diff --git a/apps/cli/src/commands/results/studio-config.ts b/apps/cli/src/commands/results/studio-config.ts
index 4be3c56a..b9777e59 100644
--- a/apps/cli/src/commands/results/studio-config.ts
+++ b/apps/cli/src/commands/results/studio-config.ts
@@ -21,8 +21,8 @@
 import { existsSync, mkdirSync, readFileSync, writeFileSync } from 'node:fs';
 import path from 'node:path';
 
-import { DEFAULT_THRESHOLD } from '@agentv/core';
-import { parse as parseYaml, stringify as stringifyYaml } from 'yaml';
+import { DEFAULT_THRESHOLD, parseYamlValue } from '@agentv/core';
+import { stringify as stringifyYaml } from 'yaml';
 
 export interface StudioConfig {
   threshold: number;
@@ -47,7 +47,7 @@ export function loadStudioConfig(agentvDir: string): StudioConfig {
   }
 
   const raw = readFileSync(configPath, 'utf-8');
-  const parsed = parseYaml(raw);
+  const parsed = parseYamlValue(raw);
 
   if (!parsed || typeof parsed !== 'object') {
     return { ...DEFAULTS };
@@ -89,7 +89,7 @@ export function saveStudioConfig(agentvDir: string, config: StudioConfig): void
   let existing: Record<string, unknown> = {};
   if (existsSync(configPath)) {
     const raw = readFileSync(configPath, 'utf-8');
-    const parsed = parseYaml(raw);
+    const parsed = parseYamlValue(raw);
     if (parsed && typeof parsed === 'object' && !Array.isArray(parsed)) {
       existing = parsed as Record<string, unknown>;
     }
diff --git a/packages/core/src/benchmarks.ts b/packages/core/src/benchmarks.ts
index 39fa6b3c..a6036c69 100644
--- a/packages/core/src/benchmarks.ts
+++ b/packages/core/src/benchmarks.ts
@@ -32,8 +32,9 @@
 import { existsSync, mkdirSync, readFileSync, readdirSync, statSync, writeFileSync } from 'node:fs';
 import path from 'node:path';
 
-import { parse as parseYaml, stringify as stringifyYaml } from 'yaml';
+import { stringify as stringifyYaml } from 'yaml';
 
+import { parseYamlValue } from './evaluation/yaml-loader.js';
 import { getAgentvConfigDir } from './paths.js';
 
 // ── Types ───────────────────────────────────────────────────────────────
@@ -101,7 +102,7 @@ export function loadBenchmarkRegistry(): BenchmarkRegistry {
   }
   try {
     const raw = readFileSync(registryPath, 'utf-8');
-    const parsed = parseYaml(raw);
+    const parsed = parseYamlValue(raw) as { benchmarks?: unknown } | null | undefined;
     if (!parsed || typeof parsed !== 'object') {
       return { benchmarks: [] };
     }
diff --git a/packages/core/src/evaluation/loaders/case-file-loader.ts b/packages/core/src/evaluation/loaders/case-file-loader.ts
index 0568d132..a14265fa 100644
--- a/packages/core/src/evaluation/loaders/case-file-loader.ts
+++ b/packages/core/src/evaluation/loaders/case-file-loader.ts
@@ -1,11 +1,11 @@
 import { readFile, readdir, stat } from 'node:fs/promises';
 import path from 'node:path';
 import fg from 'fast-glob';
-import { parse as parseYaml } from 'yaml';
 
 import { interpolateEnv } from '../interpolation.js';
 import type { JsonObject, JsonValue } from '../types.js';
 import { isJsonObject } from '../types.js';
+import { parseYamlValue } from '../yaml-loader.js';
 
 const ANSI_YELLOW = '\u001b[33m';
 const ANSI_RESET = '\u001b[0m';
@@ -38,7 +38,7 @@ function isGlobPattern(filePath: string): boolean {
  * Expects the file to contain an array of test objects.
  */
 function parseYamlCases(content: string, filePath: string): JsonObject[] {
-  const raw = parseYaml(content) as unknown;
+  const raw = parseYamlValue(content);
   const parsed = interpolateEnv(raw, process.env);
   if (!Array.isArray(parsed)) {
     throw new Error(
@@ -206,7 +206,7 @@ export async function loadCasesFromDirectory(dirPath: string): Promise<JsonObjec
       throw new Error(`Cannot read case file: ${caseFilePath}\n  ${message}`);
     }
 
