feat(FN-3816): add merger self-healing for missing workspace and environmen

Implements merger self-healing with a missing workspace entry detector, bootstrap recovery path, and environment fault retry handling, plus supporting tests for merge error recovery and verification utilities, alongside documentation updates.

Fusion-Task-Id: FN-3816

packages/engine/src/verification-utils.ts

@@ -30,6 +30,11 @@ export interface VerificationResult {
   buildResult?: VerificationCommandResult;
   allPassed: boolean;
   failedCommand?: string;
+  environmentFault?: {
+    kind: "missing-workspace-entry";
+    packageName: string;
+    recovered: boolean;
+  };
 }
 
 // ── Process group exec ─────────────────────────────────────────────────
@@ -173,6 +178,23 @@ export function truncateWithEllipsis(text: string, maxChars: number): string {
   return `${text.slice(0, maxChars)}\n... (truncated)`;
 }
 
+export function detectMissingWorkspaceEntry(stderr: string, stdout?: string): { packageName: string } | null {
+  const pattern = /Failed to resolve entry for package\s+"(@fusion\/[a-z0-9-]+|@fusion-plugin-examples\/[a-z0-9-]+)"/;
+  const stderrMatch = stderr.match(pattern);
+  if (stderrMatch) {
+    return { packageName: stderrMatch[1] };
+  }
+
+  if (stdout) {
+    const stdoutMatch = stdout.match(pattern);
+    if (stdoutMatch) {
+      return { packageName: stdoutMatch[1] };
+    }
+  }
+
+  return null;
+}
+
 function truncateOutput(output: string): string {
   if (output.length <= VERIFICATION_LOG_MAX_CHARS) return output;
   return `... output truncated to last ${VERIFICATION_LOG_MAX_CHARS} characters ...\n${output.slice(-VERIFICATION_LOG_MAX_CHARS)}`;