diff --git a/bot_bottle/backend/docker/orchestrator.py b/bot_bottle/backend/docker/orchestrator.py
index 550d99ea..6c8c45ad 100644
--- a/bot_bottle/backend/docker/orchestrator.py
+++ b/bot_bottle/backend/docker/orchestrator.py
@@ -19,7 +19,6 @@ from .util import run_docker
 from ...paths import (
     ORCHESTRATOR_TOKEN_ENV,
     bot_bottle_root,
-    host_orchestrator_token,
 )
 from ...gateway import GatewayError
 from ...orchestrator.lifecycle import (
@@ -171,7 +170,9 @@ class DockerOrchestrator(Orchestrator):
         fixed-name container first)."""
         self._ensure_control_network()
         run_docker(["docker", "rm", "--force", self.name])
-        _signing_key = host_orchestrator_token()
+        # The signing key comes through the shared provisioning contract (#476),
+        # which fail-closes rather than yield an empty key that would run OPEN.
+        _signing_key = self.control_plane_key()
         proc = run_docker([
             "docker", "run", "--detach",
             "--name", self.name,
diff --git a/bot_bottle/backend/firecracker/orchestrator.py b/bot_bottle/backend/firecracker/orchestrator.py
index 4b79808f..f2d17157 100644
--- a/bot_bottle/backend/firecracker/orchestrator.py
+++ b/bot_bottle/backend/firecracker/orchestrator.py
@@ -21,7 +21,6 @@ import time
 from pathlib import Path
 
 from ...log import die, info
-from ...paths import host_orchestrator_token
 from ...orchestrator.lifecycle import (
     DEFAULT_STARTUP_TIMEOUT_SECONDS,
     Orchestrator,
@@ -108,11 +107,13 @@ class FirecrackerOrchestrator(Orchestrator):
             data_drive=self._ensure_registry_volume(),
         )
         # Push the host-canonical signing key (the init waits for it before
-        # starting the control plane). The host token file stays the single
-        # source of truth, so a co-running docker/macOS control plane keeps
-        # working; the guest verifies tokens with the same key the CLI signs from.
+        # starting the control plane). It comes through the shared provisioning
+        # contract (#476) — the same host token file every backend uses, so a
+        # co-running docker/macOS control plane keeps working and the guest
+        # verifies tokens with the same key the CLI signs from; fail-closed, so
+        # the guest is never handed an empty key that would run it OPEN.
         infra_vm.push_secret(
-            vm, host_orchestrator_token(), infra_vm._GUEST_SIGNING_KEY_PATH,
+            vm, self.control_plane_key(), infra_vm._GUEST_SIGNING_KEY_PATH,
             "the control-plane signing key to the orchestrator VM "
             "(its control plane will not start)",
         )
diff --git a/bot_bottle/backend/macos_container/orchestrator.py b/bot_bottle/backend/macos_container/orchestrator.py
index 32802760..3831e5ba 100644
--- a/bot_bottle/backend/macos_container/orchestrator.py
+++ b/bot_bottle/backend/macos_container/orchestrator.py
@@ -18,10 +18,7 @@ import urllib.request
 from pathlib import Path
 
 from ... import log
-from ...paths import (
-    ORCHESTRATOR_TOKEN_ENV,
-    host_orchestrator_token,
-)
+from ...paths import ORCHESTRATOR_TOKEN_ENV
 from ...orchestrator.lifecycle import (
     DEFAULT_HEALTH_TIMEOUT_SECONDS,
     DEFAULT_PORT,
@@ -134,7 +131,9 @@ class MacosOrchestrator(Orchestrator):
 
     def _run_container(self, current_hash: str) -> None:
         container_mod.force_remove_container(self.name)
-        _signing_key = host_orchestrator_token()
+        # The signing key comes through the shared provisioning contract (#476),
+        # which fail-closes rather than yield an empty key that would run OPEN.
+        _signing_key = self.control_plane_key()
         argv = [
             "container", "run", "--detach",
             "--name", self.name,
diff --git a/bot_bottle/orchestrator/client.py b/bot_bottle/orchestrator/client.py
index 96ef47bd..9d51a5a5 100644
--- a/bot_bottle/orchestrator/client.py
+++ b/bot_bottle/orchestrator/client.py
@@ -18,8 +18,8 @@ import urllib.request
 from collections.abc import Iterable
 from dataclasses import dataclass
 
-from ..orchestrator_auth import ROLE_CLI, mint
-from ..paths import host_orchestrator_token
+from ..orchestrator_auth import ROLE_CLI
+from ..trust_domain import CONTROL_PLANE
 from .server import ORCHESTRATOR_AUTH_HEADER
 
 DEFAULT_TIMEOUT_SECONDS = 5.0
@@ -32,7 +32,7 @@ def _host_auth_token() -> str:
     "" means 'send no auth header' — correct against an open (unconfigured)
     control plane, and harmlessly rejected by a secured one."""
     try:
-        return mint(ROLE_CLI, host_orchestrator_token())
+        return CONTROL_PLANE.mint(ROLE_CLI)
     except (OSError, ValueError):
         return ""
 
diff --git a/bot_bottle/orchestrator/lifecycle.py b/bot_bottle/orchestrator/lifecycle.py
index 22b67988..705a540d 100644
--- a/bot_bottle/orchestrator/lifecycle.py
+++ b/bot_bottle/orchestrator/lifecycle.py
@@ -21,8 +21,7 @@ import urllib.error
 import urllib.request
 from pathlib import Path
 
-from ..orchestrator_auth import ROLE_GATEWAY, mint
-from ..paths import host_orchestrator_token
+from ..trust_domain import ControlPlaneProvisioning
 
 DEFAULT_PORT = 8099
 DEFAULT_STARTUP_TIMEOUT_SECONDS = 45.0
@@ -58,6 +57,13 @@ class Orchestrator(abc.ABC):
     so it — not the gateway — mints the gateway's role-scoped token.
     Backend-neutral."""
 