-    const raw = parseYaml(content) as unknown;
+    const raw = parseYamlValue(content);
     const parsed = interpolateEnv(raw, process.env);
     if (!isJsonObject(parsed)) {
       throw new Error(
diff --git a/packages/core/src/evaluation/loaders/config-loader.ts b/packages/core/src/evaluation/loaders/config-loader.ts
index 53386977..939afbc8 100644
--- a/packages/core/src/evaluation/loaders/config-loader.ts
+++ b/packages/core/src/evaluation/loaders/config-loader.ts
@@ -1,8 +1,8 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
 import { interpolateEnv } from '../interpolation.js';
+import { parseYamlValue } from '../yaml-loader.js';
 import type {
   EvalTargetRef,
   FailOnError,
@@ -77,7 +77,7 @@ export async function loadConfig(
 
     try {
       const rawConfig = await readFile(configPath, 'utf8');
-      const parsed = interpolateEnv(parse(rawConfig), process.env) as unknown;
+      const parsed = interpolateEnv(parseYamlValue(rawConfig), process.env) as unknown;
 
       if (!isJsonObject(parsed)) {
         logWarning(`Invalid .agentv/config.yaml format at ${configPath}`);
diff --git a/packages/core/src/evaluation/loaders/eval-yaml-transpiler.ts b/packages/core/src/evaluation/loaders/eval-yaml-transpiler.ts
index a023fc92..306b4806 100644
--- a/packages/core/src/evaluation/loaders/eval-yaml-transpiler.ts
+++ b/packages/core/src/evaluation/loaders/eval-yaml-transpiler.ts
@@ -9,7 +9,8 @@
 
 import { readFileSync } from 'node:fs';
 import path from 'node:path';
-import { parse } from 'yaml';
+
+import { parseYamlValue } from '../yaml-loader.js';
 
 // ---------------------------------------------------------------------------
 // evals.json output types
@@ -510,7 +511,7 @@ export function transpileEvalYaml(suite: unknown, source = 'EVAL.yaml'): Transpi
  */
 export function transpileEvalYamlFile(evalYamlPath: string): TranspileResult {
   const content = readFileSync(evalYamlPath, 'utf8');
-  const parsed = parse(content) as unknown;
+  const parsed = parseYamlValue(content);
   return transpileEvalYaml(parsed, path.basename(evalYamlPath));
 }
 
diff --git a/packages/core/src/evaluation/loaders/grader-parser.ts b/packages/core/src/evaluation/loaders/grader-parser.ts
index de4acf49..165de6ff 100644
--- a/packages/core/src/evaluation/loaders/grader-parser.ts
+++ b/packages/core/src/evaluation/loaders/grader-parser.ts
@@ -1,9 +1,9 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
 import { normalizePreprocessorType } from '../content-preprocessor.js';
 import { interpolateEnv } from '../interpolation.js';
+import { parseYamlValue } from '../yaml-loader.js';
 import type { ToolTrajectoryExpectedItem, ToolTrajectoryGraderConfig } from '../trace.js';
 import type {
   ContentPreprocessorConfig,
@@ -183,7 +183,7 @@ async function loadAssertionTemplateEntries(
   }
 
   const content = await readFile(resolved.resolvedPath, 'utf8');
-  const parsed = interpolateEnv(parse(content), process.env) as unknown;
+  const parsed = interpolateEnv(parseYamlValue(content), process.env) as unknown;
   if (!isJsonObject(parsed)) {
     throw new Error(
       `Invalid assertion template file in '${evalId}': ${resolved.resolvedPath} (expected a YAML object with an assertions array)`,
diff --git a/packages/core/src/evaluation/loaders/jsonl-parser.ts b/packages/core/src/evaluation/loaders/jsonl-parser.ts
index 288d0bd2..bf5b6860 100644
--- a/packages/core/src/evaluation/loaders/jsonl-parser.ts
+++ b/packages/core/src/evaluation/loaders/jsonl-parser.ts
@@ -1,12 +1,12 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
 import micromatch from 'micromatch';
-import { parse as parseYaml } from 'yaml';
 
