fix(util): parseDate rejects calendar-invalid dates (Feb 30, Feb 29 non-leap, Apr 31, ...)

[sroussey]

Summary

src/util/parseDate.ts already range-checks month (1-12) and day (1-31), but that
still admits calendar-invalid inputs — 2025-02-30, 2025-02-29 in a non-leap
year, 2025-04-31, and the equivalents for June / September / November. The
returned { year, month, day } string is subsequently handed to
new Date(...) in the storage/history layer, which silently rolls forward
(2025-02-30 → March 2), corrupting the point-in-time semantics of
ChangeLog / spac_history / offering-history change_date rows and defeating
the as_of guards.

Fix

After the existing range check, probe the calendar via a UTC Date and reject
any input the calendar refuses to preserve verbatim:

const probe = new Date(Date.UTC(year, month - 1, day));
if (
  probe.getUTCFullYear() !== year ||
  probe.getUTCMonth() !== month - 1 ||
  probe.getUTCDate() !== day
) {
  throw new Error(`Invalid calendar date: ${dateStr}`);
}

The return shape is unchanged. Real dates flow through untouched.

Tests

Added to src/util/parseDate.test.ts:

• Feb 30 rejected in any year (2024 and 2025).
• Feb 29 rejected in 2025 / 2023 / 1900 (non-leap; 1900 exercises the
  divisible-by-100-but-not-400 rule) and accepted in 2024 and 2000 (the
  divisible-by-400 rule).
• Parameterised: the impossible 31st of April / June / September / November.
• Parameterised: month 0, month 13, day 0, day 32 still throw
  Invalid date format from the existing range check (regression fence — new
  probe must not swallow the pre-existing error message).
• Regression fence: all five recognised input shapes (yyyy-MM-dd,
  yyyy/MM/dd, MM/dd/yyyy, MM-dd-yyyy, yyyyMMdd) still accept a
  well-formed real date (2024-02-29).

Verification

• bun test src/util/parseDate.test.ts — 20 pass, 0 fail (7 new tests added).
• bun test — no new failures introduced. The 7 remaining failures are
  pre-existing network timeouts on FetchQuarterlyIndexTask /
  FetchDailyIndexTask (verified by stashing the change and reproducing).
• npx tsc --noEmit — clean.

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Generated by Claude Code

[sroussey]

Integrated into #176. The parseDate calendar-validity probe is carried forward verbatim (clean merge). Verified compatible with the whole tree: the full suite there is 1577 pass / 7 pre-existing network fails — no real date path regressed from the stricter rejection. Closing in favor of #176.

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Generated by Claude Code