+    # The shared control-plane auth provisioning contract (#476). Every backend
+    # gets its signing key + gateway token through this one seam rather than
+    # re-deriving the wiring; the default topology is co-located + fail-closed,
+    # so a backend need not redeclare it (a truly isolated control plane would
+    # override this with a different `Topology`).
+    provisioning: ControlPlaneProvisioning = ControlPlaneProvisioning()
+
     def ensure_built(self) -> None:
         """Ensure the orchestrator's image / rootfs exists, building it if
         needed. Default: nothing to build (e.g. a pre-pulled image). Call before
@@ -105,9 +111,17 @@ class Orchestrator(abc.ABC):
     def mint_gateway_token(self) -> str:
         """Mint a role-scoped `gateway` JWT from the host signing key for the
         gateway to present. The orchestrator holds the key; the gateway never
-        does (#469). Backend-neutral — the same host token file is the single
-        source of truth across backends."""
-        return mint(ROLE_GATEWAY, host_orchestrator_token())
+        does (#469). Routed through the shared provisioning contract (#476), so
+        the same host token file is the single source of truth across backends."""
+        return self.provisioning.gateway_token()
+
+    def control_plane_key(self) -> str:
+        """The raw signing key the control-plane *process* must receive — the ONE
+        place a backend obtains it (docker/macOS inject it as `key_env`;
+        firecracker pushes it to the guest). Fail-closed via the provisioning
+        contract: it raises rather than yield an empty key that would run the
+        server OPEN (#476)."""
+        return self.provisioning.orchestrator_key()
 
 
 __all__ = [
@@ -117,4 +131,5 @@ __all__ = [
     "OrchestratorStartError",
     "source_hash",
     "Orchestrator",
+    "ControlPlaneProvisioning",
 ]
diff --git a/bot_bottle/orchestrator/server.py b/bot_bottle/orchestrator/server.py
index dbaecd61..a18dac3f 100644
--- a/bot_bottle/orchestrator/server.py
+++ b/bot_bottle/orchestrator/server.py
@@ -63,8 +63,8 @@ import sys
 import typing
 from urllib.parse import urlsplit
 
-from ..orchestrator_auth import ROLE_CLI, ROLES, verify
-from ..paths import ORCHESTRATOR_TOKEN_ENV
+from ..orchestrator_auth import ROLE_CLI, ROLES
+from ..trust_domain import CONTROL_PLANE
 from ..supervisor.types import TOOLS
 from .service import OrchestratorCore
 
@@ -413,11 +413,13 @@ class OrchestratorServer(socketserver.ThreadingMixIn, http.server.HTTPServer):
 
     def __init__(self, address: tuple[str, int], orchestrator: OrchestratorCore) -> None:
         self.orchestrator = orchestrator
-        self._signing_key = os.environ.get(ORCHESTRATOR_TOKEN_ENV, "").strip()
+        # The control-plane trust domain's signing key, as injected into THIS
+        # (the owning) process by the launcher (#476). Unset → open mode below.
+        self._signing_key = CONTROL_PLANE.key_from_env()
         if not self._signing_key:
             sys.stderr.write(
                 "orchestrator: WARNING — no control-plane signing key "
-                f"(${ORCHESTRATOR_TOKEN_ENV}); running WITHOUT caller "
+                f"(${CONTROL_PLANE.key_env}); running WITHOUT caller "
                 "authentication. Any client that can reach this port can drive "
                 "it. Backends that put the control plane on an agent-reachable "
                 "network MUST set this.\n"
@@ -433,7 +435,7 @@ class OrchestratorServer(socketserver.ThreadingMixIn, http.server.HTTPServer):
         role (→ per-route 401/403 in `dispatch`)."""
         if not self._signing_key:
             return ROLE_CLI
-        return verify(presented, self._signing_key)
+        return CONTROL_PLANE.verify(presented, self._signing_key)
 
 
 def make_server(
diff --git a/bot_bottle/orchestrator_auth.py b/bot_bottle/orchestrator_auth.py
index 54f47620..5b07e40e 100644
--- a/bot_bottle/orchestrator_auth.py
+++ b/bot_bottle/orchestrator_auth.py
@@ -59,12 +59,19 @@ _HEADER_SEGMENT = _b64url_encode(
 )
 
 
-def mint(role: str, secret: str) -> str:
+def mint(role: str, secret: str, *, roles: frozenset[str] = ROLES) -> str:
     """A compact HS256 token asserting `role`, signed with `secret`.
 
