diff --git a/project-facts.json b/project-facts.json
index 6cc6735..fcbcc4f 100644
--- a/project-facts.json
+++ b/project-facts.json
@@ -4,7 +4,7 @@
     "decision": "0.2.10",
     "semanticDecision": "0.3.0"
   },
-  "testCount": 226,
+  "testCount": 229,
   "discoveredHashRouteLiteralCount": 8,
   "browserModes": [
     "desktop-light",
diff --git a/scripts/browser_context_e2e.py b/scripts/browser_context_e2e.py
index 84a7672..d7a8e01 100644
--- a/scripts/browser_context_e2e.py
+++ b/scripts/browser_context_e2e.py
@@ -7,7 +7,6 @@
 import http.server
 import json
 import os
-import socketserver
 import threading
 from copy import deepcopy
 from pathlib import Path
@@ -120,7 +119,7 @@ def packet_fixture() -> dict:
 
 def run() -> None:
     handler = functools.partial(QuietHandler, directory=str(SITE))
-    with socketserver.TCPServer(("127.0.0.1", 0), handler) as server:
+    with http.server.ThreadingHTTPServer(("127.0.0.1", 0), handler) as server:
         thread = threading.Thread(target=server.serve_forever, daemon=True)
         thread.start()
         base = f"http://127.0.0.1:{server.server_address[1]}/"
diff --git a/site/manifest.sha256 b/site/manifest.sha256
index a3d5421..032b651 100644
--- a/site/manifest.sha256
+++ b/site/manifest.sha256
@@ -24,7 +24,7 @@ ada77b250aace00f9b9310d9e5447aed6c5884140b6fb1260ad9eeefb7524072  src/guided-fra
 1eeba312c1d36366f056af836a990edf3f1b9fae254ba79425253c887bcdef58  src/lib/decision-hinge.js
 f5a1892210355a1f2fada1f7af2d850758fb820b1e483d3c578a6a20d1485cfd  src/lib/decision.js
 b7214b1632b94496f09ee8fe7d0268ea420e33fac260a47dbdcc7f380634fca0  src/lib/evidence-readiness.js
-acf5f06b3935f5e2bf76674e02c0f7d1c71a27edec468eafa36af68f8c94cd8b  src/lib/governed-context.js
+5198f58a81caf8fb239d2085358ca0286965c61644329ef0dd5a033c77148edf  src/lib/governed-context.js
 2b613558bcf8c5751f9ca39363699548856364f3bc988f2b742a30bc684e59fa  src/lib/input-boundaries.js
 ccf92df01cc80bbb10f340fbcaddccb34f0fe4d318ea414ef30e198aecd87a50  src/lib/input.js
 752531dea7b1be2bddfdf00f38abe2f6cfd6739fc48f8a5f97cf4741aaf65e47  src/lib/intake.js
diff --git a/site/src/lib/governed-context.js b/site/src/lib/governed-context.js
index dd8ae59..131c3f6 100644
--- a/site/src/lib/governed-context.js
+++ b/site/src/lib/governed-context.js
@@ -18,6 +18,8 @@ const REQUIRED_V03 = [
 const SUMMARY_KEYS = ['assumed', 'contradicted', 'expired', 'known', 'unknown'];
 const SUPPORTED_CLASSIFICATIONS = new Set(['PRIVATE', 'PROTECTED']);
 const SHA256_RE = /^[a-f0-9]{64}$/;
+// Date-based freshness checks retain their existing exclusion of leap-second timestamps.
+const TIMESTAMP_RE = /^(\d{4})-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])[Tt]([01]\d|2[0-3]):[0-5]\d:[0-5]\d(?:\.\d+)?(?:[Zz]|[+-](?:[01]\d|2[0-3]):[0-5]\d)$/;
 const PACKET_ID_RE = /^DCP-[A-Z0-9-]+$/;
 const LEGACY_DIGEST_SCOPE = 'packet excluding provenance.generated_at and content_sha256';
 const PAYLOAD_SCOPE = 'decision-relevant packet content excluding integrity, origin, freshness, and provenance';
@@ -47,7 +49,15 @@ function objectsOnly(value) {
 }
 