 import { collectResolvedInputFilePaths } from '../input-message-utils.js';
 import { interpolateEnv } from '../interpolation.js';
 import type { EvalTest, JsonObject, JsonValue, TestMessage } from '../types.js';
 import { isJsonObject, isTestMessage } from '../types.js';
+import { parseYamlValue } from '../yaml-loader.js';
 import { buildSearchRoots, fileExists, resolveToAbsolutePath } from './file-resolver.js';
 import {
   coerceEvaluator,
@@ -92,7 +92,7 @@ async function loadSidecarMetadata(jsonlPath: string, verbose: boolean): Promise
 
   try {
     const content = await readFile(sidecarPath, 'utf8');
-    const parsed = interpolateEnv(parseYaml(content), process.env) as unknown;
+    const parsed = interpolateEnv(parseYamlValue(content), process.env) as unknown;
 
     if (!isJsonObject(parsed)) {
       logWarning(`Invalid sidecar metadata format in ${sidecarPath}`);
diff --git a/packages/core/src/evaluation/providers/copilot-session-discovery.ts b/packages/core/src/evaluation/providers/copilot-session-discovery.ts
index f6d58372..03bdebdd 100644
--- a/packages/core/src/evaluation/providers/copilot-session-discovery.ts
+++ b/packages/core/src/evaluation/providers/copilot-session-discovery.ts
@@ -16,7 +16,8 @@
 import { readFile, readdir, stat } from 'node:fs/promises';
 import { homedir } from 'node:os';
 import path from 'node:path';
-import { parse as parseYaml } from 'yaml';
+
+import { parseYamlValue } from '../yaml-loader.js';
 
 export interface CopilotSession {
   readonly sessionId: string;
@@ -60,7 +61,7 @@ export async function discoverCopilotSessions(opts?: DiscoverOptions): Promise<C
 
     try {
       const workspaceContent = await readFile(workspacePath, 'utf8');
-      const workspace = (parseYaml(workspaceContent) ?? {}) as Record<string, unknown>;
+      const workspace = (parseYamlValue(workspaceContent) ?? {}) as Record<string, unknown>;
 
       const cwd = String(workspace.cwd ?? '');
 
diff --git a/packages/core/src/evaluation/providers/targets-file.ts b/packages/core/src/evaluation/providers/targets-file.ts
index 7e7e366f..f17729db 100644
--- a/packages/core/src/evaluation/providers/targets-file.ts
+++ b/packages/core/src/evaluation/providers/targets-file.ts
@@ -1,8 +1,8 @@
 import { constants } from 'node:fs';
 import { access, readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
+import { parseYamlValue } from '../yaml-loader.js';
 import { TARGETS_SCHEMA_V2 } from './types.js';
 import type { TargetDefinition } from './types.js';
 
@@ -62,7 +62,7 @@ export async function readTargetDefinitions(
   }
 
   const raw = await readFile(absolutePath, 'utf8');
-  const parsed = parse(raw) as unknown;
+  const parsed = parseYamlValue(raw);
 
   if (!isRecord(parsed)) {
     throw new Error(`targets.yaml at ${absolutePath} must be a YAML object with a 'targets' field`);
diff --git a/packages/core/src/evaluation/validation/cases-validator.ts b/packages/core/src/evaluation/validation/cases-validator.ts
index d88a7a23..acea351d 100644
--- a/packages/core/src/evaluation/validation/cases-validator.ts
+++ b/packages/core/src/evaluation/validation/cases-validator.ts
@@ -1,7 +1,7 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
+import { parseYamlValue } from '../yaml-loader.js';
 import type { ValidationError, ValidationResult } from './types.js';
 
