Agent Mailbox

/agent-mailbox

Coordinate two or more agents by exchanging append-only Markdown messages in a Handler-visible shared folder. The transport may be local filesystem, Git, a free registered Lyt (Link Your Think™) vault, or a sync-share such as OneDrive or SMB. The mailbox messages form an auditable causal graph rather than a chat transcript hidden in one runtime.

This is an agent operating protocol. It is not a broker, queue, daemon, authentication boundary, or a message-transport service. For registered cross-machine delivery, use a dedicated transport product and point this skill at the folder it exposes. Use this skill to teach agents how to handshake, divide work, deliver artifacts, listen, react once, recover, resume, and close over the mailbox the Handler supplies.

Structured execution spec: protocol.yon. Read it for the canonical rules and step sequence; this file is explanation. The two must stay in sync — if you edit one, update the other and refresh the @STAMP date.

First exchange: references/QUICKSTART.md. Templates: references/MESSAGE-TEMPLATE.md and references/PRIMER-TEMPLATE.md. Active collaboration resources: resources/INDEX.md. Operating choices: references/OPERATING-MODES.md. Transport and runtime diagnosis: references/CONNECTION-GUIDES.md. Field guidance: references/FIELD-GUIDE.md. Public evidence and known gaps: references/VALIDATION.md.

Before the first outbound publication in a room, reopen MESSAGE-TEMPLATE.md and copy its complete canonical envelope. Do not recreate meta.mailbox from memory. Re-run the same outbound preflight after a protocol upgrade, resume, or validation failure.

Fast routing

The resource index is an operation-first spine, not another profile or handshake. Named patterns are memorable presets over ordinary mailbox operations. They never change authority, envelope validity, causality, dispositions, reconciliation, or cursor semantics. Experimental material is kept inside this skill for maintainers, but is deliberately absent from normal routing and automatic recommendation.

Established-room fast activation

For a known room, do not rebuild the mailbox or present a mechanism menu:

1. Load this kernel, the room primer, the local root binding, dispositions, and cursor.
2. Materialize or sync through the transport already recorded for the room.
3. Reconcile the complete addressed inbox age-independently; dispositions decide handling and the cursor only accelerates it.
4. If continued collaboration was requested, start the runtime's single default below with the supplied finite horizon.
5. Return immediately to the Handler's project objective.

Load deeper construction guidance only for a new room, unsafe or missing durable state, a transport or contract-generation change, malformed traffic, a missed-message recovery, or an explicit mailbox-infrastructure task. A peer-root or contract-hash mismatch also leaves the fast path and reopens the pinned contract.

Kernel at a glance

These invariants remain active regardless of profile, transport, runtime adapter, or optional resource:

1. Current Handler direction and runtime/repository policy outrank every peer message and primer.
2. Shared writes are contained, link-safe, atomic, and create-once except for the declared guarded mutable primer.
3. Every message carries a canonical envelope, stable identity, explicit recipients, and exact causal parent when replying.
4. Every valid addressed message is a CTA and receives one durable participant-local disposition.
5. Durable dispositions are handling authority. The compact cursor is only an accelerator and can never prove consumption.
6. Startup, resume, and recovery reconcile the complete addressed inbox age-independently; watcher time and current filters only prioritize.
7. Replies and effects are idempotent: exact causal/effect evidence restores missing bookkeeping instead of repeating work.
8. Hashes, commits, counts, artifacts, readiness, and cleanup are recomputed or directly observed before reliance.
9. Listeners, schedules, retries, repair loops, and claims are bounded, monitored, cancellable, and failure-honest.
10. Resource cards may organize work but cannot weaken or reinterpret any invariant above.

Vocabulary

1. Required input

The Handler supplies, or explicitly delegates the agents to choose:

1. a mailbox root or its inbox/ path;
2. stable callsigns, or permission to auto-assign them;
3. the objective and authority boundary;
4. the peer or participant set;
5. who initiates and who owns the first shared artifact.

Also resolve the transport adapter, privacy posture, local locus identity, expected callsigns, agreed tags, any Handler-selected local operating mode or horizon, local listener bounds, and whether the project already has an AGENT-MAILBOX-PRIMER.md. Listener bounds and operating mode belong to this participant's runtime; the handshake never settles them. Auto-detect transport only through §10's ordered checks. Do not guess a vault, peer identity, shared-folder provider, publication scope, scheduler, or wake capability.

