feat(realism): canary cultivator on the realism contract

Stage 7 — final stage of the realism migration. Canary plants are
now scheduled by the same realism planner that handles inert content,
keeping the orchestrator as the single decision point and avoiding
duplicate diurnal / persona / rate-limit logic in the canary
subsystem.

New surface:

- decnet/canary/cultivator.py: cultivate(plan, repo) builds a
  CanaryContext, calls the right generator (canary_aws_creds ->
  aws_creds, canary_mysql_dump -> mysql_dump, …), persists the
  canary_tokens row before plant so the canary worker can attribute
  callbacks even on plant-time previews. Resolves canary placements
  to credible operator paths (~/.aws/credentials, ~/.ssh/id_rsa,
  /var/backups/db_backup.sql).
- realism/planner.py adds 8 canary content_classes uniformly weighted
  inside a 3% probability gate. Hard-capped: each tick at most one
  canary; create branch falls through to inert otherwise.
- scheduler.pick_file dispatches canary content_class to the
  cultivator; FileAction grows an optional content_bytes field so
  binary canary artifacts (DOCX/PDF/honeydoc) survive the wire
  intact instead of being utf-8 round-tripped.
- SSHDriver._run_file uses content_bytes when set, falls back to
  encoding the str content otherwise.

Stealth (per feedback_stealth.md): cultivator does not introduce
any DECNET literal; the underlying generators are already
stealth-clean and the test suite asserts the contract holds.

Tests cover round-tripping every canary class through the cultivator,
verifying placement-path conventions, persona-login normalisation
("John Smith" -> /home/johnsmith/.aws/credentials), and the
no-DECNET-leak invariant.