-    Raises ValueError for an unknown role (mint only what the control plane will
+    `roles` is the role set the caller's *trust domain* recognises (default: the
+    orchestrator control plane's `{gateway, cli}`). A domain names its own set so
+    each credential boundary mints only its own roles — a separate boundary
+    (e.g. a host controller) instantiates a distinct domain with a distinct key
+    and role set rather than adding a role here, so its key cannot forge the
+    other domain's tokens (see `trust_domain.py`, issues #476/#468).
+
+    Raises ValueError for a role outside `roles` (mint only what that domain will
     accept) or an empty signing key (an unsigned credential is never valid)."""
-    if role not in ROLES:
+    if role not in roles:
         raise ValueError(f"unknown control-plane role {role!r}")
     if not secret:
         raise ValueError("cannot mint a control-plane token without a signing key")
@@ -73,10 +80,11 @@ def mint(role: str, secret: str) -> str:
     return f"{signing_input}.{_sign(secret, signing_input)}"
 
 
-def verify(token: str, secret: str) -> str | None:
+def verify(token: str, secret: str, *, roles: frozenset[str] = ROLES) -> str | None:
     """The role a valid `token` carries, or None if it is malformed, wrongly
-    signed, or names an unknown role. Constant-time signature check; rejects any
-    header whose alg isn't HS256 (no alg-confusion / `none`)."""
+    signed, or names a role outside `roles` (the verifying trust domain's set —
+    default `{gateway, cli}`). Constant-time signature check; rejects any header
+    whose alg isn't HS256 (no alg-confusion / `none`)."""
     if not token or not secret:
         return None
     parts = token.split(".")
@@ -94,7 +102,7 @@ def verify(token: str, secret: str) -> str | None:
     if not isinstance(header, dict) or header.get("alg") != _ALG:
         return None
     role = payload.get("role") if isinstance(payload, dict) else None
-    return role if isinstance(role, str) and role in ROLES else None
+    return role if isinstance(role, str) and role in roles else None
 
 
 __all__ = ["ROLE_GATEWAY", "ROLE_CLI", "ROLES", "mint", "verify"]
diff --git a/bot_bottle/paths.py b/bot_bottle/paths.py
index 7b991cbf..7f7841e4 100644
--- a/bot_bottle/paths.py
+++ b/bot_bottle/paths.py
@@ -97,16 +97,19 @@ def host_gateway_ca_dir() -> Path:
     return ca_dir
 
 
-def host_orchestrator_token() -> str:
-    """The per-host control-plane secret, minted (256-bit, url-safe) and
-    persisted 0600 on first use, then reused.
+def host_signing_key(filename: str) -> str:
+    """A per-host signing key at `<root>/<filename>`, minted (256-bit, url-safe)
+    and persisted 0600 on first use, then reused.
 
-    This is the shared secret the launchers inject into the control-plane and
-    gateway containers and that the host CLI presents on every call. It is a
-    *host* artifact — the file lives under the root the agent never mounts, and
-    the env var is set only on the trusted containers — so reading it here is
-    safe on the host launch path but the value never reaches a bottle."""
-    path = bot_bottle_root() / ORCHESTRATOR_TOKEN_FILENAME
+    The generic form of `host_orchestrator_token()`: a *trust domain*
+    (`trust_domain.py`) names its own key file so each credential boundary gets a
+    distinct host-canonical key — the orchestrator control plane names one file,
+    a separate boundary (e.g. a host controller) names another, and neither can
+    read the other's key (issues #476/#468). It is a *host* artifact: the file
+    lives under the root the agent never mounts, and its value is injected only
+    into the trusted control-plane process, so reading it here is safe on the
+    host launch path but the value never reaches a bottle."""
+    path = bot_bottle_root() / filename
     try:
         existing = path.read_text().strip()
         if existing:
@@ -128,6 +131,14 @@ def host_orchestrator_token() -> str:
     return token
 
