diff --git a/.changeset/proposal-gate-absence.md b/.changeset/proposal-gate-absence.md
new file mode 100644
index 000000000..01c6cb27a
--- /dev/null
+++ b/.changeset/proposal-gate-absence.md
@@ -0,0 +1,8 @@
+---
+"@adcp/sdk": patch
+---
+
+fix(conformance): skip proposal storyboards when supports_proposals is absent
+
+Treat omitted `media_buy.supports_proposals` as unsupported for proposal lifecycle
+`requires_capability` gates, including profiles without raw capabilities.
diff --git a/src/lib/testing/storyboard/runner.ts b/src/lib/testing/storyboard/runner.ts
index c81386175..2cb910017 100644
--- a/src/lib/testing/storyboard/runner.ts
+++ b/src/lib/testing/storyboard/runner.ts
@@ -283,6 +283,12 @@ export function evaluateCapabilityPredicate(
   // a real spec-coverage gap (under-declared agent) rather than a behavior
   // the agent affirmatively refused. Skip ONLY when the agent declared a
   // value AND that value disagrees with the predicate.
+  //
+  // Exception: optional proposal lifecycle storyboards require an explicit
+  // seller opt-in. Absent support is equivalent to unsupported.
+  if (actual === undefined && isProposalLifecycleGate(predicate)) {
+    return `Capability predicate \`${predicate.path} === true\` not satisfied: ` + `agent did not declare support.`;
+  }
   if (actual !== undefined && actual !== predicate.equals) {
     return (
       `Capability predicate \`${predicate.path} === ${JSON.stringify(predicate.equals)}\` not satisfied: ` +
@@ -292,6 +298,13 @@ export function evaluateCapabilityPredicate(
   return null;
 }
 
+function isProposalLifecycleGate(predicate: {
+  path: string;
+  equals?: boolean | string | number | null;
+}): predicate is { path: 'media_buy.supports_proposals'; equals: true } {
+  return predicate.path === 'media_buy.supports_proposals' && predicate.equals === true;
+}
+
 function buildSkip(reason: RunnerSkipReason, detail?: string): { reason: RunnerSkipReason; detail: string } {
   return { reason, detail: detail ?? SKIP_DETAILS[reason] };
 }
@@ -1593,9 +1606,9 @@ async function executeStoryboardPass(
   // tests (e.g. `adcp.idempotency.supported: false`), skip the whole storyboard
   // rather than producing a cascade of misleading per-phase failures.
   if (storyboard.requires_capability) {
+    const cap = storyboard.requires_capability;
     const rawCaps = profile?.raw_capabilities;
     if (rawCaps !== undefined) {
-      const cap = storyboard.requires_capability;
       const actual = resolveCapabilityPath(rawCaps, cap.path);
       const unmetDetail = evaluateCapabilityPredicate(cap, actual);
       if (unmetDetail !== null) {
@@ -1605,6 +1618,19 @@ async function executeStoryboardPass(
           notices: preflightNotices,
         };
       }
+    } else if (
+      isProposalLifecycleGate(cap) &&
+      profile !== undefined &&
+      !profile.tools.includes('get_adcp_capabilities')
+    ) {
+      const unmetDetail = evaluateCapabilityPredicate(cap, undefined);
+      if (unmetDetail !== null) {
+        if (!options._client) await closeConnections(options.protocol);
+        return {
+          ...buildCapabilityUnsupportedResult(agentUrls, storyboard, unmetDetail),
+          notices: preflightNotices,
+        };
+      }
     }
   }
 
diff --git a/test/lib/storyboard-capability-gate.test.js b/test/lib/storyboard-capability-gate.test.js
index 20ae2b5cb..cf3251705 100644
--- a/test/lib/storyboard-capability-gate.test.js
+++ b/test/lib/storyboard-capability-gate.test.js
@@ -52,6 +52,32 @@ const disabledProfile = {
   raw_capabilities: { adcp: { idempotency: { supported: false } } },
 };
 
