feat: support custom delimiters in the serve web workbench

.gitignore

@@ -8,3 +8,4 @@ coverage/
 /.cache
 /.tmp
 .claude/
+.playwright-mcp/

.structlint.yaml

@@ -45,6 +45,7 @@ file_naming_pattern:
     - "*.png"
     - "*.jpg"
     - "*.svg"
+    - "*.gif"
     - "README*"
     - "LICENSE*"
     - "CHANGELOG*"

COMMANDS.md

@@ -96,6 +96,7 @@ Use `serve` when you want:
 - file-level placeholder trees
 - evaluated transform previews
 - idle refresh while editing values
+- edit the delimiter pair in the browser and rescan instantly, no restart
 - saved presets per repo/template in browser IndexedDB
 - JSON import/export for presets
 

EXAMPLES.md

@@ -39,6 +39,8 @@ Open `http://127.0.0.1:17817`, then use:
 
 The workbench shows a file tree for each placeholder and evaluated transform previews such as `APP_NAME:toUpperCase -> TEMPLATETESTER`.
 
+If the repo uses a different delimiter pair, you don't need to restart the server: edit the `[[` `]]` pair shown next to the directory path and click **Set** to rescan with the new pair. It applies to Local, Clone, and Generate alike.
+
 ## Clone with SSH auth
 
 ```sh

README.md

@@ -1,7 +1,7 @@
 # YankRun
 
 <div align="center">
-  <img src="doc/banner.png" alt="YankRun" width="400">
+  <img src="doc/yankrun-logo.png" alt="YankRun" width="400">
   <p>
     <img src="https://img.shields.io/badge/Go-1.25%2B-00ADD8?style=flat-square&logo=go" alt="Go Version">
     <img src="https://img.shields.io/badge/OS-Linux%20%7C%20macOS%20%7C%20Windows-darkblue?style=flat-square&logo=windows" alt="OS Support">
@@ -11,6 +11,8 @@
 
 **Template smarter**: Clone repos, replace tokens, or template existing projects — safely, with custom delimiters that won't clash with Helm, Jinja, or any other template language.
 
+![yankrun serve workbench: scan, fill placeholders, preview, apply](doc/serve-demo.gif)
+
 ## TL;DR
 
 ```sh
@@ -47,7 +49,7 @@ yankrun template --dir ./project --input values.yaml --startDelim "<%" --endDeli
 - **Transformation functions** (`toUpperCase`, `toLowerCase`, `gsub`)
 - **Template file processing** (`.tpl` files processed and renamed)
 - **Caching** for `generate` - caches GitHub repos and template variables in `~/.yankrun/cache.yaml`
-- **Interactive workbench** (`serve`) for local/clone/generate workflows with file trees, evaluated transform previews, saved presets, and JSON import/export
+- **Interactive workbench** (`serve`) for local/clone/generate workflows with file trees, evaluated transform previews, saved presets, JSON import/export, and in-browser custom delimiters
 - **Safe terminal workflow** (`tui`) for preview-first directory templating
 