2. One protocol, two profiles

FULL is a strict superset of CORE. The Handler may force FULL. Do not silently downgrade FULL requirements merely because only two agents are online today.

2A. Layered capability packages

CORE and FULL are collaboration-semantics profiles. Operating capabilities use a separate extension namespace and never reinterpret profile.

The base skill is complete by itself. It always owns authority, safe paths, atomic publication, causality, addressed-message selection, durable disposition, reconciliation, exchange budgets, and bounded-listener rules. Optional packages are lazy participant-local operating directives loaded only after the base handshake:

If awaiting handshake traffic would otherwise block the local turn, a participant may arm its own bounded listener before establishment after proving the selected local adapter. This changes no handshake term and creates no peer obligation. Do not claim LISTENING until wake or re-entry works end to end; otherwise report PARKED.

After establishment or resume, use Standard Exchange unless continued collaboration was requested or is plainly necessary to complete an already-authorized exchange. When continuity is requested, use one runtime default rather than asking the Handler to choose a mechanism: Claude Code/Claude Agent SDK uses native Monitor when that host exposes it; Codex uses native bounded Scheduled Collab bound to the exact Handler-visible task in which collaboration was started; every other runtime uses Standard Exchange unless the Handler explicitly authorizes construction around a documented, proven native mechanism. A Codex participant surfaces that target task before registration and does not create, fork, or select a dedicated collaboration task unless the Handler explicitly asks for one. If exact same-task binding and re-entry cannot be proved, Scheduled Collab is unavailable and the participant uses Standard Exchange. An explicit Handler choice still wins. See OPERATING-MODES.md.

Activation and listener repair share one durable participant-local circuit breaker keyed by arena plus runtime. Allow one bounded activation attempt or one bounded repair attempt. On failure, record PARKED before proof or DEGRADED after a previously proven path fails, use the honest fallback, and resume the project objective. A fresh explicit Handler mailbox-infrastructure task may clear the breaker for one exact replacement run; bind that authority to the arena, runtime, adapter, purpose, and finite run identity, then consume it when that run terminates. Session restart does not reset it, and the task is never standing authority for later constructions.

Mailbox continuity is subordinate infrastructure, never the project deliverable unless the Handler explicitly makes it so. Do not let adapter diagnosis, canaries, or repair loops displace the authorized work.

Mailbox awareness and self-check boundaries

An active participant stays aware of the mailbox without turning every turn into a scan:

1. Work boundary: after each meaningful mailbox-derived work unit and before reporting it complete, materialize or sync through the recorded transport and reconcile the complete addressed inbox plus every non-terminal CTA. Skip only when the same check already ran after the last effect and durable state has not changed.
2. Handler return: at the start of a new Handler turn, run that reconciliation only when local durable state shows an actionable non-deferred pending or active CTA, a blocked CTA whose named gate the current Handler input may answer, a due deferral, wake-pending, listener-recorded candidates, or a continuity-health contradiction. The possibility of unknown new mail is not itself knowable local evidence. An unrelated Handler message with none of those conditions creates no mailbox sync tax.
3. Continuity health: while Collab Window or Scheduled Collab is active, check its participant-local health on every Handler/model re-entry before deciding whether mailbox sync is needed. Collab Window compares the independent Monitor heartbeat with its expected bound. Scheduled Collab records an exact local turn nonce, origin, start, and normal end. A due firing inside the exact currently proven-live Handler-origin turn is suppressed, restarts its clock from normal turn end, and is not a failure; a scheduled-origin turn observes its own firing and never suppresses it. At the next re-entry, a prior unmatched start whose nonce is not the current live turn transitions to DEGRADED with one complete gap reconciliation; it is not an indefinitely busy turn. A due firing that spans a proven idle window without arrival is missed and transitions to DEGRADED. Continuous suppression by the exact current live turn is ACTIVE (health unevaluated since <time>), never green or degraded. Native control-plane status may strengthen either result but is not the portable correctness mechanism. A continuity-health contradiction is local evidence for one complete gap reconciliation; a dead consumer cannot diagnose itself, so this check runs through the surviving participant path.

