fix(go-agent): align agent debug input form with Python (#16654)

## Summary

- derive Go Agent debug input forms from prompt variable references
instead of Agent meta fields
- seed `sys.*` debug params into `CanvasState.Sys` so single-component
debug resolves prompt variables like Python
- restore Agent test-run parity for form rendering and debug execution

## Tests

- `go test ./internal/agent/component -run
'TestAgent_(GetInputForm_UsesPromptReferences|GetInputForm_DeduplicatesPromptReferences|Meta_DefaultsToEmpty|Reset_NoTools)$'`
- `go test ./internal/handler -run
'Test(DebugComponent_SeedsSysInputsIntoCanvasState|DebugComponent_HappyPath_Begin|GetComponentInputForm_HappyPath)$'`

AFTER:
<img width="669" height="456" alt="image"
src="https://github.com/user-attachments/assets/4fd86559-aafc-4027-91ae-6e666137ee1b"
/>

internal/agent/component/agent.go

@@ -15,6 +15,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"sort"
 	"strings"
 
 	einotool "github.com/cloudwego/eino/components/tool"
@@ -282,17 +283,16 @@ func chunksFromState(ctx context.Context) []prompts.CitationSource {
 	return out
 }
 
-// GetInputForm aggregates the Agent's own meta-schema with each
-// sub-tool's input form. Mirrors Python's `Agent.get_input_form`.
+// GetInputForm aggregates the Agent's own user-callable parameters with each
+// sub-tool's input form. Mirrors Python's `Agent.get_input_form`, which
+// returns a flat field-definition map keyed by input name.
 //
 // Today the sub-tool input forms are aggregated via an optional
 // `InputForm() map[string]any` method on the eino tool (when tools
 // implement it); tools that don't expose a structured input form
 // are skipped silently.
 func (c *AgentComponent) GetInputForm() map[string]any {
-	out := map[string]any{
-		"self": c.param.Meta,
-	}
+	out := extractAgentPromptInputForm(c.param.SystemPrompt, c.param.UserPrompt)
 	tools, err := buildAgentTools(c.param)
 	if err != nil {
 		return out
@@ -314,6 +314,41 @@ func (c *AgentComponent) GetInputForm() map[string]any {
 	return out
 }
 
+func extractAgentPromptInputForm(systemPrompt, userPrompt string) map[string]any {
+	out := map[string]any{}
+	seen := map[string]struct{}{}
+	matches := append(runtime.VarRefPattern.FindAllStringSubmatch(systemPrompt, -1), runtime.VarRefPattern.FindAllStringSubmatch(userPrompt, -1)...)
+	for _, match := range matches {
+		if len(match) < 2 {
+			continue
+		}
+		key := strings.TrimSpace(match[1])
+		if key == "" {
+			continue
+		}
+		if _, ok := seen[key]; ok {
+			continue
+		}
+		seen[key] = struct{}{}
+		out[key] = map[string]any{
+			"type":     "line",
+			"name":     key,
+			"optional": false,
+		}
+	}
+	return out
+}
+
+func sortedAgentPromptInputKeys(systemPrompt, userPrompt string) []string {
+	form := extractAgentPromptInputForm(systemPrompt, userPrompt)
+	keys := make([]string, 0, len(form))
+	for key := range form {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
 // Reset calls Reset on every sub-tool that implements the Resetter
 // interface. Mirrors Python's per-tool reset() — useful for clearing
 // per-invocation state (caches, scratch buffers) between calls.

internal/agent/component/agent_meta_test.go

@@ -22,33 +22,43 @@ import (
 	"github.com/cloudwego/eino/schema"
 )
 
