diff --git a/.claude-plugin/plugin.json b/.claude-plugin/plugin.json
index b53b413..bffe736 100644
--- a/.claude-plugin/plugin.json
+++ b/.claude-plugin/plugin.json
@@ -1,6 +1,6 @@
 {
   "name": "pstack",
-  "version": "0.15.25-shared.5",
+  "version": "0.15.25-shared.6",
   "description": "Shared pstack engineering workflows for Claude Code and Codex, with one configuration and host-specific runtime adapters.",
   "author": {
     "name": "Local adaptation; upstream Lauren Tan"
diff --git a/.codex-plugin/plugin.json b/.codex-plugin/plugin.json
index 46ae614..990901f 100644
--- a/.codex-plugin/plugin.json
+++ b/.codex-plugin/plugin.json
@@ -1,6 +1,6 @@
 {
   "name": "pstack-codex",
-  "version": "0.15.25-shared.5",
+  "version": "0.15.25-shared.6",
   "description": "Shared pstack engineering workflows for Codex and Claude Code, with one configuration and native host adapters.",
   "author": {
     "name": "Lauren Tan; local Codex adaptation"
diff --git a/bin/transcripts.mjs b/bin/transcripts.mjs
index f1a0aa3..4133c4b 100644
--- a/bin/transcripts.mjs
+++ b/bin/transcripts.mjs
@@ -180,19 +180,30 @@ function listTranscripts({ host, cwds, since, until }) {
   };
 }
 
+// The proleptic Gregorian calendar Date.parse uses, independent of the local time zone.
+function isCalendarDate(year, month, date) {
+  const leap = year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
+  return month >= 1 && month <= 12 && date >= 1 && date <= [31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month - 1];
+}
+
+// setFullYear, unlike the Date constructor, does not map years 0 to 99 onto 1900 to 1999.
+function localMidnight(year, monthIndex, date) {
+  const day = new Date(0);
+  day.setFullYear(year, monthIndex, date);
+  return day.setHours(0, 0, 0, 0);
+}
+
 // A bare date is a local calendar day: --since starts at its midnight and --until includes the whole day.
+// Date.parse rolls a date-time's day past the month's end into the next month, so both forms check the date first.
 function parseTime(value, flag, { endOfDay }) {
-  const day = /^(\d{4})-(\d{2})-(\d{2})$/.exec(value);
-  if (day) {
-    const [year, month, date] = day.slice(1).map(Number);
-    const start = new Date(year, month - 1, date);
-    if (start.getFullYear() !== year || start.getMonth() !== month - 1 || start.getDate() !== date) {
-      throw new Error(`${flag} ${value} is not a calendar date`);
-    }
-    return endOfDay ? new Date(year, month - 1, date + 1).getTime() - 1 : start.getTime();
-  }
-  const time = /^\d{4}-\d{2}-\d{2}T/.test(value) ? Date.parse(value) : Number.NaN;
-  if (Number.isNaN(time)) throw new Error(`${flag} must be YYYY-MM-DD or an ISO 8601 date-time`);
+  const malformed = `${flag} must be YYYY-MM-DD or an ISO 8601 date-time`;
+  const day = /^(\d{4})-(\d{2})-(\d{2})(T.*)?$/.exec(value);
+  if (!day) throw new Error(malformed);
+  const [year, month, date] = day.slice(1, 4).map(Number);
+  if (!isCalendarDate(year, month, date)) throw new Error(`${flag} ${value} is not a calendar date`);
+  if (day[4] === undefined) return endOfDay ? localMidnight(year, month - 1, date + 1) - 1 : localMidnight(year, month - 1, date);
+  const time = Date.parse(value);
+  if (Number.isNaN(time)) throw new Error(malformed);
   return time;
 }
 
diff --git a/scripts/transcripts.test.mjs b/scripts/transcripts.test.mjs
index d2b7bc2..cd3196e 100644
--- a/scripts/transcripts.test.mjs
+++ b/scripts/transcripts.test.mjs
@@ -170,6 +170,17 @@ test("Given relocated host homes and several checkouts, When listed, Then CLAUDE
   assert.deepEqual(paths(list(home, ["--host", "codex", "--cwd", "/work/repo"], env)), [rollout]);
 });
 
+test("Given bounds in years 0 to 99 or on a day the local calendar skipped, When the CLI parses them, Then it keeps the dates as written", (t) => {
+  const home = tempHome(t);
+  const ancient = list(home, ["--host", "claude", "--since", "0000-01-01T00:00:00Z", "--until", "0000-01-02T00:00:00Z"], { TZ: "UTC" });
+  assert.equal(ancient.since, "0000-01-01T00:00:00.000Z");
+  const bare = list(home, ["--host", "claude", "--since", "0050-01-01", "--until", "0050-01-01"], { TZ: "UTC" });
+  assert.deepEqual([bare.since, bare.until], ["0050-01-01T00:00:00.000Z", "0050-01-01T23:59:59.999Z"]);
+  // Samoa skipped 2011-12-30 locally, but that UTC date still exists.
+  const skipped = list(home, ["--host", "claude", "--since", "2011-12-30T12:00:00Z", "--until", "2011-12-31T00:00:00Z"], { TZ: "Pacific/Apia" });
+  assert.equal(skipped.since, "2011-12-30T12:00:00.000Z");
+});
+
 test("Given invalid arguments, When the CLI runs, Then it exits 1 with the reason", (t) => {
   const home = tempHome(t);
   const cases = [
@@ -177,6 +188,8 @@ test("Given invalid arguments, When the CLI runs, Then it exits 1 with the reaso
     [["--host", "cursor"], /host must be one of claude or codex/],
     [["--host", "claude", "--since", "last week"], /--since must be YYYY-MM-DD or an ISO 8601 date-time/],
     [["--host", "claude", "--until", "2026-02-30"], /--until 2026-02-30 is not a calendar date/],
+    [["--host", "claude", "--until", "2026-02-30T23:00:00Z"], /--until 2026-02-30T23:00:00Z is not a calendar date/],
+    [["--host", "claude", "--since", "2026-04-31T00:00"], /--since 2026-04-31T00:00 is not a calendar date/],
     [["--host", "claude", "--since", "2026-10-10", "--until", "2026-10-01"], /since must not be later than until/],
     [["--host", "claude", "--host", "codex"], /may only be provided once/],
     [["--host", "codex", "--cwd"], /--cwd requires a value/],