 type JsonValue = string | number | boolean | null | JsonObject | JsonArray;
@@ -26,7 +26,7 @@ export async function validateCasesFile(filePath: string): Promise<ValidationRes
   let parsed: unknown;
   try {
     const content = await readFile(absolutePath, 'utf8');
-    parsed = parse(content);
+    parsed = parseYamlValue(content);
   } catch (error) {
     errors.push({
       severity: 'error',
diff --git a/packages/core/src/evaluation/validation/config-validator.ts b/packages/core/src/evaluation/validation/config-validator.ts
index 50d55f60..df695f12 100644
--- a/packages/core/src/evaluation/validation/config-validator.ts
+++ b/packages/core/src/evaluation/validation/config-validator.ts
@@ -1,6 +1,6 @@
 import { readFile } from 'node:fs/promises';
-import { parse } from 'yaml';
 
+import { parseYamlValue } from '../yaml-loader.js';
 import type { ValidationError, ValidationResult } from './types.js';
 
 /**
@@ -11,7 +11,7 @@ export async function validateConfigFile(filePath: string): Promise<ValidationRe
 
   try {
     const content = await readFile(filePath, 'utf8');
-    const parsed = parse(content) as unknown;
+    const parsed = parseYamlValue(content);
 
     // Check if parsed content is an object
     if (typeof parsed !== 'object' || parsed === null) {
diff --git a/packages/core/src/evaluation/validation/eval-validator.ts b/packages/core/src/evaluation/validation/eval-validator.ts
index 4aec7132..be91f3b5 100644
--- a/packages/core/src/evaluation/validation/eval-validator.ts
+++ b/packages/core/src/evaluation/validation/eval-validator.ts
@@ -1,10 +1,10 @@
 import { readFile, readdir, stat } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
 import { interpolateEnv } from '../interpolation.js';
 import { loadCasesFromDirectory, loadCasesFromFile } from '../loaders/case-file-loader.js';
 import { isGraderKind } from '../types.js';
+import { parseYamlValue } from '../yaml-loader.js';
 import type { ValidationError, ValidationResult } from './types.js';
 
 type JsonValue = string | number | boolean | null | JsonObject | JsonArray;
@@ -165,7 +165,7 @@ export async function validateEvalFile(filePath: string): Promise<ValidationResu
   let parsed: unknown;
   try {
     const content = await readFile(absolutePath, 'utf8');
-    parsed = interpolateEnv(parse(content), process.env);
+    parsed = interpolateEnv(parseYamlValue(content), process.env);
   } catch (error) {
     errors.push({
       severity: 'error',
@@ -514,7 +514,7 @@ async function validateWorkspaceConfig(
 
   try {
     const workspaceContent = await readFile(workspacePath, 'utf8');
-    const parsedWorkspace = interpolateEnv(parse(workspaceContent), process.env);
+    const parsedWorkspace = interpolateEnv(parseYamlValue(workspaceContent), process.env);
     if (!isObject(parsedWorkspace)) {
       errors.push({
         severity: 'error',
diff --git a/packages/core/src/evaluation/validation/file-reference-validator.ts b/packages/core/src/evaluation/validation/file-reference-validator.ts
index f6773ff1..805beb09 100644
--- a/packages/core/src/evaluation/validation/file-reference-validator.ts
+++ b/packages/core/src/evaluation/validation/file-reference-validator.ts
@@ -1,8 +1,8 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
 import { buildSearchRoots, findGitRoot, resolveFileReference } from '../file-utils.js';
+import { parseYamlValue } from '../yaml-loader.js';
 import type { ValidationError } from './types.js';
 
 type JsonValue = string | number | boolean | null | JsonObject | JsonArray;
@@ -40,7 +40,7 @@ export async function validateFileReferences(
   let parsed: unknown;
   try {
     const content = await readFile(absolutePath, 'utf8');
-    parsed = parse(content);
+    parsed = parseYamlValue(content);
   } catch {
     // Parse errors are already caught by eval-validator
     return errors;
diff --git a/packages/core/src/evaluation/validation/file-type.ts b/packages/core/src/evaluation/validation/file-type.ts
index 464610c6..261d4e45 100644
--- a/packages/core/src/evaluation/validation/file-type.ts
+++ b/packages/core/src/evaluation/validation/file-type.ts
@@ -1,7 +1,7 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
+import { parseYamlValue } from '../yaml-loader.js';
 import type { FileType } from './types.js';
 
