spec/v0.2.0

## [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:/<id>`
  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<string, unknown>` field for
  provider-specific message metadata, mirroring the MCP `_meta` convention
  already used on `MessageAttachmentBase`, `ToolDefinition`, `ToolCallBase`,
  `UsageInfo`, and `SessionState`.