decnet/canary/cultivator.py

@@ -0,0 +1,172 @@
+"""Realism contract adapter for canary generators.
+
+Stage 7 of the realism migration.  The orchestrator's planner picks a
+``canary_*`` :class:`~decnet.realism.taxonomy.ContentClass` 1–3% of
+the time on file ticks; this module turns that pick into a
+:class:`~decnet.canary.base.CanaryArtifact` (bytes the SSH driver
+plants) plus a persisted :class:`~decnet.web.db.models.CanaryToken`
+row so the canary worker recognises the slug when an attacker trips
+it.
+
+What this is NOT: it doesn't pick *when* canaries fire — that's the
+realism planner's job.  It doesn't decide *where* on the filesystem
+the canary lands beyond what realism naming + persona conventions
+already produce.  It's a thin bytes-and-row factory bolted onto the
+realism contract.
+
+Stealth (per ``feedback_stealth.md``): we never leak the
+``DECNET`` literal into anything that survives to the planted file.
+The underlying generators are already stealth-clean; this wrapper
+must not undo that.
+"""
+from __future__ import annotations
+
+import os
+import secrets as _secrets
+from datetime import datetime, timezone
+from typing import Any, Optional
+
+from decnet.canary.base import CanaryArtifact, CanaryContext
+from decnet.canary.factory import get_generator
+from decnet.logging import get_logger
+from decnet.realism.taxonomy import ContentClass, Plan
+
+log = get_logger("canary.cultivator")
+
+
+# realism content_class → canary generator name.  Mirrors
+# :data:`decnet.canary.factory.KNOWN_GENERATORS`.
+_CLASS_TO_GENERATOR: dict[ContentClass, str] = {
+    ContentClass.CANARY_AWS_CREDS: "aws_creds",
+    ContentClass.CANARY_ENV_FILE: "env_file",
+    ContentClass.CANARY_GIT_CONFIG: "git_config",
+    ContentClass.CANARY_SSH_KEY: "ssh_key",
+    ContentClass.CANARY_HONEYDOC: "honeydoc",
+    ContentClass.CANARY_HONEYDOC_DOCX: "honeydoc_docx",
+    ContentClass.CANARY_HONEYDOC_PDF: "honeydoc_pdf",
+    ContentClass.CANARY_MYSQL_DUMP: "mysql_dump",
+}
+
+
+# Path conventions per generator.  The realism planner doesn't know
+# about decoy-realistic credential locations (``~/.aws/credentials``,
+# ``~/.git/config``); we map them per-class here so the planted
+# artifact lands somewhere an attacker would actually look.
+_DEFAULT_PATH: dict[ContentClass, str] = {
+    ContentClass.CANARY_AWS_CREDS: "/home/{persona}/.aws/credentials",
+    ContentClass.CANARY_ENV_FILE: "/home/{persona}/app/.env",
+    ContentClass.CANARY_GIT_CONFIG: "/home/{persona}/.git/config",
+    ContentClass.CANARY_SSH_KEY: "/home/{persona}/.ssh/id_rsa",
+    ContentClass.CANARY_HONEYDOC: "/home/{persona}/Documents/notes.html",
+    ContentClass.CANARY_HONEYDOC_DOCX: "/home/{persona}/Documents/Q3-Operations-Review.docx",
+    ContentClass.CANARY_HONEYDOC_PDF: "/home/{persona}/Documents/Q3-Operations-Review.pdf",
+    ContentClass.CANARY_MYSQL_DUMP: "/var/backups/db_backup.sql",
+}
+
+
+def _persona_login(persona: str) -> str:
+    """Mirror :func:`decnet.realism.naming._home`'s username conventions."""
+    candidate = persona.lower().replace(" ", "")
+    if candidate.isalnum() and candidate.isascii() and candidate:
+        return candidate
+    return "user"
+
+
+def _path_for(plan: Plan) -> str:
+    """Produce the canary placement path for *plan*.
+
+    The realism planner already filled in ``plan.target_path`` from
+    the namer, but canary placements have stronger conventions
+    (``~/.aws/credentials``, ``~/.ssh/id_rsa``) than the realism
+    namer's vocabulary.  When :data:`_DEFAULT_PATH` has an entry,
+    that wins.
+    """
+    template = _DEFAULT_PATH.get(plan.content_class)
+    if template is None:
+        return plan.target_path
+    return template.format(persona=_persona_login(plan.persona))
+
+
+def _new_callback_token() -> str:
+    """16 url-safe bytes — same shape canary slug fields use elsewhere."""
+    return _secrets.token_urlsafe(16)
+
+
+async def cultivate(
+    plan: Plan,
+    repo: Any,
+    *,
+    http_base: Optional[str] = None,
+    dns_zone: Optional[str] = None,
+    created_by: str = "system",
+) -> CanaryArtifact:
+    """Realism-driven canary plant.
+
+    Build a :class:`CanaryContext`, ask the right generator for bytes,
+    persist a ``canary_tokens`` row so the canary worker can attribute
+    callbacks to this token, and return the artifact for the SSH
+    driver to plant.
+
+    *http_base* and *dns_zone* default to ``DECNET_CANARY_HTTP_BASE``
+    and ``DECNET_CANARY_DNS_ZONE`` env vars respectively — same
+    pattern the canary worker uses.  When both are empty, generators
+    that need a callback host (``ssh_key`` DNS, ``mysql_dump``)
+    raise; the planner's caller logs and falls back to a non-canary
+    plan.
+    """
+    if not plan.content_class.is_canary():
+        raise ValueError(
+            f"cultivate() called with non-canary content_class="
+            f"{plan.content_class!r}"
+        )
+    gen_name = _CLASS_TO_GENERATOR.get(plan.content_class)
+    if gen_name is None:
+        raise KeyError(
+            f"no canary generator mapped for content_class="
+            f"{plan.content_class!r}"
+        )
+
+    callback_token = _new_callback_token()
+    ctx = CanaryContext(
+        callback_token=callback_token,
+        http_base=http_base or os.environ.get("DECNET_CANARY_HTTP_BASE", ""),
+        dns_zone=dns_zone or os.environ.get("DECNET_CANARY_DNS_ZONE", ""),
+        persona="linux",  # all our deckies are POSIX in MVP
+    )
+    generator = get_generator(gen_name)
+    artifact = generator.generate(ctx)
+
+    # The generator returns ``path=""`` (planter fills it normally).
+    # We have a realism-derived path on hand; stuff it in for the SSH
+    # driver's plant_file call AND the canary_tokens row.
+    placement_path = _path_for(plan)
+
+    # Persist the token row before planting so the canary worker can
+    # attribute a callback if the artifact trips during the plant
+    # itself (improbable but possible — DOCX viewers can preview
+    # autoplay-style).
+    await repo.create_canary_token({
+        "kind": "http",  # MVP: all realism-cultivated tokens use HTTP
+        "decky_name": plan.decky_name,
+        "instrumenter": None,
+        "generator": gen_name,
+        "placement_path": placement_path,
+        "callback_token": callback_token,
+        "secret_seed": callback_token,  # deterministic re-seed compatible
+        "placed_at": datetime.now(timezone.utc),
+        "created_by": created_by,
+        "state": "planted",
+    })
+
+    # Carry the placement_path on the artifact so the orchestrator's
+    # plant_file call uses it.  We don't mutate the generator's
+    # original — copy with the new path.
+    return CanaryArtifact(
+        path=placement_path,
+        content=artifact.content,
+        mode=artifact.mode,
+        mtime_offset=artifact.mtime_offset,
+        instrumenter=artifact.instrumenter,
+        generator=artifact.generator,
+        notes=list(artifact.notes),
+    )

decnet/orchestrator/drivers/ssh.py

@@ -198,15 +198,19 @@ class SSHDriver(ActivityDriver):
         return result
 
     async def _run_file(self, action: FileAction) -> ActivityResult:
-        # FileAction's content is a string; the realism path uses
-        # bytes-typed plant_file so binary blobs (DOCX/PDF, future
-        # canary artifacts) survive the wire.  Encode-once here.
+        # FileAction.content_bytes wins when set — canary artifacts
+        # (DOCX/PDF/honeydoc binaries) need their bytes preserved
+        # exactly. Falls back to utf-8 encoding the str content for
+        # the inert-realism path.
         # mtime carries through from the realism planner so the file
         # doesn't stamp at wall-clock-now (the realism failure today).
+        body = action.content_bytes
+        if body is None:
+            body = action.content.encode("utf-8")
         return await self.plant_file(
             action.dst_name,
             action.path,
-            action.content.encode("utf-8"),
+            body,
             mode=0o644,
             mtime=action.mtime,
         )