 const SCHEMA_EVAL_V2 = 'agentv-eval-v2';
@@ -18,7 +18,7 @@ const SCHEMA_CONFIG_V2 = 'agentv-config-v2';
 export async function detectFileType(filePath: string): Promise<FileType> {
   try {
     const content = await readFile(filePath, 'utf8');
-    const parsed = parse(content) as unknown;
+    const parsed = parseYamlValue(content);
 
     // YAML array root → cases file (array of test case objects)
     if (Array.isArray(parsed)) {
diff --git a/packages/core/src/evaluation/validation/targets-validator.ts b/packages/core/src/evaluation/validation/targets-validator.ts
index 7d50eb73..5e1ce818 100644
--- a/packages/core/src/evaluation/validation/targets-validator.ts
+++ b/packages/core/src/evaluation/validation/targets-validator.ts
@@ -1,6 +1,5 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
 import {
   CLI_PLACEHOLDERS,
@@ -8,6 +7,7 @@ import {
   findDeprecatedCamelCaseTargetWarnings,
 } from '../providers/targets.js';
 import { KNOWN_PROVIDERS, PROVIDER_ALIASES } from '../providers/types.js';
+import { parseYamlValue } from '../yaml-loader.js';
 import type { ValidationError, ValidationResult } from './types.js';
 
 type JsonValue = string | number | boolean | null | JsonObject | JsonArray;
@@ -280,7 +280,7 @@ export async function validateTargetsFile(filePath: string): Promise<ValidationR
   let parsed: unknown;
   try {
     const content = await readFile(absolutePath, 'utf8');
-    parsed = parse(content);
+    parsed = parseYamlValue(content);
   } catch (error) {
     errors.push({
       severity: 'error',
diff --git a/packages/core/src/evaluation/validation/workspace-path-validator.ts b/packages/core/src/evaluation/validation/workspace-path-validator.ts
index a5879568..7fd0f0ea 100644
--- a/packages/core/src/evaluation/validation/workspace-path-validator.ts
+++ b/packages/core/src/evaluation/validation/workspace-path-validator.ts
@@ -1,7 +1,7 @@
 import { access, readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
+import { parseYamlValue } from '../yaml-loader.js';
 import type { ValidationError } from './types.js';
 
 type JsonValue = string | number | boolean | null | JsonObject | JsonArray;
@@ -38,7 +38,7 @@ export async function validateWorkspacePaths(
   let parsed: unknown;
   try {
     const content = await readFile(absolutePath, 'utf8');
-    parsed = parse(content);
+    parsed = parseYamlValue(content);
   } catch {
     // Parse errors are already caught by eval-validator
     return errors;
@@ -55,7 +55,7 @@ export async function validateWorkspacePaths(
     const workspaceFilePath = path.resolve(evalDir, workspaceRaw);
     try {
       const wsContent = await readFile(workspaceFilePath, 'utf8');
-      const wsParsed = parse(wsContent);
+      const wsParsed = parseYamlValue(wsContent);
       if (isObject(wsParsed)) {
         const wsDir = path.dirname(workspaceFilePath);
         await validateWorkspaceObject(wsParsed, wsDir, absolutePath, 'workspace', errors);
diff --git a/packages/core/src/evaluation/workspace/deps-scanner.ts b/packages/core/src/evaluation/workspace/deps-scanner.ts
index 0378273d..285b9436 100644
--- a/packages/core/src/evaluation/workspace/deps-scanner.ts
+++ b/packages/core/src/evaluation/workspace/deps-scanner.ts
@@ -17,10 +17,10 @@
  */
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
-import { parse } from 'yaml';
 
 import { interpolateEnv } from '../interpolation.js';
 import type { RepoCheckout, RepoClone, RepoSource } from '../types.js';
+import { parseYamlValue } from '../yaml-loader.js';
 import { parseRepoCheckout, parseRepoClone, parseRepoSource } from './repo-config-parser.js';
 
