fix(transcript): reject impossible calendar dates

CHANGELOG.md

@@ -8,6 +8,10 @@ All notable changes to this project are documented here. Format follows
 
 ### Fixed
 
+- Transcript parsing now rejects calendar-impossible RFC 3339 timestamps instead of
+  letting JavaScript normalize values such as 2026-02-31 into March before deadline
+  guards see them; valid leap days, offsets and fractional seconds remain accepted (#188).
+
 - `tclk_post_frame` now accepts exact decimal-string nonces in addition to safe integer
   numbers, so signed Technocore nonces above JavaScript's safe-integer range are preserved
   without precision loss. Unsafe numeric nonces (> 2^53 - 1) are rejected at the MCP schema

src/transcript.ts

@@ -18,6 +18,17 @@ const SIGNATURE = /^[A-Za-z0-9_-]{85}[AQgw]$/;
 const TIMESTAMP = /^\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])T(?:[01]\d|2[0-3]):[0-5]\d:[0-5]\d(?:\.\d+)?(?:Z|[+-](?:[01]\d|2[0-3]):[0-5]\d)$/;
 const DID_PREFIX = "did:key:z";
 
+function hasValidCalendarDate(timestamp: string): boolean {
+  const match = /^(\d{4})-(\d{2})-(\d{2})T/.exec(timestamp);
+  if (match === null) return false;
+  const year = Number(match[1]);
+  const month = Number(match[2]);
+  const day = Number(match[3]);
+  const leap = year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
+  const monthDays = [31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+  return day <= monthDays[month - 1]!;
+}
+
 /**
  * One normalized technocore record. `line` is the exact stored text; `sender`, `nonce`
  * and `signature` authenticate it for `room`. `timestampMs` and `seq` are venue metadata,
@@ -128,6 +139,9 @@ export function transcriptRecord(room: string, value: unknown): TranscriptRecord
   if (!TIMESTAMP.test(message.ts)) {
     throw new Error("tclk: transcript message timestamp must be timezone-qualified RFC 3339");
   }
+  if (!hasValidCalendarDate(message.ts)) {
+    throw new Error("tclk: transcript message timestamp has an invalid calendar date");
+  }
   const timestampMs = Date.parse(message.ts);
   if (!Number.isSafeInteger(timestampMs) || timestampMs < 0) {
     throw new Error("tclk: transcript message timestamp is invalid");

tests/transcript.test.ts

@@ -215,6 +215,23 @@ describe("trusted transcript records", () => {
     });
     expect(() => parseTranscriptExport(BOARD, withoutTimezone)).toThrow(/timezone-qualified/);
     expect(() => parseTranscriptExport(BOARD, localeTimestamp)).toThrow(/timezone-qualified/);
+
+
+    for (const ts of [
+      "2026-02-29T00:00:00Z",
+      "2026-02-31T00:00:00Z",
+      "2026-04-31T00:00:00+01:00",
+    ]) {
+      const impossibleDate = JSON.stringify({ ...JSON.parse(raw), ts });
+      expect(() => parseTranscriptExport(BOARD, impossibleDate)).toThrow(/invalid calendar date/);
+    }
+
+    const leapDay = JSON.stringify({
+      ...JSON.parse(raw),
+      ts: "2024-02-29T03:04:05.123+02:30",
+    });
+    expect(parseTranscriptExport(BOARD, leapDay)[0]?.timestampMs)
+      .toBe(Date.parse("2024-02-29T03:04:05.123+02:30"));
   });
 
   it("never synthesizes offer-before-accept order while selecting a board handshake", () => {