgement).
+
+## Open Questions
+
+_None recorded yet._
+
+## Audit Notes
+
+_Empty. Populated by intent-auditor when intent moves to shipped/._

.abcd/development/intents/drafts/itd-2609151838327688-an-opt-in-adapter-to-a-local-message-broker-brings-push-deli.md

@@ -0,0 +1,49 @@
+---
+id: itd-2609151838327688
+slug: an-opt-in-adapter-to-a-local-message-broker-brings-push-deli
+spec_id: null
+kind: null
+suggested_kind: null
+reclassification_history: []
+builds_on: [itd-2609151838312703]
+severity: minor
+impact: additive
+origin: researcher-authored
+production_mode: dictated-and-formatted
+---
+
+# An opt-in adapter to a local message broker brings push delivery and cross-machine reach to the session mailbox: with the adapter enabled a session is woken the moment a message arrives, machines on the local network exchange messages without a shared mount, and every delivered message is still mirrored to the mailbox as a record; without it the mailbox works as before
+
+## Press Release
+
+> _Seeded from a quoted-text intent capture. Expand into the full press-release narrative before planning._
+
+## Why This Matters
+
+An opt-in adapter to a local message broker brings push delivery and cross-machine reach to the session mailbox: with the adapter enabled a session is woken the moment a message arrives, machines on the local network exchange messages without a shared mount, and every delivered message is still mirrored to the mailbox as a record; without it the mailbox works as before
+
+## Mechanism
+
+> _Prompted (the claim-recording gradient): why the authors expect this to work, as a falsifiable "we expect X because Y" — not the outcome restated. Replace this line with the claim, or with the exact token `None stated.` alone on its line to record the claim as considered and declined._
+
+## Scope Conditions
+
+> _Required (the claim-recording gradient): the population, platform, scale, or assumptions this claim holds under, one per top-level bullet — `abcd intent plan` stamps each with a persistent identity. Replace this line with those bullets, or with the exact token `None stated.` alone on its line._
+
+## Acceptance Criteria
+
+> _Required (the itd-1 discipline): add at least one Given-When-Then bullet describing the verifiable bar for "shipped" before this draft can be planned._
+
+## Prior Art
+
+- [itd-2609151838312703](itd-2609151838312703-sessions-on-one-machine-or-one-local-network-leave-each-othe.md) — the basic this adapter extends; sequenced after it, and it shares the mailbox's record contract.
+- [2026-09-15-agent-messaging-on-a-local-network](../../research/notes/2026-09-15-agent-messaging-on-a-local-network.md) — ranks an embedded NATS server with JetStream as the adapter, with an MCP mailbox server as the runner-up.
+- [basics-built-in-adapters-bring-power](../../principles/basics-built-in-adapters-bring-power.md) — the stance; the adapter is opt-in and never a precondition.
+
+## Open Questions
+
+_None recorded yet._
+
+## Audit Notes
+
+_Empty. Populated by intent-auditor when intent moves to shipped/._

