Add validation.commitStatus setting to gate GitHub commit status posting

post-commit now skips silently unless validation.commitStatus is true in
.chunk/config.json. Enable with: chunk config set validation.commitStatus true

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: webster

internal/cmd/config.go

@@ -62,7 +62,7 @@ func newConfigSetCmd() *cobra.Command {
 	return &cobra.Command{
 		Use:   "set <key> <value>",
 		Short: "Set a config value",
-		Long:  "Set a config value. Use 'chunk auth set <provider>' to store credentials with validation.\n\nUser keys: model\nProject keys: orgID, validation.sidecarImage",
+		Long:  "Set a config value. Use 'chunk auth set <provider>' to store credentials with validation.\n\nUser keys: model\nProject keys: orgID, validation.sidecarImage, validation.commitStatus",
 		Args:  cobra.ExactArgs(2),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			io := iostream.FromCmd(cmd)
@@ -85,6 +85,11 @@ func newConfigSetCmd() *cobra.Command {
 						projCfg.Validation = &config.ValidationConfig{}
 					}
 					projCfg.Validation.SidecarImage = value
+				case "validation.commitStatus":
+					if projCfg.Validation == nil {
+						projCfg.Validation = &config.ValidationConfig{}
+					}
+					projCfg.Validation.CommitStatus = value == "true"
 				default:
 					return fmt.Errorf("internal: unhandled project config key %q", key)
 				}
@@ -98,7 +103,7 @@ func newConfigSetCmd() *cobra.Command {
 			if !config.ValidConfigKeys[key] {
 				return &userError{
 					msg:    fmt.Sprintf("Unknown config key: %q.", key),
-					detail: "Supported keys: model, orgID, validation.sidecarImage.",
+					detail: "Supported keys: model, orgID, validation.sidecarImage, validation.commitStatus.",
 					errMsg: fmt.Sprintf("unknown config key %q", key),
 				}
 			}

internal/cmd/validate.go

@@ -168,12 +168,7 @@ func newValidateCmd() *cobra.Command {
 			}
 
 			results, execErr := runValidate(cmd.Context(), workDir, name, inlineCmd, save, sidecarID, identityFile, workdir, allRemote, cfg, statusFn, streams)
-
-			if results != nil {
-				if treeSHA, treeErr := gitutil.ComputeTreeSHA(workDir); treeErr == nil {
-					_ = validate.SaveResults(treeSHA, results)
-				}
-			}
+			saveValidateResults(workDir, results)
 
 			if hook != nil {
 				maxAttempts := cfg.StopHookMaxAttempts
@@ -343,6 +338,11 @@ func newPostCommitCmd() *cobra.Command {
 				}
 			}
 
+			projCfg, cfgErr := config.LoadProjectConfig(workDir)
+			if cfgErr != nil || projCfg.Validation == nil || !projCfg.Validation.CommitStatus {
+				return nil
+			}
+
 			treeOut, err := exec.Command("git", "-C", workDir, "rev-parse", "HEAD^{tree}").Output()
 			if err != nil {
 				return fmt.Errorf("resolve HEAD tree: %w", err)
@@ -524,6 +524,15 @@ func resolveOrCreateSidecarID(ctx context.Context, sidecarID *string, orgID, ima
 	return nil
 }
 
+func saveValidateResults(workDir string, results []validate.CommandResult) {
+	if len(results) == 0 {
+		return
+	}
+	if treeSHA, err := gitutil.ComputeTreeSHA(workDir); err == nil {
+		_ = validate.SaveResults(treeSHA, results)
+	}
+}
+
 func mapValidateError(err error) error {
 	if errors.Is(err, validate.ErrNotConfigured) {
 		return &userError{

internal/config/config.go

@@ -268,4 +268,5 @@ var ValidConfigKeys = map[string]bool{
 var ValidProjectConfigKeys = map[string]bool{
 	"orgID":                   true,
 	"validation.sidecarImage": true,
+	"validation.commitStatus": true,
 }

internal/config/project.go

@@ -48,6 +48,7 @@ type VCSConfig struct {
 // ValidationConfig holds project-level defaults for validation behaviour.
 type ValidationConfig struct {
 	SidecarImage string `json:"sidecarImage,omitempty"`
+	CommitStatus bool   `json:"commitStatus,omitempty"`
 }
 
 // ProjectConfig is the per-repo configuration stored in .chunk/config.json.