feat: Phase F-3 + F-4 — exp backoff + agent tool surface (batch 1)

F-3 refinements:
- internal/inbound: replace fixed 3s reconnect wait with exponential
  backoff (1s → 60s, ×2, reset when prior session lasted >30s); proxy
  for "healthy" vs "flapping" and avoids hot reconnect loops when the
  server is sick

F-4 agent tool surface (port of openclaw plugin's tools.ts):
- internal/tools/tools.go (~370 LOC): Registry binds Deps {Client,
  Tokens, Identities} and exposes 8 agent-facing tools:
    fabric-send-message     post a normal message to any channel
    fabric-send-sys-msg     post a kind=sys message (bypasses turn engine)
    fabric-channel-list     list channels visible in a guild
    fabric-guild-list       list guilds the agent is in
    fabric-message-history  paginate channel messages by seq
    fabric-channel-set-purpose  PATCH the channel's purpose
    fabric-channel          fetch metadata + members for one channel
    fabric-canvas           get/share/update/remove channel canvas
- internal/tools/contracts.go: static ToolContract list — kept in sync
  with install.sh's manifest emitter
- Every agent-scoped tool requires agent_id in input args (Plexum SDK
  doesn't propagate calling agent id through CallTool today)
- guild_node_id defaults to agent's first guild for fabric-send-message

internal/fabric/client.go: new REST methods needed by tools —
PostSystemMessage, CreateChannel, CloseChannel, JoinChannel,
LeaveChannel, SetChannelPurpose, GetCanvas, ShareCanvas, UpdateCanvas,
RemoveCanvas, SyncCommands.

cmd/plexum-fabric-channel-plugin/main.go:
- Manifest declares the tool surface via tools.New(...).Contracts()
- CallTool dispatches "send" to handleSend (outbound for channel
  manager), everything else to tools.Registry.Handler(name)

scripts/install.sh:
- Manifest tools[] now lists all 9 tools with schemas — matches what
  internal/tools/contracts.go advertises

Live verified against running Fabric stack:
  $ plexum plugin-call fabric-guild-list '{"agent_id":"fabrictester"}'
    → "guilds for agent fabrictester (1): test-guild2 @ http://localhost:7003"
  $ plexum plugin-call fabric-channel-list '{...,"guild_node_id":"test-guild2"}'
    → 2 channels listed
  $ plexum plugin-call fabric-message-history '{...,"limit":5}'
    → 5 messages with timestamps + authors

F-5+ deferred:
- create-{chat,work,report,discussion}-channel (batch 2)
- sub-discussion family (state store + 3 tools)
- presence-sync + command-sync
- attachments

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

cmd/plexum-fabric-channel-plugin/main.go

@@ -29,6 +29,7 @@ import (
 	"git.hangman-lab.top/hzhang/Plexum-fabric-channel-plugin/internal/identity"
 	"git.hangman-lab.top/hzhang/Plexum-fabric-channel-plugin/internal/inbound"
 	"git.hangman-lab.top/hzhang/Plexum-fabric-channel-plugin/internal/tokens"
+	"git.hangman-lab.top/hzhang/Plexum-fabric-channel-plugin/internal/tools"
 )
 
 // HostConfig is the plugin's own config at
@@ -51,6 +52,7 @@ type fabricPlugin struct {
 	byFabric   config.ByFabricChannel
 	client     *fabric.Client
 	tokens     *tokens.Cache
+	tools      *tools.Registry
 
 	// Goroutine handle for the inbound supervisor. Cancelled on
 	// plugin shutdown (we don't have an explicit shutdown signal in
@@ -66,12 +68,10 @@ type fabricPlugin struct {
 }
 