 
+def host_orchestrator_token() -> str:
+    """The per-host control-plane signing key — the host-canonical key the
+    launchers inject into the control-plane process and the host CLI mints its
+    own `cli` token from. The `control-plane` trust domain's specialization of
+    `host_signing_key()`."""
+    return host_signing_key(ORCHESTRATOR_TOKEN_FILENAME)
+
+
 __all__ = [
     "HOST_DB_FILENAME",
     "ORCHESTRATOR_TOKEN_FILENAME",
@@ -138,5 +149,6 @@ __all__ = [
     "host_db_path",
     "host_db_dir",
     "host_gateway_ca_dir",
+    "host_signing_key",
     "host_orchestrator_token",
 ]
diff --git a/bot_bottle/trust_domain.py b/bot_bottle/trust_domain.py
new file mode 100644
index 00000000..66d64c2e
--- /dev/null
+++ b/bot_bottle/trust_domain.py
@@ -0,0 +1,189 @@
+"""Trust domains: the unit of control-plane auth provisioning (issue #476).
+
+A *trust domain* is one **credential boundary** — a single host-canonical
+signing key plus the role set that key is allowed to sign, plus the env vars the
+key and a pre-minted token are carried in. Provisioning is parameterized *per
+domain*, not per key: the orchestrator control plane is one domain
+(`CONTROL_PLANE` — key `orchestrator-token`, roles `{gateway, cli}`); a future
+boundary (e.g. the host controller of #468) instantiates its **own** domain with
+its **own** key, verifier, and role set rather than adding a role to this one.
+
+That distinction is the security invariant behind the split: adding a `host`
+role to the control plane's `ROLES` frozenset would let anything holding the
+control-plane signing key (the orchestrator itself) mint host-controller tokens,
+collapsing the boundary #468 needs — the host controller owns the orchestrator's
+lifecycle, so it must not be forgeable *by* the orchestrator. Two keys, two
+verifiers, two role sets.
+
+`ControlPlaneProvisioning` is the single shared contract every backend launcher
+satisfies instead of re-deriving, by hand, how to generate the signing key,
+scope it to the orchestrator process, mint the gateway JWT, and keep the host
+key canonical (the bug class that took PR #471 three review rounds — see
+`docs/prds/prd-new-control-plane-auth-provisioning.md`).
+
+Stdlib-only; the crypto lives in `orchestrator_auth` (untouched HMAC), the key
+file lives in `paths` (no bot-bottle imports, safe to copy flat), and this module
+composes the two into the provisioning seam.
+"""
+
+from __future__ import annotations
+
+import os
+from collections.abc import Mapping
+from dataclasses import dataclass, field
+
+from . import orchestrator_auth
+from .orchestrator_auth import ROLE_GATEWAY
+from .paths import (
+    ORCHESTRATOR_AUTH_JWT_ENV,
+    ORCHESTRATOR_TOKEN_ENV,
+    ORCHESTRATOR_TOKEN_FILENAME,
+    host_signing_key,
+)
+
+
+class ProvisioningError(RuntimeError):
+    """A control-plane auth invariant would be violated (e.g. starting a
+    co-located control plane without its signing key — which would run OPEN)."""
+
+
+@dataclass(frozen=True)
+class TrustDomain:
+    """One credential boundary: a host-canonical signing key + the role set it
+    signs + the env vars its key and a pre-minted token ride in.
+
+    `signing_key()` reads-or-mints the host-canonical key (never a guest's); the
+    orchestrator process that *owns* the domain receives that raw key (via
+    `key_env`), while a delegate (the data plane) receives only a pre-minted,
+    role-scoped token (via `token_env`) it cannot rewrite. `mint`/`verify` are
+    scoped to this domain's `roles`, so a token minted here neither carries nor
+    verifies a role from another domain."""
+
+    name: str
+    key_filename: str
+    roles: frozenset[str]
+    key_env: str
+    token_env: str
+
+    def signing_key(self) -> str:
+        """The host-canonical signing key for this domain (minted 0600 on first
+        use). Host-side only — the value is injected into the owning process, not
+        read there."""
+        return host_signing_key(self.key_filename)
+
+    def key_from_env(self, environ: Mapping[str, str] | None = None) -> str:
+        """The signing key as seen by the *owning process* — read from `key_env`
+        in the environment (default `os.environ`). "" when unset: the caller
+        decides whether that is fatal (see `OrchestratorServer`'s open-mode
+        fallback) or fail-closed (see `ControlPlaneProvisioning`)."""
+        env = os.environ if environ is None else environ
+        return env.get(self.key_env, "").strip()
+
+    def mint(self, role: str) -> str:
+        """A role-scoped token for a delegate, signed with this domain's key.
+        Raises ValueError for a role outside this domain (mint only what this
+        boundary accepts)."""
+        if role not in self.roles:
+            raise ValueError(f"role {role!r} is not in trust domain {self.name!r}")
+        return orchestrator_auth.mint(role, self.signing_key(), roles=self.roles)
+
+    def verify(self, token: str, key: str) -> str | None:
+        """The role `token` carries under `key`, or None. `key` is passed
+        explicitly (not read from the host file) because the verifier — the
+        control-plane process — holds it in `key_env`, not on disk in its guest."""
+        return orchestrator_auth.verify(token, key, roles=self.roles)
+
+
+# The orchestrator control-plane domain: the signing key held by the
+# orchestrator + host CLI, the `gateway` token handed to the data plane, and the
+# `cli` token the CLI mints for itself.
+CONTROL_PLANE = TrustDomain(
+    name="control-plane",
+    key_filename=ORCHESTRATOR_TOKEN_FILENAME,
+    roles=orchestrator_auth.ROLES,
+    key_env=ORCHESTRATOR_TOKEN_ENV,
+    token_env=ORCHESTRATOR_AUTH_JWT_ENV,
+)
+
+
+@dataclass(frozen=True)
+class Topology:
+    """What a backend *is*, for control-plane auth provisioning (#476) — the
+    backend declares this instead of encoding the provisioning decision by hand
+    in its launcher.
+
+    `data_plane_shares_control_host` — the data plane runs on the same host/VM as
+    the control plane, so a reachable-but-OPEN control plane would hand that
+    co-located data plane full `cli`. This is the default and the case that makes
+    the signing key **mandatory** (open mode unreachable). Every current backend
+    is co-located (docker/macOS: two containers on one host; firecracker: two VMs
+    on one host, agents L3-isolated). A backend with a genuinely isolated control
+    plane on a separate trusted host may declare False.
+
+    `combined_guest` — control plane and data plane share a single guest (the
+    retired combined infra VM). Informational today; kept so a future combined
+    backend *declares* it rather than rediscovering the provisioning."""
+
+    data_plane_shares_control_host: bool = True
+    combined_guest: bool = False
+
+
+# The default posture: data plane co-located with the control plane. Fail-closed
+# — the signing key is mandatory. A backend opts out only by declaring otherwise.
+COLOCATED = Topology(data_plane_shares_control_host=True)
+
+
+@dataclass(frozen=True)
+class ControlPlaneProvisioning:
+    """The single shared control-plane auth provisioning contract (#476).
+
+    A backend launcher satisfies THIS instead of re-deriving the four invariants
+    that each took a PR #471 review round to get right:
+
+      1. **Host-canonical key.** The signing key is `domain.signing_key()` — a
+         guest is *handed* it, never generates or overwrites it (round 3's bug:
+         the Firecracker guest clobbered the host key).
+      2. **Split credential.** Only the orchestrator process gets the raw key
+         (`orchestrator_key`); the data plane gets a pre-minted, role-scoped
+         token (`gateway_token`) it cannot rewrite into `cli` (round 1's bug).
+      3. **CLI validity across backends.** The host CLI mints its `cli` token
+         from this same canonical key, so it stays valid no matter which backend
+         (or how many) are co-running.
+      4. **No open mode.** `orchestrator_key` fail-closes for any topology whose
+         data plane shares the control plane's host/VM, so a launcher cannot
+         start the control plane OPEN (round 2's bug)."""
+
+    domain: TrustDomain = CONTROL_PLANE
+    topology: Topology = field(default=COLOCATED)
+
+    def orchestrator_key(self) -> str:
+        """The raw signing key the control-plane *process* must receive (carry it
+        in `domain.key_env`). Fail-closed: raises `ProvisioningError` rather than
+        returning "" for a co-located topology, because an empty key makes the
+        server run OPEN and hand the co-located data plane full `cli` (#476
+        invariant 4)."""
+        key = self.domain.signing_key()
+        if not key and self.topology.data_plane_shares_control_host:
