feat: multi-chat sessions

CHANGELOG.md

@@ -47,11 +47,26 @@ Spec version: `0.4.0`
   Resolving or re-anchoring an annotation no longer requires replacing the
   whole annotation via `annotations/set`. Omitted fields are left unchanged;
   the annotation's `entries`, `id`, and `_meta` are never touched.
+- `ahp-chat:` channel for per-chat conversation state; `SessionState.chats[]` catalog; `SessionState.defaultChat?` input-routing hint; `ChatOrigin` provenance union; `createChat` command.
+- `ChatSummary.workingDirectory?` — optional per-chat working directory. When absent, chats inherit the session's `workingDirectory`. Enables agent-swarm patterns where multiple chats in one session operate on independent worktrees.
+- Three discrete chat-catalog actions on the session channel — `session/chatAdded` (upsert by `summary.resource`), `session/chatRemoved`, and `session/chatUpdated` (partial-update with `Partial<ChatSummary>`) — mirroring the root-channel `root/sessionAdded` / `root/sessionRemoved` / `root/sessionSummaryChanged` pattern.
 - `RootState` now carries an optional `_meta` property bag for
   implementation-defined metadata about the agent host itself, mirroring the
   MCP `_meta` convention. A well-known `hostBuild` key may carry build
   information (version, commit, date) about the program hosting the agent host.
 
+### Changed
+
+- `fetchTurns` and `completions` now target an `ahp-chat:` channel; `PROTOCOL_VERSION` bumped to `0.4.0`.
+- `ChatState` is now **flat** — the previous `summary: ChatSummary` sub-object has been replaced by inlined `resource` / `title` / `status` / `activity` / `modifiedAt` / `model` / `agent` / `origin` / `workingDirectory` fields. `ChatSummary` remains as the standalone catalog entry on `SessionState.chats`.
+- `ChatSummary.modifiedAt` and `ChatState.modifiedAt` are now ISO 8601 strings instead of numeric milliseconds.
+- `SessionSummary` now documents how its aggregate fields (`status`, `activity`, `modifiedAt`) are derived from the session's chats, including `InputNeeded` / `Error` promotion when any chat raises the flag.
+
+### Removed
+
+- `SessionState.turns`, `SessionState.activeTurn`, `SessionState.steeringMessage`, `SessionState.queuedMessages`, `SessionState.inputRequests` (moved to `ChatState`).
+- `session/chatsChanged` full-replacement action (replaced by `session/chatAdded` / `session/chatRemoved` / `session/chatUpdated`).
+
 ## [0.3.0] — 2026-06-05
 
 Spec version: `0.3.0`

clients/go/CHANGELOG.md

@@ -44,13 +44,23 @@ tag whose matching `## [X.Y.Z]` heading is missing from this file.
   resending its entries. Handled by the annotations reducer (no-op on unknown
   id).
 
-### Added
-
+- `ahp-chat:` channel for per-chat conversation state; `SessionState.chats[]` catalog; `SessionState.defaultChat?` input-routing hint; `ChatOrigin` provenance union; `createChat` / `disposeChat` commands.
+- `ChatSummary.WorkingDirectory` — optional per-chat working directory. Falls back to the session's `WorkingDirectory` when absent.
+- Three discrete chat-catalog actions on the session channel — `SessionChatAddedAction` (upsert by `Summary.Resource`), `SessionChatRemovedAction`, and `SessionChatUpdatedAction` (partial-update payload).
 - `RootState` now exposes an optional `_meta` property bag (`Meta
   map[string]json.RawMessage`) for implementation-defined agent-host metadata,
   such as a well-known `hostBuild` key carrying the host's build
   version/commit/date.
 
+### Changed
+
+- `ChatState` is now flat — the previous embedded `Summary` has been replaced with inlined `Resource` / `Title` / `Status` / `Activity` / `ModifiedAt` / `Model` / `Agent` / `Origin` / `WorkingDirectory` fields. `ChatSummary` remains as the standalone catalog entry on `SessionState.Chats`.
+- `ChatSummary.ModifiedAt` and `ChatState.ModifiedAt` are now ISO 8601 `string` values instead of integer milliseconds.
+
+### Removed
+
+- `SessionChatsChangedAction` (replaced by the three discrete chat-catalog actions above).
+
 ## [0.3.0] — 2026-06-05
 
 Implements AHP 0.3.0.
@@ -96,11 +106,14 @@ Implements AHP 0.3.0.
 