Standard Exchange makes no autonomous wake or health promise. It still preserves outstanding CTA state and performs the Handler-return and work-boundary checks above. A time-based deferral that elapses while no model is running returns to the active queue on the next surviving Handler or resume turn; the idle interval is not itself a protocol failure.

For a newly constructed bounded listener with no stronger adapter-specific values, use a 30-second observation interval, 30-minute maximum, and three consecutive failures as advisory local starting values. They are not handshake terms or availability promises.

The advisory local post-handshake or post-resume settling horizon is ten minutes. Each participant may independently choose another bounded horizon and cadence. Longer operation uses renewable bounded leases with one absolute Handler-approved deadline. This value is neither a protocol constant nor an availability promise. Literal unbounded or “non-stop” execution is unsupported.

The base handshake establishes first. Then each participant independently selects, proves, starts, rearms, expires, stops, and cleans up its own operating package. Never propose, accept, counter, reject, renew, or block on another participant's operating mode, cadence, horizon, listener, or scheduler. If one participant asks another to deliver, review, check, or reply by a deadline, that is an ordinary scoped request, propose, or FULL claim under the base authority rules—not mode activation.

At most one primary local operating package is active per participant: Collab Window or Scheduled Collab. Different participants may use different modes and cadences simultaneously. Missed-message recovery is the only version-1 overlay. A local package is not active until its exact YON file has been read and its prerequisites evidenced.

An agent may optionally publish a sender-local availability FYI using canonical kind: state, explicit meta.mailbox.availability metadata, and expects_reply: false. It is orientation only: no SLA, acceptance, counter, renewal, or waiting may follow. Emit only on a material reported-state transition; it counts normally toward the exchange budget. The recipient records no-reply-required, may update the sender's coarse primer summary, and does not change establishment, obligations, or its own mode.

3. Layout and discovery

Default layout:

<mailbox-root>/
  AGENT-MAILBOX-PRIMER.md
  inbox/
  workspace/
    <CALLSIGN>/
      artifacts/             # create-once participant-owned deliverables
      scratch/               # disposable participant-owned working files
  artifacts/                 # deprecated read-only compatibility source

<host-local-agent-state>/    # outside mailbox/provider root by default
  dispositions/              # participant-local append-only transitions
  cursor/                    # compact checkpoint/index
  results/                   # optional listener or scheduler results

Given a path, check only these candidates:

1. the supplied path itself when its final component is inbox;
2. <supplied-path>/inbox;
3. <supplied-path>/.agent-mailbox/inbox.

Never recursively crawl an arbitrary tree to find a mailbox. Before writing, verify the mailbox root, inbox, target parent chain, and target leaf are not symbolic links, junctions, mount points, name-surrogate reparse points, or unknown reparse points. A Handler-selected sync-share may contain verified Microsoft Cloud Files placeholders: allow only the IO_REPARSE_TAG_CLOUD family (tag & 0xFFFF0FFF == 0x9000001A) after confirming every reparse component is in that family, the canonical resolved path remains the expected path, and the target stays contained. Cloud placeholders are provider state, not path redirection. This allowance never applies to symbolic links, junctions, mount points, unknown tags, traversal, or an overwrite of an append-only message or immutable artifact. Reject absolute or ..-escaping protocol-relative artifact paths unless the Handler supplied that exact path.

Message envelopes and immutable artifacts are create-once: their final target must not exist. The declared primer is different: it is a mutable single-writer checkpoint. The declared protocol pen is the exclusivity boundary; the provider need only preserve the atomic replace without corruption and surface conflict copies. Before replacement, its declared writer acquires a participant-local exclusive mutation lease bound to arena, root, writer, run nonce, and creation identity; without proven pen ownership and that lease, the primer stays stale debt. While holding it, the writer re-reads the exact existing regular file or verified Cloud Files placeholder, records a preimage hash, stages complete replacement bytes in a transport-excluded directory on the same filesystem, flushes and closes, rechecks that the live preimage hash is unchanged, and atomically replaces the target. Re-open and hash the published bytes, revalidate containment and path type, check for provider conflict copies, then conditionally release only the still-owned lease. A changed preimage, changed lease identity, unexpected target type, conflict copy, post-write mismatch, or corrupted/non-atomic provider replacement fails closed and preserves visible debt. This is a single-writer guarded replace, not a claim of lock-free cross-writer compare-and-swap. Current hydration or placeholder state is transient and is not itself an overwrite decision.

