diff --git a/tests/lib/profile-application.test.mjs b/tests/lib/profile-application.test.mjs
index 6a36513..5f334a5 100644
--- a/tests/lib/profile-application.test.mjs
+++ b/tests/lib/profile-application.test.mjs
@@ -50,6 +50,20 @@ test('SC #5: loadProfile("premium") returns all-opus', () => {
   }
 });
 
+test('SC #5: loadProfile("fable") returns all-fable (BUILTIN_NAMES canary)', () => {
+  // Throws PROFILE_NOT_FOUND if 'fable' regresses out of BUILTIN_NAMES —
+  // the silent-fallback-to-premium failure mode this pin exists to catch.
+  const p = loadProfile('fable');
+  assert.equal(p.name, 'fable');
+  for (const phase of ['brief', 'research', 'plan', 'execute', 'review', 'continue']) {
+    assert.equal(p.phase_models[phase], 'fable', `fable ${phase} should be fable`);
+  }
+  assert.equal(p.parallel_agents_min, 6);
+  assert.equal(p.parallel_agents_max, 8);
+  assert.equal(p.external_research_enabled, true);
+  assert.equal(p.brief_reviewer_iter_cap, 3);
+});
+
 test('SC #5: loadProfile throws PROFILE_NOT_FOUND for unknown profile', () => {
   try {
     loadProfile('does-not-exist-xyz');
diff --git a/tests/lib/profile-resolver.test.mjs b/tests/lib/profile-resolver.test.mjs
index 4eef940..f87fb42 100644
--- a/tests/lib/profile-resolver.test.mjs
+++ b/tests/lib/profile-resolver.test.mjs
@@ -60,3 +60,30 @@ test('resolvePhaseModel — Case 6 (defensive): null briefPath falls through to
   assert.equal(r.model, 'opus', 'premium.plan default = opus');
   assert.equal(r.source, 'default');
 });
+
+// v5.9 — fable profile composition (brief SC 4) + effort passthrough coherence
+
+test('resolvePhaseModel — --profile fable: all six phases resolve model fable (no brief signal)', () => {
+  for (const phase of ['brief', 'research', 'plan', 'execute', 'review', 'continue']) {
+    const r = resolvePhaseModel(phase, null, ['--profile', 'fable'], {});
+    assert.equal(r.model, 'fable', `fable.${phase} should be fable; got ${JSON.stringify(r)}`);
+    assert.equal(r.source, 'flag');
+  }
+});
+
+test('resolvePhaseModel — brief signal (opus) beats --profile fable (composition precedence pin)', () => {
+  // brief-effort-high.md pins execute to model: opus. Brief must beat the fable profile.
+  const r = resolvePhaseModel('execute', FIXTURE('brief-effort-high.md'), ['--profile', 'fable'], {});
+  assert.equal(r.model, 'opus', `brief signal should beat fable profile; got ${JSON.stringify(r)}`);
+  assert.equal(r.source, 'brief-signal');
+});
+
+test('resolvePhaseModel — composed output carries {effort, model} atomically (v5.9 passthrough)', () => {
+  // brief-effort-high.md: execute → {effort: high, model: opus}. The composed
+  // resolver must return BOTH fields from one call — the split-CLI design this
+  // passthrough replaced could drift effort and model apart.
+  const r = resolvePhaseModel('execute', FIXTURE('brief-effort-high.md'), [], {});
+  assert.equal(r.effort, 'high', `effort must pass through; got ${JSON.stringify(r)}`);
+  assert.equal(r.model, 'opus');
+  assert.equal(r.source, 'brief-signal');
+});