 ## Documentation
@@ -301,12 +303,15 @@ yankrun serve --dir ./my-project --addr 127.0.0.1:19090
 yankrun serve --dir ./my-project --input values.yaml --dryRun
 ```
 
+See it in action in the demo GIF at the top of this README.
+
 The workbench supports:
 
 - local scan, preview, and apply using the same replacement logic as `template`
 - clone from SSH or HTTPS repositories using the existing cloner/auth behavior
 - generate from configured templates and GitHub discovery
 - file-level placeholder trees and evaluated transform previews
+- **custom delimiters from the browser** — edit the `[[` `]]` pair next to the directory path and click **Set** to rescan with a new pair, no restart required (still `--startDelim`/`--endDelim` to set the starting pair)
 - local saved presets in IndexedDB, with JSON import/export
 
 **Flags:**

docs/AI/README.md

@@ -82,7 +82,7 @@ User Command → main.go → actions/*.go → internal/workflow → services/*.g
 | `services/cloner.go` | Git clone operations | `CloneRepository()`, `CloneRepositoryBranch()` |
 | `services/configio.go` | Config file management | `Load()`, `Save()`, `Reset()` |
 | `internal/workflow/workflow.go` | Shared workflow used by CLI/TUI/web | `ScanDir()`, `ApplyDir()`, `CloneAndApply()` |
-| `internal/web/server.go` | Embedded local workbench API | `Scan()`, `Apply()`, `Clone()`, `Generate()` |
+| `internal/web/server.go` | Embedded local workbench API | `Scan()`, `Apply()`, `Clone()`, `Generate()`, `SetDelimiters()`, `ValidateDelimiters()` |
 | `internal/tui/tui.go` | Preview-first terminal workflow | `Run()` |
 | `actions/clone.go` | Clone command handler | `Execute()` |
 | `actions/template.go` | Template command handler | `Execute()` |
@@ -92,6 +92,7 @@ User Command → main.go → actions/*.go → internal/workflow → services/*.g
 - `serve` embeds `internal/web/templates` and `internal/web/static` into the single binary.
 - The web UI supports local scan/apply, direct clone, and generate from configured templates.
 - Preview responses include file-level placeholder trees and evaluated transform previews.
+- `POST /api/delimiters` lets the browser change the active start/end delimiter pair at runtime (`Server.SetDelimiters`); it validates with `ValidateDelimiters` (rejects empty, equal, or mutually-containing pairs — an empty pair would otherwise hang the literal scan in `services/replacer.go`), updates `Server.startDelim`/`endDelim` under `Server.mu`, and returns a fresh scan. The new pair applies to Local, Clone, and Generate alike since they all read it from the same `Server.settings()`.
 - Browser IndexedDB stores saved presets locally; JSON import/export is client-side only.
 - `tui` uses the same workflow engine for local directory scan/apply and remains preview-first.
 

docs/user/README.md

@@ -348,6 +348,7 @@ The workbench provides:
 - file-level placeholder trees so you can see what will change
 - evaluated transform previews, for example `APP_NAME:toUpperCase -> MYAPP`
 - idle refresh after value edits so previews stay current
+- editable delimiters in the browser — change the `[[` `]]` pair shown next to the directory path and click **Set** to rescan the whole workbench (Local, Clone, and Generate) with the new pair, no restart needed
 - saved presets stored in browser IndexedDB, searchable by repo/template/branch/output/value keys
 - preset JSON export/import for moving saved runs between browsers
 
@@ -372,9 +373,12 @@ Typical flow:
 
 1. Start the server with an optional local directory and values file.
 2. Use **Local**, **Clone**, or **Generate** mode.
-3. Click **Preview** before applying.
-4. Edit values; evaluated previews refresh after a short idle delay.
-5. Restore prior work from the left preset rail when repeating a repo/template.
+3. If your files use a different delimiter pair, edit it next to the directory path and click **Set** to rescan — no restart needed.
+4. Click **Preview** before applying.
+5. Edit values; evaluated previews refresh after a short idle delay.
+6. Restore prior work from the left preset rail when repeating a repo/template.
+