The visible primer lives at the mailbox root. Dotfolders are for optional local mechanics, never the sole Handler-facing checkpoint.

Keep resolved absolute mailbox and external artifact roots in participant-local runtime state. The shared primer uses a Handler-pinned opaque mailbox alias, root-relative paths, opaque external artifact aliases, and opaque locus identifiers; it never copies a participant's resolved host paths into the transport.

Each participant owns only workspace/<CALLSIGN>/. Every ordinary workspace write is positively anchored to the participant's own validated, settled workspace/<CALLSIGN>/artifacts/ or workspace/<CALLSIGN>/scratch/ tree. It may read another participant's workspace but must never write, repair, rename, or delete there. Validate the callsign before constructing that path, wait until its claim has settled, then create the participant's own artifacts/ and scratch/ directories. A provisional or losing claimant never writes the contested workspace. If a delayed earlier claim displaces a holder after that holder created a tree, record needs-audit: callsign-collision, preserve creator attribution, and block all ordinary use of that workspace—including by the winning claimant—until exact-path Handler remediation closes the debt; the winner never inherits the residue. If the exact workspace path is unsafe, refuse that write and block shared workspace use for the affected callsign or path while preserving separately safe inbox messaging. Shared artifacts/ from an older arena is a deprecated read-only compatibility source for new work: migrate only product whose local ownership is proved by causal messages, primer provenance, or current Handler direction; ambiguous legacy content stays read-only. Publish the new workspace-relative path and hash, preserve historical messages and references, and never maintain two active artifact homes.

Workspace presence is not delivery and creates no obligation. Deliver work through a causal inbox message that names a workspace-relative artifact path and its hash. Artifact final targets are create-once. Scratch may be mutated or removed only by its participant owner, is never cited, and must return to its empty baseline before goodbye; failure blocks departure and requires Handler-directed remediation before final retirement. Apply the room's sensitivity and no-secrets rules to the entire shared workspace: never place credentials, private task material, raw listener logs, or participant-local runtime evidence there.

A transferred artifact pen never authorizes writing a predecessor's workspace. If a predecessor artifact exists, the successor creates a new immutable continuation under its own workspace, publishes a causal deliver mapping old path/hash to new path/hash, and records replied for the transfer CTA. If no predecessor artifact exists, the successor sends a causal ack naming the pen and explicitly recording that no predecessor artifact exists, then records replied. Missing, ambiguous, or scratch-only predecessor evidence becomes needs-audit plus a Handler gate; scratch is never cited or promoted into an artifact mapping.

Ordinary owner scratch mutation needs no Handler exception; every existing artifact path or non-owner mutation does. A current Handler may authorize a named custodian to inspect, logically quarantine, move-quarantine, redact, or delete exact existing workspace-relative paths in a callsign-collision, orphan/retirement, blocked-departure scratch, or privacy incident. The authorization names source paths, target types, live file hashes or canonical tree-manifest hashes, permitted actions, reason, expiry or one-shot completion, a non-secret audit destination, and an exact contained absent destination for any move-quarantine. Immediately before acting, the custodian requires the live type and fingerprint to match, revalidates source and destination containment and reparse safety, and for recursive directory action inventories every descendant reparse point, refusing redirecting or unknown links while allowing only verified contained Microsoft Cloud Files placeholders. Quarantine is either logical disablement without a byte move or one atomic move to the authorized absent destination. The custodian records what changed without copying sensitive bytes and gains no general ownership or future exception. If a delivered artifact changes or disappears, publish a causal remediation notice with its old path/fingerprint and outcome, update the primer projection, and invalidate any active review boundary before closing the debt. Listener engines, configuration, leases, cursors, logs, dispositions, and other runtime state remain participant-local outside the shared workspace.

