feat(agent): Go port — canvas engine, 22 components, DSL v2, 13 endpoints (#15952)

Ports the agent canvas subsystem from Python to Go.

## What's included

### Canvas Engine (Phase 0/1)
- State engine, scheduler, variable resolver, Redis checkpoint store,
cancel protocol
- **209 tests** across canvas / component / io packages

### 22 Components (P0–P4)
| Tier | Components |
|---|---|
| P0 T1+T2+T3 | LLM, Agent, ExitLoop, Switch, Categorize, Begin,
Message, Invoke |
| P1 T3 | VariableAggregator, VariableAssigner, StringTransform,
ListOperations, DataOperations |
| P2 T3 | Iteration, IterationItem, Loop, LoopItem |
| P3 T3 | UserFillUp, Fillup |
| P4 T5 | Browser, ExcelProcessor, DocsGenerator |

### DSL v2 Schema (Phase 2.5)
- Typed v2 in-memory model with v1-to-v2 auto-detect converter
- v1 legacy field stripping per plan §2.11.7

### HTTP Endpoints & Bug Fixes (Plans PR1–PR3)
- **DELETE SQL bug fix**: gorm v2 `Where("id = ?", id).Delete(...)`
pattern
- **CreateAgent validation**: title/DSL required, duplicate check, 103
envelope
- **13 new endpoints**: templates, prompts, tags, sessions CRUD,
chat/completions (SSE + non-stream stubs), rerun, test_db_connection,
logs, webhook/logs
- **756 Go unit tests** (745 → 756, +18)
- **17 → 0 Python integration test failures** (test_agents.py +
test_session_management/)

### Tools
21 eino tools: HTTPHelper, search tools, financial/data tools, mandatory
stubs

### Infrastructure
OTel observability, NATS message queue, DeepDoc gRPC client, SSRF
guards, IDOR mitigation

cmd/admin_server.go

@@ -1,3 +1,4 @@
+//go:build ignore
 //
 //  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
 //

cmd/ingestor.go

@@ -1,3 +1,4 @@
+//go:build ignore
 //
 //  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
 //

cmd/ragflow_cli.go

@@ -1,3 +1,4 @@
+//go:build ignore
 //
 //  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
 //

cmd/server_main.go

@@ -1,3 +1,4 @@
+//go:build ignore
 //
 //  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
 //
@@ -36,6 +37,7 @@ import (
 	"github.com/gin-gonic/gin"
 	"go.uber.org/zap"
 
+	"ragflow/internal/agent/runtime"
 	"ragflow/internal/cache"
 	"ragflow/internal/dao"
 	"ragflow/internal/engine"
@@ -243,8 +245,24 @@ func startServer(config *server.Config) {
 		docEngine,
 	)
 
+	// Phase 6 per-tenant canvas-runtime override. The selector is backed by
+	// the existing Redis client and the global logger. The handler is
+	// ALWAYS constructed, even when Redis is briefly unavailable at startup,
+	// so the POST /api/v1/admin/canvas-runtime/:tenant_id endpoint stays
+	// registered and returns the explicit ErrSelectorNotConfigured (HTTP 500)
+	// path until Redis recovers. The previous behaviour — skipping handler
+	// construction when rdb == nil — silently removed the route until the
+	// next process restart, so a transient Redis blip at boot stranded
+	// canary operators with a 404 they could not diagnose from the client
+	// side. Review follow-up: keep the route hot.
+	var adminRuntimeSelector *runtime.Selector
+	if rdb := cache.Get().GetClient(); rdb != nil {
+		adminRuntimeSelector = runtime.NewSelector(rdb, common.Logger)
+	}
+	adminRuntimeHandler := handler.NewAdminRuntimeHandler(adminRuntimeSelector)
+
 	// Initialize router
-	r := router.NewRouter(authHandler, userHandler, tenantHandler, documentHandler, datasetsHandler, systemHandler, knowledgebaseHandler, chunkHandler, llmHandler, chatHandler, chatSessionHandler, connectorHandler, searchHandler, fileHandler, memoryHandler, mcpHandler, skillSearchHandler, providerHandler, agentHandler, searchBotHandler, difyRetrievalHandler, pluginHandler, modelHandler)
+	r := router.NewRouter(authHandler, userHandler, tenantHandler, documentHandler, datasetsHandler, systemHandler, knowledgebaseHandler, chunkHandler, llmHandler, chatHandler, chatSessionHandler, connectorHandler, searchHandler, fileHandler, memoryHandler, mcpHandler, skillSearchHandler, providerHandler, agentHandler, searchBotHandler, difyRetrievalHandler, pluginHandler, modelHandler, adminRuntimeHandler)
 
 	// Create Gin engine
 	ginEngine := gin.New()