 function parseTimestamp(value) {
-  if (typeof value !== 'string' || !value.trim()) return null;
+  if (typeof value !== 'string') return null;
+  const parts = TIMESTAMP_RE.exec(value);
+  if (!parts || parts[0] !== value) return null;
+  const year = Number(parts[1]);
+  const month = Number(parts[2]);
+  const day = Number(parts[3]);
+  const leapYear = year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
+  const monthDays = [31, leapYear ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+  if (day > monthDays[month - 1]) return null;
   const date = new Date(value);
   return Number.isFinite(date.getTime()) ? date : null;
 }
@@ -148,7 +158,10 @@ function freshnessState(packet, now) {
   const sourceAsOf = parseTimestamp(freshness?.source_as_of);
   const reviewDue = freshness?.review_due_at === null ? null : parseTimestamp(freshness?.review_due_at);
   const validUntil = freshness?.valid_until === null ? null : parseTimestamp(freshness?.valid_until);
-  if (!issued || !sourceAsOf) return { state: 'INVALID', error: 'Packet freshness timestamps are invalid.' };
+  if (!issued) return { state: 'INVALID', error: 'Packet issued_at must be a supported RFC 3339 timestamp.' };
+  if (!sourceAsOf) return { state: 'INVALID', error: 'Packet source_as_of must be a supported RFC 3339 timestamp.' };
+  if (freshness.review_due_at !== null && !reviewDue) return { state: 'INVALID', error: 'Packet review_due_at must be a supported RFC 3339 timestamp or null.' };
+  if (freshness.valid_until !== null && !validUntil) return { state: 'INVALID', error: 'Packet valid_until must be a supported RFC 3339 timestamp or null.' };
   if (sourceAsOf > issued) return { state: 'INVALID', error: 'Packet source_as_of is later than issued_at.' };
   if (issued.getTime() > now.getTime() + CLOCK_SKEW_MS) return { state: 'INVALID', error: 'Packet issued_at is unacceptably future-dated.' };
   if (reviewDue && reviewDue < sourceAsOf) return { state: 'INVALID', error: 'Packet review_due_at is earlier than source_as_of.' };
diff --git a/tests/governed-context.test.js b/tests/governed-context.test.js
index 7354b57..50f186b 100644
--- a/tests/governed-context.test.js
+++ b/tests/governed-context.test.js
@@ -180,6 +180,73 @@ test('missing freshness boundaries are not active-eligible', async () => {
   assert.equal(result.trust.freshness, 'NOT_ESTABLISHED');
 });
 
+test('freshness timestamps reject malformed formats, types, and impossible dates with recomputed integrity', async () => {
+  const invalid = [
+    '', ' ', 'not-a-date', 42, false, {}, [],
+    'September 16, 2026', '2026-09-16', '2026-09-16 00:00:00Z',
+    '2026-09-16T00:00:00', '2026-09-16T00:00Z',
+    '2026-09-16T00:00:00Z\n', '2026-09-16T00:00:00.Z',
+    '2026-02-29T00:00:00Z', '1900-02-29T00:00:00Z', '2100-02-29T00:00:00Z',
+    '2026-04-31T00:00:00Z', '2026-13-01T00:00:00Z', '2026-09-00T00:00:00Z',
+    '2026-09-32T00:00:00Z', '2026-09-16T24:00:00Z', '2026-09-16T00:60:00Z',
+    '2026-09-16T00:00:61Z', '2026-09-16T00:00:00+24:00', '2026-09-16T00:00:00+01:60',
+  ];
+  for (const field of ['issued_at', 'source_as_of', 'review_due_at', 'valid_until']) {
+    for (const value of invalid) {
+      const packet = await packetFixture();
+      packet.freshness[field] = value;
+      packet.integrity.envelope_sha256 = await decisionContextEnvelopeDigest(packet);
+      const result = await validateDecisionContextPacket(packet, { now: NOW });
+      assert.equal(result.valid, false, `${field}: ${JSON.stringify(value)}`);
+      assert.equal(result.activeEligible, false);
+      assert.equal(result.trust.freshness, 'INVALID');
+      assert.ok(result.errors.some((message) => message.includes(field)));
+    }
+  }
+});
+
+test('null is permitted only for nullable freshness boundaries', async () => {
+  for (const field of ['issued_at', 'source_as_of']) {
+    const packet = await packetFixture();
+    packet.freshness[field] = null;
+    packet.integrity.envelope_sha256 = await decisionContextEnvelopeDigest(packet);
+    const result = await validateDecisionContextPacket(packet, { now: NOW });
+    assert.equal(result.valid, false);
+    assert.equal(result.activeEligible, false);
+    assert.equal(result.trust.freshness, 'INVALID');
+    assert.ok(result.errors.some((message) => message.includes(field)));
+  }
+  for (const field of ['review_due_at', 'valid_until']) {
+    const packet = await packetFixture();
+    packet.freshness[field] = null;
+    packet.integrity.envelope_sha256 = await decisionContextEnvelopeDigest(packet);
+    const result = await validateDecisionContextPacket(packet, { now: NOW });
+    assert.equal(result.valid, true);
+    assert.equal(result.activeEligible, true);
+    assert.equal(result.trust.freshness, 'CURRENT');
+  }
+});
+
+test('RFC 3339 offsets, lower-case separators, fractions, and leap-year dates remain valid', async () => {
+  const fields = ['issued_at', 'source_as_of', 'review_due_at', 'valid_until'];
+  for (const value of [
+    '2026-09-14T00:00:00Z', '2026-09-14t00:00:00z',
+    '2026-09-14T00:00:00+00:00', '2026-09-14T00:00:00-00:00',
+    '2026-09-14T05:30:00+05:30', '2026-09-13T16:00:00-08:00',
+    '2026-09-14T23:59:00+23:59', '2026-09-14T00:00:00.123456Z',
+    '2000-02-29T00:00:00Z', '2024-02-29T00:00:00Z',
+  ]) {
+    const packet = await packetFixture();
+    for (const field of fields) packet.freshness[field] = value;
+    packet.integrity.envelope_sha256 = await decisionContextEnvelopeDigest(packet);
+    const result = await validateDecisionContextPacket(packet, { now: new Date(value) });
+    assert.equal(result.valid, true, value);
+    assert.equal(result.activeEligible, true);
+    assert.equal(result.trust.freshness, 'CURRENT');
+    assert.deepEqual(result.errors, []);
+  }
+});
+
 test('self-asserted authenticated origin is rejected without an external trust verifier', async () => {
   const packet = await packetFixture();
   packet.origin.authentication_state = 'AUTHENTICATED';