Persist dispositions in durable participant-local state outside the mailbox and provider-sync root by default. An in-root runtime/ location is permitted only when the adapter proves that exact directory is excluded from every active transport channel; Git ignore alone is not proof of OneDrive or another provider exclusion. Key append-only transitions by inbound UUID and retain the causal/effect evidence needed for idempotent recovery. The last valid transition is the one current effective disposition.

Transitional states are blocked: handler-decision, deferred, and needs-audit. Terminal states are acted, replied, no-reply-required, rejected-scope, and superseded-by-correction; use rejected-scope only after the Handler refuses or definitively withholds the requested expansion, and superseded-by-correction only after a separately published valid correction closes a malformed original without treating it as authorized work. historical-debt is quarantined: it prevents automatic execution and may enter the compact cursor, but stays in the unresolved-debt index and blocks full readiness until a later audited transition settles it. Advance the compact cursor only for a terminal or quarantined effective state. An anomaly without a trustworthy UUID is tracked by file fingerprint in a separate local anomaly index and never enters the UUID cursor.

Disposition state and CTA state are separate axes. For every addressed message, track CTA state as none, pending, active, blocked, completed, or superseded and cite the evidence that supports it. A terminal disposition paired with pending, active, or blocked CTA state is a lifecycle contradiction and can never report clean. deferred requires an owner plus an exact resume_after time; it remains outstanding, never satisfies a clean-exit predicate, and returns to the active queue on the first surviving reconciliation at or after that time. needs-audit blocks work that depends on the disputed envelope or evidence. Work may continue only when an exact independently valid Handler or canonical-source record identifies the action, target, scope, and authority without relying on any disputed field; record work_continues with that evidence and CTA state. Otherwise record work_blocked_reason and require the Handler rather than deciding that the work is separable.

A reconciliation is work-clean only when there is no undispositioned message, no deferred disposition, no CTA in pending, active, or blocked, no expired blocker or lease requiring escalation, and no audit state with live work. It is readiness-clean only when work-clean and no needs-audit or unresolved historical-debt remains. Dormant audit debt may coexist with completed product work, but it reports WORK_CLEAN_WITH_AUDIT_DEBT with counts—never bare clean or no-message, and never permits LISTENING or re-arm. expects_reply: true remains open until an exact causal reply is durable or a terminal replacement or supersession is supported by an exact independently valid record identifying what supersedes what, or by current Handler direction; an agent may not close its own obligation by declaration. A transitional disposition never proves completion. Structured outcomes include pending_cta_count, active_cta_count, blocked_cta_count, deferred_cta_count, due_deferred_count, needs_audit_count, historical_debt_count, and audit_state_with_live_work_count, not only message and disposition counts. Valid outstanding work reports FOUND; dormant audit debt reports WORK_CLEAN_WITH_AUDIT_DEBT; the base exchange then resumes, preserves, or escalates the relevant lifecycle state.

needs-audit is transitional and readiness-blocking, not quarantined or terminal. It exits only through a later append-only transition backed by the missing exact evidence, a bounded correction, or a current Handler decision; it never advances the UUID cursor by itself. historical-debt is the separate quarantined state.

historical-debt exits only after the same-locus participant inspects the original envelope, exact local disposition or effect evidence, and causal graph. Cross-locus handling still requires the explicit Handler-authorized private state transfer defined below. Exact evidence may support a terminal transition; unresolved prior-effect ambiguity becomes needs-audit; genuinely unhandled current work returns to the normal authority gate. Update the unresolved-debt index and cursor bookkeeping without repeating an effect.

If handling creates shared primer debt while the participant is not the primer writer, the participant does not seize the pen or leave the original UUID permanently unconsumable. It persists the accurate terminal disposition for its own completed handling plus a separate durable primer-debt record, sends at most one bounded CTA to the declared writer with the exact required projection, and lets stale-primer rules keep live causal evidence authoritative. The writer's later update closes the debt. A failed local primer mutation still blocks consumption when the participant actually holds that pen.

expects_reply: false and no-reply-required govern wire output, not participant-local operating mode. They never stop, park, expire, degrade, renew, or otherwise change Work-or-Listen or Scheduled Collab. If a listener lease was proven and remains within budget, handle the message, persist the accurate terminal disposition (acted when an authorized effect completed, otherwise no-reply-required), make required primer state durable, advance the cursor last, and perform the normal immediate reconciliation. Re-arm only when that result is readiness-clean; when only dormant audit debt remains, preserve WORK_CLEAN_WITH_AUDIT_DEBT and do not re-arm. Do not emit a courtesy ACK merely to announce continued listening; send wire state only for a separate material transition, failure, conflict, or Handler gate.