 /** A single git repo dependency discovered from eval files. */
@@ -115,7 +115,7 @@ interface RawRepo {
 
 async function extractReposFromEvalFile(filePath: string): Promise<RawRepo[]> {
   const content = await readFile(filePath, 'utf8');
-  const parsed = interpolateEnv(parse(content), process.env);
+  const parsed = interpolateEnv(parseYamlValue(content), process.env);
   if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) return [];
   const obj = parsed as Record<string, unknown>;
   const evalFileDir = path.dirname(path.resolve(filePath));
@@ -148,7 +148,7 @@ async function extractReposFromWorkspaceRaw(raw: unknown, evalFileDir: string):
     // External workspace file reference
     const workspaceFilePath = path.resolve(evalFileDir, raw);
     const content = await readFile(workspaceFilePath, 'utf8');
-    const parsed = interpolateEnv(parse(content), process.env);
+    const parsed = interpolateEnv(parseYamlValue(content), process.env);
     if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) return [];
     return extractReposFromObject(parsed as Record<string, unknown>);
   }
diff --git a/packages/core/src/evaluation/yaml-loader.ts b/packages/core/src/evaluation/yaml-loader.ts
new file mode 100644
index 00000000..02d56845
--- /dev/null
+++ b/packages/core/src/evaluation/yaml-loader.ts
@@ -0,0 +1,32 @@
+/**
+ * Shared YAML parse boundary for AgentV configs.
+ *
+ * Why this exists:
+ * - We use the `yaml` package (eemeli/yaml). In its YAML 1.2 default mode it
+ *   leaves the `<<` merge key as a literal sibling key instead of merging the
+ *   referenced map into the parent. That leaks `<<` into downstream consumers
+ *   (e.g. JSONL `metadata.governance` artifacts). The YAML 1.1 merge-key
+ *   behavior must be opted into via `{ merge: true }`.
+ * - Every `*.eval.yaml`, `agentv.config.yaml`, workspace YAML, etc. is parsed
+ *   here so behavior is uniform across loaders. Do NOT call `parse` from the
+ *   `yaml` package directly elsewhere — funnel through these helpers.
+ *
+ * To extend:
+ *   - For new YAML inputs that should support anchors + merge keys, import
+ *     `parseYaml` (object form) or `parseYamlValue` (any-shape form) from here.
+ *   - Do not duplicate the `{ merge: true }` option at call sites.
+ */
+import { parse } from 'yaml';
+
+/** Options forwarded to the `yaml` package. `merge: true` is always set. */
+const PARSE_OPTIONS = { merge: true } as const;
+
+/**
+ * Parse a YAML document and return its top-level value as `unknown`.
+ *
+ * Use this when the document may be any shape (string, array, object, etc.).
+ * Anchor merges (`<<: *anchor`) are unwrapped into sibling keys.
+ */
+export function parseYamlValue(content: string): unknown {
+  return parse(content, PARSE_OPTIONS) as unknown;
+}
diff --git a/packages/core/src/evaluation/yaml-parser.ts b/packages/core/src/evaluation/yaml-parser.ts
index 29909476..444ec1ce 100644
--- a/packages/core/src/evaluation/yaml-parser.ts
+++ b/packages/core/src/evaluation/yaml-parser.ts
@@ -1,7 +1,6 @@
 import { readFile, stat } from 'node:fs/promises';
 import path from 'node:path';
 import micromatch from 'micromatch';
-import { parse } from 'yaml';
 
 import { collectResolvedInputFilePaths } from './input-message-utils.js';
 import { interpolateEnv } from './interpolation.js';
@@ -61,6 +60,7 @@ import type {
 } from './types.js';
 import { isJsonObject, isTestMessage } from './types.js';
 import { parseRepoConfig } from './workspace/repo-config-parser.js';
+import { parseYamlValue } from './yaml-loader.js';
 