+            raise ProvisioningError(
+                f"refusing to provision the {self.domain.name} control plane "
+                "without a signing key: its data plane shares this host/VM, so "
+                "an OPEN control plane would grant that data plane full `cli` "
+                "(#476)"
+            )
+        return key
+
+    def gateway_token(self) -> str:
+        """The pre-minted `gateway`-role token the data plane receives (carry it
+        in `domain.token_env`) — minted from the canonical key, never the key
+        itself, so a compromised data plane cannot forge a `cli` token."""
+        return self.domain.mint(ROLE_GATEWAY)
+
+
+__all__ = [
+    "ProvisioningError",
+    "TrustDomain",
+    "CONTROL_PLANE",
+    "Topology",
+    "COLOCATED",
+    "ControlPlaneProvisioning",
+]
diff --git a/docs/prds/prd-new-control-plane-auth-provisioning.md b/docs/prds/prd-new-control-plane-auth-provisioning.md
new file mode 100644
index 00000000..da80ef9c
--- /dev/null
+++ b/docs/prds/prd-new-control-plane-auth-provisioning.md
@@ -0,0 +1,141 @@
+# PRD prd-new: Uniform control-plane auth provisioning
+
+- **Status:** Draft
+- **Author:** claude
+- **Created:** 2026-07-26
+- **Issue:** #476
+
+## Summary
+
+Hoist control-plane auth provisioning out of the per-backend launchers into a
+single shared contract, parameterized per **trust domain**. A backend obtains
+its signing key and the data plane's token through one seam
+(`trust_domain.ControlPlaneProvisioning`) instead of re-deriving, by hand, how
+to generate the signing key, scope it to the orchestrator, mint the `gateway`
+JWT, and keep the host key canonical. This removes the integration-bug class
+that took PR #471 three review rounds to land, and gives issue #468's host
+controller a clean seam to instantiate its **own** domain (own key, own roles)
+without weakening the control plane's.
+
+## Problem
+
+Each launcher (`docker` gateway, `docker` infra, `macos` infra, `firecracker`
+infra) implemented the control-plane auth invariants independently. Every
+blocking finding in PR #471 was the same class of *integration* bug — not a flaw
+in the auth primitive (`orchestrator_auth.mint`/`verify`), but in how each
+backend wired it:
+
+- **Round 1 (High):** the data plane got the full-power control-plane token, so
+  a compromised egress/git-gate could approve its own supervise proposals. Fixed
+  with role-scoped JWTs (`gateway` vs `cli`).
+- **Round 2 (High):** the Firecracker infra VM never provisioned the signing key
+  or a `gateway` JWT, so the control plane fell into **open mode** and handed
+  every unauthenticated caller the `cli` role.
+- **Round 3 (High):** the Firecracker fix then clobbered the host-canonical
+  `orchestrator-token` with its guest key, 401'ing every already-running
+  Docker/macOS orchestrator.
+
+Miss one step per bespoke launcher and it's either a security hole or a
+cross-backend coexistence regression — and the tests didn't catch it because each
+backend's provisioning was hand-rolled.
+
+## Goals / Success Criteria
+
+- One shared seam every backend satisfies for control-plane auth provisioning;
+  no launcher re-derives the four invariants.
+- The signing key is **host-canonical** — a guest is handed it, never generates
+  or overwrites it.
+- Only the orchestrator process receives the raw key; the data plane receives a
+  pre-minted, role-scoped `gateway` token it cannot rewrite into `cli`.
+- The host CLI's `cli` token is minted from the same canonical key, so it stays
+  valid across simultaneously-running backends.
+- Open mode is unreachable for any backend whose data plane shares a host/VM
+  with the control plane (fail-closed by default).
+- Provisioning is parameterized **per trust domain**, so #468 adds a separate
+  host-controller domain (own key, own verifier, own role set) rather than a
+  `host` role on the control plane's frozenset.
+- Adding a backend or a data-plane daemon means *implementing the contract*, not
+  rediscovering the invariants.
+
+## Non-goals
+
+- Not a rewrite of the auth primitive. `orchestrator_auth`'s HMAC mint/verify is
+  unchanged except for an optional `roles=` argument (default preserved) so a
+  domain can scope its own role set.
+- Not the #468 host-controller domain itself — this only provides the seam it
+  will instantiate.
+- Not a change to network topology, the plane split (#469), or the server's
+  documented open-mode fallback for tests/isolated control planes.
+- The complementary #469 hardening (distinct non-root UIDs for co-located
+  daemons) stays separate.
+
+## Design
+
+### Trust domain — the unit of provisioning
+
+A **trust domain** (`trust_domain.TrustDomain`) is one credential boundary: a
+host-canonical signing key file, the role set that key may sign, and the env
+vars the raw key and a pre-minted token ride in. `mint`/`verify` are scoped to
+the domain's roles, so a token minted in one domain neither carries nor verifies
+a role from another.
+
+The orchestrator control plane is one domain, `CONTROL_PLANE` (key
+`orchestrator-token`, roles `{gateway, cli}`). The security reason provisioning
+is per-domain and not per-key: adding a `host` role to `CONTROL_PLANE.roles`
+would let anything holding the control-plane key (the orchestrator itself) mint
+host-controller tokens, collapsing the boundary #468 needs — the host controller
+owns the orchestrator's lifecycle, so it must not be forgeable *by* the
+orchestrator. Two keys, two verifiers, two role sets.
+
+`paths.host_signing_key(filename)` generalizes the old
+`host_orchestrator_token()` (now a thin specialization) so each domain names its
+own host-canonical key file.
+
+### The provisioning contract
+
+`ControlPlaneProvisioning` composes a domain with a declared `Topology` and
+answers the four invariants once:
+
+- `orchestrator_key()` → the raw key the control-plane **process** receives.
+  Fail-closed: raises `ProvisioningError` for a co-located topology when the key
+  is empty (which would run the server OPEN).
+- `gateway_token()` → the pre-minted `gateway` token the data plane receives,
+  minted from the canonical key, never the key itself.
+
+The `Orchestrator` ABC (`orchestrator/lifecycle.py`) holds one
+`ControlPlaneProvisioning` and exposes `control_plane_key()` and
+`mint_gateway_token()` over it. Each backend's orchestrator obtains its key
+through `control_plane_key()` and applies it via its own transport (docker/macOS:
+env var `key_env`; firecracker: SSH push to the guest) — the transport differs,
+the derivation no longer does.
+
+### Topology — the backend declares what it is
+
+`Topology` captures the provisioning-relevant dimensions the issue names
+(combined-guest vs standalone, data plane co-located vs isolated). The default,
+`COLOCATED`, makes the signing key mandatory (fail-closed). Every current backend
+is co-located (docker/macOS: two containers on one host; firecracker: two VMs on
+one host, agents L3-isolated), so none needs to redeclare it — the safe posture
+is the default, and a genuinely isolated control plane opts out explicitly.
+
+### Data flow
+
+```
+host key file (per-domain, 0600, host-canonical)
+        │  paths.host_signing_key(domain.key_filename)
+        ▼
+TrustDomain ── mint(role) ─────────────► gateway token ─► data-plane process (token_env / SSH)
+        │  signing_key()                 (gateway role, unrewritable)
+        ▼
+ControlPlaneProvisioning.orchestrator_key()  ─► control-plane process (key_env / SSH)
+        │  (fail-closed for co-located topology)
+        ▼
+OrchestratorClient ── CONTROL_PLANE.mint(cli) ─► host CLI's own operator token
+```
+
+## Open questions
+
+None blocking. #468 will add its host-controller domain as a second
+`TrustDomain` + `ControlPlaneProvisioning`-shaped consumer; whether the
+provisioning class is renamed to a domain-neutral `DomainProvisioning` at that
+point is a cosmetic call to make when #468 lands.
diff --git a/tests/unit/test_docker_orchestrator.py b/tests/unit/test_docker_orchestrator.py
index d94ff52a..fea4e845 100644
--- a/tests/unit/test_docker_orchestrator.py
+++ b/tests/unit/test_docker_orchestrator.py
@@ -19,7 +19,9 @@ _ORCH = "bot_bottle.backend.docker.orchestrator"
 _RUN = f"{_ORCH}.run_docker"
 _SLEEP = f"{_ORCH}.time.sleep"
 _MONOTONIC = f"{_ORCH}.time.monotonic"
-_TOKEN = f"{_ORCH}.host_orchestrator_token"
+# The signing key is read through the shared provisioning contract (#476); patch
+# its host-canonical key file read to keep it off the real host file.
+_TOKEN = "bot_bottle.trust_domain.host_signing_key"
 # The ABC's is_healthy probes /health via urllib in the lifecycle module.
 _URLOPEN = "bot_bottle.orchestrator.lifecycle.urllib.request.urlopen"
 
