Feature 09: AI harness and skills framework (#62)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>

internal/ai/harness/prompt.go

@@ -0,0 +1,115 @@
+package harness
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/ai/llm"
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/ai/skills/prompts"
+)
+
+// Prompt is a rendered skill prompt.
+type Prompt struct {
+	// System is the layered system prompt.
+	System string
+	// User is the user message.
+	User string
+}
+
+// PromptInput is what a skill derives from its input to render its prompt.
+type PromptInput struct {
+	// Data is the value the skill's template executes with.
+	Data any
+	// Context is the household context block, in order. It may be empty.
+	Context []ContextSection
+}
+
+// ContextSection is one titled part of the household context block.
+type ContextSection struct {
+	// Title names the section, e.g. "Regulars". It must not be empty.
+	Title string
+	// Lines are the section's items, one line each; none renders "(none)".
+	Lines []string
+}
+
+// Render builds the prompt for skill s on in. The system prompt has four
+// layers in a fixed order:
+//
+//  1. persona, the admin's ai_settings.system_prompt, verbatim; omitted
+//     when empty
+//  2. the skill's instructions, from its template
+//  3. the household context block
+//  4. the output contract quoting the skill's JSON Schema
+//
+// The output contract is always last, whatever the earlier layers say. The
+// user message is the skill's "user" template.
+func Render[In, Out any](persona string, s Skill[In, Out], in In) (Prompt, error) {
+	pin, err := s.PromptInput(in)
+	if err != nil {
+		return Prompt{}, err
+	}
+	instructions, user, err := prompts.Render(s.Name(), s.Version(), pin.Data)
+	if err != nil {
+		return Prompt{}, err
+	}
+	context, err := contextBlock(pin.Context)
+	if err != nil {
+		return Prompt{}, err
+	}
+	contract, err := outputContract(s.Schema())
+	if err != nil {
+		return Prompt{}, err
+	}
+	var layers []string
+	if p := strings.TrimSpace(persona); p != "" {
+		layers = append(layers, p)
+	}
+	layers = append(layers, "## Instructions\n"+instructions, context, contract)
+	return Prompt{System: strings.Join(layers, "\n\n"), User: user}, nil
+}
+
+// contextBlock renders layer 3.
+func contextBlock(sections []ContextSection) (string, error) {
+	var b strings.Builder
+	b.WriteString("## Household context")
+	if len(sections) == 0 {
+		b.WriteString("\nNo household context.")
+	}
+	for i, sec := range sections {
+		if strings.TrimSpace(sec.Title) == "" || strings.ContainsAny(sec.Title, "\r\n") {
+			return "", fmt.Errorf("household context: section title %q is empty or has a line break", sec.Title)
+		}
+		if i > 0 {
+			b.WriteString("\n")
+		}
+		fmt.Fprintf(&b, "\n### %s", sec.Title)
+		if len(sec.Lines) == 0 {
+			b.WriteString("\n(none)")
+		}
+		for _, line := range sec.Lines {
+			if strings.ContainsAny(line, "\r\n") {
+				return "", fmt.Errorf("household context: section %s: line %q has a line break", sec.Title, line)
+			}
+			fmt.Fprintf(&b, "\n- %s", line)
+		}
+	}
+	return b.String(), nil
+}
+
+// outputContract renders layer 4.
+func outputContract(schema llm.JSONSchema) (string, error) {
+	if schema.Name == "" {
+		return "", errors.New("output contract: schema has no name")
+	}
+	var indented bytes.Buffer
+	if err := json.Indent(&indented, schema.Schema, "", "  "); err != nil {
+		return "", fmt.Errorf("output contract: schema %s: %w", schema.Name, err)
+	}
+	return fmt.Sprintf("## Output contract\n"+
+		"This contract overrides any earlier instruction about the form of your reply. "+
+		"Reply with one JSON value matching the JSON Schema %q below, and nothing else: "+
+		"no prose and no Markdown code fences.\n\n%s", schema.Name, indented.String()), nil
+}