fix(create_project): substitute the whole tree, rename cmd dir, resolve branch (#42)

create_project_from_template returned files_substituted:null and produced a
non-building scaffold. Three root causes, all fixed:

1. Empty branch: /generate omits default_branch, so every SubstituteFile read
   hit an empty ref and 404'd → nothing substituted. Resolve the branch
   explicitly (re-fetch the repo; fall back to "main"). The old unit test hid
   this by mocking default_branch:"main".
2. Incomplete + rename-incapable: substitution ran over a fixed 6-file list
   that missed cmd/__PROJECT_NAME__/main.go and could not rename the
   cmd/__PROJECT_NAME__/ directory. Replace with a recursive tree walk:
   content-substitute every blob, and for any path carrying a placeholder,
   rename it (POST-create new path + delete old).
3. Stale module host: __MODULE_PATH__ used gitea.d-ma.be (the pre-rename host,
   which breaks `go mod download` downstream). Use git.d-ma.be.

Also: fail loud — if nothing was substituted, populate partial_failure instead
of returning silent success (the null that started this).

Tests rewritten to drive the tree-walk flow and assert: cmd/ rename (new path
POST + old path delete), git.d-ma.be module substitution, empty-generate-branch
fallback, and the loud-on-nothing path.

Closes #42.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/tools/create_project_from_template.go

@@ -2,10 +2,12 @@ package tools
 
 import (
 	"context"
+	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"regexp"
+	"strings"
 
 	"gitea.d-ma.be/mathias/gitea-mcp/internal/allowlist"
 	"gitea.d-ma.be/mathias/gitea-mcp/internal/gitea"
@@ -14,22 +16,22 @@ import (
 
 var nameRe = regexp.MustCompile(`^[a-z][a-z0-9-]{1,38}[a-z0-9]$`)
 
-var substitutionFiles = []string{
-	"go.mod",
-	"Taskfile.yml",
-	"Dockerfile",
-	".gitea/workflows/cd.yml",
-	"README.md",
-	".context/PROJECT.md",
-}
-
 func substitutions(owner, name string) map[string]string {
 	return map[string]string{
 		"__PROJECT_NAME__": name,
-		"__MODULE_PATH__":  "gitea.d-ma.be/" + owner + "/" + name,
+		// git.d-ma.be is the canonical module host (the gitea.d-ma.be → git.d-ma.be
+		// rename; a stale host breaks `go mod download` for downstream consumers).
+		"__MODULE_PATH__": "git.d-ma.be/" + owner + "/" + name,
 	}
 }
 
+func applyReplacements(s string, repls map[string]string) string {
+	for k, v := range repls {
+		s = strings.ReplaceAll(s, k, v)
+	}
+	return s
+}
+
 // CreateProjectFromTemplate is the exported type so tests can reference it.
 type CreateProjectFromTemplate struct {
 	c             *gitea.Client
@@ -45,7 +47,7 @@ func NewCreateProjectFromTemplate(c *gitea.Client, a *allowlist.Allowlist, tmplO
 func (t *CreateProjectFromTemplate) Descriptor() registry.ToolDescriptor {
 	return registry.ToolDescriptor{
 		Name:        "create_project_from_template",
-		Description: "Create a new project repo from a template, applying placeholder substitutions to known files. Defaults to the server-configured template; pass template_name to override (e.g. template-go-agent).",
+		Description: "Create a new project repo from a template, substituting placeholders (__PROJECT_NAME__, __MODULE_PATH__) in every file's content AND path (e.g. renaming cmd/__PROJECT_NAME__/) so the result builds. Defaults to the server-configured template; pass template_name to override (e.g. template-go-agent).",
 		InputSchema: json.RawMessage(`{
 			"type":"object",
 			"properties":{
@@ -135,21 +137,105 @@ func (t *CreateProjectFromTemplate) Call(ctx context.Context, raw json.RawMessag
 		DefaultBranch: newRepo.DefaultBranch,
 	}
 
