SSM-Clock Stamp – Canonical Day & Selection (3.1)

Purpose. Define exactly which stamps belong to a given day’s anchor for SSM-Clock Stamp. All rules are plain ASCII and deterministic.

Day key (UTC, must)

  • From iso_utc = "YYYY-MM-DDThh:mm:ssZ", derive the UTC day key: YYYY-MM-DD.
  • Timezones/offsets are not allowed; day selection is strictly UTC.

Inclusion rule (must)

  • Include all stamps whose iso_utc shares the target UTC day key.
  • Identity of a stamp is the entire line as recorded (base or with kv: tail):
    SSMCLOCK1|iso_utc|rasi_idx|theta_deg|sha256(file)|chain[|kv:...]

Edge conditions (clarifications)

  • Subseconds: not allowed. Only whole seconds appear in iso_utc.
  • Leap second: stamping at 23:59:60 is forbidden; such stamps must not exist.
  • Cross-midnight sources: data produced near midnight must still obey the iso_utc day key. Local timezones are irrelevant; only the Z-suffix timestamp decides membership.

Practical selection procedure (copy-ready)

  1. Read each stamp line; parse iso_utc.
  2. Compute day key YYYY-MM-DD from iso_utc (UTC).
  3. If day key equals the target day → include the full line.
  4. Keep the included lines unchanged (including any kv: tail) for the next step (ordering).

Why this matters

  • Using a UTC day key ensures everyone selects the same set regardless of locale.
  • Because identity is the exact ASCII line, later hashing steps become unambiguous.

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