+Delimiters set from the browser apply to every mode (Local, Clone, Generate) for the rest of the session; a rejected change (empty, identical, or overlapping delimiters) leaves the previous pair active and shows the reason in the notice banner.
 
 For clone mode:
 

internal/web/server.go

@@ -110,6 +110,11 @@ type GenerateRequest struct {
 	DryRun    bool              `json:"dryRun"`
 }
 
+type DelimitersRequest struct {
+	StartDelim string `json:"startDelim"`
+	EndDelim   string `json:"endDelim"`
+}
+
 func New(opts Options) (*Server, error) {
 	page, err := loadTemplate()
 	if err != nil {
@@ -191,18 +196,22 @@ func (s *Server) routes() {
 	s.mux.HandleFunc("/api/templates", s.handleTemplates)
 	s.mux.HandleFunc("/api/clone", s.handleClone)
 	s.mux.HandleFunc("/api/generate", s.handleGenerate)
+	s.mux.HandleFunc("/api/delimiters", s.handleSetDelimiters)
 }
 
 func (s *Server) handleIndex(w http.ResponseWriter, r *http.Request) {
 	if r.URL.Path != "/" {
 		http.NotFound(w, r)
 		return
 	}
+	s.mu.Lock()
+	dir, startDelim, endDelim := s.dir, s.startDelim, s.endDelim
+	s.mu.Unlock()
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	_ = s.page.Execute(w, map[string]any{
-		"Dir":         s.dir,
-		"StartDelim":  s.startDelim,
-		"EndDelim":    s.endDelim,
+		"Dir":         dir,
+		"StartDelim":  startDelim,
+		"EndDelim":    endDelim,
 		"ForceDryRun": s.forceDryRun,
 	})
 }
@@ -259,6 +268,67 @@ func (s *Server) handleEvaluate(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, summary, nil)
 }
 
+func (s *Server) handleSetDelimiters(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	defer r.Body.Close()
+	var req DelimitersRequest
+	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<10)).Decode(&req); err != nil {
+		http.Error(w, "invalid JSON body", http.StatusBadRequest)
+		return
+	}
+	summary, err := s.SetDelimiters(req.StartDelim, req.EndDelim)
+	if err != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		_ = json.NewEncoder(w).Encode(map[string]string{"error": err.Error()})
+		return
+	}
+	writeJSON(w, summary, nil)
+}
+
+// SetDelimiters swaps the active start/end delimiters and returns a fresh scan
+// of the current directory using them.
+func (s *Server) SetDelimiters(start, end string) (PlaceholderSummary, error) {
+	start, end, err := ValidateDelimiters(start, end)
+	if err != nil {
+		return PlaceholderSummary{}, err
+	}
+	s.mu.Lock()
+	s.startDelim = start
+	s.endDelim = end
+	s.mu.Unlock()
+	return s.Scan()
+}
+
+// ValidateDelimiters rejects delimiter pairs that would make scanning hang or
+// silently corrupt results, and returns the trimmed start/end pair to use.
+//
+// The literal scan (walkAndAnalyzeFiles in services/replacer.go) finds each
+// delimiter with strings.Index, which returns 0 without consuming any input
+// for an empty needle. If both delimiters were empty the scan loop would spin
+// forever on any non-empty file, hanging the request goroutine indefinitely -
+// so empty (or whitespace-only) delimiters are rejected outright. Requiring
+// start != end and that neither contains the other rules out the remaining
+// cases where the scan and regex-based replace paths would silently disagree
+// on where a placeholder begins and ends.
+func ValidateDelimiters(start, end string) (string, string, error) {
+	start = strings.TrimSpace(start)
+	end = strings.TrimSpace(end)
+	if start == "" || end == "" {
+		return "", "", fmt.Errorf("start and end delimiters are required")
+	}
+	if start == end {
+		return "", "", fmt.Errorf("start and end delimiters must be different")
+	}
+	if strings.Contains(start, end) || strings.Contains(end, start) {
+		return "", "", fmt.Errorf("start and end delimiters must not contain each other")
+	}
+	return start, end, nil
+}
+
 func (s *Server) Scan() (PlaceholderSummary, error) {
 	s.mu.Lock()
 	dir := s.dir
@@ -422,6 +492,8 @@ func writeJSON(w http.ResponseWriter, payload any, err error) {
 }
 
 func (s *Server) settings() workflow.TemplateSettings {
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	return workflow.TemplateSettings{
 		StartDelim:       s.startDelim,
 		EndDelim:         s.endDelim,