decnet/orchestrator/scheduler.py

@@ -56,6 +56,11 @@ class FileAction:
     content_class: str = ContentClass.NOTE.value
     mtime: Optional[datetime] = None
     description: str = "file:create"
+    # Canary artifacts (DOCX/PDF/honeydoc binaries) carry their bytes
+    # here so re-encoding ``content`` from utf-8 doesn't mangle them.
+    # When set, the SSH driver uses these bytes directly and ignores
+    # ``content``.
+    content_bytes: Optional[bytes] = None
 
 
 @dataclass(frozen=True)
@@ -183,6 +188,38 @@ async def pick_file(
             mtime=plan.mtime,
         )
 
+    # Canary branch — the cultivator builds the bytes, picks the
+    # placement path, and persists the canary_tokens row.  We map
+    # the resulting CanaryArtifact to a FileAction so the SSH
+    # driver's plant_file path is reused unchanged.
+    if plan.content_class.is_canary():
+        try:
+            from decnet.canary import cultivator as _cultivator
+            artifact = await _cultivator.cultivate(plan, repo)
+        except Exception:  # noqa: BLE001
+            # Cultivation failed (no http_base/dns_zone configured,
+            # generator raised, repo write failed).  Fall through to
+            # an inert file plant so the tick isn't wasted.
+            return FileAction(
+                dst_uuid=plan.decky_uuid,
+                dst_name=plan.decky_name,
+                path=plan.target_path or f"/tmp/.cache-{secrets.token_hex(3)}",  # nosec B108
+                content=plan.body_hint or "",
+                persona=plan.persona,
+                content_class=plan.content_class.value,
+                mtime=plan.mtime,
+            )
+        return FileAction(
+            dst_uuid=plan.decky_uuid,
+            dst_name=plan.decky_name,
+            path=artifact.path,
+            content="",  # ignored when content_bytes is set
+            content_bytes=artifact.content,
+            persona=plan.persona,
+            content_class=plan.content_class.value,
+            mtime=plan.mtime,
+        )
+
     # Create branch.  If LLM is wired, optionally swap body_hint for
     # an LLM-authored body.  Always keep the deterministic body_hint
     # as the fallback the function call returns when LLM

decnet/realism/planner.py

@@ -45,6 +45,21 @@ _SYSTEM_CLASS_WEIGHTS: tuple[tuple[ContentClass, int], ...] = (
     (ContentClass.LOG_DAEMON, 8),
     (ContentClass.CACHE_TMP, 5),
 )
+# Canary classes are picked rarely.  Each plant materialises a real
+# CanaryToken row + DNS slug + HTTP URL — flooding the fleet with
+# canaries makes the dashboard noisy and the per-decky alert surface
+# explode.  ~3% of file picks land here.
+_CANARY_CLASS_WEIGHTS: tuple[tuple[ContentClass, int], ...] = (
+    (ContentClass.CANARY_AWS_CREDS, 1),
+    (ContentClass.CANARY_ENV_FILE, 1),
+    (ContentClass.CANARY_GIT_CONFIG, 1),
+    (ContentClass.CANARY_SSH_KEY, 1),
+    (ContentClass.CANARY_HONEYDOC, 1),
+    (ContentClass.CANARY_HONEYDOC_DOCX, 1),
+    (ContentClass.CANARY_HONEYDOC_PDF, 1),
+    (ContentClass.CANARY_MYSQL_DUMP, 1),
+)
+_CANARY_PROBABILITY = 0.03
 
 
 def _weighted_pick(
@@ -117,6 +132,33 @@ def pick(
 
     decky, persona = rng.choice(eligible)
 
+    # Canary first — they're rare (~3% of file picks), uniformly
+    # weighted across generators.  Falling here means the orchestrator
+    # plants a callback-bearing artifact this tick instead of an
+    # inert one.
+    if rng.random() < _CANARY_PROBABILITY:
+        content_class = _weighted_pick(_CANARY_CLASS_WEIGHTS, rng)
+        # Canary placement is the cultivator's job — plan.target_path
+        # is advisory; a "" lets the cultivator override entirely.
+        target_path = ""
+        body_hint = None
+        mtime = sample_mtime(persona.active_hours, now, rand=rng)
+        return Plan(
+            decky_uuid=decky["uuid"],
+            decky_name=decky["name"],
+            persona=persona.name,
+            content_class=content_class,
+            action="create",
+            target_path=target_path,
+            mtime=mtime,
+            body_hint=body_hint,
+            notes=(
+                f"persona={persona.name}",
+                f"class={content_class.value}",
+                "kind=canary",
+            ),
+        )
+
     # User vs system content — biased toward user (realism wins are
     # bigger there).
     if rng.random() < 0.7: