feat(delivery): docker sandbox adapter + owner-only infrastructure (v2 phase A3-1)

The execution boundary for v2. Adds the local docker/podman sandbox adapter
and the hardened host subprocess runner every other delivery adapter will use.

- adapters/process.py: the one place the platform shells out. argv-only (no
  shell), start_new_session + killpg on timeout, concurrent stdout/stderr
  drains with a byte cap, explicit minimal env (never os.environ), and a
  missing binary reported as spawn_failed rather than an exception.
- adapters/docker_sandbox.py: DockerSandboxAdapter over SandboxProviderPort.
  --user 1000:1000, --cap-drop ALL, no-new-privileges, pids/cpu/memory limits,
  --read-only with tmpfs scratch, one bind mount (the work tree, never the git
  dir), labels, no published ports. Path-safe file access; secrets refused in
  `docker exec -e`. Extras for later phases: start_demo_container (loopback
  publish only), list_managed_containers, remove_container.
- registry: SANDBOX_PROVIDER=docker, cached singleton so the workspace registry
  survives create_workspace -> start_session.
- sandbox_gateway worker: reap_orphans() removes labelled containers no live
  session points at, audited as sandbox.reap; run_pass() does both passes.
- sandbox router: every mutating route now requires the platform owner
  (PLAN-v2 §7.7); read-only status routes stay open to org members.
- sandbox-panel: canManageInfra prop (fails closed) hides the create form,
  the session panel and the action buttons from non-owners.

Tests: 346 API (+37), 67 web (+3); ruff, mypy, tsc and lint clean.
Three existing tests now drive the sandbox as the platform owner, since that
is who may touch it.

Report: docs/plan/reports/agent-3-phase-1.md

apps/api/app/workers/sandbox_gateway.py

@@ -23,10 +23,19 @@ from datetime import timedelta
 from app.application.container import build_sandbox_service
 from app.application.ports.realtime import emit_sandbox_reaped
 from app.core.config import settings
-from app.domain.audit.models import AuditAction, AuditEvent
+from app.domain.audit.models import (
+    AuditAction,
+    AuditEvent,
+    ErrorSeverity,
+    ErrorSource,
+)
 from app.domain.base import utcnow
+from app.infrastructure.error_log import record_error
 from app.infrastructure.repositories.audit import AuditRepository
-from app.infrastructure.repositories.sandbox import WorkspaceRepository
+from app.infrastructure.repositories.sandbox import (
+    SandboxSessionRepository,
+    WorkspaceRepository,
+)
 from app.workers.base import WorkerOutcome, worker_session
 
 #: Sessions are considered abandoned after this long with no activity.
@@ -38,6 +47,22 @@ class SandboxGatewayWorker:
 
     name = "sandbox-gateway"
 
+    async def run_pass(
+        self, *, idle_minutes: int = DEFAULT_IDLE_MINUTES, limit: int = 200
+    ) -> WorkerOutcome:
+        """One housekeeping pass: idle sessions first, then orphan containers.
+
+        Combined into one pass so a cron entry needs a single invocation and an
+        operator sees one summary line per run.
+        """
+        outcome = await self.reap(idle_minutes=idle_minutes, limit=limit)
+        orphans = await self.reap_orphans(limit=limit)
+        outcome.processed += orphans.processed
+        outcome.failed += orphans.failed
+        for note in orphans.notes:
+            outcome.note(note)
+        return outcome
+
     async def reap(
         self, *, idle_minutes: int = DEFAULT_IDLE_MINUTES, limit: int = 200
     ) -> WorkerOutcome:
@@ -98,5 +123,86 @@ class SandboxGatewayWorker:
         outcome.note("egress policy default = deny_all (set per resource limit)")
         return outcome
 
+    async def reap_orphans(self, *, limit: int = 200) -> WorkerOutcome:
+        """Remove labelled containers that no live session row points at.
+
+        ``reap`` above stops *sessions*; this stops *containers*. The two are
+        not the same: a session row can be stopped (or the database restored
+        from a backup) while the container keeps running, and a container can be
+        started by a process that then died before writing its row. Without this
+        pass those containers hold CPU, memory and disk forever, because nothing
+        in the application knows they exist.
+
+        Only the container runtime is inspected. A provider without
+        ``list_managed_containers`` (the mock, the remote adapters) has nothing
+        to reap and is skipped silently — this is not an error condition.
+        """
+        outcome = WorkerOutcome(name=self.name)
+
+        from app.infrastructure.adapters.registry import get_sandbox_provider
+
+        provider = get_sandbox_provider()
+        lister = getattr(provider, "list_managed_containers", None)
+        if lister is None:
+            outcome.skipped += 1
+            outcome.note("provider does not expose managed containers; nothing to reap")
+            return outcome
+
+        try:
+            containers = await lister()
+        except Exception as exc:  # noqa: BLE001 - a CLI outage must not kill the worker
+            await record_error(
+                kind="sandbox_orphan_list_failed",
+                message=str(exc),
+                exc=exc,
+                source=ErrorSource.WORKER,
+                severity=ErrorSeverity.WARNING,
+                metadata={"worker": self.name},
+            )
+            outcome.failed += 1
+            return outcome
+
+        async with worker_session() as session:
+            live = await SandboxSessionRepository(session).list_active_external_ids()
+            audit = AuditRepository(session)
+
+            reaped = 0
+            for container in containers:
+                if reaped >= limit:
+                    break
+                if container.container_id in live:
+                    continue
+                # A demo/build container is owned by the delivery pipeline, which
+                # tracks it in its own table. Until that table exists it is left
+                # alone rather than guessed at.
+                if container.role and container.role != "workspace":
+                    outcome.skipped += 1
+                    continue
+                removed = await provider.remove_container(container.container_id)
+                if not removed:
+                    outcome.failed += 1
+                    continue
+                reaped += 1
+                outcome.processed += 1
+                outcome.note(f"removed orphan container {container.container_id}")
+                await audit.record(
+                    event=AuditEvent(
+                        action=AuditAction.SANDBOX_REAP,
+                        organization_id=container.organization_id or None,
+                        target_type="sandbox_container",
+                        target_id=container.container_id,
+                        metadata_json={
+                            "reason": "orphan_container",
+                            "project_id": container.project_id,
+                            "role": container.role,
+                        },
+                    )
+                )
+
+            if not reaped:
+                outcome.skipped += 1
+
+        return outcome
+
 
 __all__ = ["DEFAULT_IDLE_MINUTES", "SandboxGatewayWorker"]