 func (p *fabricPlugin) Manifest() plugin.Manifest {
-	// Manifest channels are populated dynamically from channels/*.json
-	// at startup: the operator adds a channels/<name>.json + restarts
-	// the gateway, and the matching ChannelContract entry surfaces here.
-	// Both halves needed because Plexum's host registry reads the
-	// manifest's channel names too.
 	channels := p.dynamicChannelContracts()
+	// Tool surface = the agent-facing tool family (port of openclaw
+	// plugin's tools.ts, F-4). The "send" outbound is also there for
+	// the host's channel manager.
 	return plugin.Manifest{
 		Name:       config.PluginName,
 		Version:    "0.1.0",
@@ -79,21 +79,7 @@ func (p *fabricPlugin) Manifest() plugin.Manifest {
 		Executable: "plexum-fabric-channel-plugin",
 		Contracts: plugin.Contracts{
 			Channels: channels,
-			Tools: []plugin.ToolContract{
-				{
-					Name:        "send",
-					Description: "Post a plain-text message to the bound Fabric channel as the agent user.",
-					InputSchema: json.RawMessage(`{
-						"type": "object",
-						"properties": {
-							"channel_name": {"type": "string"},
-							"session_id":   {"type": "string"},
-							"message":      {"type": "string"}
-						},
-						"required": ["channel_name", "message"]
-					}`),
-				},
-			},
+			Tools:    tools.New(tools.Deps{}).Contracts(),
 		},
 	}
 }
@@ -169,6 +155,11 @@ func (p *fabricPlugin) Init(ctx context.Context, host plugin.HostAPI) error {
 		return p.client.AgentLogin(loginCtx, entry.FabricAPIKey)
 	})
 
+	// Agent-facing tool surface (port of openclaw's tools.ts).
+	p.tools = tools.New(tools.Deps{
+		Client: p.client, Tokens: p.tokens, Identities: p.identities,
+	})
+
 	host.Log("info", "fabric channel plugin initialized", map[string]any{
 		"center":            p.cfg.CenterAPIBase,
 		"identity_path":     idPath,
@@ -284,11 +275,22 @@ func (p *fabricPlugin) warmSessions(ctx context.Context) error {
 	return firstErr
 }
 
-// CallTool handles the "send" outbound tool.
+// CallTool dispatches by tool name. "send" is the host-side channel
+// outbound (driven by Plexum's channel manager); everything else
+// delegates to the tools.Registry built at init time.
 func (p *fabricPlugin) CallTool(ctx context.Context, name string, input json.RawMessage) (plugin.ToolResult, error) {
-	if name != "send" {
-		return plugin.ToolResult{}, fmt.Errorf("unknown tool: %s", name)
+	if name == "send" {
+		return p.handleSend(ctx, input)
 	}
+	if handler := p.tools.Handler(name); handler != nil {
+		return handler(ctx, input)
+	}
+	return plugin.ToolResult{}, fmt.Errorf("unknown tool: %s", name)
+}
+
+// handleSend implements the "send" outbound tool: posts the assistant
+// reply via Fabric REST as the agent bound to the Plexum channel name.
+func (p *fabricPlugin) handleSend(ctx context.Context, input json.RawMessage) (plugin.ToolResult, error) {
 	var args struct {
 		ChannelName string `json:"channel_name"`
 		SessionID   string `json:"session_id"`
@@ -304,7 +306,6 @@ func (p *fabricPlugin) CallTool(ctx context.Context, name string, input json.Raw
 		"channel_name": args.ChannelName, "len": len(args.Message),
 	})
 
-	// Find the binding for this plexum channel name.
 	var binding *config.FabricBinding
 	for i := range p.bindings {
 		if p.bindings[i].PlexumChannelName == args.ChannelName {
@@ -316,19 +317,12 @@ func (p *fabricPlugin) CallTool(ctx context.Context, name string, input json.Raw
 		return errResult("unknown plexum channel: " + args.ChannelName), nil
 	}
 
-	// Resolve the bound agent's session (may need refresh — F-2 will
-	// add a proper TTL + background refresh; for F-1 we re-login lazily
-	// if the cache is empty).
 	sess, err := p.sessionFor(ctx, binding.AgentID)
 	if err != nil {
 		return errResult("session for agent " + binding.AgentID + ": " + err.Error()), nil
 	}
 
-	// Pick the guild endpoint + token for the target guild_node_id.
-	var (
-		endpoint string
-		token    string
-	)
+	var endpoint, token string
 	for _, g := range sess.Guilds {
 		if g.NodeID == binding.FabricGuildNodeID {
 			endpoint = g.Endpoint