diff --git a/tests/unit/test_firecracker_orchestrator.py b/tests/unit/test_firecracker_orchestrator.py
index 28fa2c43..5e1524ba 100644
--- a/tests/unit/test_firecracker_orchestrator.py
+++ b/tests/unit/test_firecracker_orchestrator.py
@@ -44,7 +44,7 @@ class TestEnsureRunning(unittest.TestCase):
         vm = infra_vm.InfraVm(guest_ip="10.243.255.1", private_key=Path("/k"), vm=MagicMock())
         with patch.object(infra_vm, "boot_vm", return_value=vm) as boot, \
                 patch.object(infra_vm, "push_secret") as push, \
-                patch(f"{_ORCH}.host_orchestrator_token", return_value="host-key"), \
+                patch("bot_bottle.trust_domain.host_signing_key", return_value="host-key"), \
                 patch.object(orch, "is_running", return_value=False), \
                 patch.object(orch, "_ensure_registry_volume", return_value=Path("/reg")), \
                 patch.object(orch, "_wait_for_health"):
diff --git a/tests/unit/test_macos_orchestrator.py b/tests/unit/test_macos_orchestrator.py
index 845c099d..11fad373 100644
--- a/tests/unit/test_macos_orchestrator.py
+++ b/tests/unit/test_macos_orchestrator.py
@@ -33,7 +33,7 @@ class TestMacosOrchestratorRun(unittest.TestCase):
     def _run(self) -> list[str]:
         run = Mock(return_value=_ok())
         with patch(f"{_ORCH}.container_mod") as mod, \
-                patch(f"{_ORCH}.host_orchestrator_token", return_value="k"):
+                patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
             mod.dns_server.return_value = "1.1.1.1"
             mod.bind_mount_spec.side_effect = _spec
             mod.run_container_argv = run
@@ -65,7 +65,7 @@ class TestMacosOrchestratorRun(unittest.TestCase):
 