.abcd/development/principles/basics-built-in-adapters-bring-power.md

@@ -0,0 +1,45 @@
+# Basics built in, an external dependency brings full power
+
+**The rule.** Every abcd capability ships with a basic form that works with
+no daemon and no dependency beyond the abcd binary and the operating system,
+and offers an opt-in adapter to an external dependency for the full form. The
+basic is never a stub: it does the job at the scale a single person or a small
+team hits first, and it keeps working when the adapter is absent. The adapter
+never becomes a precondition: a repository or a machine that declines it
+loses reach or speed, not the capability.
+
+**Why.** abcd is for people who know what they want to build and need help
+shipping it; a capability that needs a broker, a service, or a network before
+it does anything is a capability most of them will never switch on, and a
+capability that only works through a vendor's cloud is one they cannot trust
+with their record. The basic form is also where the contract is discovered,
+which is the same reason the [script-first MVP](script-first-mvp.md) puts the
+first cut in a script: the on-disk shapes, the failure modes and the verbs
+worth having stabilise under real use before the adapter has to preserve
+them. And the adapter's cost is real: a running process, an authentication
+story, a second audit trail; it should be paid by the people who need what it
+buys, not by everyone.
+
+**Bounds.**
+
+- The basic form and the adapter share one record contract. What the basic
+  writes as a file, the adapter mirrors as a file; a capability is never
+  auditable in one form and opaque in the other.
+- The adapter is host-agnostic in the same way the basic is: it depends on
+  the external tool, never on a particular agent harness or a vendor's
+  cloud. A local-network dependency qualifies; a hosted relay does not.
+- "Basic" is measured at the user surface, not at the code: the test is
+  whether a person with the binary alone can do the thing, not whether the
+  code path is short.
+
+**Live instances.** The oracle backends (host-delegated by default; native,
+CLI, API and MCP as opt-in adapters). The secret scanners (the native
+detector is the default; gitleaks and trufflehog are opt-in dependencies the
+install offers). The session mailbox (a shared-directory mailbox is the
+basic; an embedded broker is the adapter).
+
+**Promotion.** This principle is the standing statement of the "host-delegated
+by default" boundary in the conventions, widened from LLM work to every
+external dependency. No enforcement hook exists; per the promotion path in
+this directory's [README](README.md), it becomes a discipline-kind intent
+the moment one does.

.abcd/development/research/notes/2026-08-15-decomposition-calibration.md

@@ -1684,6 +1684,12 @@ Per hand-run, append:
 - **Proposal:** whenever a user is interviewed, provide the appropriate
   context: before asking whether acceptance criteria stand, show them; for
   every interaction during the interview.
+### 2026-09-15 — messaging between sessions on one machine and one local network (hand-run at filing)
+
+- **Proposal:** the best way for a local setup that lets agents communicate
+  across user accounts and machines on the same network; whether Hermes or
+  OpenClaw answer it; whether abcd can carry it, given that abcd comes with
+  basic functionality and an external dependency brings full power.
 - **Table:**
 
   | Part | Type | Home |
@@ -1731,3 +1737,23 @@ Per hand-run, append:
   advisories triaged today ended in three different states (fixed and released;
   fix in progress; not a vulnerability, won't-fix), which is the case split the
   intent's criteria have to cover.
+  | A shared-directory mailbox between sessions, across accounts and mounts, delivered by the prompt hook | capability | intent `itd-2609151838312703` |
+  | An opt-in adapter to an embedded broker for push delivery and cross-machine reach | capability | intent `itd-2609151838327688`, sequenced after the mailbox |
+  | "abcd comes with basic functionality; an external dependency brings full power" | stance | principle `basics-built-in-adapters-bring-power` |
+  | The survey with its sources and rankings | reference | research note `2026-09-15-agent-messaging-on-a-local-network` |
+  | A message from another account is untrusted input: signed, size-capped, sanitised, injected only from a mailbox the recipient owns | trust rule | an ADR at the mailbox's planning; not filed yet |
+
+- **Links:** the adapter `builds_on` the mailbox; both refine the
+  host-delegated-by-default boundary in the conventions. No reversal.
+- **Verdict:** four options offered (SPLIT into two intents plus principle
+  and note; one intent covering both halves; HOLD with the note and the
+  principle only; decide later); the maintainer chose SPLIT. The table's
+  routing survived as offered.
+- **Notes:** two constraints arrived mid-run and reshaped the survey before
+  it returned: local machine and local network only, and the
+  basics-plus-adapter stance. The first removed the harness's own
+  cross-machine path (vendor-relayed) from consideration; the second turned
+  a ranking of transports into a pair of rungs. The named tools both turned
+  out to be agent runtimes with their own peer protocols, not message paths
+  for a foreign harness, which is the finding that made "build it into abcd"
+  the answer rather than "adopt one of them".