 // Re-export public APIs from modules
 export { buildPromptInputs, type PromptInputs } from './formatting/prompt-builder.js';
@@ -172,7 +172,7 @@ export async function readTestSuiteMetadata(testFilePath: string): Promise<{
   try {
     const absolutePath = path.resolve(testFilePath);
     const content = await readFile(absolutePath, 'utf8');
-    const parsed = interpolateEnv(parse(content), process.env) as unknown;
+    const parsed = interpolateEnv(parseYamlValue(content), process.env) as unknown;
 
     if (!isJsonObject(parsed)) {
       return {};
@@ -308,7 +308,7 @@ async function loadTestsFromYaml(
   const config = await loadConfig(absoluteTestPath, repoRootPath);
 
   const rawFile = await readFile(absoluteTestPath, 'utf8');
-  const interpolated = interpolateEnv(parse(rawFile), process.env) as unknown;
+  const interpolated = interpolateEnv(parseYamlValue(rawFile), process.env) as unknown;
   if (!isJsonObject(interpolated)) {
     throw new Error(`Invalid test file format: ${evalFilePath}`);
   }
@@ -783,7 +783,7 @@ async function resolveWorkspaceConfig(
     } catch {
       throw new Error(`Workspace file not found: ${raw} (resolved to ${workspaceFilePath})`);
     }
-    const parsed = interpolateEnv(parse(content), process.env) as unknown;
+    const parsed = interpolateEnv(parseYamlValue(content), process.env) as unknown;
     if (!isJsonObject(parsed)) {
       throw new Error(
         `Invalid workspace file format: ${workspaceFilePath} (expected a YAML object)`,
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index d77011e4..3a7edf09 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -1,6 +1,7 @@
 export * from './evaluation/content.js';
 export * from './evaluation/types.js';
 export * from './evaluation/trace.js';
+export { parseYamlValue } from './evaluation/yaml-loader.js';
 export * from './evaluation/yaml-parser.js';
 export {
   isAgentSkillsFormat,
diff --git a/packages/core/test/evaluation/yaml-loader.test.ts b/packages/core/test/evaluation/yaml-loader.test.ts
new file mode 100644
index 00000000..b971482f
--- /dev/null
+++ b/packages/core/test/evaluation/yaml-loader.test.ts
@@ -0,0 +1,43 @@
+/**
+ * Regression test: YAML merge keys (`<<: *anchor`) are unwrapped at the parse
+ * boundary so the literal `<<` key never reaches downstream consumers.
+ *
+ * Bug history: PR #1166's red-team eval used `governance: { <<: *gov, ... }`.
+ * Because the `yaml` package leaves `<<` as a literal key in YAML 1.2 mode,
+ * `<<` leaked into JSONL `metadata.governance`. The fix funnels all parses
+ * through `parseYamlValue`, which sets `{ merge: true }`.
+ */
+import { describe, expect, it } from 'bun:test';
+
+import { parseYamlValue } from '../../src/evaluation/yaml-loader.js';
+
+describe('parseYamlValue', () => {
+  it('unwraps `<<: *anchor` merge keys without leaving `<<` as a sibling key', () => {
+    const yaml = `
+gov: &gov
+  schema_version: "1.0"
+  owasp_llm_top_10_2025: [LLM01]
+  risk_tier: high
+
+case:
+  <<: *gov
+  owasp_llm_top_10_2025: [LLM01, LLM06]
+`;
+
+    const parsed = parseYamlValue(yaml) as { case: Record<string, unknown> };
+
+    // The `<<` key must NOT survive the parse — it should be unwrapped.
+    expect(Object.keys(parsed.case).sort()).toEqual([
+      'owasp_llm_top_10_2025',
+      'risk_tier',
+      'schema_version',
+    ]);
+
+    // Anchor fields are merged into the case.
+    expect(parsed.case.schema_version).toBe('1.0');
+    expect(parsed.case.risk_tier).toBe('high');
+
+    // Case-level overrides win over anchor values for the same key.
+    expect(parsed.case.owasp_llm_top_10_2025).toEqual(['LLM01', 'LLM06']);
+  });
+});