     def test_start_failure_raises(self) -> None:
         with patch(f"{_ORCH}.container_mod") as mod, \
-                patch(f"{_ORCH}.host_orchestrator_token", return_value="k"):
+                patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
             mod.dns_server.return_value = "1.1.1.1"
             mod.run_container_argv = Mock(return_value=_fail())
             with self.assertRaises(OrchestratorStartError):
diff --git a/tests/unit/test_orchestrator_auth.py b/tests/unit/test_orchestrator_auth.py
index 78e25596..ea9880f2 100644
--- a/tests/unit/test_orchestrator_auth.py
+++ b/tests/unit/test_orchestrator_auth.py
@@ -82,5 +82,26 @@ class TestMintVerify(unittest.TestCase):
             mint(ROLE_GATEWAY, "")
 
 
+class TestCustomRoleSet(unittest.TestCase):
+    """The `roles=` seam a trust domain other than the control plane uses (#476):
+    mint/verify are scoped to the passed role set, not the module default."""
+
+    _ROLES = frozenset({"host"})
+
+    def test_round_trips_a_role_in_the_custom_set(self) -> None:
+        tok = mint("host", _KEY, roles=self._ROLES)
+        self.assertEqual("host", verify(tok, _KEY, roles=self._ROLES))
+
+    def test_mint_rejects_a_role_outside_the_custom_set(self) -> None:
+        with self.assertRaises(ValueError):
+            mint(ROLE_CLI, _KEY, roles=self._ROLES)
+
+    def test_verify_rejects_a_role_outside_the_verifiers_set(self) -> None:
+        # A validly signed token whose role isn't in the verifier's set fails —
+        # this is what keeps one domain's key from asserting another's role.
+        tok = mint(ROLE_CLI, _KEY)  # a control-plane `cli` token
+        self.assertIsNone(verify(tok, _KEY, roles=self._ROLES))
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/unit/test_orchestrator_client.py b/tests/unit/test_orchestrator_client.py
index a9f77da2..aa04a3e4 100644
--- a/tests/unit/test_orchestrator_client.py
+++ b/tests/unit/test_orchestrator_client.py
@@ -20,13 +20,15 @@ _URLOPEN = "bot_bottle.orchestrator.client.urllib.request.urlopen"
 
 class TestHostAuthToken(unittest.TestCase):
     def test_mints_a_cli_token_from_the_host_key(self) -> None:
-        with patch("bot_bottle.orchestrator.client.host_orchestrator_token",
+        # The CLI mints its `cli` token from the control-plane trust domain's
+        # host-canonical key (#476) — patch the key file read underneath it.
+        with patch("bot_bottle.trust_domain.host_signing_key",
                    return_value="signing-key"):
             tok = _host_auth_token()
         self.assertEqual(ROLE_CLI, verify(tok, "signing-key"))
 
     def test_returns_empty_when_key_unreadable(self) -> None:
-        with patch("bot_bottle.orchestrator.client.host_orchestrator_token",
+        with patch("bot_bottle.trust_domain.host_signing_key",
                    side_effect=OSError("no host root")):
             self.assertEqual("", _host_auth_token())
 
