feat: Phase F-5+F-7 — command-sync + sub-discussion + channel-create tools

Bundles the remaining "agent does things in Fabric" surface, skipping
presence-sync (Plexum's state machine isn't 1:1 with HF status semantics)
and attachments (Plexum has no media pipeline yet) — both deferred.

internal/subdisc/ (~140 LOC + 5 tests): persistent KV at
<profile>/state/plugin-kv/fabric-sub-discussions.json
- Entry: SubChannelID, HostAgentID, HostUserID, GuestUserIDs,
  HostGuide, GuestGuide, CallbackGuildNodeID, CallbackChannelID, CreatedAt
- Open / Lookup / LookupForHost (host-enforcement) / Add / Remove / All
- atomic tmp+rename persistence; corrupt file = start empty

internal/tools/tools.go — 7 new tools:
- create-chat-channel       (xType=general)
- create-work-channel       (xType=work)
- create-report-channel     (xType=report)
- create-discussion-channel (xType=discuss)
- discussion-complete       (post summary + close channel)
- create-sub-discussion     (create + invite + KV store + greeting)
- close-sub-discussion      (host-only; posts callback to parent + closes)

internal/fabric/client.go: CreateChannel / CloseChannel /
JoinChannel / LeaveChannel / SetChannelPurpose / Canvas CRUD /
SyncCommands (added in earlier F-4 commit; reused here)

cmd/plexum-fabric-channel-plugin/main.go:
- subdisc.Store opened from DefaultPath at init; passed into tools.Deps
- HostConfig adds commands_sync_key + sync_commands (defaults
  ["new","stop"]) — F-5 command-sync to every (agent,guild) pair at
  init when key is set; silently skips when omitted
- syncCommandsToGuilds: best-effort PUT per guild, logs per-guild
  outcome

scripts/install.sh: manifest tools[] expanded to 16 entries
(9 from F-4 + 7 new). create-channel variants share a schema shape.

Live verified:
  $ plexum plugin-call create-chat-channel \
      '{"agent_id":"fabrictester","guild_node_id":"test-guild2",
        "name":"plexum-f7-smoke","is_public":true}'
    → "created general channel plexum-f7-smoke (id=6315e636-...)"
  $ plexum plugin-call fabric-channel-list ...
    → 3 channels listed including the new one

F-6 (attachments) + F-5b (presence-sync) + F-8 (coalesce) deliberately
deferred — see DEV-NOTES.

Tests: 5 new in internal/subdisc (27 total in this repo).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/tools/contracts.go

@@ -136,4 +136,77 @@ var allContracts = []plugin.ToolContract{
 			"required": ["agent_id", "guild_node_id", "channel_id", "op"]
 		}`),
 	},
+	// ---- channel creation (4 x-types share the same shape) ----
+	createChannelContract("create-chat-channel", "Create a chat channel (xType=general)."),
+	createChannelContract("create-work-channel", "Create a work channel (xType=work)."),
+	createChannelContract("create-report-channel", "Create a report channel (xType=report)."),
+	createChannelContract("create-discussion-channel", "Create a discussion channel (xType=discuss)."),
+	{
+		Name:        "discussion-complete",
+		Description: "Post a summary then close the channel — concludes a discussion.",
+		InputSchema: json.RawMessage(`{
+			"type": "object",
+			"properties": {
+				"agent_id":      {"type": "string"},
+				"guild_node_id": {"type": "string"},
+				"channel_id":    {"type": "string"},
+				"summary":       {"type": "string"}
+			},
+			"required": ["agent_id", "guild_node_id", "channel_id", "summary"]
+		}`),
+	},
+	{
+		Name:        "create-sub-discussion",
+		Description: "Spawn a new sub-discussion channel with the calling agent as host + invited guests; remembered in plugin KV so close-sub-discussion can post the callback to the parent channel.",
+		InputSchema: json.RawMessage(`{
+			"type": "object",
+			"properties": {
+				"agent_id":          {"type": "string"},
+				"guild_node_id":     {"type": "string"},
+				"name":              {"type": "string"},
+				"guest_user_ids":    {"type": "array", "items": {"type": "string"}},
+				"host_guide":        {"type": "string"},
+				"guest_guide":       {"type": "string"},
+				"parent_channel_id":{"type": "string"},
+				"greeting":          {"type": "string"},
+				"x_type":            {"type": "string", "enum": ["discuss","work","report","general"]}
+			},
+			"required": ["agent_id", "guild_node_id", "name", "parent_channel_id"]
+		}`),
+	},
+	{
+		Name:        "close-sub-discussion",
+		Description: "Close a sub-discussion the calling agent originally created; posts a callback message to the parent channel.",
+		InputSchema: json.RawMessage(`{
+			"type": "object",
+			"properties": {
+				"agent_id":       {"type": "string"},
+				"sub_channel_id":{"type": "string"},
+				"summary":        {"type": "string"}
+			},
+			"required": ["agent_id", "sub_channel_id"]
+		}`),
+	},
+}
+
+// createChannelContract returns the shared schema for the four
+// create-*-channel tool variants.
+func createChannelContract(name, description string) plugin.ToolContract {
+	return plugin.ToolContract{
+		Name: name, Description: description,
+		InputSchema: json.RawMessage(`{
+			"type": "object",
+			"properties": {
+				"agent_id":         {"type": "string"},
+				"guild_node_id":    {"type": "string"},
+				"name":             {"type": "string"},
+				"is_public":        {"type": "boolean"},
+				"member_user_ids": {"type": "array", "items": {"type": "string"}},
+				"listeners":        {"type": "array", "items": {"type": "string"}},
+				"on_duty":          {"type": "string"},
+				"purpose":          {"type": "string"}
+			},
+			"required": ["agent_id", "guild_node_id", "name"]
+		}`),
+	}
 }