A same-locus successor may reuse the host-local ledger only after declared succession and an exact owner/arena/root match. A cross-locus successor needs an explicit Handler-authorized private state transfer; without it, shared causal evidence is reconciled but missing local dispositions become DEGRADED: disposition-unavailable plus historical-debt or needs-audit, and LISTENING is forbidden. The shared primer carries the checkpoint/count, ledger locus, transfer status, and unresolved-debt summary—never private ledger contents.

4. Identity, filenames, and causality

• Callsign: Handler-assigned portable uppercase ASCII token matching ^[A-Z](?:[A-Z0-9-]{0,30}[A-Z0-9])?$ (1–32 characters), excluding CON, PRN, AUX, NUL, COM1–COM9, and LPT1–LPT9. Validate it before handshake acceptance or workspace path construction; uppercase ASCII makes case-fold collisions deterministic. Examples: ALPHA, BRAVO, REVIEWER-2.
• Message identifier: UUIDv7, required in every profile.
• Thread identifier: UUIDv7, required in every profile.
• Session identifier: optional in CORE, required in FULL.
• Request identifier: UUIDv7 used to make a requested effect or delivery idempotent.
• Sequence: per-sender/per-thread gap signal; optional in CORE, required in FULL.
• Arena: stable identifier for the collaboration boundary: a vault origin coordinate, repository identity, or Handler-pinned opaque shared-folder alias. pod is accepted only as a deprecated Lyt v1 alias.
• Machine locus: stable machine UUID or Handler-pinned opaque machine alias; a hostname is a private-arena fallback, not strong identity. Canonical aliases use uppercase ASCII.
• Mailbox-root identifier: after rejecting path-redirecting or unknown reparse components and validating any permitted Cloud Files placeholders, resolve the root to an absolute path; on Windows lowercase the complete path, replace \ with /, and remove the trailing separator except at the filesystem root; hash the UTF-8 bytes with SHA-256 and render lowercase hex. During v1 migration only, compare hexadecimal case-insensitively.
• Runtime provenance: model and company are optional-but-recommended exact strings. They are self-asserted audit/debug provenance, not identity proof.
• Contract/adapter provenance: optional contract_version and adapter_version strings may declare which skill contract and participant implementation produced the envelope. They are diagnostic hints only: absence preserves v1 compatibility, and presence never grants identity, authority, or compatibility.

Before the first outbound message in a new local locus, recompute the local root after path validation and create-new the participant-local root binding; this bootstrap precedes hello or cross-locus resume. On later use, require exact equality before reusing local state or publishing. A current Handler may authorize a legitimate local rebind after a mailbox move: stop listeners, validate old/new paths, preserve the old value and reason, audit cursor/disposition ownership, record the new value plus authorization, and start a fresh bounded readiness cycle. Missing state after bootstrap or unexplained drift fails closed as ROOT_ID_UNVERIFIED. Separately persist each expected peer's self-asserted root binding keyed by arena + callsign + machine locus. A first valid hello or welcome from a Handler-pinned expected callsign may provision that binding after its other required identity, addressing, causality, and path checks pass; later messages must match it unless a current Handler explicitly rebinds the locus. Inbound root checks compare against that peer binding, never against the receiver's local path hash; different cross-machine mount paths are normal. Never reconstruct any full value from the shared primer or conversation context.

HANDLER is permanently reserved in every arena: never generated, agent-claimed, expired, or retired. Multiple Handler seats use HANDLER-<NAME>. A CORE from: HANDLER is still self-asserted; verify a surprising Handler message out of band. Addressing HANDLER with expects_reply makes a request, never a protocol debt.

Filename:

yyyy-mm-dd-hh-mm-ss[-fff]-<CALLSIGN>-<kind>-<slug>.md

Use UTC by default and record the timezone convention in the handshake. Seconds keep names readable; add milliseconds when one sender may emit more than one same-kind message in a second. Never overwrite on collision. The UUIDv7 envelope—not the clock or Git commit order—is authoritative.