diff --git a/tests/unit/test_trust_domain.py b/tests/unit/test_trust_domain.py
new file mode 100644
index 00000000..c8d775c8
--- /dev/null
+++ b/tests/unit/test_trust_domain.py
@@ -0,0 +1,113 @@
+"""Unit: trust domains + the shared control-plane provisioning contract (#476)."""
+
+from __future__ import annotations
+
+import unittest
+from unittest.mock import patch
+
+from bot_bottle import orchestrator_auth
+from bot_bottle.orchestrator_auth import ROLE_CLI, ROLE_GATEWAY
+from bot_bottle.trust_domain import (
+    CONTROL_PLANE,
+    ControlPlaneProvisioning,
+    ProvisioningError,
+    Topology,
+    TrustDomain,
+)
+
+# A second, unrelated domain — the shape #468's host controller would take: its
+# own key file, its own role, its own env vars. Distinct from CONTROL_PLANE.
+_HOST_CTRL = TrustDomain(
+    name="host-controller",
+    key_filename="host-controller-token",
+    roles=frozenset({"host"}),
+    key_env="BOT_BOTTLE_HOST_CONTROLLER_TOKEN",
+    token_env="BOT_BOTTLE_HOST_CONTROLLER_JWT",
+)
+
+
+class TestTrustDomainMintVerify(unittest.TestCase):
+    def test_mint_verify_round_trips_within_a_domain(self) -> None:
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            tok = CONTROL_PLANE.mint(ROLE_GATEWAY)
+        self.assertEqual(ROLE_GATEWAY, CONTROL_PLANE.verify(tok, "k"))
+
+    def test_mint_rejects_a_role_outside_the_domain(self) -> None:
+        # `host` is a valid role in _HOST_CTRL but not in the control plane —
+        # the control-plane key must refuse to mint it.
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            with self.assertRaises(ValueError):
+                CONTROL_PLANE.mint("host")
+
+    def test_a_custom_role_set_verifies_its_own_role(self) -> None:
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            tok = _HOST_CTRL.mint("host")
+        self.assertEqual("host", _HOST_CTRL.verify(tok, "k"))
+
+    def test_key_from_env_reads_the_domains_env_var(self) -> None:
+        self.assertEqual(
+            "secret", CONTROL_PLANE.key_from_env({CONTROL_PLANE.key_env: " secret "}))
+        self.assertEqual("", CONTROL_PLANE.key_from_env({}))
+
+
+class TestDomainBoundary(unittest.TestCase):
+    """The #476/#468 invariant: two domains, two keys, two role sets — one
+    domain's key can neither mint nor verify the other's tokens."""
+
+    def test_a_control_plane_token_does_not_verify_under_another_domains_key(
+        self,
+    ) -> None:
+        # Even with an IDENTICAL underlying key, a `cli` token minted under the
+        # control-plane domain must not verify as a role in the host-controller
+        # domain — the role isn't in that domain's set.
+        cli_tok = orchestrator_auth.mint(ROLE_CLI, "shared-bytes")
+        self.assertIsNone(_HOST_CTRL.verify(cli_tok, "shared-bytes"))
+
+    def test_distinct_keys_do_not_cross_verify(self) -> None:
+        # The realistic case: distinct host-canonical keys per domain. A token
+        # signed by one key never verifies under the other.
+        host_tok = orchestrator_auth.mint(
+            "host", "host-ctrl-key", roles=_HOST_CTRL.roles)
+        self.assertIsNone(_HOST_CTRL.verify(host_tok, "control-plane-key"))
+        self.assertEqual("host", _HOST_CTRL.verify(host_tok, "host-ctrl-key"))
+
+
+class TestControlPlaneProvisioning(unittest.TestCase):
+    def test_orchestrator_key_returns_the_canonical_key(self) -> None:
+        prov = ControlPlaneProvisioning()
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="key"):
+            self.assertEqual("key", prov.orchestrator_key())
+
+    def test_orchestrator_key_fail_closes_when_colocated_and_empty(self) -> None:
+        # Invariant 4: a co-located backend must never start the control plane
+        # without a key (it would run OPEN and hand the co-located data plane
+        # full `cli`).
+        prov = ControlPlaneProvisioning()  # default topology: co-located
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value=""):
+            with self.assertRaises(ProvisioningError):
+                prov.orchestrator_key()
+
+    def test_orchestrator_key_allows_empty_when_isolated(self) -> None:
+        # A genuinely isolated control plane (no co-located data plane) may run
+        # without a key — the only topology where open mode is permissible.
+        prov = ControlPlaneProvisioning(
+            topology=Topology(data_plane_shares_control_host=False))
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value=""):
+            self.assertEqual("", prov.orchestrator_key())
+
+    def test_gateway_token_is_a_verifiable_gateway_role_token(self) -> None:
+        prov = ControlPlaneProvisioning()
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            tok = prov.gateway_token()
+        self.assertEqual(ROLE_GATEWAY, CONTROL_PLANE.verify(tok, "k"))
+
+    def test_gateway_token_cannot_be_reused_as_cli(self) -> None:
+        # The data plane's token is `gateway`-scoped: it never carries `cli`.
+        prov = ControlPlaneProvisioning()
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            tok = prov.gateway_token()
+        self.assertNotEqual(ROLE_CLI, CONTROL_PLANE.verify(tok, "k"))
+
+
+if __name__ == "__main__":
+    unittest.main()