fix(dgw): change AgentInfo.last_seen from epoch-ms integer to RFC 3339 date-time

[Copilot]

The unpublished Agent Tunnel API exposed last_seen_ms: Option<u64> on AgentInfo, an implementation-unit-leaking encoding. Since the API/clients aren't published yet, this is the right time to switch to a semantic date-time boundary instead.

API model (devolutions-gateway/src/api/tunnel.rs)

• Renamed last_seen_ms: Option<u64> → last_seen: Option<time::OffsetDateTime>, serialized via time::serde::rfc3339::option (consistent with the existing MonitorResult::request_start_time convention).
• Added last_seen_ms_to_datetime, a panic-free conversion from the registry's epoch-millisecond u64 to OffsetDateTime, returning None on overflow instead of panicking.
• Internal agent_tunnel::registry::AgentInfo::last_seen_ms is unchanged — the registry still tracks milliseconds internally.
• None is still returned for agents with no runtime/tunnel heartbeat (offline agents).

fn last_seen_ms_to_datetime(last_seen_ms: u64) -> Option<OffsetDateTime> {
    let nanos = i128::from(last_seen_ms).checked_mul(1_000_000)?;
    OffsetDateTime::from_unix_timestamp_nanos(nanos).ok()
}

Tests

• Updated unit tests for populated/null last_seen.
• Added coverage for zero timestamp and out-of-range (u64::MAX) conversion.
• Updated the agent tunnel testsuite assertion (last_seen_ms → last_seen).

Generated artifacts

Regenerated via the repository's existing generate-openapi and generate_clients scripts (no manual edits):

• gateway-api.yaml: field is now type: string, format: date-time, nullable: true.
• AsciiDoc reference doc updated.
• .NET client: LastSeenMs (long?) → LastSeen (DateTime?), including removal of the now-obsolete minimum-value validation.
• TypeScript client: last_seen_ms?: number | null → last_seen?: string | null.

[Benoît Cortier (CBenoit)]

LGTM

[Copilot]

🟡 Changes recommended

The populated RFC 3339 JSON representation lacks direct test coverage.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Updates the unpublished Agent Tunnel API to expose last-seen timestamps as RFC 3339 date-times.

Changes:

• Converts registry epoch milliseconds to OffsetDateTime.
• Updates API tests and OpenAPI schema.
• Regenerates TypeScript, .NET, and reference documentation.

File summaries

File	Description
testsuite/tests/cli/agent/tunnel.rs	Updates the null-field assertion.
devolutions-gateway/src/api/tunnel.rs	Adds date-time conversion and API field.
devolutions-gateway/openapi/ts-angular-client/model/agentInfo.ts	Updates the TypeScript model.
devolutions-gateway/openapi/gateway-api.yaml	Declares the RFC 3339 field.
devolutions-gateway/openapi/dotnet-client/src/Devolutions.Gateway.Client/Model/AgentInfo.cs	Updates the .NET model.
devolutions-gateway/openapi/dotnet-client/docs/AgentInfo.md	Updates .NET model documentation.
devolutions-gateway/openapi/doc/index.adoc	Updates API reference documentation.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 1
• Review effort level: Balanced

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[irvingouj@Devolutions (irvingoujAtDevolution)]

LGTM