Render captured prompt templates without reloading sources

internal/configuration/prompts.go

@@ -333,3 +333,15 @@ func (state *loaded) GetPromptDefinition(ctx context.Context, id, version string
 	definition, _, err := state.GetPromptSnapshot(ctx, id, version)
 	return definition, err
 }
+
+// GetCompiledTemplates returns construction-time parses for one exact prompt.
+func (state *loaded) GetCompiledTemplates(id, version string) (prompt.CompiledTemplates, bool) {
+	if state == nil {
+		return prompt.CompiledTemplates{}, false
+	}
+	entry := state.prompts[id][version]
+	if entry == nil {
+		return prompt.CompiledTemplates{}, false
+	}
+	return prompt.CompiledTemplates{Session: entry.session, Messages: entry.messages}, true
+}

internal/engine/engine.go

@@ -131,7 +131,7 @@ func New(cfg Config, options Options) (*Engine, error) {
 		reader = artifact.NewCompositeReader()
 	}
 
-	return &Engine{runner: usecase.NewRunnerWithRepairer(snapshot, snapshot, snapshot, reader, prompt.NewGoRenderer(), client, validator, usecase.NewDefaultOutputRepairer(client), manager, defaultRetries)}, nil
+	return &Engine{runner: usecase.NewRunnerWithRepairer(snapshot, snapshot, snapshot, reader, prompt.NewCompiledRenderer(snapshot), client, validator, usecase.NewDefaultOutputRepairer(client), manager, defaultRetries)}, nil
 }
 
 func validateSourceFS(fsys fs.FS, root string) error {

internal/prompt/go_renderer.go

@@ -21,12 +21,20 @@ var (
 
 const artifactTextChunkSize = 64 * 1024
 
-type goRenderer struct{}
+type goRenderer struct {
+	templates TemplateLookup
+}
 
 func NewGoRenderer() Renderer {
 	return &goRenderer{}
 }
 
+// NewCompiledRenderer renders definitions using templates captured with the
+// configuration snapshot. Per-call clones bind request-specific input helpers.
+func NewCompiledRenderer(templates TemplateLookup) Renderer {
+	return &goRenderer{templates: templates}
+}
+
 func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefinition, inputs map[string]*domain.Artifact, vars map[string]string) (*domain.RenderedPrompt, error) {
 	if err := ctx.Err(); err != nil {
 		return nil, err
@@ -49,11 +57,30 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 	funcs := template.FuncMap{
 		"input": resolver.resolve,
 	}
+	var compiled CompiledTemplates
+	if r.templates != nil {
+		var found bool
+		compiled, found = r.templates.GetCompiledTemplates(definition.ID, definition.Version)
+		if !found || len(compiled.Messages) != len(definition.Templates) {
+			return nil, fmt.Errorf("%w: captured templates are unavailable", ErrRenderFailure)
+		}
+	}
 
 	if err := ctx.Err(); err != nil {
 		return nil, err
 	}
-	sessionID, err := renderSessionID(ctx, definition.SessionID, funcs, vars)
+	var sessionID string
+	var err error
+	if r.templates != nil {
+		if definition.SessionID != "" {
+			if compiled.Session == nil {
+				return nil, fmt.Errorf("%w: captured session template is unavailable", ErrRenderFailure)
+			}
+			sessionID, err = renderCompiledSessionID(ctx, compiled.Session, funcs, vars)
+		}
+	} else {
+		sessionID, err = renderSessionID(ctx, definition.SessionID, funcs, vars)
+	}
 	if err != nil {
 		return nil, err
 	}
@@ -76,7 +103,19 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 		if err := ctx.Err(); err != nil {
 			return nil, err
 		}
-		tmpl, parseErr := parseTemplate(fmt.Sprintf("msg_%d", i), tmplMsg.Content, funcs)
+		var tmpl *template.Template
+		var parseErr error
+		if r.templates != nil {
+			if compiled.Messages[i] == nil {
+				return nil, fmt.Errorf("%w: captured message template is unavailable", ErrRenderFailure)
+			}
+			tmpl, parseErr = compiled.Messages[i].Clone()
+			if parseErr == nil {
+				tmpl.Funcs(funcs)
+			}
+		} else {
+			tmpl, parseErr = parseTemplate(fmt.Sprintf("msg_%d", i), tmplMsg.Content, funcs)
+		}
 		if err := ctx.Err(); err != nil {
 			return nil, err
 		}
@@ -174,7 +213,25 @@ func renderSessionID(ctx context.Context, raw string, funcs template.FuncMap, va
 	if parseErr != nil {
 		return "", fmt.Errorf("%w: session_id: %v", ErrInvalidTemplate, parseErr)
 	}
+	return executeSessionTemplate(ctx, tmpl, vars)
+}
 
+func renderCompiledSessionID(ctx context.Context, compiled *template.Template, funcs template.FuncMap, vars map[string]string) (string, error) {
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
+	tmpl, err := compiled.Clone()
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
+	if err != nil {
+		return "", fmt.Errorf("%w: session_id: %v", ErrRenderFailure, err)
+	}
+	tmpl.Funcs(funcs)
+	return executeSessionTemplate(ctx, tmpl, vars)
+}
+
+func executeSessionTemplate(ctx context.Context, tmpl *template.Template, vars map[string]string) (string, error) {
 	if err := ctx.Err(); err != nil {
 		return "", err
 	}

internal/prompt/template.go

@@ -2,6 +2,18 @@ package prompt
 
 import "text/template"
 
+// CompiledTemplates is the immutable parsed template set for one captured
+// prompt. Callers must not mutate its templates after handing it to a renderer.
+type CompiledTemplates struct {
+	Session  *template.Template
+	Messages []*template.Template
+}
+
+// TemplateLookup provides parsed templates for a captured prompt identity.
+type TemplateLookup interface {
+	GetCompiledTemplates(id, version string) (CompiledTemplates, bool)
+}
+
 // CompileTemplate checks static syntax with the same grammar and function
 // names as rendering, without evaluating request inputs or variables.
 func CompileTemplate(name, raw string) (*template.Template, error) {