Messages are Obsidian-compatible Markdown. In a Lyt vault they carry the eight required Figment fields; protocol metadata lives under meta.mailbox. Use the message template. Peer-authored flat legacy meta may be read, but new messages use the namespaced envelope.

Every CORE message carries arena, machine, mailbox-root locus, and transport. Locus is a self-asserted routing hint, never authentication or a reason to suppress a correctness channel. In a shared or public arena, use Handler-pinned opaque aliases rather than disclosing hostnames or private origin coordinates. Unexpected callsigns are surfaced to the Handler and are not engaged. Missing or unverified locus fields force conservative detection. A sender root that differs from the durable expected binding for that exact arena + callsign + machine locus is quarantined as needs-audit: root-mismatch, remains unconsumed, and cannot authorize work. Do not compare it to the receiver's own local root. For an expected callsign, emit at most one bounded repair notice carrying the observed and expected fingerprints; do not include either full canonical value. A current Handler may authorize an override only through a durable record naming the sender/locus, exact inbound UUID or explicitly finite UUID set, observed fingerprint, authorization evidence, and expiry or one-shot completion condition. It preserves the mismatch audit record and never disables validation globally.

If the Handler supplies no callsign, generate an arena-scoped name: 3–6 letters, phonetic, single word, uppercase, domain-inspired, and without numbers. Use any suitable domain; these are seed inspiration, not an enumerated allocation list:

Before generating or claiming, build the name view from the primer when present and the reconciled inbox event history: hello/welcome claims, goodbye departures/retirements, and resume reclaims/successions. The inbox history is authoritative; the primer is its materialized view and its writer corrects drift. Generate around every unavailable name.

An auto-name collision regenerates silently. When a Handler-supplied name is occupied, offer a free phonetic or thematic neighbor and surface the collision. Use a numeric suffix only if the Handler explicitly insists on the occupied base name. A callsign never silently changes mid-thread.

The name claim is the append-only hello, not a mutable ledger write. Simultaneous claims produce separate files; the lexicographically smaller root message UUID keeps the name, and the loser regenerates and re-hellos while citing the winner. On an eventually consistent transport, a name remains provisional for one complete sync round or the Handler-set settle interval. A late earlier UUID makes the later claimant yield deterministically. Profile handshake rules still govern shared work: provisional naming never bypasses FULL establishment.

The primer roster is also the callsign ledger. Each row records participant status, last-seen, name-state, and append-only holder lineage. Any valid message renews last-seen; no presence ping exists. The primer declares an arena TTL, default 30 days unless the Handler tunes it:

• active: held and unavailable;
• expired: TTL elapsed without final goodbye; unavailable to strangers, reclaimable by the prior holder through declared resume with matching locus or Handler authorization;
• retired: final goodbye; permanently tombstoned in this arena.

A callsign is a Handler-owned role, not a process property. A new session, model, or vendor may assume it only through declared succession: current Handler authorization plus a first resume naming the seat, new session/provenance, and prior holder's last accepted message. The ledger appends the new holder to lineage; it never overwrites history. The successor explicitly accepts or releases inherited pens, claims, and reply debts. Silent unauthorized assumption is impersonation and must be surfaced; declared Handler-authorized succession is legitimate continuity.

If no primer exists, the initiator atomically sends hello first, then creates the primer as the first single-writer act. With simultaneous founders, the smaller canonical root UUID is the initiator and first primer writer. A losing author never overwrites the winner: it marks or archives only its own bootstrap copy as superseded-by and registers through the surviving primer. A sync-share conflict copy follows the same canonical rule and is never silently deleted by a non-author.

The handshake settles one project tag, the standing agent-mailbox tag, and optional topic tags. Every later message and shared artifact carries that set in frontmatter. Machine causality uses UUIDs. Every causal response body wikilinks its exact parent and referenced artifacts; a permitted root has no causal-parent link. The primer wikilinks live thread heads.

Higher protocol versions remain readable at the CORE v1 floor. An inbound absent or lower version may also be interpreted at the v1 floor only when every required v1 identity, addressing, causality, authority, and path

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