microsoft/agent-host-protocol spec/v0.2.0

AHP Spec v0.2.0

Repository: microsoft/agent-host-protocol

Tag: spec/v0.2.0

Published: 2026-05-28T22:44:19Z

Prerelease: no

Release notes:

[0.2.0] — 2026-05-28

Spec version: 0.2.0

This is the first version released through the unified spec release pipeline (spec/v* git tags → GitHub Release with attached schema artifacts). Changes to the protocol shape that landed under this version are tracked in the commits between spec/v0.1.0 (not yet tagged) and spec/v0.2.0. Highlights:

• Channels reorganization — every command and notification carries a top-level

channel: URI; per-channel state types and action unions live under types/channels-*/ (see PR #97 and PR #152).

• New otlp/* notifications for telemetry export

(exportLogs / exportTraces / exportMetrics).

• New session/agentChanged, session/customizationRemoved,

session/changesetsChanged, and the changeset/* action family.

• Customizations redesigned as a typed two-level tree.
• New resourceResolve (stat + realpath; throws NotFound for the

existence check) and resourceMkdir (mkdir -p semantics) requests.

• New createResourceWatch request plus the ahp-resource-watch:/

channel with the resourceWatch/changed action — long-lived file-change streams over the standard subscription mechanism.

• resourceWrite extended with mode (truncate | append | insert),

position, and ifMatch for optimistic concurrency. New Conflict (-32011) error code for stale ifMatch writes.

• The entire content-bearing resource* family is now formally

bidirectional — the methods appear in ServerCommandMap and may be initiated by either peer (matches VS Code's existing implementation).

• UserMessage._meta optional Record field for

provider-specific message metadata, mirroring the MCP _meta convention already used on MessageAttachmentBase, ToolDefinition, ToolCallBase, UsageInfo, and SessionState.