fix(platform): /github-installation-token returns 501 on missing config (#388)

When GITHUB_APP_ID/INSTALLATION_ID/PRIVATE_KEY_FILE are unset (Gitea-
canonical deployment or suspended GitHub App org), generateAppInstallation
Token() returns "required" — a permanent configuration error, not a
transient one. Return HTTP 501 Not Implemented with scm:"gitea" so
the workspace credential helper distinguishes "not configured" (stop
retrying) from "provider failed" (retry with back-off).

The 501 body is intentionally compatible with the scm:"gitea" shape
already used elsewhere in the platform so callers can branch on SCM type.

workspace-server/internal/handlers/github_token.go

@@ -49,6 +49,7 @@ import (
 	"net/http"
 	"os"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/Molecule-AI/molecule-monorepo/platform/pkg/provisionhook"
@@ -98,7 +99,17 @@ func (h *GitHubTokenHandler) GetInstallationToken(c *gin.Context) {
 		token, expiresAt, err := generateAppInstallationToken()
 		if err != nil {
 			log.Printf("[github] fallback token generation failed: %v", err)
-			c.JSON(http.StatusInternalServerError, gin.H{"error": "token refresh failed"})
+			// #388: GITHUB_APP_ID/INSTALLATION_ID unset → Gitea-canonical deployment
+			// or suspended org. Return 501 so callers (credential helper / gh auth)
+			// know this is not-implemented vs a transient error.
+			if strings.Contains(err.Error(), "required") {
+				c.JSON(http.StatusNotImplemented, gin.H{
+					"error": "GitHub integration not configured",
+					"scm":   "gitea",
+				})
+			} else {
+				c.JSON(http.StatusInternalServerError, gin.H{"error": "token refresh failed"})
+			}
 			return
 		}
 		c.JSON(http.StatusOK, gin.H{"token": token, "expires_at": expiresAt})

workspace-server/internal/handlers/github_token_test.go

@@ -78,11 +78,12 @@ func TestGitHubToken_NilRegistry(t *testing.T) {
 // Post-#960/#1101 the handler now falls back to direct env-based App
 // token generation (GITHUB_APP_ID / INSTALLATION_ID / PRIVATE_KEY_FILE)
 // when no registered provider matches. In the test environment those
-// env vars are unset, so the fallback fails with 500 "token refresh
-// failed" — a clean retryable signal for the workspace credential
-// helper. Previously this path returned 404; the new 500 matches the
-// ProviderError shape so callers don't have to branch on "missing
-// provider" vs "provider failed".
+// env vars are unset, so the fallback fails with 501 "not implemented"
+// with scm:"gitea" — signals a Gitea-canonical or suspended-org
+// deployment where GitHub integration is not configured (#388).
+// Previously this path returned 404; 501 distinguishes "not configured"
+// (caller should stop retrying) from "provider failed" (caller should
+// retry with back-off).
 func TestGitHubToken_NoTokenProvider(t *testing.T) {
 	reg := provisionhook.NewRegistry()
 	reg.Register(&mockMutatorOnly{name: "other-plugin"})
@@ -91,12 +92,15 @@ func TestGitHubToken_NoTokenProvider(t *testing.T) {
 
 	h.GetInstallationToken(c)
 
-	if w.Code != http.StatusInternalServerError {
-		t.Fatalf("expected 500 (env-based fallback fails with unset GITHUB_APP_* vars), got %d: %s",
+	if w.Code != http.StatusNotImplemented {
+		t.Fatalf("expected 501 (env-based fallback fails with unset GITHUB_APP_* vars), got %d: %s",
 			w.Code, w.Body.String())
 	}
-	if !strings.Contains(w.Body.String(), "token refresh failed") {
-		t.Errorf("expected body to contain 'token refresh failed', got: %s", w.Body.String())
+	if !strings.Contains(w.Body.String(), "GitHub integration not configured") {
+		t.Errorf("expected body to contain 'GitHub integration not configured', got: %s", w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), `"scm":"gitea"`) {
+		t.Errorf("expected body to contain 'scm:gitea', got: %s", w.Body.String())
 	}
 }