 ### Changed
 
+- Reducers split into per-chat and session-aggregate handlers to match the multi-chat protocol shape.
+- `fetchTurns` and `completions` now target an `ahp-chat:` channel; `PROTOCOL_VERSION` bumped to `0.4.0`.
 - Renamed the `ChangesetSummary` type to `Changeset`. The on-the-wire shape is unchanged.
 - Moved the `changesets` catalogue from `SessionSummary` to `SessionState`. The `session/changesetsChanged` action now updates `state.changesets` directly instead of `state.summary.changesets`.
 
 ### Removed
 
+- `SessionState.turns`, `SessionState.activeTurn`, `SessionState.steeringMessage`, `SessionState.queuedMessages`, `SessionState.inputRequests` (moved to `ChatState`).
 - Removed the `additions`, `deletions`, and `files` fields from `ChangesetSummary`. Aggregate counts now live on `SessionSummary.changes`; per-changeset views derive their own totals from `ChangesetState.files`.
 
 ### Changed

clients/go/ahp/multi_host_state_mirror.go

@@ -22,12 +22,13 @@ type HostedResourceKey struct {
 // The mirror has no opinion about how snapshots are kept in sync with
 // the server — that's the consumer's job, typically by feeding action
 // envelopes from a [HostSubscriptionEvent] stream through the matching
-// [ApplyActionToRoot] / [ApplyActionToSession] / [ApplyActionToTerminal]
-// reducer and re-storing the result.
+// [ApplyActionToRoot] / [ApplyActionToSession] / [ApplyActionToChat] /
+// [ApplyActionToTerminal] reducer and re-storing the result.
 type MultiHostStateMirror struct {
 	mu      sync.RWMutex
 	roots   map[string]ahptypes.RootState
 	session map[HostedResourceKey]ahptypes.SessionState
+	chat    map[HostedResourceKey]ahptypes.ChatState
 	term    map[HostedResourceKey]ahptypes.TerminalState
 	changes map[HostedResourceKey]ahptypes.ChangesetState
 }
@@ -37,6 +38,7 @@ func NewMultiHostStateMirror() *MultiHostStateMirror {
 	return &MultiHostStateMirror{
 		roots:   make(map[string]ahptypes.RootState),
 		session: make(map[HostedResourceKey]ahptypes.SessionState),
+		chat:    make(map[HostedResourceKey]ahptypes.ChatState),
 		term:    make(map[HostedResourceKey]ahptypes.TerminalState),
 		changes: make(map[HostedResourceKey]ahptypes.ChangesetState),
 	}
@@ -74,6 +76,22 @@ func (m *MultiHostStateMirror) Session(hostID string, uri ahptypes.URI) (ahptype
 	return v, ok
 }
 
+// PutChat stores a chat snapshot under (hostID, uri).
+func (m *MultiHostStateMirror) PutChat(hostID string, uri ahptypes.URI, c ahptypes.ChatState) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.chat[HostedResourceKey{hostID, uri}] = c
+}
+
+// Chat returns the chat snapshot at (hostID, uri), or
+// (zero, false) if none is recorded.
+func (m *MultiHostStateMirror) Chat(hostID string, uri ahptypes.URI) (ahptypes.ChatState, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	v, ok := m.chat[HostedResourceKey{hostID, uri}]
+	return v, ok
+}
+
 // PutTerminal stores a terminal snapshot under (hostID, uri).
 func (m *MultiHostStateMirror) PutTerminal(hostID string, uri ahptypes.URI, t ahptypes.TerminalState) {
 	m.mu.Lock()
@@ -117,6 +135,11 @@ func (m *MultiHostStateMirror) DropHost(hostID string) {
 			delete(m.session, k)
 		}
 	}
+	for k := range m.chat {
+		if k.HostID == hostID {
+			delete(m.chat, k)
+		}
+	}
 	for k := range m.term {
 		if k.HostID == hostID {
 			delete(m.term, k)
@@ -136,6 +159,7 @@ func (m *MultiHostStateMirror) DropResource(hostID string, uri ahptypes.URI) {
 	defer m.mu.Unlock()
 	k := HostedResourceKey{hostID, uri}
 	delete(m.session, k)
+	delete(m.chat, k)
 	delete(m.term, k)
 	delete(m.changes, k)
 }