-	// Substitute placeholders in known files (best-effort).
-	repls := substitutions(args.Owner, args.Name)
+	// The /generate response often omits default_branch — resolve it explicitly,
+	// otherwise every file read below hits an empty ref and nothing substitutes
+	// (the silent-null bug: gitea-mcp#42).
 	branch := newRepo.DefaultBranch
-	for _, path := range substitutionFiles {
-		if err := t.c.SubstituteFile(ctx, args.Owner, args.Name, branch, path, repls); err != nil {
-			// Files that don't exist in this template are silently skipped.
-			if errors.Is(err, gitea.ErrNotFound) {
-				continue
-			}
-			// Any other error halts the substitution pass with partial_failure recorded.
-			result.PartialFailure = fmt.Sprintf("%s: %v", path, err)
+	if branch == "" {
+		if r, gerr := t.c.GetRepo(ctx, args.Owner, args.Name); gerr == nil && r.DefaultBranch != "" {
+			branch = r.DefaultBranch
+		} else {
+			branch = "main"
+		}
+	}
+	result.DefaultBranch = branch
+
+	// Substitute across the WHOLE tree: content in every blob, plus a path rename
+	// for any file whose path carries a placeholder (e.g. cmd/__PROJECT_NAME__/main.go).
+	// A fixed known-files list can't rename directories or cover every templated
+	// file, which is why the old scaffold didn't build.
+	repls := substitutions(args.Owner, args.Name)
+	tree, err := t.c.GetTree(ctx, args.Owner, args.Name, branch, true)
+	if err != nil {
+		result.PartialFailure = fmt.Sprintf("tree walk (%s@%s): %v", args.Name, branch, err)
+		return textOK(result)
+	}
+
+	for _, e := range tree.Tree {
+		if e.Type != "blob" {
+			continue
+		}
+		substituted, fail := t.substituteEntry(ctx, args.Owner, args.Name, branch, e.Path, repls)
+		if fail != "" {
+			result.PartialFailure = fail
 			break
 		}
-		result.FilesSubstituted = append(result.FilesSubstituted, path)
+		if substituted != "" {
+			result.FilesSubstituted = append(result.FilesSubstituted, substituted)
+		}
+	}
+
+	// Fail loud: a scaffold that still holds placeholders does not build. Nothing
+	// substituted (with no explicit failure) means the walk found no placeholders —
+	// suspicious for a real template. Surface it instead of returning silent success.
+	if result.PartialFailure == "" && len(result.FilesSubstituted) == 0 {
+		result.PartialFailure = fmt.Sprintf("no placeholders substituted in %s@%s — verify the scaffold is not left templated", args.Name, branch)
 	}
 
 	return textOK(result)
 }
+
+// substituteEntry substitutes placeholders in one blob. If the path carries a
+// placeholder it renames the file (write new + delete old); otherwise it rewrites
+// content in place when changed. Returns a human-readable description of what was
+// substituted ("" if nothing), and a non-empty partial-failure string on error.
+func (t *CreateProjectFromTemplate) substituteEntry(ctx context.Context, owner, name, branch, path string, repls map[string]string) (substituted, failure string) {
+	newPath := applyReplacements(path, repls)
+
+	fc, err := t.c.GetFileContents(ctx, owner, name, path, branch)
+	if err != nil {
+		if errors.Is(err, gitea.ErrNotFound) {
+			return "", "" // vanished between tree walk and read; skip
+		}
+		return "", fmt.Sprintf("read %s: %v", path, err)
+	}
+	decoded, err := base64.StdEncoding.DecodeString(fc.Content)
+	if err != nil {
+		return "", fmt.Sprintf("decode %s: %v", path, err)
+	}
+	newContent := applyReplacements(string(decoded), repls)
+	renamed := newPath != path
+	changed := newContent != string(decoded)
+	if !renamed && !changed {
+		return "", "" // nothing to do
+	}
+	enc := base64.StdEncoding.EncodeToString([]byte(newContent))
+
+	if renamed {
+		if _, err := t.c.UpsertFile(ctx, owner, name, newPath, gitea.UpsertFileArgs{
+			Branch:  branch,
+			Content: enc,
+			Message: fmt.Sprintf("template: substitute + rename %s -> %s", path, newPath),
+		}); err != nil {
+			return "", fmt.Sprintf("write %s: %v", newPath, err)
+		}
+		if _, err := t.c.DeleteFile(ctx, owner, name, path, gitea.DeleteFileArgs{
+			Branch:  branch,
+			Sha:     fc.Sha,
+			Message: fmt.Sprintf("template: drop placeholder path %s", path),
+		}); err != nil {
+			return "", fmt.Sprintf("delete %s: %v", path, err)
+		}
+		return path + " -> " + newPath, ""
+	}
+
+	if _, err := t.c.UpsertFile(ctx, owner, name, path, gitea.UpsertFileArgs{
+		Branch:  branch,
+		Content: enc,
+		Message: "template: substitute placeholders",
+		Sha:     fc.Sha,
+	}); err != nil {
+		return "", fmt.Sprintf("write %s: %v", path, err)
+	}
+	return path, ""
+}