chore: version 2.0.0-alpha.5 + plan-5 completion doc

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -3,6 +3,38 @@
 All notable changes to Void 2.0 are documented here.
 Format: [Keep a Changelog](https://keepachangelog.com).
 
+## [2.0.0-alpha.5] — 2026-06-01
+
+### Added (Plan 5: Companion chat)
+
+- **Right-rail companion chat** — an always-visible, per-Space AI assistant.
+  Label-led turns (YOU / Companion) with left/right alignment, live
+  tool-activity chips, streamed answers (markdown via DOMPurify), and inline
+  approve/reject draft cards. Loads its space's history on first paint via the
+  `space-active` state event.
+- **Lean agent runtime** (`lib/ai/agent/runtime.js`) on the Anthropic SDK
+  directly — no Mastra. `runTurn` drives a tool-use loop (max-iteration
+  guarded), streams text deltas, and emits `tool` / `delta` / `draft` events.
+  `callModel` is injectable (the SSE endpoint takes a fake in tests, so the
+  suite never hits the network).
+- **Extensible shared tool registry** (`lib/ai/agent/registry.js`) with four
+  v1 tools: `search` (hybrid FTS), `read`, `context` (resolves the active
+  view), and `propose_change`. Adding a tool is a one-line `registerTool`;
+  a future MCP server re-exposes the same defs.
+- **`propose_change` never applies** — it only writes a `pending_changes` row,
+  capability-gated via `canAct` (default `suggest`). Prompt-injection
+  containment is structural: a poisoned document can at most produce a draft
+  the owner must approve. Drafts render inline in chat AND in the Inbox (same
+  row; approving from either flips it).
+- **Companion API** — `GET /api/spaces/:id/companion` (history) and
+  `POST /api/spaces/:id/companion/turn` (SSE). One ambient conversation per
+  Space (`conversations.space_id` via migration 007); one assistant message
+  per turn with the tool trace + draft ids in `metadata`.
+- **`@anthropic-ai/sdk`** dependency; key resolved via the `env:`/`file:`
+  `vault_path` resolver (`lib/ai/secret.js`) — Vaultwarden swap still deferred.
+- Default model `claude-sonnet-4-6`, overridable per-agent (`agents.model`)
+  and via `ANTHROPIC_MODEL` — the seam for scope-C local personas.
+
 ## [2.0.0-alpha.4] — 2026-06-01
 
 ### Added (Plan 4: Python void-workers)