-// TestAgent_GetInputForm_IncludesSelfMeta: GetInputForm returns the
-// Agent's own meta-schema under the "self" key, even when no tools
-// are configured.
-func TestAgent_GetInputForm_IncludesSelfMeta(t *testing.T) {
+// TestAgent_GetInputForm_UsesPromptReferences verifies the Agent input form
+// follows Python's behavior: it is derived from prompt template references.
+func TestAgent_GetInputForm_UsesPromptReferences(t *testing.T) {
 	c := NewAgentComponent(AgentParam{
-		ModelID: "echo",
-		Meta: AgentMeta{
-			Name:        "research_agent",
-			Description: "Performs multi-step research",
-			Parameters: map[string]AgentMetaParam{
-				"user_prompt": {Type: "string", Description: "The question", Required: true},
-			},
-		},
+		ModelID:      "echo",
+		SystemPrompt: "Use {sys.query} and {{sys.user_id}} to answer.",
+		UserPrompt:   "Question: {sys.query}",
 	})
 	form := c.GetInputForm()
 	if form == nil {
 		t.Fatal("GetInputForm returned nil")
 	}
-	self, ok := form["self"].(AgentMeta)
+	if _, ok := form["self"]; ok {
+		t.Fatalf("form unexpectedly contains synthetic self key: %#v", form["self"])
+	}
+	queryField, ok := form["sys.query"].(map[string]any)
 	if !ok {
-		t.Fatalf("form['self'] type=%T, want AgentMeta", form["self"])
+		t.Fatalf("form['sys.query'] type=%T, want map[string]any", form["sys.query"])
 	}
-	if self.Name != "research_agent" {
-		t.Errorf("Name=%q, want research_agent", self.Name)
+	if queryField["type"] != "line" {
+		t.Errorf("sys.query.type=%v, want line", queryField["type"])
 	}
-	if self.Parameters["user_prompt"].Type != "string" {
-		t.Errorf("user_prompt type=%q, want string", self.Parameters["user_prompt"].Type)
+	if queryField["name"] != "sys.query" {
+		t.Errorf("sys.query.name=%v, want 'sys.query'", queryField["name"])
+	}
+	if queryField["optional"] != false {
+		t.Errorf("sys.query.optional=%v, want false", queryField["optional"])
+	}
+	userIDField, ok := form["sys.user_id"].(map[string]any)
+	if !ok {
+		t.Fatalf("form['sys.user_id'] type=%T, want map[string]any", form["sys.user_id"])
+	}
+	if userIDField["name"] != "sys.user_id" {
+		t.Errorf("sys.user_id.name=%v, want sys.user_id", userIDField["name"])
+	}
+	if userIDField["optional"] != false {
+		t.Errorf("sys.user_id.optional=%v, want false", userIDField["optional"])
 	}
 }
 
@@ -59,17 +69,27 @@ func TestAgent_Reset_NoTools(t *testing.T) {
 	c.Reset() // should not panic
 }
 
-// TestAgent_Meta_DefaultsToEmpty: zero-value AgentParam.Meta is the
-// empty AgentMeta struct (not a nil map dereference).
+// TestAgent_GetInputForm_DeduplicatesPromptReferences ensures repeated refs
+// across system and user prompts collapse to one input field.
+func TestAgent_GetInputForm_DeduplicatesPromptReferences(t *testing.T) {
+	c := NewAgentComponent(AgentParam{
+		ModelID:      "echo",
+		SystemPrompt: "A {sys.query}",
+		UserPrompt:   "B {{sys.query}}",
+	})
+	keys := sortedAgentPromptInputKeys(c.param.SystemPrompt, c.param.UserPrompt)
+	if len(keys) != 1 || keys[0] != "sys.query" {
+		t.Fatalf("keys=%v, want [sys.query]", keys)
+	}
+}
+
+// TestAgent_Meta_DefaultsToEmpty: prompts without variable references yield
+// an empty input-form map.
 func TestAgent_Meta_DefaultsToEmpty(t *testing.T) {
 	c := NewAgentComponent(AgentParam{ModelID: "echo"})
 	form := c.GetInputForm()
-	self, ok := form["self"].(AgentMeta)
-	if !ok {
-		t.Fatalf("form['self'] type=%T, want AgentMeta", form["self"])
-	}
-	if self.Name != "" || self.Description != "" {
-		t.Errorf("expected empty meta, got %+v", self)
+	if len(form) != 0 {
+		t.Fatalf("expected empty input form, got %+v", form)
 	}
 }