+const proposalLifecycleGatedStoryboard = {
+  id: 'proposal_lifecycle_optional_feature_gate_test',
+  version: '1.0.0',
+  title: 'Proposal lifecycle (optional feature gated)',
+  category: 'test',
+  summary: 'Skipped when media-buy proposal lifecycle support is not advertised.',
+  narrative: '',
+  agent: { interaction_model: 'media_buy_seller', capabilities: [] },
+  caller: { role: 'buyer_agent' },
+  requires_capability: { path: 'media_buy.supports_proposals', equals: true },
+  phases: [
+    {
+      id: 'proposal_lifecycle',
+      title: 'Proposal lifecycle phase',
+      steps: [
+        {
+          id: 'proposal_finalize',
+          title: 'Finalize a proposal',
+          task: 'proposal_finalize',
+          sample_request: { proposal_id: 'proposal_test' },
+        },
+      ],
+    },
+  ],
+};
+
 describe('requires_capability storyboard skip gate (#933)', () => {
   test('emits capability_unsupported skip when agent declares supported: false', async () => {
     // _profile bypasses discoverAgentProfile; no network calls made because
@@ -139,6 +165,43 @@ describe('requires_capability storyboard skip gate (#933)', () => {
     assert.ok(typeof result === 'function' || result === undefined);
   });
 
+  test('optional proposal lifecycle feature skips when omitted', async () => {
+    const result = await runStoryboard('http://fake-local-99990', proposalLifecycleGatedStoryboard, {
+      _profile: {
+        name: 'Test Agent (no proposal support declared)',
+        tools: ['get_adcp_capabilities', 'proposal_finalize'],
+        raw_capabilities: { media_buy: {} },
+      },
+    });
+
+    assert.equal(result.overall_passed, true);
+    assert.equal(result.skipped_count, 1);
+    const step = result.phases[0].steps[0];
+    assert.equal(step.skipped, true);
+    assert.equal(step.skip_reason, 'capability_unsupported');
+    assert.equal(step.skip.reason, 'unsatisfied_contract');
+    assert.ok(step.skip.detail.includes('media_buy.supports_proposals'));
+    assert.ok(step.skip.detail.includes('did not declare'));
+  });
+
+  test('optional proposal lifecycle feature skips when raw capabilities are unavailable', async () => {
+    const result = await runStoryboard('http://fake-local-99989', proposalLifecycleGatedStoryboard, {
+      _profile: {
+        name: 'Test Agent (proposal capability unavailable)',
+        tools: ['proposal_finalize'],
+      },
+    });
+
+    assert.equal(result.overall_passed, true);
+    assert.equal(result.skipped_count, 1);
+    const step = result.phases[0].steps[0];
+    assert.equal(step.skipped, true);
+    assert.equal(step.skip_reason, 'capability_unsupported');
+    assert.equal(step.skip.reason, 'unsatisfied_contract');
+    assert.ok(step.skip.detail.includes('media_buy.supports_proposals'));
+    assert.ok(step.skip.detail.includes('did not declare'));
+  });
+
   test('DETAILED_SKIP_TO_CANONICAL maps capability_unsupported to unsatisfied_contract', () => {
     assert.equal(
       DETAILED_SKIP_TO_CANONICAL['capability_unsupported'],
@@ -269,6 +332,10 @@ describe('requires_capability `present:` matcher (#1811)', () => {
     const presentTrue = { path: 'x.y', present: true };
     const presentFalse = { path: 'x.y', present: false };
     const equalsTrue = { path: 'x.y', equals: true };
+    const proposalFeatureEqualsTrue = {
+      path: 'media_buy.supports_proposals',
+      equals: true,
+    };
 
     // present: true
     assert.equal(evaluateCapabilityPredicate(presentTrue, undefined)?.includes('must be present'), true);
@@ -291,6 +358,17 @@ describe('requires_capability `present:` matcher (#1811)', () => {
       true,
       'declared mismatch skips with `not satisfied` detail'
     );
+    assert.equal(
+      evaluateCapabilityPredicate(proposalFeatureEqualsTrue, undefined)?.includes('did not declare'),
+      true,
+      'supports_proposals is an optional feature gate: absent skips'
+    );
+    assert.equal(evaluateCapabilityPredicate(proposalFeatureEqualsTrue, true), null);
+    assert.equal(
+      evaluateCapabilityPredicate(proposalFeatureEqualsTrue, false)?.includes('not satisfied'),
+      true,
+      'supports_proposals: false skips proposal lifecycle storyboards'
+    );
   });
 });