Capability Advertisement

Dynamic scanner capability reporting from agents to server.

Overview

Agents dynamically report which scanners they have available. The server maintains a live view of agent capabilities without requiring registration updates.

Capability Detection

Process:

1. Agent checks each scanner's availability (DetectAvailable())
2. Agent reports available scanners in check-in payload
3. Server diff against existing subsystem rows
4. Server inserts new scanners, updates existing
5. Server removes stale scanners (if configured)

Implementation:

Detection: agent/internal/scanner/*.go:DetectAvailable()
Sync: server/internal/api/handlers/agents.go:syncAvailableScanners()

Scanner Types

Scanner	Platform	Detection Method
APT	Linux	Check `/var/lib/apt/lists/lock`
DNF	Linux	Check `dnf version` availability
Winget	Windows	Check `winget` CLI availability
WUA	Windows	Check WindowsUpdate Agent service
Docker	All	Check Docker socket/CLI availability
Package (upstream)	All	Check upstream registry sync capability

Sync Pattern (Idempotent)

INSERT new scanners:

INSERT INTO agent_subsystems (agent_id, name, enabled)
VALUES ($1, $2, true)
ON CONFLICT (agent_id, name) DO NOTHING

UPDATE existing:

UPDATE agent_subsystems SET enabled = true WHERE agent_id = $1 AND name = $2

No DELETE on transient signal:

Brief IsAvailable()=false doesn't remove scanner
Removal requires explicit admin action or stale threshold

Footer: Assumptions & Connections

Assumption: Capabilities can change post-registration (Docker installed after agent deploy).

Connection: Capability sync (flows/05-capability-advertisement.md) implements ETHOS #4 (idempotent scanner sync).

Connection: syncAvailableScanners() (flows/05-capability-advertisement.md) called on every agent check-in.

Connection: Capability badges (flows/05-capability-advertisement.md) rendered in AgentHealth.tsx dashboard.

Connection: Scanner detection (agent/internal/scanner/*.go:DetectAvailable()) called during registration and polling.

Last reviewed: 2026-05-26

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